Registration Dossier
Registration Dossier
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EC number: 204-697-4 | CAS number: 124-40-3
Endpoint summary
Administrative data
Description of key information
Repeated dose toxicity: oral exposure
Darad et al.,1983, Toxicology Letters, 17 (1983) 125-130, 30 rats (Wistar), exposed daily via drinking water. The results are indicating a free radical-mediated damage to the cellular and subcellular membranes. In conclusion DMA is able to disturb the barrier function of the skin by altering the protective characteristics.
Repeated dose toxicity: inhalation exposure
Buckley et al., 1985, Fundamental applied toxicology.V. 5, 341-352 (1985), exposure of rats or mice by inhalation to 0, 10, 50, or 175 ppm dimethylamine (DMA) for 6 hr/day, 5 days/week for 12 months. LOAEC = 10 ppm = 18.45 mg/m³ for local effects and NOAEC (systemic) = 50 ppm = 92.26 mg/m³ for systemic effects (conversion of ppm value into mg/m³ value was performed taking into account the temperature of 76 °F of the Buckley study).
Repeated dose toxicity: dermal exposure
no study available
Key value for chemical safety assessment
Repeated dose toxicity: via oral route - systemic effects
Link to relevant study records
- Endpoint:
- chronic toxicity: oral
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 1982
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- other: acceptable well-documented publication, which meets basic scientific principles
- Principles of method if other than guideline:
- Rats are fed nitrite and/or DMA, and the influence on microsomal lipoperoxidation, enzyme activities of acid phosphatase and cathepsin as lysosomal enzymes as well as the enzyme activity of superoxide dismutase (SOD) are evaluated.
- GLP compliance:
- no
- Limit test:
- yes
- Species:
- rat
- Strain:
- Wistar
- Sex:
- male
- Details on test animals or test system and environmental conditions:
- weanling male Wistar strain rats maintained on a laboratory stock diet composed of: Bengal gram (Cicer arietinum) 20%) wheat 70%) fish meal 5 %, yeast powder 4%) shark liver oil 0.25 % and purified vegetable oil 0.75%.
- Route of administration:
- oral: drinking water
- Vehicle:
- water
- Analytical verification of doses or concentrations:
- not specified
- Duration of treatment / exposure:
- 9 month
- Frequency of treatment:
- ad libitum
- Dose / conc.:
- 0.2 other: %
- Remarks:
- nominal in water
- No. of animals per sex per dose:
- 30 males per group, 6 groups
one group with sodium nitrite, one with DMA, one with sodium nitrite and DMA, one with 0.5 % BHT, one with 0.5 %v BHT, sodium nitrite and MDA, one control. (BHT significates: butylated hydroxtoluene) - Control animals:
- yes, concurrent no treatment
- Details on study design:
- Administration through the drinking water: nitrite (0.2%) and dimethylamine (DMA) (0.2 %), either singly or in combination for 9 month.
- Observations and examinations performed and frequency:
- no data
- Sacrifice and pathology:
- after 9 month killed by decapitation,
collection of the livers (cleaned and placed in suitable ice-cold media) - Other examinations:
- For the study of in vitro microsomal lipoperoxidation, the livers were homogenised in 8 ~01s. of 50 mM Tris-maleate buffer (pH 6.5) containing 155 mM NaCl, and the microsomes isolated by differential centrifugation. Malondialdehyde formation was followed by the thiobarbituric acid method. Acid phosphatase and cathepsin in 10% liver homogenate were assayed in acetate buffers at pH 5.0 and 3.8, respectively. Bound activities of these enzymes were measured by including 0.1 ml of 0.25% Triton X-100 in the incubation media. For SOD activity, 10% liver homogenate was made in 0.25 M sucrose, and mitochondria and post-mitochondrial supernatant were separated at 20000 x g. The enzyme activity of both these fractions was estimated by the pyrogallol method.
- Statistics:
- no data
- Clinical signs:
- not specified
- Mortality:
- not specified
- Body weight and weight changes:
- not specified
- Food consumption and compound intake (if feeding study):
- not specified
- Food efficiency:
- not specified
- Water consumption and compound intake (if drinking water study):
- not specified
- Ophthalmological findings:
- not specified
- Haematological findings:
- not specified
- Clinical biochemistry findings:
- effects observed, treatment-related
- Description (incidence and severity):
- increased lipoperoxidation, increased cytosolic superoxide dismutase, increased freee activity of acid phosphatase and cathepsin
- Urinalysis findings:
- not specified
- Behaviour (functional findings):
- not specified
- Organ weight findings including organ / body weight ratios:
- not specified
- Gross pathological findings:
- not specified
- Histopathological findings: non-neoplastic:
- not specified
- Histopathological findings: neoplastic:
- not specified
- Details on results:
- Nitrite and DMA, individually, cause significantly higher hepatic microsomal peroxidation.
However, when fed together, the two chemicals do not elicit such a response and the lipoperoxidative values of these animals are similar to those of the control.
In the DMA-administered rats the free activities of acid phosphatase and cathepsin were both increased, the increase in cathepsin being more marked.
The administration of nitrite or DMA appears to decrease the total activity of both the lysosomal enzymes.
The results on SOD (superoxide dismutase) activities (Table III) of both the mitochondrial and the postmitochondrial fractions show that nitrite, both singly and in combination with DMA, significantly enhances the level of the enzyme in the supernatant. DMA alone, however, does not have any effect on SOD activity.
Rats administered nitrite and DMA are significantly protected against the increase in the enzyme activity, when their diet is supplemented with BHT (butylated hydroxtoIuene). - Basis for effect level:
- other: The results indicate that nitrite and DMA may induce toxicity through some free radical reactions and that BHT can provide some protection.
- Remarks on result:
- not measured/tested
- Remarks:
- Effect level not specified
- Critical effects observed:
- not specified
- Conclusions:
- Many of the parameters examined in the present studies are indicative of a free radical-mediated damage to the cellular and subcellular membrane in rats administered nitrite and/or DMA.
- Executive summary:
The administration of nitrite or DMA appears to decrease the total activity of both the lysosomal enzymes.
In animals fed both nitrite and dimethylamine, the proportion of the free activity of both the enzymes is increased, in spite of a significant reduction in total activity. In these animals, BHT feeding affords marked protection and the increase in the percentage of free activities is restored to control levels.
Nitrite, both singly and in combination with DMA, significantly enhances the level of the enzyme in the supernatant. DMA alone, however, does not have any effect on SOD (superoxide dismutase) activity.
Likewise, rats administered nitrite and DMA are significantly protected against the increase in the enzyme activity, when their diet is supplemented with BHT (butylated hydroxytoluene).
The increased levels of the cytosolic SOD due to the administration of nitrite or DMA may indicate a higher generation of the superoxide radicals. The oxidation of haemoglobin by nitrite has been reported to involve the superoxide radicals.
Reference
The increase in lipoperoxidation may result in membrane damage and is further indicated by the labilisation of lysosomal enzymes.
The increased levels of the cytosolic SOD (superoxide dismutase) due to the administration of nitrite or DMA may indicate a higher generation of the superoxide radicals.
Nitrite, as well as DMA, caused higher in vitro lipoperoxidation, free lysosomal enzyme activities and cytosolic superoxide dismutase activity in liver. Some of these increases viz., the enzyme activities in liver, were counteracted to a significant extent in the rats receiving a dietary supplement of BHT (butylated hydroxytoluene). The results indicate that nitrite and DMA may induce toxicity through some free radical reactions and that BHT can provide some protection.
Nitrite and DMA, individually, cause significantly higher peroxidation. However, when fed together, the two chemicals do not elicit such a response and the lipoperox idative values of these animals are similar to those of the control.
In the nitrite-administered animals, the free activities of acid phosphatase and cathepsin were both increased, the change in acid phosphatase being statistically significant. In the DMA-administered rats a similar trend in both the enzymes is seen, the increase in cathepsin being more marked
Repeated dose toxicity: inhalation - systemic effects
Link to relevant study records
- Endpoint:
- chronic toxicity: inhalation
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- other: acceptable, well-documented publication, which meets basis scientific principles
- Reason / purpose for cross-reference:
- reference to same study
- Principles of method if other than guideline:
- Male and female F-344 rats and B6C3Fl mice were exposed by inhalation to 0, 10, 50, or 175 ppm dimethylamine (DMA) for 6 hr/day, 5 days/week for 12 months. Groups of 9-10 male and female rats and mice were necropsied atIer 6 and 12 months of exposure.
The purpose of this study was to investigate the toxicity associated with chronic inhalation exposure of F-344 rats and B6C3Fl mice to DMA for 2 years. This report summarizes the clinical and pathologic data found for the first 12-month period. - GLP compliance:
- no
- Limit test:
- yes
- Species:
- mouse
- Strain:
- B6C3F1
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River breeding laboratories, Kingston, New York, and Portage, Michigan, respectively
- Age at study initiation: 4-8 weeks
- Housing: individually in hanging stainless steel wire mesh cages in the exposure chambers
- Diet (e.g. ad libitum): NIH-07 open formula diet, Ziegler Brothers, Gardners, Pa.; analyzed for contaminants by Lancaster Labs, Lancaster, Pa.), ad libitum during periods of non-exposure
- Water (e.g. ad libitum): tap water via an automatic watering system, ad libitum during periods of non-exposure
- Acclimation period: 14 days
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 68 - 76 °F
- Humidity (%): 45 - 65 % ( real: 35 - 74 %)
- Air changes (per hr): airflow of 2200 liters/min
- Photoperiod (hrs dark / hrs light): 12-hr light/dark cycle - Route of administration:
- inhalation
- Type of inhalation exposure:
- whole body
- Vehicle:
- air
- Remarks on MMAD:
- MMAD / GSD: no data
- Details on inhalation exposure:
- Test atmospheres were generated by metering pure DMA directly from the cylinder via flowmeters (Fischer-Porter, Warminster, Pa., or Calibrating and Measuring Equipment, Inc., Manassas, Va.) into the supply air stream.
- Details on analytical verification of doses or concentrations:
- 99,97 % pure
Analysis of the test atmospheres was performed four times per hour by infrared spectrometry at a wavelength of 3.5 pm and a path length of 20.25 m (MIRAN 801, Foxboro-W&s, Norwalk, Conn.). The spectrophotometer was set to zero optical density with ultra zero air containing approximately 350 ppm Co, (Ma&son Gas, Morrow, Ga.) and adjusted to approximately 50% relative humidity. Temperature and relative humidity were recorded hourly.
The distribution of the analytical concentration of DMA in the chambers was determined to be uniform within ± 6 % of target concentrations.
The mean time-weighted average (TWA) analytical chamber concentrations for the 12 month period, derived from daily TWA concentrations, with standard deviations and ranges were 175 ppm ± 2.0 (167-188), 50.0 ppm ± 1.0 (45.8-54.0), and 10.0 ppm ± 0.3 (9.0-10.8). The average percentage ratios of analytical/nominal concentrations (± standard deviations) were 81 ± 8, 87 ± 7, and 76 ± 15% for the 175-, 50-, and 10-ppm chambers, respectively, thus indicating a fairly constant loss of DMA on the chamber surfaces and animals for each chamber. - Duration of treatment / exposure:
- 6 h /day, 5 days a week, for 12 month
- Frequency of treatment:
- daily
- Dose / conc.:
- 0 ppm (nominal)
- Dose / conc.:
- 10 ppm (nominal)
- Dose / conc.:
- 50 ppm (nominal)
- Dose / conc.:
- 175 ppm (nominal)
- No. of animals per sex per dose:
- 95 animals / sex
- Control animals:
- yes, concurrent no treatment
- Details on study design:
- In studies at our laboratory (unpublished observations), F-344 rats exposed to 175 or 250 ppm DMA (6 hr/day, 5 days) or 500 ppm DMA (6 hr/day, 3 days) had ulcerative rhinitis, severe congestion, and squamous metaplasia in the respiratory tract. These lesions were most severe in the anterior sections of the nasal passages.
- Observations and examinations performed and frequency:
- The animals were observed for clinical abnormalities twice daily and were weighed once per week for the first 13 weeks, and biweekly thereafter.
- Sacrifice and pathology:
- After 6 and 12 months, 9-10 animals of each species, sex, and treatment group were fasted overnight and weighed just prior to necropsy.
Male mice were not included in the 12-month sacrifice because of the hi rate of unscheduled mortality in this group.
Animals were anesthetized with pentobarbital by ip injection, and blood was drawn from the heart for hematology and serum chemistry. Each animal was examined for gross abnormalities, and 45 tissues and any gross lesions were collected and placed in 10 % buffered formalin. The nasal passages were flushed, the lungs inflated, and the lumen of the gastrointestinal tract infused with formalin. The liver, kidneys, and brain were weighed. All tissues from the control and 175~ppm exposed animals and target tissues (nasal turbinates) from the 10- and 50- ppm exposed animals were processed for light microscopic examination. Tissues containing bone were placed in 10 % buffered formalin for 48 hr, decakSed in Cal-ex solution (Fisher Scientific, Raleigh, N.C.) for 2 days, then rinsed with tap water for at least 4 hr, and replaced in formalin. Tissues were then dehydrated in graded alcohols, cleared with xylene, and embedded in pa&in wax. Transverse blocks of the nose were cut and prepared to yield histologic sections at the following levels: (1) just anterior to the incisor teeth, (2) approximately onethird of the distance from the posterior aspect of the incisor teeth to the incisive papilla, (3) at the incisive papilla, (4) at the crest of the second palatial ridge, and (5) at the center of the second molar tooth. Embedded tissues were sectioned at 5 pm and stained with hematoxylin and eosin for light microscopic examination. For photography, selected tissues were removed from pan&n, reembedded in glycol methacrylate (GMA), and 2- to 3- am-thick sections were cut and stained with Lee’s methylene blue. Selected nasal sections were stained with Alcian blue at pH 2.5 for acidic mucous glycoproteins. - Other examinations:
- Hematological data were collected using a Coulter S Plus II counter (Coulter Electronics, Inc., Hialeah, Ha.). Sodium and potassium determinations were performed with a Flame photometer 343 (Instrument Lab, Lexington, Mass). Chloride analyses were performed with a Coming Chloride 920 M meter (Coming Scientific Inst., Mechield, Mass.). An Abbott VP clinical analyzer (Abbott Labs, Chicago, Ill.) was used for determination of serum chemistries.
- Statistics:
- Data for body weights, serum chemistry, hematology, and organ weights were analyzed using an analysis of variance. Dunnett’s test was employed to detect differences between control and treatment groups (Steel and Torrie, 1980). Red blood cell morphology and histopathologic findings were analyzed using the Kolmorgomov-Smimov test (Daniel, 1978). In all cases, the preselected significance level was p ≤ 0.05.
- Clinical signs:
- effects observed, treatment-related
- Description (incidence and severity):
- Alopecia, 56 death
- Mortality:
- mortality observed, treatment-related
- Description (incidence):
- Alopecia, 56 death
- Body weight and weight changes:
- effects observed, treatment-related
- Description (incidence and severity):
- significant loss at 175 ppm
- Food consumption and compound intake (if feeding study):
- not examined
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- not examined
- Ophthalmological findings:
- not examined
- Haematological findings:
- not specified
- Clinical biochemistry findings:
- effects observed, treatment-related
- Description (incidence and severity):
- increased glucose (females, 175 ppm)
- Endocrine findings:
- not examined
- Urinalysis findings:
- not examined
- Behaviour (functional findings):
- not examined
- Immunological findings:
- not examined
- Organ weight findings including organ / body weight ratios:
- not specified
- Gross pathological findings:
- not specified
- Neuropathological findings:
- effects observed, treatment-related
- Description (incidence and severity):
- At the 50-ppm exposure level, lesions in the nasal passages were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus.
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Description (incidence and severity):
- Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In mice, there was no apparent progression or increase in severity of the nasal lesions from 6 to 12 months. The lesions were present in two areas of the nose: (1) the respiratory epithelium and underlying tissues adjacent to the vestibule, and (2) the olfactory epithelium in the medial portion of the dorsal meatus with variable involvement of more posterior olfactory areas. There was a distinct concentration-response relationship for the severity and frequency of both lesions.
(1) Lesions in respiratory epithelium. The lesions in the respiratory area were most severe on the anterior septum, just posterior to the vestibule, and on the free margins of the naso- and maxilloturbinates, with lesser involvement of the lateral wall. In the 175 ppm exposure group, there was variable destruction of the anterior portions of the naso- and maxilloturbinates, and fenestration of the nasal septum. In areas of destruction of the turbinates and septum, the surface was covered by nonkeratinizing squamous epithelium. Evidence of both acute and chronic inflammatory response included focal to diffuse mucosal and submucosal infiltration of mononuclear leukocytes and some neutrophils. Exudate was minimal or absent. Other lesions included epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to diffuse squamous metaplasia. No Goblet cell hyperplasia was observed on the ventral aspect of the nasal septum in mice. Globules of eosinophilic material were observed in the respiratory epithelium of the anterior nasal passages. The globules were present in the basal half of the affected cells, and the dense, oval to round nucleus appeared to be compressed between the globules and the basement membrane. The cell type containing the globules was not identified. Small, basophilic bodies, which were laminated and presumably mineralized, with the globules in mice.
At the 50-ppm exposure level, lesions in the respiratory epithelium were minimal in both rats and mice. Changes were confined to focal squamous metaplasia on the free margins of the turbinates in mice after 6 months of exposure, and eosinophilic globules with mild inflammation and epithelial hypertrophy and hyperplasia after 12 months. A slightly higher incidence of chronic inflammation was observed in the vestibule and the respiratory epithelium of rats in the 10-ppm exposure group.
(2) Lesions in the olfactory region. DMA exposure induced a concentration-dependent destruction of the olfactory epithelium which was most severe in the middle third of the dorsal meatus, with variable involvement of the free margins of the ectoturbinates. The most widespread change, which was found consistently in DMA exposed mice, was degeneration of olfactory sensory cells with variable vacuolation of the olfactory epithelium. Another lesion often observed in areas of the olfactory epithelium was characterized by accumulation of hyaline, eosinophilic material in sustentacular cells, which were often markedly hypertrophic. The eosinophilic material was also present as large globules in the overlying airway, suggesting that it may be a secretory product of the sustentacular cells. Similar material was present in the large submucosal glands at the junction of olfactory and respiratory epithelium. These lesions were almost always accompanied by atrophy of the olfactory nerves in the lamina propria. Bowman’s glands exhibited or focal hyperplasia. In the more severely affected cases, olfactory epithelium was replaced by well-differentiated, ciliated respiratory epithelium. These metaplastic areas of ciliated respiratory epithelium were found, in several cases, to be continuous with ciliated ducts of hypertrophic or hyperplastic Bowman’s glands. There were foci of fusiform cells near the basal layer in rats, but not in mice, in areas of respiratory metaplasia in the dorsal meatus. In the underlying, edematous connective tissue, the basement membrane appeared thickened and separated from the epithelium. No basal cell hyperplasia was observed in the olfactory epithelium of in mice. At the 50-ppm exposure level, lesions were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus. However, most of the animals exposed to 50 ppm exhibited olfactory epithelial lesions. After 12 months, only a few animals at the 10-ppm exposure level were affected, and lesions were confined to focal degeneration of the olfactory epithelium in the dorsal meatus.
Additionally, a number of neoplastic and nonneoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure. - Histopathological findings: neoplastic:
- no effects observed
- Description (incidence and severity):
- A number of neoplastic and nonneoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure.
- Details on results:
- A number of neoplastic and nonneoplastic lesions were found in both rats and mice, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure.
- Dose descriptor:
- LOAEC
- Remarks:
- local effects
- Effect level:
- 10 ppm
- Based on:
- test mat.
- Sex:
- male/female
- Basis for effect level:
- clinical signs
- gross pathology
- Dose descriptor:
- NOAEC
- Remarks:
- systemic effects
- Effect level:
- 50 ppm
- Based on:
- test mat.
- Sex:
- male/female
- Basis for effect level:
- clinical signs
- Critical effects observed:
- not specified
- Conclusions:
- The highest concentration: 175 ppm induced severe alterations in the nasal passages.
The middle concentration of 50 ppm did cause sigfnificantly lower alterations and the lowest dose of 10 ppm only caused slight alterations in a few animals. - Executive summary:
The mean body weight gain of rats and mice exposed to 175 ppm DMA was depressed to approximately 90 % of control after 3 weeks of exposure. The only other treatment-related changes were concentration related lesions in the nasal passages. Two distinct locations in the nose were affected: the respiratory epithelium in the anterior nasal passages, and the olfactory epithelium, especially that lining the anterior dorsal meatus. There was focal destruction of the anterior nasoturbinate and nasal septum, local inflammation, and focal squamous metaplasia of the respiratory epithelium in rats and mice. The olfactory epithelium exhibited extensive loss of sensory cells with less damage to sustentacular cells. There was also loss of olfactory nerves, hypertrophy of Bowman’s glands, and distension of the ducts of these glands by serocellular debris in regions underlying degenerating olfactory epithelium. At the 175-ppm exposure level, rats had more extensive olfactory lesions than mice, with hyperplasia of small basophilic cells adjacent to the basement membrane being present in rats but not mice. After 12 months of exposure to 10 ppm DMA, minimal loss of olfactory sensory cells and their axons in olfactory nerve bundles was observed in the nasal passages of a few rats and mice.
These results indicate that the olfactory sensory cell is highly sensitive to the toxic effects of DMA, with minor lesions being produced in rodents even at the current threshold limit value of 10 ppm.
- Endpoint:
- chronic toxicity: inhalation
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- other: acceptable, well-documented publication, which meets basis scientific principles
- Reason / purpose for cross-reference:
- reference to same study
- Principles of method if other than guideline:
- Male and female F-344 rats and B6C3Fl mice were exposed by inhalation to 0, 10, 50, or 175 ppm dimethylamine (DMA) for 6 hr/day, 5 days/week for 12 months. Groups of 9-10 male and female rats and mice were necropsied after 6 and 12 months of exposure.
The purpose of this study was to investigate the toxicity associated with chronic inhalation exposure of F-344 rats and B6C3Fl mice to DMA for 2 years. This report summarizes the clinical and pathologic data found for the first 12-month period. - GLP compliance:
- no
- Limit test:
- yes
- Species:
- rat
- Strain:
- Fischer 344
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River breeding laboratories, Kingston, New York, and Portage, Michigan, respectively
- Age at study initiation: 4-8 weeks
- Housing: individually in hanging stainless steel wire mesh cages in the exposure chambers
- Diet (e.g. ad libitum): NIH-07 open formula diet, Ziegler Brothers, Gardners, Pa.; analyzed for contaminants by Lancaster Labs, Lancaster, Pa.), ad libitum during periods of non-exposure
- Water (e.g. ad libitum): tap water via an automatic watering system, ad libitum during periods of non-exposure
- Acclimation period: 14 days
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 68 - 76 °F
- Humidity (%): 45 - 65 % (real: 35 - 74 %)
- Air changes (per hr): airflow of 2200 liters/min
- Photoperiod (hrs dark / hrs light): 12-hr light/dark cycle - Route of administration:
- inhalation
- Type of inhalation exposure:
- whole body
- Vehicle:
- air
- Remarks on MMAD:
- MMAD / GSD: no data
- Details on inhalation exposure:
- Test atmospheres were generated by metering pure DMA directly from the cylinder via flowmeters (Fischer-Porter, Warminster, Pa., or Calibrating and Measuring Equipment, Inc., Manassas, Va.) into the supply air stream.
- Analytical verification of doses or concentrations:
- yes
- Details on analytical verification of doses or concentrations:
- 99,97 % pure
Analysis of the test atmospheres was performed four times per hour by infrared spectrometry at a wavelength of 3.5 pm and a path length of 20.25 m (MIRAN 801, Foxboro-W&s, Norwalk, Conn.). The spectrophotometer was set to zero optical density with ultra zero air containing approximately 350 ppm Co, (Ma&son Gas, Morrow, Ga.) and adjusted to approximately 50% relative humidity. Temperature and relative humidity were recorded hourly.
The distribution of the analytical concentration of DMA in the chambers was determined to be uniform within ± 6 % of target concentrations.
The mean time-weighted average (TWA) analytical chamber concentrations for the 12 month period, derived from daily TWA concentrations, with standard deviations and ranges were 175 ppm ± 2.0 (167-188), 50.0 ppm ± 1.0 (45.8-54.0), and 10.0 ppm ± 0.3 (9.0-10.8). The average percentage ratios of analytical/nominal concentrations (± standard deviations) were 81 ± 8, 87 ± 7, and 76 ± 15% for the 175-, 50-, and 10-ppm chambers, respectively, thus indicating a fairly constant loss of DMA on the chamber surfaces and animals for each chamber. - Duration of treatment / exposure:
- 6 h /day, 5 days a week, for 12 month
- Frequency of treatment:
- daily
- Dose / conc.:
- 0 ppm (nominal)
- Dose / conc.:
- 10 ppm (nominal)
- Dose / conc.:
- 50 ppm (nominal)
- Dose / conc.:
- 175 ppm (nominal)
- No. of animals per sex per dose:
- 95 animals / sex
- Control animals:
- yes, concurrent no treatment
- Details on study design:
- In studies at our laboratory (unpublished observations), F-344 rats exposed to 175 or 250 ppm DMA (6 hr/day, 5 days) or 500 ppm DMA (6 hr/day, 3 days) had ulcerative rhinitis, severe congestion, and squamous metaplasia in the respiratory tract. These lesions were most severe in the anterior sections of the nasal passages.
- Observations and examinations performed and frequency:
- The animals were observed for clinical abnormalities twice daily and were weighed once per week for the first 13 weeks, and biweekly thereafter.
- Sacrifice and pathology:
- After 6 and 12 months, 9-10 animals of each species, sex, and treatment group were fasted overnight and weighed just prior to necropsy.
Male mice were not included in the 12-month sacrifice because of the hi rate of unscheduled mortality in this group.
Animals were anesthetized with pentobarbital by ip injection, and blood was drawn from the heart for hematology and serum chemistry. Each animal was examined for gross abnormalities, and 45 tissues and any gross lesions were collected and placed in 10% buffered formalin. The nasal passages were flushed, the lungs inflated, and the lumen of the gastrointestinal tract infused with formalin. The liver, kidneys, and brain were weighed. All tissues from the control and 175~ppm exposed animals and target tissues (nasal turbinates) from the 10- and 50- ppm exposed animals were processed for light microscopic examination. Tissues containing bone were placed in 10% buffered formalin for 48 hr, decakSed in Cal-ex solution (Fisher Scientific, Raleigh, N.C.) for 2 days, then rinsed with tap water for at least 4 hr, and replaced in formalin. Tissues were then dehydrated in graded alcohols, cleared with xylene, and embedded in pa&in wax. Transverse blocks of the nose were cut and prepared to yield histologic sections at the following levels: (1) just anterior to the incisor teeth, (2) approximately onethird of the distance from the posterior aspect of the incisor teeth to the incisive papilla, (3) at the incisive papilla, (4) at the crest of the second palatial ridge, and (5) at the center of the second molar tooth. Embedded tissues were sectioned at 5 pm and stained with hematoxylin and eosin for light microscopic examination. For photography, selected tissues were removed from pan&n, reembedded in glycol methacrylate (GMA), and 2- to 3- am-thick sections were cut and stained with Lee’s methylene blue. Selected nasal sections were stained with Alcian blue at pH 2.5 for acidic mucous glycoproteins. - Other examinations:
- Hematological data were collected using a Coulter S Plus II counter (Coulter Electronics, Inc., Hialeah, Ha.). Sodium and potassium determinations were performed with a Flame photometer 343 (Instrument Lab, Lexington, Mass). Chloride analyses were performed with a Coming Chloride 920 M meter (Coming Scientific Inst., Mechield, Mass.). An Abbott VP clinical analyzer (Abbott Labs, Chicago, Ill.) was used for determination of serum chemistries.
- Statistics:
- Data for body weights, serum chemistry, hematology, and organ weights were analyzed using an analysis of variance. Dunnett’s test was employed to detect differences between control and treatment groups (Steel and Torrie, 1980). Red blood cell morphology and histopathologic findings were analyzed using the Kolmorgomov-Smimov test (Daniel, 1978). In all cases, the preselected significance levei was p ≤ 0.05.
- Clinical signs:
- effects observed, treatment-related
- Description (incidence and severity):
- Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In mice, there was no apparent progression or increase in severity of the nasal lesions from 6 to 12 months, while in rats, increased exposure time was associated with more extensive involvement of the olfactory area.
- Body weight and weight changes:
- effects observed, treatment-related
- Description (incidence and severity):
- significant loss at 175 ppm (90 % of control)
- Food consumption and compound intake (if feeding study):
- not examined
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- not examined
- Ophthalmological findings:
- not examined
- Haematological findings:
- effects observed, treatment-related
- Description (incidence and severity):
- decreased platelet counts (175 ppm), increased counts of atypical lymphocytes in females (175 ppm), decreased mean red blood cell volume (females, 175 ppm)
- Clinical biochemistry findings:
- effects observed, treatment-related
- Description (incidence and severity):
- decreased protein (175 ppm), increased alkaline phosphatase (females, 175 ppm)
- Endocrine findings:
- not specified
- Urinalysis findings:
- not specified
- Behaviour (functional findings):
- not examined
- Immunological findings:
- not examined
- Organ weight findings including organ / body weight ratios:
- not specified
- Gross pathological findings:
- not specified
- Neuropathological findings:
- not specified
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Description (incidence and severity):
- Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In rats, increased exposure time (from 6 to 12 month) was associated with more extensive involvement of the olfactory area. The lesions were present in two areas of the nose: (1) the respiratory epithelium and underlying tissues adjacent to the vestibule, and (2) the olfactory epithelium in the medial portion of the dorsal meatus with variable involvement of more posterior olfactory areas. There was a distinct concentration-response relationship for the severity and frequency of both lesions.
(1) Lesions in respiratory epithelium. The lesions in the respiratory area were most severe on the anterior septum, just posterior to the vestibule, and on the free margins of the naso- and maxilloturbinates, with lesser involvement of the lateral wall. In the 175 ppm exposure group, there was variable destruction of the anterior portions of the naso- and maxilloturbinates, and fenestration of the nasal septum. In areas of destruction of the turbinates and septum, the surface was covered by nonkeratinizing squamous epithelium. Evidence of both acute and chronic inflammatory response included focal to diffuse mucosal and submucosal infiltration of mononuclear leukocytes and some neutrophils. Exudate was minimal or absent. Other lesions included epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to diffuse squamous metaplasia. Goblet cell hyperplasia of mild to moderate severity was observed on the ventral aspect of the nasal septum in rats. Globules of eosinophilic material were observed in the respiratory epithelium of the anterior nasal passages. The globules were present in the basal half of the affected cells, and the dense, oval to round nucleus appeared to be compressed between the globules and the basement membrane. The cell type containing the globules was not identified. Small, basophilic bodies, which were laminated and presumably mineralized, with the globules in mice.
At the 50-ppm exposure level, lesions in the respiratory epithelium were minimal in rats. A slightly higher incidence of chronic inflammation was observed in the vestibule and the respiratory epithelium of rats in the 10-ppm exposure group.
(2) Lesions in the olfactory region. DMA exposure induced a concentration-dependent destruction of the olfactory epithelium which was most severe in the middle third of the dorsal meatus, with variable involvement of the free margins of the ectoturbinates. The most widespread change, which was found consistently in DMA exposed rats, was degeneration of olfactory sensory cells with variable vacuolation of the olfactory epithelium. Another lesion often observed in areas of the olfactory epithelium was characterized by accumulation of hyaline, eosinophilic material in sustentacular cells, which were often markedly hypertrophic. The eosinophilic material was also present as large globules in the overlying airway, suggesting that it may be a secretory product of the sustentacular cells. Similar material was present in the large submucosal glands at the junction of olfactory and respiratory epithelium. These lesions were almost always accompanied by atrophy of the olfactory nerves in the lamina propria. Bowman’s glands exhibited or focal hyperplasia. In the more severely affected cases, olfactory epithelium was replaced by well-differentiated, ciliated respiratory epithelium. These metaplastic areas of ciliated respiratory epithelium were found, in several cases, to be continuous with ciliated ducts of hypertrophic or hyperplastic Bowman’s glands. There were foci of fusiform cells near the basal layer in rats in areas of respiratory metaplasia in the dorsal meatus. In the underlying, edematous connective tissue, the basement membrane appeared thickened and separated from the epithelium. Basal cell hyperplasia was frequently observed in the olfactory epithelium of rats. This lesion was characterized by a zone of polyhedral to fusiform cells lying beneath any remaining sustentacular cells. The basal cells had indistinct cytoplasmic boundaries and dark round nuclei and formed cords, sheets, or acinar arrangements. At the 50-ppm exposure level, lesions were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus. However, most of the animals exposed to 50 ppm exhibited olfactory epithelial lesions. After 12 months, only a few animals at the 10-ppm exposure level were affected, and lesions were confined to focal degeneration of the olfactory epithelium in the dorsal meatus.
Additionally a number of neoplastic and non-neoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure. - Histopathological findings: neoplastic:
- effects observed, non-treatment-related
- Description (incidence and severity):
- A number of neoplastic and non-neoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure.
- Details on results:
- A number of neoplastic and non-neoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure.
- Dose descriptor:
- LOAEC
- Remarks:
- local effects
- Effect level:
- 10 ppm
- Based on:
- other:
- Sex:
- male/female
- Basis for effect level:
- clinical signs
- gross pathology
- Dose descriptor:
- NOAEC
- Remarks:
- systemic
- Effect level:
- 50 ppm
- Based on:
- test mat.
- Sex:
- male/female
- Basis for effect level:
- body weight and weight gain
- Critical effects observed:
- not specified
- Conclusions:
- The highest concentration: 175 ppm induced severe alterations in the nasal passages.
The middle concentration of 50 ppm did cause significantly lower alterations and the lowest dose of 10 ppm only caused slight alterations in a few animals. - Executive summary:
The mean body weight gain of rats and mice exposed to 175 ppm DMA was depressed to approximately 90 % of control after 3 weeks of exposure. The only other treatment-related changes were concentration-related lesions in the nasal passages. Two distinct locations in the nose were affected~ the respiratory epithelium in the anterior nasal passages, and the olfactory epithelium, especially that lining the anterior dorsal meatus. There was focal destruction of the anterior nasoturbinate and nasal septum, local inflammation, and focal squamous metaplasia of the respiratory epithelium in rats and mice. Mild goblet cell hyperplasia was observed only in rats. The olfactory epithelium exhibited extensive loss of sensory cells with less damage to sustentacular cells. There was also loss of olfactory nerves, hypertrophy of Bowman’s glands, and distension of the ducts of these glands by serocellular debris in regions underlying degenerating olfactory epithelium. At the 175-ppm exposure level, rats had more extensive olfactory lesions than mice, with hyperplasia of small basophilic cells adjacent to the basement membrane being present in rats but not mice. After 12 months of exposure to 10 ppm DMA, minimal loss of olfactory sensory cells and their axons in olfactory nerve bundles was observed in the nasal passages of a few rats and mice. These results indicate that the olfactory sensory cell is highly sensitive to the toxic effects of DMA, with minor lesions being produced in rodents even at the current threshold limit value of 10 ppm.
The following effect level were derived: LOAEC = 10 ppm = 18.45 mg/m³ for local effects and NOAEC (systemic) = 50 ppm = 92.26 mg/m³ for systemic effects (conversion of ppm value into mg/m³ value was performed taking into account the temperature of 76 °F of the Buckley study).
Referenceopen allclose all
Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In mice, there was no apparent progression or increase in severity of the nasal lesions from 6 to 12 months, while in rats, increased exposure time was associated with more extensive involvement of the olfactory area. The lesions were present in two areas of the nose: (1) the respiratory epithelium and underlying tissues adjacent to the vestibule, and (2) the olfactory epithelium in the medial portion of the dorsal meatus with variable involvement of more posterior olfactory areas. There was a distinct concentration-response relationship for the severity and frequency of both lesions.
(1) Lesions in respiratory epithelium. The lesions in the respiratory area were most severe on the anterior septum, just posterior to the vestibule, and on the free margins of the naso- and maxilloturbinates, with lesser involvement of the lateral wall. In the 175 ppm exposure group, there was variable destruction of the anterior portions of the naso- and maxilloturbinates, and fenestration of the nasal septum. In areas of destruction of the turbinates and septum, the surface was covered by nonkeratinizing squamous epithelium. Evidence of both acute and chronic inflammatory response included focal to diffuse mucosal and submucosal infiltration of mononuclear leukocytes and some neutrophils. Exudate was minimal or absent. Other lesions included epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to diffuse squamous metaplasia. Goblet cell hyperplasia of mild to moderate severity was observed on the ventral aspect of the nasal septum in rats, but not in mice. Globules of eosinophilic material were observed in the respiratory epithelium of the anterior nasal passages. The globules were present in the basal half of the affected cells, and the dense, oval to round nucleus appeared to be compressed between the globules and the basement membrane. The cell type containing the globules was not identified. Small, basophilic bodies, which were laminated and presumably mineralized, with the globules in mice.
At the 50-ppm exposure level, lesions in the respiratory epithelium were minimal in both rats and mice. Changes were confined to focal squamous metaplasia on the free margins of the turbinates in mice after 6 months of exposure, and eosinophilic globules with mild inflammation and epithelial hypertrophy and hyperplasia after 12 months. A slightly higher incidence of chronic inflammation was observed in the vestibule and the respiratory epithelium of rats in the 10-ppm exposure group.
(2) Lesions in the olfactory region. DMA exposure induced a concentration-dependent destruction of the olfactory epithelium which was most severe in the middle third of the dorsal meatus, with variable involvement of the free margins of the ectoturbinates. The most widespread change, which was found consistently in DMA exposed rats and mice, was degeneration of olfactory sensory cells with variable vacuolation of the olfactory epithelium. Another lesion often observed in areas of the olfactory epithelium was characterized by accumulation of hyaline, eosinophilic material in sustentacular cells, which were often markedly hypertrophic. The eosinophilic material was also present as large globules in the overlying airway, suggesting that it may be a secretory product of the sustentacular cells. Similar material was present in the large submucosal glands at the junction of olfactory and respiratory epithelium. These lesions were almost always accompanied by atrophy of the olfactory nerves in the lamina propria. Bowman’s glands exhibited or focal hyperplasia. In the more severely affected cases, olfactory epithelium was replaced by well-differentiated, ciliated respiratory epithelium. These metaplastic areas of ciliated respiratory epithelium were found, in several cases, to be continuous with ciliated ducts of hypertrophic or hyperplastic Bowman’s glands. There were foci of fusiform cells near the basal layer in rats, but not in mice, in areas of respiratory metaplasia in the dorsal meatus. In the underlying, edematous connective tissue, the basement membrane appeared thickened and separated from the epithelium. Basal cell hyperplasia was frequently observed in the olfactory epithelium of rats, but was not observed in mice. This lesion was characterized by a zone of polyhedral to fusiform cells lying beneath any remaining sustentacular cells. The basal cells had indistinct cytoplasmic boundaries and dark round nuclei and formed cords, sheets, or acinar arrangements. At the 50-ppm exposure level, lesions were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus. However, most of the animals exposed to 50 ppm exhibited olfactory epithelial lesions. After 12 months, only a few animals at the 10-ppm exposure level were affected, and lesions were confined to focal degeneration of the olfactory epithelium in the dorsal meatus.
TABLE 1. Lesions in Nasal Passages of Rats and Mice Exposed to DMA for 12 Months |
|||||
DMA (ppm) |
|
Squamous epithelium (level I)a |
Respiratory epithelium (levels I, II)b |
Olfactory epithelium |
Chronic inflammation (levels I, II, III) |
0 |
Rats |
— |
— |
+/- |
+ |
Mice |
— |
— |
— |
— |
|
10 |
Rats |
— |
+/- |
+ |
+ |
Mice |
— |
+/- |
+ |
— |
|
50 |
Rats |
— |
+ |
++ |
++ |
Mice |
— |
+ |
++ |
+ |
|
175 |
Rats |
+/- |
+++ |
+++ |
++ |
Mice |
+/- |
+++ |
+++ |
+ |
|
Note. — =No abnormality detected. +/- = very slight changes of doubtful significance, + = minimal change, ++ = moderate change, +++ = severe change. |
|||||
Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In mice, there was no apparent progression or increase in severity of the nasal lesions from 6 to 12 months, while in rats, increased exposure time was associated with more extensive involvement of the olfactory area. The lesions were present in two areas of the nose: (1) the respiratory epithelium and underlying tissues adjacent to the vestibule, and (2) the olfactory epithelium in the medial portion of the dorsal meatus with variable involvement of more posterior olfactory areas. There was a distinct concentration-response relationship for the severity and frequency of both lesions.
(1) Lesions in respiratory epithelium. The lesions in the respiratory area were most severe on the anterior septum, just posterior to the vestibule, and on the free margins of the naso- and maxilloturbinates, with lesser involvement of the lateral wall. In the 175 ppm exposure group, there was variable destruction of the anterior portions of the naso- and maxilloturbinates, and fenestration of the nasal septum. In areas of destruction of the turbinates and septum, the surface was covered by nonkeratinizing squamous epithelium. Evidence of both acute and chronic inflammatory response included focal to diffuse mucosal and submucosal infiltration of mononuclear leukocytes and some neutrophils. Exudate was minimal or absent. Other lesions included epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to diffuse squamous metaplasia. Goblet cell hyperplasia of mild to moderate severity was observed on the ventral aspect of the nasal septum in rats, but not in mice. Globules of eosinophilic material were observed in the respiratory epithelium of the anterior nasal passages. The globules were present in the basal half of the affected cells, and the dense, oval to round nucleus appeared to be compressed between the globules and the basement membrane. The cell type containing the globules was not identified. Small, basophilic bodies, which were laminated and presumably mineralized, with the globules in mice.
At the 50-ppm exposure level, lesions in the respiratory epithelium were minimal in both rats and mice. Changes were confined to focal squamous metaplasia on the free margins of the turbinates in mice after 6 months of exposure, and eosinophilic globules with mild inflammation and epithelial hypertrophy and hyperplasia after 12 months. A slightly higher incidence of chronic inflammation was observed in the vestibule and the respiratory epithelium of rats in the 10-ppm exposure group.
(2) Lesions in the olfactory region. DMA exposure induced a concentration-dependent destruction of the olfactory epithelium which was most severe in the middle third of the dorsal meatus, with variable involvement of the free margins of the ectoturbinates. The most widespread change, which was found consistently in DMA exposed rats and mice, was degeneration of olfactory sensory cells with variable vacuolation of the olfactory epithelium. Another lesion often observed in areas of the olfactory epithelium was characterized by accumulation of hyaline, eosinophilic material in sustentacular cells, which were often markedly hypertrophic. The eosinophilic material was also present as large globules in the overlying airway, suggesting that it may be a secretory product of the sustentacular cells. Similar material was present in the large submucosal glands at the junction of olfactory and respiratory epithelium. These lesions were almost always accompanied by atrophy of the olfactory nerves in the lamina propria. Bowman’s glands exhibited or focal hyperplasia. In the more severely affected cases, olfactory epithelium was replaced by well-differentiated, ciliated respiratory epithelium. These metaplastic areas of ciliated respiratory epithelium were found, in several cases, to be continuous with ciliated ducts of hypertrophic or hyperplastic Bowman’s glands. There were foci of fusiform cells near the basal layer in rats, but not in mice, in areas of respiratory metaplasia in the dorsal meatus. In the underlying, edematous connective tissue, the basement membrane appeared thickened and separated from the epithelium. Basal cell hyperplasia was frequently observed in the olfactory epithelium of rats, but was not observed in mice. This lesion was characterized by a zone of polyhedral to fusiform cells lying beneath any remaining sustentacular cells. The basal cells had indistinct cytoplasmic boundaries and dark round nuclei and formed cords, sheets, or acinar arrangements. At the 50-ppm exposure level, lesions were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus. However, most of the animals exposed to 50 ppm exhibited olfactory epithelial lesions. After 12 months, only a few animals at the 10-ppm exposure level were affected, and lesions were confined to focal degeneration of the olfactory epithelium in the dorsal meatus.
TABLE 1. Lesions in Nasal Passages of Rats and Mice Exposed to DMA for 12 Months |
|||||
DMA (ppm) |
|
Squamous epithelium (level I)a |
Respiratory epithelium (levels I, II)b |
Olfactory epithelium |
Chronic inflammation (levels I, II, III) |
0 |
Rats |
— |
— |
+/- |
+ |
Mice |
— |
— |
— |
— |
|
10 |
Rats |
— |
+/- |
+ |
+ |
Mice |
— |
+/- |
+ |
— |
|
50 |
Rats |
— |
+ |
++ |
++ |
Mice |
— |
+ |
++ |
+ |
|
175 |
Rats |
+/- |
+++ |
+++ |
++ |
Mice |
+/- |
+++ |
+++ |
+ |
|
Note. — =No abnormality detected. +/- = very slight changes of doubtful significance, + = minimal change, ++ = moderate change, +++ = severe change. |
|||||
Endpoint conclusion
- Endpoint conclusion:
- adverse effect observed
- Dose descriptor:
- NOAEC
- 92.26 mg/m³
- Study duration:
- chronic
- Experimental exposure time per week (hours/week):
- 30
- Species:
- rat
Repeated dose toxicity: inhalation - local effects
Link to relevant study records
- Endpoint:
- chronic toxicity: inhalation
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- other: acceptable, well-documented publication, which meets basis scientific principles
- Reason / purpose for cross-reference:
- reference to same study
- Principles of method if other than guideline:
- Male and female F-344 rats and B6C3Fl mice were exposed by inhalation to 0, 10, 50, or 175 ppm dimethylamine (DMA) for 6 hr/day, 5 days/week for 12 months. Groups of 9-10 male and female rats and mice were necropsied after 6 and 12 months of exposure.
The purpose of this study was to investigate the toxicity associated with chronic inhalation exposure of F-344 rats and B6C3Fl mice to DMA for 2 years. This report summarizes the clinical and pathologic data found for the first 12-month period. - GLP compliance:
- no
- Limit test:
- yes
- Species:
- rat
- Strain:
- Fischer 344
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River breeding laboratories, Kingston, New York, and Portage, Michigan, respectively
- Age at study initiation: 4-8 weeks
- Housing: individually in hanging stainless steel wire mesh cages in the exposure chambers
- Diet (e.g. ad libitum): NIH-07 open formula diet, Ziegler Brothers, Gardners, Pa.; analyzed for contaminants by Lancaster Labs, Lancaster, Pa.), ad libitum during periods of non-exposure
- Water (e.g. ad libitum): tap water via an automatic watering system, ad libitum during periods of non-exposure
- Acclimation period: 14 days
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 68 - 76 °F
- Humidity (%): 45 - 65 % (real: 35 - 74 %)
- Air changes (per hr): airflow of 2200 liters/min
- Photoperiod (hrs dark / hrs light): 12-hr light/dark cycle - Route of administration:
- inhalation
- Type of inhalation exposure:
- whole body
- Vehicle:
- air
- Remarks on MMAD:
- MMAD / GSD: no data
- Details on inhalation exposure:
- Test atmospheres were generated by metering pure DMA directly from the cylinder via flowmeters (Fischer-Porter, Warminster, Pa., or Calibrating and Measuring Equipment, Inc., Manassas, Va.) into the supply air stream.
- Analytical verification of doses or concentrations:
- yes
- Details on analytical verification of doses or concentrations:
- 99,97 % pure
Analysis of the test atmospheres was performed four times per hour by infrared spectrometry at a wavelength of 3.5 pm and a path length of 20.25 m (MIRAN 801, Foxboro-W&s, Norwalk, Conn.). The spectrophotometer was set to zero optical density with ultra zero air containing approximately 350 ppm Co, (Ma&son Gas, Morrow, Ga.) and adjusted to approximately 50% relative humidity. Temperature and relative humidity were recorded hourly.
The distribution of the analytical concentration of DMA in the chambers was determined to be uniform within ± 6 % of target concentrations.
The mean time-weighted average (TWA) analytical chamber concentrations for the 12 month period, derived from daily TWA concentrations, with standard deviations and ranges were 175 ppm ± 2.0 (167-188), 50.0 ppm ± 1.0 (45.8-54.0), and 10.0 ppm ± 0.3 (9.0-10.8). The average percentage ratios of analytical/nominal concentrations (± standard deviations) were 81 ± 8, 87 ± 7, and 76 ± 15% for the 175-, 50-, and 10-ppm chambers, respectively, thus indicating a fairly constant loss of DMA on the chamber surfaces and animals for each chamber. - Duration of treatment / exposure:
- 6 h /day, 5 days a week, for 12 month
- Frequency of treatment:
- daily
- Dose / conc.:
- 0 ppm (nominal)
- Dose / conc.:
- 10 ppm (nominal)
- Dose / conc.:
- 50 ppm (nominal)
- Dose / conc.:
- 175 ppm (nominal)
- No. of animals per sex per dose:
- 95 animals / sex
- Control animals:
- yes, concurrent no treatment
- Details on study design:
- In studies at our laboratory (unpublished observations), F-344 rats exposed to 175 or 250 ppm DMA (6 hr/day, 5 days) or 500 ppm DMA (6 hr/day, 3 days) had ulcerative rhinitis, severe congestion, and squamous metaplasia in the respiratory tract. These lesions were most severe in the anterior sections of the nasal passages.
- Observations and examinations performed and frequency:
- The animals were observed for clinical abnormalities twice daily and were weighed once per week for the first 13 weeks, and biweekly thereafter.
- Sacrifice and pathology:
- After 6 and 12 months, 9-10 animals of each species, sex, and treatment group were fasted overnight and weighed just prior to necropsy.
Male mice were not included in the 12-month sacrifice because of the hi rate of unscheduled mortality in this group.
Animals were anesthetized with pentobarbital by ip injection, and blood was drawn from the heart for hematology and serum chemistry. Each animal was examined for gross abnormalities, and 45 tissues and any gross lesions were collected and placed in 10% buffered formalin. The nasal passages were flushed, the lungs inflated, and the lumen of the gastrointestinal tract infused with formalin. The liver, kidneys, and brain were weighed. All tissues from the control and 175~ppm exposed animals and target tissues (nasal turbinates) from the 10- and 50- ppm exposed animals were processed for light microscopic examination. Tissues containing bone were placed in 10% buffered formalin for 48 hr, decakSed in Cal-ex solution (Fisher Scientific, Raleigh, N.C.) for 2 days, then rinsed with tap water for at least 4 hr, and replaced in formalin. Tissues were then dehydrated in graded alcohols, cleared with xylene, and embedded in pa&in wax. Transverse blocks of the nose were cut and prepared to yield histologic sections at the following levels: (1) just anterior to the incisor teeth, (2) approximately onethird of the distance from the posterior aspect of the incisor teeth to the incisive papilla, (3) at the incisive papilla, (4) at the crest of the second palatial ridge, and (5) at the center of the second molar tooth. Embedded tissues were sectioned at 5 pm and stained with hematoxylin and eosin for light microscopic examination. For photography, selected tissues were removed from pan&n, reembedded in glycol methacrylate (GMA), and 2- to 3- am-thick sections were cut and stained with Lee’s methylene blue. Selected nasal sections were stained with Alcian blue at pH 2.5 for acidic mucous glycoproteins. - Other examinations:
- Hematological data were collected using a Coulter S Plus II counter (Coulter Electronics, Inc., Hialeah, Ha.). Sodium and potassium determinations were performed with a Flame photometer 343 (Instrument Lab, Lexington, Mass). Chloride analyses were performed with a Coming Chloride 920 M meter (Coming Scientific Inst., Mechield, Mass.). An Abbott VP clinical analyzer (Abbott Labs, Chicago, Ill.) was used for determination of serum chemistries.
- Statistics:
- Data for body weights, serum chemistry, hematology, and organ weights were analyzed using an analysis of variance. Dunnett’s test was employed to detect differences between control and treatment groups (Steel and Torrie, 1980). Red blood cell morphology and histopathologic findings were analyzed using the Kolmorgomov-Smimov test (Daniel, 1978). In all cases, the preselected significance levei was p ≤ 0.05.
- Clinical signs:
- effects observed, treatment-related
- Description (incidence and severity):
- Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In mice, there was no apparent progression or increase in severity of the nasal lesions from 6 to 12 months, while in rats, increased exposure time was associated with more extensive involvement of the olfactory area.
- Body weight and weight changes:
- effects observed, treatment-related
- Description (incidence and severity):
- significant loss at 175 ppm (90 % of control)
- Food consumption and compound intake (if feeding study):
- not examined
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- not examined
- Ophthalmological findings:
- not examined
- Haematological findings:
- effects observed, treatment-related
- Description (incidence and severity):
- decreased platelet counts (175 ppm), increased counts of atypical lymphocytes in females (175 ppm), decreased mean red blood cell volume (females, 175 ppm)
- Clinical biochemistry findings:
- effects observed, treatment-related
- Description (incidence and severity):
- decreased protein (175 ppm), increased alkaline phosphatase (females, 175 ppm)
- Endocrine findings:
- not specified
- Urinalysis findings:
- not specified
- Behaviour (functional findings):
- not examined
- Immunological findings:
- not examined
- Organ weight findings including organ / body weight ratios:
- not specified
- Gross pathological findings:
- not specified
- Neuropathological findings:
- not specified
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Description (incidence and severity):
- Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In rats, increased exposure time (from 6 to 12 month) was associated with more extensive involvement of the olfactory area. The lesions were present in two areas of the nose: (1) the respiratory epithelium and underlying tissues adjacent to the vestibule, and (2) the olfactory epithelium in the medial portion of the dorsal meatus with variable involvement of more posterior olfactory areas. There was a distinct concentration-response relationship for the severity and frequency of both lesions.
(1) Lesions in respiratory epithelium. The lesions in the respiratory area were most severe on the anterior septum, just posterior to the vestibule, and on the free margins of the naso- and maxilloturbinates, with lesser involvement of the lateral wall. In the 175 ppm exposure group, there was variable destruction of the anterior portions of the naso- and maxilloturbinates, and fenestration of the nasal septum. In areas of destruction of the turbinates and septum, the surface was covered by nonkeratinizing squamous epithelium. Evidence of both acute and chronic inflammatory response included focal to diffuse mucosal and submucosal infiltration of mononuclear leukocytes and some neutrophils. Exudate was minimal or absent. Other lesions included epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to diffuse squamous metaplasia. Goblet cell hyperplasia of mild to moderate severity was observed on the ventral aspect of the nasal septum in rats. Globules of eosinophilic material were observed in the respiratory epithelium of the anterior nasal passages. The globules were present in the basal half of the affected cells, and the dense, oval to round nucleus appeared to be compressed between the globules and the basement membrane. The cell type containing the globules was not identified. Small, basophilic bodies, which were laminated and presumably mineralized, with the globules in mice.
At the 50-ppm exposure level, lesions in the respiratory epithelium were minimal in rats. A slightly higher incidence of chronic inflammation was observed in the vestibule and the respiratory epithelium of rats in the 10-ppm exposure group.
(2) Lesions in the olfactory region. DMA exposure induced a concentration-dependent destruction of the olfactory epithelium which was most severe in the middle third of the dorsal meatus, with variable involvement of the free margins of the ectoturbinates. The most widespread change, which was found consistently in DMA exposed rats, was degeneration of olfactory sensory cells with variable vacuolation of the olfactory epithelium. Another lesion often observed in areas of the olfactory epithelium was characterized by accumulation of hyaline, eosinophilic material in sustentacular cells, which were often markedly hypertrophic. The eosinophilic material was also present as large globules in the overlying airway, suggesting that it may be a secretory product of the sustentacular cells. Similar material was present in the large submucosal glands at the junction of olfactory and respiratory epithelium. These lesions were almost always accompanied by atrophy of the olfactory nerves in the lamina propria. Bowman’s glands exhibited or focal hyperplasia. In the more severely affected cases, olfactory epithelium was replaced by well-differentiated, ciliated respiratory epithelium. These metaplastic areas of ciliated respiratory epithelium were found, in several cases, to be continuous with ciliated ducts of hypertrophic or hyperplastic Bowman’s glands. There were foci of fusiform cells near the basal layer in rats in areas of respiratory metaplasia in the dorsal meatus. In the underlying, edematous connective tissue, the basement membrane appeared thickened and separated from the epithelium. Basal cell hyperplasia was frequently observed in the olfactory epithelium of rats. This lesion was characterized by a zone of polyhedral to fusiform cells lying beneath any remaining sustentacular cells. The basal cells had indistinct cytoplasmic boundaries and dark round nuclei and formed cords, sheets, or acinar arrangements. At the 50-ppm exposure level, lesions were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus. However, most of the animals exposed to 50 ppm exhibited olfactory epithelial lesions. After 12 months, only a few animals at the 10-ppm exposure level were affected, and lesions were confined to focal degeneration of the olfactory epithelium in the dorsal meatus.
Additionally a number of neoplastic and non-neoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure. - Histopathological findings: neoplastic:
- effects observed, non-treatment-related
- Description (incidence and severity):
- A number of neoplastic and non-neoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure.
- Details on results:
- A number of neoplastic and non-neoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure.
- Dose descriptor:
- LOAEC
- Remarks:
- local effects
- Effect level:
- 10 ppm
- Based on:
- other:
- Sex:
- male/female
- Basis for effect level:
- clinical signs
- gross pathology
- Dose descriptor:
- NOAEC
- Remarks:
- systemic
- Effect level:
- 50 ppm
- Based on:
- test mat.
- Sex:
- male/female
- Basis for effect level:
- body weight and weight gain
- Critical effects observed:
- not specified
- Conclusions:
- The highest concentration: 175 ppm induced severe alterations in the nasal passages.
The middle concentration of 50 ppm did cause significantly lower alterations and the lowest dose of 10 ppm only caused slight alterations in a few animals. - Executive summary:
The mean body weight gain of rats and mice exposed to 175 ppm DMA was depressed to approximately 90 % of control after 3 weeks of exposure. The only other treatment-related changes were concentration-related lesions in the nasal passages. Two distinct locations in the nose were affected~ the respiratory epithelium in the anterior nasal passages, and the olfactory epithelium, especially that lining the anterior dorsal meatus. There was focal destruction of the anterior nasoturbinate and nasal septum, local inflammation, and focal squamous metaplasia of the respiratory epithelium in rats and mice. Mild goblet cell hyperplasia was observed only in rats. The olfactory epithelium exhibited extensive loss of sensory cells with less damage to sustentacular cells. There was also loss of olfactory nerves, hypertrophy of Bowman’s glands, and distension of the ducts of these glands by serocellular debris in regions underlying degenerating olfactory epithelium. At the 175-ppm exposure level, rats had more extensive olfactory lesions than mice, with hyperplasia of small basophilic cells adjacent to the basement membrane being present in rats but not mice. After 12 months of exposure to 10 ppm DMA, minimal loss of olfactory sensory cells and their axons in olfactory nerve bundles was observed in the nasal passages of a few rats and mice. These results indicate that the olfactory sensory cell is highly sensitive to the toxic effects of DMA, with minor lesions being produced in rodents even at the current threshold limit value of 10 ppm.
The following effect level were derived: LOAEC = 10 ppm = 18.45 mg/m³ for local effects and NOAEC (systemic) = 50 ppm = 92.26 mg/m³ for systemic effects (conversion of ppm value into mg/m³ value was performed taking into account the temperature of 76 °F of the Buckley study).
- Endpoint:
- chronic toxicity: inhalation
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- other: acceptable, well-documented publication, which meets basis scientific principles
- Reason / purpose for cross-reference:
- reference to same study
- Principles of method if other than guideline:
- Male and female F-344 rats and B6C3Fl mice were exposed by inhalation to 0, 10, 50, or 175 ppm dimethylamine (DMA) for 6 hr/day, 5 days/week for 12 months. Groups of 9-10 male and female rats and mice were necropsied atIer 6 and 12 months of exposure.
The purpose of this study was to investigate the toxicity associated with chronic inhalation exposure of F-344 rats and B6C3Fl mice to DMA for 2 years. This report summarizes the clinical and pathologic data found for the first 12-month period. - GLP compliance:
- no
- Limit test:
- yes
- Species:
- mouse
- Strain:
- B6C3F1
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River breeding laboratories, Kingston, New York, and Portage, Michigan, respectively
- Age at study initiation: 4-8 weeks
- Housing: individually in hanging stainless steel wire mesh cages in the exposure chambers
- Diet (e.g. ad libitum): NIH-07 open formula diet, Ziegler Brothers, Gardners, Pa.; analyzed for contaminants by Lancaster Labs, Lancaster, Pa.), ad libitum during periods of non-exposure
- Water (e.g. ad libitum): tap water via an automatic watering system, ad libitum during periods of non-exposure
- Acclimation period: 14 days
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 68 - 76 °F
- Humidity (%): 45 - 65 % ( real: 35 - 74 %)
- Air changes (per hr): airflow of 2200 liters/min
- Photoperiod (hrs dark / hrs light): 12-hr light/dark cycle - Route of administration:
- inhalation
- Type of inhalation exposure:
- whole body
- Vehicle:
- air
- Remarks on MMAD:
- MMAD / GSD: no data
- Details on inhalation exposure:
- Test atmospheres were generated by metering pure DMA directly from the cylinder via flowmeters (Fischer-Porter, Warminster, Pa., or Calibrating and Measuring Equipment, Inc., Manassas, Va.) into the supply air stream.
- Details on analytical verification of doses or concentrations:
- 99,97 % pure
Analysis of the test atmospheres was performed four times per hour by infrared spectrometry at a wavelength of 3.5 pm and a path length of 20.25 m (MIRAN 801, Foxboro-W&s, Norwalk, Conn.). The spectrophotometer was set to zero optical density with ultra zero air containing approximately 350 ppm Co, (Ma&son Gas, Morrow, Ga.) and adjusted to approximately 50% relative humidity. Temperature and relative humidity were recorded hourly.
The distribution of the analytical concentration of DMA in the chambers was determined to be uniform within ± 6 % of target concentrations.
The mean time-weighted average (TWA) analytical chamber concentrations for the 12 month period, derived from daily TWA concentrations, with standard deviations and ranges were 175 ppm ± 2.0 (167-188), 50.0 ppm ± 1.0 (45.8-54.0), and 10.0 ppm ± 0.3 (9.0-10.8). The average percentage ratios of analytical/nominal concentrations (± standard deviations) were 81 ± 8, 87 ± 7, and 76 ± 15% for the 175-, 50-, and 10-ppm chambers, respectively, thus indicating a fairly constant loss of DMA on the chamber surfaces and animals for each chamber. - Duration of treatment / exposure:
- 6 h /day, 5 days a week, for 12 month
- Frequency of treatment:
- daily
- Dose / conc.:
- 0 ppm (nominal)
- Dose / conc.:
- 10 ppm (nominal)
- Dose / conc.:
- 50 ppm (nominal)
- Dose / conc.:
- 175 ppm (nominal)
- No. of animals per sex per dose:
- 95 animals / sex
- Control animals:
- yes, concurrent no treatment
- Details on study design:
- In studies at our laboratory (unpublished observations), F-344 rats exposed to 175 or 250 ppm DMA (6 hr/day, 5 days) or 500 ppm DMA (6 hr/day, 3 days) had ulcerative rhinitis, severe congestion, and squamous metaplasia in the respiratory tract. These lesions were most severe in the anterior sections of the nasal passages.
- Observations and examinations performed and frequency:
- The animals were observed for clinical abnormalities twice daily and were weighed once per week for the first 13 weeks, and biweekly thereafter.
- Sacrifice and pathology:
- After 6 and 12 months, 9-10 animals of each species, sex, and treatment group were fasted overnight and weighed just prior to necropsy.
Male mice were not included in the 12-month sacrifice because of the hi rate of unscheduled mortality in this group.
Animals were anesthetized with pentobarbital by ip injection, and blood was drawn from the heart for hematology and serum chemistry. Each animal was examined for gross abnormalities, and 45 tissues and any gross lesions were collected and placed in 10 % buffered formalin. The nasal passages were flushed, the lungs inflated, and the lumen of the gastrointestinal tract infused with formalin. The liver, kidneys, and brain were weighed. All tissues from the control and 175~ppm exposed animals and target tissues (nasal turbinates) from the 10- and 50- ppm exposed animals were processed for light microscopic examination. Tissues containing bone were placed in 10 % buffered formalin for 48 hr, decakSed in Cal-ex solution (Fisher Scientific, Raleigh, N.C.) for 2 days, then rinsed with tap water for at least 4 hr, and replaced in formalin. Tissues were then dehydrated in graded alcohols, cleared with xylene, and embedded in pa&in wax. Transverse blocks of the nose were cut and prepared to yield histologic sections at the following levels: (1) just anterior to the incisor teeth, (2) approximately onethird of the distance from the posterior aspect of the incisor teeth to the incisive papilla, (3) at the incisive papilla, (4) at the crest of the second palatial ridge, and (5) at the center of the second molar tooth. Embedded tissues were sectioned at 5 pm and stained with hematoxylin and eosin for light microscopic examination. For photography, selected tissues were removed from pan&n, reembedded in glycol methacrylate (GMA), and 2- to 3- am-thick sections were cut and stained with Lee’s methylene blue. Selected nasal sections were stained with Alcian blue at pH 2.5 for acidic mucous glycoproteins. - Other examinations:
- Hematological data were collected using a Coulter S Plus II counter (Coulter Electronics, Inc., Hialeah, Ha.). Sodium and potassium determinations were performed with a Flame photometer 343 (Instrument Lab, Lexington, Mass). Chloride analyses were performed with a Coming Chloride 920 M meter (Coming Scientific Inst., Mechield, Mass.). An Abbott VP clinical analyzer (Abbott Labs, Chicago, Ill.) was used for determination of serum chemistries.
- Statistics:
- Data for body weights, serum chemistry, hematology, and organ weights were analyzed using an analysis of variance. Dunnett’s test was employed to detect differences between control and treatment groups (Steel and Torrie, 1980). Red blood cell morphology and histopathologic findings were analyzed using the Kolmorgomov-Smimov test (Daniel, 1978). In all cases, the preselected significance level was p ≤ 0.05.
- Clinical signs:
- effects observed, treatment-related
- Description (incidence and severity):
- Alopecia, 56 death
- Mortality:
- mortality observed, treatment-related
- Description (incidence):
- Alopecia, 56 death
- Body weight and weight changes:
- effects observed, treatment-related
- Description (incidence and severity):
- significant loss at 175 ppm
- Food consumption and compound intake (if feeding study):
- not examined
- Food efficiency:
- not examined
- Water consumption and compound intake (if drinking water study):
- not examined
- Ophthalmological findings:
- not examined
- Haematological findings:
- not specified
- Clinical biochemistry findings:
- effects observed, treatment-related
- Description (incidence and severity):
- increased glucose (females, 175 ppm)
- Endocrine findings:
- not examined
- Urinalysis findings:
- not examined
- Behaviour (functional findings):
- not examined
- Immunological findings:
- not examined
- Organ weight findings including organ / body weight ratios:
- not specified
- Gross pathological findings:
- not specified
- Neuropathological findings:
- effects observed, treatment-related
- Description (incidence and severity):
- At the 50-ppm exposure level, lesions in the nasal passages were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus.
- Histopathological findings: non-neoplastic:
- effects observed, treatment-related
- Description (incidence and severity):
- Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In mice, there was no apparent progression or increase in severity of the nasal lesions from 6 to 12 months. The lesions were present in two areas of the nose: (1) the respiratory epithelium and underlying tissues adjacent to the vestibule, and (2) the olfactory epithelium in the medial portion of the dorsal meatus with variable involvement of more posterior olfactory areas. There was a distinct concentration-response relationship for the severity and frequency of both lesions.
(1) Lesions in respiratory epithelium. The lesions in the respiratory area were most severe on the anterior septum, just posterior to the vestibule, and on the free margins of the naso- and maxilloturbinates, with lesser involvement of the lateral wall. In the 175 ppm exposure group, there was variable destruction of the anterior portions of the naso- and maxilloturbinates, and fenestration of the nasal septum. In areas of destruction of the turbinates and septum, the surface was covered by nonkeratinizing squamous epithelium. Evidence of both acute and chronic inflammatory response included focal to diffuse mucosal and submucosal infiltration of mononuclear leukocytes and some neutrophils. Exudate was minimal or absent. Other lesions included epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to diffuse squamous metaplasia. No Goblet cell hyperplasia was observed on the ventral aspect of the nasal septum in mice. Globules of eosinophilic material were observed in the respiratory epithelium of the anterior nasal passages. The globules were present in the basal half of the affected cells, and the dense, oval to round nucleus appeared to be compressed between the globules and the basement membrane. The cell type containing the globules was not identified. Small, basophilic bodies, which were laminated and presumably mineralized, with the globules in mice.
At the 50-ppm exposure level, lesions in the respiratory epithelium were minimal in both rats and mice. Changes were confined to focal squamous metaplasia on the free margins of the turbinates in mice after 6 months of exposure, and eosinophilic globules with mild inflammation and epithelial hypertrophy and hyperplasia after 12 months. A slightly higher incidence of chronic inflammation was observed in the vestibule and the respiratory epithelium of rats in the 10-ppm exposure group.
(2) Lesions in the olfactory region. DMA exposure induced a concentration-dependent destruction of the olfactory epithelium which was most severe in the middle third of the dorsal meatus, with variable involvement of the free margins of the ectoturbinates. The most widespread change, which was found consistently in DMA exposed mice, was degeneration of olfactory sensory cells with variable vacuolation of the olfactory epithelium. Another lesion often observed in areas of the olfactory epithelium was characterized by accumulation of hyaline, eosinophilic material in sustentacular cells, which were often markedly hypertrophic. The eosinophilic material was also present as large globules in the overlying airway, suggesting that it may be a secretory product of the sustentacular cells. Similar material was present in the large submucosal glands at the junction of olfactory and respiratory epithelium. These lesions were almost always accompanied by atrophy of the olfactory nerves in the lamina propria. Bowman’s glands exhibited or focal hyperplasia. In the more severely affected cases, olfactory epithelium was replaced by well-differentiated, ciliated respiratory epithelium. These metaplastic areas of ciliated respiratory epithelium were found, in several cases, to be continuous with ciliated ducts of hypertrophic or hyperplastic Bowman’s glands. There were foci of fusiform cells near the basal layer in rats, but not in mice, in areas of respiratory metaplasia in the dorsal meatus. In the underlying, edematous connective tissue, the basement membrane appeared thickened and separated from the epithelium. No basal cell hyperplasia was observed in the olfactory epithelium of in mice. At the 50-ppm exposure level, lesions were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus. However, most of the animals exposed to 50 ppm exhibited olfactory epithelial lesions. After 12 months, only a few animals at the 10-ppm exposure level were affected, and lesions were confined to focal degeneration of the olfactory epithelium in the dorsal meatus.
Additionally, a number of neoplastic and nonneoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure. - Histopathological findings: neoplastic:
- no effects observed
- Description (incidence and severity):
- A number of neoplastic and nonneoplastic lesions were found, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure.
- Details on results:
- A number of neoplastic and nonneoplastic lesions were found in both rats and mice, including variable degrees of hair loss, ovarian cysts, testicular discoloration and atrophy, enlargement of the preputial glands, and other minor findings. These changes were typical of animals of these strains and ages and were not considered to be related to DMA exposure.
- Dose descriptor:
- LOAEC
- Remarks:
- local effects
- Effect level:
- 10 ppm
- Based on:
- test mat.
- Sex:
- male/female
- Basis for effect level:
- clinical signs
- gross pathology
- Dose descriptor:
- NOAEC
- Remarks:
- systemic effects
- Effect level:
- 50 ppm
- Based on:
- test mat.
- Sex:
- male/female
- Basis for effect level:
- clinical signs
- Critical effects observed:
- not specified
- Conclusions:
- The highest concentration: 175 ppm induced severe alterations in the nasal passages.
The middle concentration of 50 ppm did cause sigfnificantly lower alterations and the lowest dose of 10 ppm only caused slight alterations in a few animals. - Executive summary:
The mean body weight gain of rats and mice exposed to 175 ppm DMA was depressed to approximately 90 % of control after 3 weeks of exposure. The only other treatment-related changes were concentration related lesions in the nasal passages. Two distinct locations in the nose were affected: the respiratory epithelium in the anterior nasal passages, and the olfactory epithelium, especially that lining the anterior dorsal meatus. There was focal destruction of the anterior nasoturbinate and nasal septum, local inflammation, and focal squamous metaplasia of the respiratory epithelium in rats and mice. The olfactory epithelium exhibited extensive loss of sensory cells with less damage to sustentacular cells. There was also loss of olfactory nerves, hypertrophy of Bowman’s glands, and distension of the ducts of these glands by serocellular debris in regions underlying degenerating olfactory epithelium. At the 175-ppm exposure level, rats had more extensive olfactory lesions than mice, with hyperplasia of small basophilic cells adjacent to the basement membrane being present in rats but not mice. After 12 months of exposure to 10 ppm DMA, minimal loss of olfactory sensory cells and their axons in olfactory nerve bundles was observed in the nasal passages of a few rats and mice.
These results indicate that the olfactory sensory cell is highly sensitive to the toxic effects of DMA, with minor lesions being produced in rodents even at the current threshold limit value of 10 ppm.
Referenceopen allclose all
Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In mice, there was no apparent progression or increase in severity of the nasal lesions from 6 to 12 months, while in rats, increased exposure time was associated with more extensive involvement of the olfactory area. The lesions were present in two areas of the nose: (1) the respiratory epithelium and underlying tissues adjacent to the vestibule, and (2) the olfactory epithelium in the medial portion of the dorsal meatus with variable involvement of more posterior olfactory areas. There was a distinct concentration-response relationship for the severity and frequency of both lesions.
(1) Lesions in respiratory epithelium. The lesions in the respiratory area were most severe on the anterior septum, just posterior to the vestibule, and on the free margins of the naso- and maxilloturbinates, with lesser involvement of the lateral wall. In the 175 ppm exposure group, there was variable destruction of the anterior portions of the naso- and maxilloturbinates, and fenestration of the nasal septum. In areas of destruction of the turbinates and septum, the surface was covered by nonkeratinizing squamous epithelium. Evidence of both acute and chronic inflammatory response included focal to diffuse mucosal and submucosal infiltration of mononuclear leukocytes and some neutrophils. Exudate was minimal or absent. Other lesions included epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to diffuse squamous metaplasia. Goblet cell hyperplasia of mild to moderate severity was observed on the ventral aspect of the nasal septum in rats, but not in mice. Globules of eosinophilic material were observed in the respiratory epithelium of the anterior nasal passages. The globules were present in the basal half of the affected cells, and the dense, oval to round nucleus appeared to be compressed between the globules and the basement membrane. The cell type containing the globules was not identified. Small, basophilic bodies, which were laminated and presumably mineralized, with the globules in mice.
At the 50-ppm exposure level, lesions in the respiratory epithelium were minimal in both rats and mice. Changes were confined to focal squamous metaplasia on the free margins of the turbinates in mice after 6 months of exposure, and eosinophilic globules with mild inflammation and epithelial hypertrophy and hyperplasia after 12 months. A slightly higher incidence of chronic inflammation was observed in the vestibule and the respiratory epithelium of rats in the 10-ppm exposure group.
(2) Lesions in the olfactory region. DMA exposure induced a concentration-dependent destruction of the olfactory epithelium which was most severe in the middle third of the dorsal meatus, with variable involvement of the free margins of the ectoturbinates. The most widespread change, which was found consistently in DMA exposed rats and mice, was degeneration of olfactory sensory cells with variable vacuolation of the olfactory epithelium. Another lesion often observed in areas of the olfactory epithelium was characterized by accumulation of hyaline, eosinophilic material in sustentacular cells, which were often markedly hypertrophic. The eosinophilic material was also present as large globules in the overlying airway, suggesting that it may be a secretory product of the sustentacular cells. Similar material was present in the large submucosal glands at the junction of olfactory and respiratory epithelium. These lesions were almost always accompanied by atrophy of the olfactory nerves in the lamina propria. Bowman’s glands exhibited or focal hyperplasia. In the more severely affected cases, olfactory epithelium was replaced by well-differentiated, ciliated respiratory epithelium. These metaplastic areas of ciliated respiratory epithelium were found, in several cases, to be continuous with ciliated ducts of hypertrophic or hyperplastic Bowman’s glands. There were foci of fusiform cells near the basal layer in rats, but not in mice, in areas of respiratory metaplasia in the dorsal meatus. In the underlying, edematous connective tissue, the basement membrane appeared thickened and separated from the epithelium. Basal cell hyperplasia was frequently observed in the olfactory epithelium of rats, but was not observed in mice. This lesion was characterized by a zone of polyhedral to fusiform cells lying beneath any remaining sustentacular cells. The basal cells had indistinct cytoplasmic boundaries and dark round nuclei and formed cords, sheets, or acinar arrangements. At the 50-ppm exposure level, lesions were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus. However, most of the animals exposed to 50 ppm exhibited olfactory epithelial lesions. After 12 months, only a few animals at the 10-ppm exposure level were affected, and lesions were confined to focal degeneration of the olfactory epithelium in the dorsal meatus.
TABLE 1. Lesions in Nasal Passages of Rats and Mice Exposed to DMA for 12 Months |
|||||
DMA (ppm) |
|
Squamous epithelium (level I)a |
Respiratory epithelium (levels I, II)b |
Olfactory epithelium |
Chronic inflammation (levels I, II, III) |
0 |
Rats |
— |
— |
+/- |
+ |
Mice |
— |
— |
— |
— |
|
10 |
Rats |
— |
+/- |
+ |
+ |
Mice |
— |
+/- |
+ |
— |
|
50 |
Rats |
— |
+ |
++ |
++ |
Mice |
— |
+ |
++ |
+ |
|
175 |
Rats |
+/- |
+++ |
+++ |
++ |
Mice |
+/- |
+++ |
+++ |
+ |
|
Note. — =No abnormality detected. +/- = very slight changes of doubtful significance, + = minimal change, ++ = moderate change, +++ = severe change. |
|||||
Treatment-induced lesions were confined to the nasal passages (very similar in nature between the species and sexes). In mice, there was no apparent progression or increase in severity of the nasal lesions from 6 to 12 months, while in rats, increased exposure time was associated with more extensive involvement of the olfactory area. The lesions were present in two areas of the nose: (1) the respiratory epithelium and underlying tissues adjacent to the vestibule, and (2) the olfactory epithelium in the medial portion of the dorsal meatus with variable involvement of more posterior olfactory areas. There was a distinct concentration-response relationship for the severity and frequency of both lesions.
(1) Lesions in respiratory epithelium. The lesions in the respiratory area were most severe on the anterior septum, just posterior to the vestibule, and on the free margins of the naso- and maxilloturbinates, with lesser involvement of the lateral wall. In the 175 ppm exposure group, there was variable destruction of the anterior portions of the naso- and maxilloturbinates, and fenestration of the nasal septum. In areas of destruction of the turbinates and septum, the surface was covered by nonkeratinizing squamous epithelium. Evidence of both acute and chronic inflammatory response included focal to diffuse mucosal and submucosal infiltration of mononuclear leukocytes and some neutrophils. Exudate was minimal or absent. Other lesions included epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to diffuse squamous metaplasia. Goblet cell hyperplasia of mild to moderate severity was observed on the ventral aspect of the nasal septum in rats, but not in mice. Globules of eosinophilic material were observed in the respiratory epithelium of the anterior nasal passages. The globules were present in the basal half of the affected cells, and the dense, oval to round nucleus appeared to be compressed between the globules and the basement membrane. The cell type containing the globules was not identified. Small, basophilic bodies, which were laminated and presumably mineralized, with the globules in mice.
At the 50-ppm exposure level, lesions in the respiratory epithelium were minimal in both rats and mice. Changes were confined to focal squamous metaplasia on the free margins of the turbinates in mice after 6 months of exposure, and eosinophilic globules with mild inflammation and epithelial hypertrophy and hyperplasia after 12 months. A slightly higher incidence of chronic inflammation was observed in the vestibule and the respiratory epithelium of rats in the 10-ppm exposure group.
(2) Lesions in the olfactory region. DMA exposure induced a concentration-dependent destruction of the olfactory epithelium which was most severe in the middle third of the dorsal meatus, with variable involvement of the free margins of the ectoturbinates. The most widespread change, which was found consistently in DMA exposed rats and mice, was degeneration of olfactory sensory cells with variable vacuolation of the olfactory epithelium. Another lesion often observed in areas of the olfactory epithelium was characterized by accumulation of hyaline, eosinophilic material in sustentacular cells, which were often markedly hypertrophic. The eosinophilic material was also present as large globules in the overlying airway, suggesting that it may be a secretory product of the sustentacular cells. Similar material was present in the large submucosal glands at the junction of olfactory and respiratory epithelium. These lesions were almost always accompanied by atrophy of the olfactory nerves in the lamina propria. Bowman’s glands exhibited or focal hyperplasia. In the more severely affected cases, olfactory epithelium was replaced by well-differentiated, ciliated respiratory epithelium. These metaplastic areas of ciliated respiratory epithelium were found, in several cases, to be continuous with ciliated ducts of hypertrophic or hyperplastic Bowman’s glands. There were foci of fusiform cells near the basal layer in rats, but not in mice, in areas of respiratory metaplasia in the dorsal meatus. In the underlying, edematous connective tissue, the basement membrane appeared thickened and separated from the epithelium. Basal cell hyperplasia was frequently observed in the olfactory epithelium of rats, but was not observed in mice. This lesion was characterized by a zone of polyhedral to fusiform cells lying beneath any remaining sustentacular cells. The basal cells had indistinct cytoplasmic boundaries and dark round nuclei and formed cords, sheets, or acinar arrangements. At the 50-ppm exposure level, lesions were much less severe than at 175 ppm and were confined to loss of sensory cells and olfactory nerves, primarily in the middle third of the dorsal meatus. However, most of the animals exposed to 50 ppm exhibited olfactory epithelial lesions. After 12 months, only a few animals at the 10-ppm exposure level were affected, and lesions were confined to focal degeneration of the olfactory epithelium in the dorsal meatus.
TABLE 1. Lesions in Nasal Passages of Rats and Mice Exposed to DMA for 12 Months |
|||||
DMA (ppm) |
|
Squamous epithelium (level I)a |
Respiratory epithelium (levels I, II)b |
Olfactory epithelium |
Chronic inflammation (levels I, II, III) |
0 |
Rats |
— |
— |
+/- |
+ |
Mice |
— |
— |
— |
— |
|
10 |
Rats |
— |
+/- |
+ |
+ |
Mice |
— |
+/- |
+ |
— |
|
50 |
Rats |
— |
+ |
++ |
++ |
Mice |
— |
+ |
++ |
+ |
|
175 |
Rats |
+/- |
+++ |
+++ |
++ |
Mice |
+/- |
+++ |
+++ |
+ |
|
Note. — =No abnormality detected. +/- = very slight changes of doubtful significance, + = minimal change, ++ = moderate change, +++ = severe change. |
|||||
Endpoint conclusion
- Endpoint conclusion:
- adverse effect observed
- Dose descriptor:
- LOAEC
- 18.45 mg/m³
- Study duration:
- chronic
- Species:
- rat
Repeated dose toxicity: dermal - systemic effects
Endpoint conclusion
- Endpoint conclusion:
- no study available
Repeated dose toxicity: dermal - local effects
Endpoint conclusion
- Endpoint conclusion:
- no study available
Additional information
Repeated dose toxicity: oral
Darad et al. performed in 1983 a chronic repeated dose toxicity test. 30 rats (Wistar) each were exposed to a daily oral administration of dimethylamine through drinking water. Nitrite, as well as DMA, caused higher in vitro lipoperoxidation, free lysosomal enzyme activities and cytosolic superoxide dismutase activity in liver. Many of the parameters examined (microsomal lipoperoxidation, enzyme activities of acid phosphatase and cathepsin as lysosomal enzymes, enzyme activity of superoxide dismutase) are indicative of a free radical-mediated damage to the cellular and subcellular membrane in rats administered nitrite and/or DMA. The administration of nitrite or DMA appears to decrease the total activity of both the lysosomal enzymes. DMA alone did not have any effect on SOD activity. The increased levels of the cytosolic SOD due to the administration of nitrite or DMA may indicate a higher generation of the superoxide radicals. The increase in lipoperoxidation may result in membrane damage and is further indicated by the labialization of lysosomal enzymes. The results are indicating a free radical-mediated damage to the cellular and subcellular membranes. In conclusion DMA is able to disturb the barrier function of the skin by altering the protective characteristics.
Repeated dose toxicity: inhalation
Gross et al. performed in 1987 a chronic test on Fisher 344 rats with dimethylamine by the route of inhalation. The test duration was 2 years; the substance was administered 6 hours per day at concentrations of 175 ppm. The animals showed a treatment-induced destruction of nasal tissues including loss of the anterior third of the nasoturbinate and the anterodorsal margins of the maxilloturbinate. Modified mucus flow patterns with mucus bypassing affected regions. Mucus flow rates were generally increased over those of chronic control animals. In four out of six animals in the chronic study mucociliary activity resembling that in areas lined by respiratory epithelium was observed as a posterior extension of ciliated epithelium into regions normally lined by olfactory epithelium. This was seen during the visual examination and was presumed to represent respiratory metaplasia. Additionally focal degeneration of the squamous epithelium in the nasal vestibule and extensive vacuolation of both the respiratory and olfactory epithelia in the anterior nasal passages was found. These findings are indicating that a considerable repair occurs in the regions lined by squamous epithelium and resolution of the vacuolation following chronic exposure. In histopathological examinations the tissues showed varying degrees of chronic inflammation in the nose. It is interesting that metaplasia to a respiratory-type epithelium occurs at both extremities of the respiratory tract. However, it remains to be determined whether these responses are protective in nature or whether similar mechanisms are responsible for these changes in the nose and lung. It is of interest that despite severe tissue destruction in the anterior nose following a single 6 hr exposure, the nasal lesions exhibited very little evidence of progression, even after 2 years of exposure. These findings indicate a possible regional susceptibility to DMA toxicity or a degree of adaptation by the rat to continued DMA exposure. The acute epithelial degeneration led to squamous metaplasia in chronically exposed animals in both the present study and the study reported by Buckley et al. (1985) presumably as a protective or adaptive response.
In the respiratory epithelial-lined regions of the anterior nasal cavity, acute epithelial degeneration led to squamous metaplasia in chronically exposed animals in both the present study and the study reported by Buckley et al. (1985) presumably as a protective or adaptive response. The lesions in rats exposed to DMA for 2 years (reported by Gross et al., 1987) were very similar to those reported previously for rats exposed for 6 or 12 months (Buckley et al.,1985). Lesions were most severe in the anterior regions of the nose and comprised focal or regional squamous metaplasia, with the normal respiratory epithelium being replaced by a stratified squamous epithelium. This response was associated with chronic active inflammation and occurred in regions with complete loss of mucociliary function. The only consistent response to exposure was moderate to severe goblet cell hyperplasia. At the highest concentration (175 ppm) Buckley et al. reported a depressed mean body weight gain of rats and mice to approximately 90 % of control after 3 weeks of exposure. They found severe alterations in the nasal passages. The middle concentration of 50 ppm did cause significantly lower alterations and the lowest dose of 10 ppm only caused slight alterations in a few animals. Two distinct locations in the nose were affected: the respiratory epithelium in the anterior nasal passages, and the olfactory epithelium, especially that lining the anterior dorsal meatus. There was focal destruction of the anterior nasoturbinate and nasal septum, local inflammation, and focal squamous metaplasia of the respiratory epithelium in rats and mice. Mild goblet cell hyperplasia was observed only in rats. The olfactory epithelium exhibited extensive loss of sensory cells with less damage to sustentacular cells. There was also loss of olfactory nerves, hypertrophy of Bowman’s glands, and distension of the ducts of these glands by serocellular debris in regions underlying degenerating olfactory epithelium. At the 175-ppm exposure level, rats had more extensive olfactory lesions than mice, with hyperplasia of small basophilic cells adjacent to the basement membrane being present in rats but not mice. After 12 months of exposure to 10 ppm DMA, minimal loss of olfactory sensory cells and their axons in olfactory nerve bundles was observed in the nasal passages of a few rats and mice. These results indicate that the olfactory sensory cell is highly sensitive to the toxic effects of DMA, with minor lesions being produced in rodents even at the current threshold limit value of 10 ppm. A LOAEC for local effects can be set at 10 ppm (18.45 mg/m³), since only a few animals were affected with slight alterations. Furthermore, a NOAEC for systemic effects can be set at 50 ppm (92.26 mg/m³). The conversion of these ppm values into mg/m³ value was performed taking into account the temperature of 76 °F of the Buckley study).
Both values were taken further for the DNEL derivation.
A 14-Day Whole-Body Inhalation Toxicity Study (Wang, 2019) was conducted in Rats as a Dose-range-Finder for a subsequent OECD 422. The objective of this study was to determine exposure concentrations of the test substance, Dimethylamine (DMA) to be evaluated in a future combined repeated dose toxicity study with
the reproduction/developmental toxicity screening test (OECD 422) in rats. The study design was as follows: Group 1: Filtered Air = 0 ppm DMA, Group 2: 50 ppm DMA, Group 3: 100 ppm, Group 4: 250 ppm (Each group consisted of 5 male and 5 female animals)
Animals were exposed via whole-body inhalation for 6 hours daily during Study Days 0–13. The following parameters and end points were evaluated in this study: clinical signs, body weights, body weight gains, food consumption, gross necropsy findings, organ weights, and histopathologic examinations.
All males and females in the control, 50, 100, and 250 ppm groups survived to the scheduled necropsy. No remarkable clinical observations were noted at the daily examinations or 1–2 hours post-exposure. In the 250 ppm group males and females, lower mean body weight gains were noted throughout the exposure period and when the entire exposure period (Study Days 0–14) was evaluated. Correspondingly, slightly lower mean food consumption was noted in the 250 ppm group males during Study Days 4–14. As a result, mean absolute body weight in the 250 ppm group males was 4.4 % lower than the control group on Study Day 14; however, mean absolute body weights for the 250 ppm group females were comparable to the control group throughout the study. Mean absolute body weights and body weight gains in the 50 and 100 ppm groups and mean food consumption in males and females in the 50 and 100 ppm groups, and females in 250 ppm group were comparable to the control group throughout the study. There were no remarkable gross necropsy findings or effects on organ weights in the 50, 100, and 250 ppm groups. Test-substance related histologic findings were noted in the 50, 100, and 250 ppm group males and females. Test substance-related findings included ulceration (250 ppm), mixed cell inflammation (50, 100, and 250 ppm), and degeneration/regeneration of respiratory and transitional epithelium (50, 100, and 250 ppm).
In conclusion, lower mean absolute body weights and/or mean body weight gains were noted in the 250 mg/kg/day group males and females, with corresponding lower mean food consumption in males. In addition, histologic findings were noted in the 50, 100, and 250 mg/kg/day groups. Based on these data, exposure levels of 8, 25, and 75 ppm were selected for the combined repeated dose toxicity study with the reproduction/developmental toxicity screening test (OECD 422) when Crl:CD(SD) rats were exposed to dimethylamine via whole body inhalation.
Furthermore, the results were obtained in a OECD 422 - the combined repeated dose toxicity test with the reproductive / developmental toxicity screening test (Wang, 2020). The objective of this study was to provide preliminary information on the potential adverse effects of the test substance, Dimethylamine (DMA), on male and female reproduction within the scope of an OECD 422 study. The study design was as follows: Group 1 - 0 ppm (Filtered Air); Group 2 - 8 ppm DMA; Group 3 - 25 ppm DMA; Group 4 - 75 ppm DMA (Each group contained 10 males and 10 females). Animals were exposed via whole-body inhalation for 6 hours daily. Males were exposed for 14 days prior to mating and continuing throughout mating for a total of 28 days. Females were exposed for 14 days prior to mating and continuing through Gestation Day 20; exposure resumed on Lactation Day 5 and continued until Lactation Day 28 for a total of 58–65 days. Focussing on the repeated dose part of the study, the following parameters and end points were evaluated in this study: clinical signs, body weights, body weight gains, food consumption, neurobehavior, thyroid hormones, clinical pathology, gross necropsy findings, organ weights, and histopathologic examinations. Analyzed F0 mean exposure concentrations were 0.1, 9.2, 26.9, and 75.9 ppm in the control, 8, 25, and 75 ppm groups, respectively. On Study Days 3 and 4, non-zero concentrations of DMA were noted in the control chamber. Because no test substance was being directed to the control system, and the chambers were under ambient conditions on these 2 exposure days, there should have been no DMA in the chamber. Therefore, although the reason of non-zero values in the control chamber could not be determined, carryover within the gas chromatogram/sampling setup was suspected to be the cause. The non-zero values were included in the daily average (and study mean as 0.1 ppm) for the control group. No detection of test substance was noted for the rest of the exposure period.
All F0 animals survived to the scheduled necropsies. There were no test substance-related clinical observations noted at the daily examinations or 0.5 – 3 hours following the completion of exposure at 8, 25, and 75 ppm. No test substance-related effects were noted on mean body weights, body weight changes, or food consumption throughout the F0 generation at any exposure level. No test substance-related effects were noted on the functional observational battery or motor activity in the F0 males on Study Day 27 or F0 females on Lactation Day 28. Hematology, coagulation, and serum chemistry parameters in the 8, 25, and 75 ppm group F0 males and females and mean T4 levels in the F0 males were unaffected by test substance exposure. There were no test substance-related macroscopic findings or effects on organ weights noted at the scheduled F0 necropsies at any exposure level. Test substance-related lesions within Level II of the nasal cavity in the 8, 25, and 75 ppm group F0 males and females consisted of minimal or mild transitional and/or respiratory epithelial hyperplasia and mixed cell type inflammation in all test substance exposure groups. Although no systemic adverse effects were noted at any exposure level, based on the corrosive nature of DMA gas and the findings from the previous tolerability/range-finding study, port of entry effects were expected in the current study. Therefore, local effects that were restricted to Level II of the nasal cavity, not associated with clinical signs, were considered adverse at 75 ppm.
In conclusion, no systemic toxicity was noted in the F0 generation at exposure up to 75 ppm (the highest level tested). Therefore, the no-observed-adverse-effect level for F0 male and female systemic and reproductive toxicity was 75 ppm. Based on test substance-related adverse port of entry findings, consisting of respiratory epithelial hyperplasia and mixed cell type inflammation, and/or ulceration noted in all exposure levels the LOAEL for port of entry effects for F0 generation was 8 ppm.
A study performed in 1969 by Coon et al. investigated the reaction of various animals to inhalation of DMA at a concentration of 9 mg/m³. The duration of exposure was 90 days continuously. No death or signs of toxicity were found. Additionally all hematologic values were normal. On histopathologic examination only interstitial inflammatory changes were noted in the lungs of all species. Since only one experiment each was made for formaldehyde, dimethylamine, and ethanol, there are insufficient data to apply to a CSG. The continuous exposure to dimethylamine at 9 mg/m³ produced mild inflammatory changes in the lungs of all species and dilated bronchi in 3 of 3 rabbits and 2 of 3 monkeys.
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