Dimethyl succinate

Endpoint summary

Description of key information

In a repeat-dose toxicity study with rats by the inhalation route with animals exposed 6 hours / day / 5 days / week for 14 weeks a NOAEC could not be established based on squamous metaplasia in the olfactory epithelium of the nose - a local effect thought to be an irritant response. The LOAEC may be considered to be 0.16 mg/L/day (160 mg/m3). An exposure concentration of 0.4 mg/L (400 mg/m3) may be regarded as a NOAEC for systemic toxicity. A second study has been described by Keenan et.al. (Fund Appl Toxicol 15: 381-393, 1990) in which groups of 20 male and 20 female rats were exposed, by inhalation, 6 hours/day/5 days/week, for 13 weeks. Animals were exposed at concentrations of 20, 76 and 390 mg/m3. Again degeneration was observed in the rat olfactory epithelium and a NOAEC could not be determined as a result.

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

Deviations:

not specified

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:Charles River Breding Laboratories, Kingston, NY, USA
- Age at study initiation: 4 weeks
- Weight at study initiation: 60 - 123 g
- Fasting period before study: Not applicable
- Housing: Paired, in stainless steel wire mesh cages
- Diet (e.g. ad libitum): Ad libiutum except during exposure
- Water (e.g. ad libitum): Ad libitum except during exposure
- Acclimation period: Approximately 1 week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24 deg C
- Humidity (%): 42 - 63%
- Photoperiod (hrs dark / hrs light): 12 / 12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

whole body

Vehicle:

air

Mass median aerodynamic diameter (MMAD):

5.6 µm

Remarks on MMAD:

MMAD / GSD: Aerosol particle size measured by cascade impactor and reported as mass median aerodynamic diameter and % of particles less than 10 micron aerodynamic diameter.
Mean particle size was 5.6 micron 72% of the generated aerosol was <10 micron
Chamber aerosol mass concentration determined by drawing known quantities of the chamber atmosphere through glass-fibre filters and calculating the filter weight gain per volume of atmosphere sampled.

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: NYU style inhalation chamber
- Method of holding animals in test chamber: stainless steel "modules"
- Source and rate of air: Ambient air, 300L/minute
- Method of conditioning air: Not reported
- System of generating particulates/aerosols: nebuliser
- Temperature, humidity, pressure in air chamber: Measured but not reported
- Air flow rate: 300l/minute
- Air change rate: Not reported
- Method of particle size determination: Cascade impactor
- Treatment of exhaust air: Not reported

TEST ATMOSPHERE
- Brief description of analytical method used: Mass concentration determined gravimetrically following trapping on glass fibre filters. Identity by GC analysis of solvent traps collecting both aerosol and vapour
- Samples taken from breathing zone: yes

VEHICLE (if applicable)
- Justification for use and choice of vehicle: None used

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples were analysed by gas chromatography (GC/FID). Isothermal separation at 1500 deg C on glass column packed with 10% SP-1000 on Chromosorb W-AW 100/120 mesh. The GC response of the samples was compared with that obtained from standard samples prepared by quantitative dilution of DBE in acetone to determine chamber concentration. The method permitted separation / identification of the 3 components to determine changes in composition

Duration of treatment / exposure:

98 days (males); 99 days (females)

Frequency of treatment:

5 days / week, 6 hours / day

Dose / conc.:

0 mg/L air

Remarks:

Control

Dose / conc.:

0.16 mg/L air

Dose / conc.:

0.4 mg/L air

Dose / conc.:

1 mg/L air

No. of animals per sex per dose:

10 males, 10 females

Control animals:

yes, sham-exposed

Details on study design:

- Dose selection rationale: Higest dose level selected regarded as maximum tolerated dose
- Rationale for animal assignment (if not random): Random

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule for examinations: Weekly

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No data

WATER CONSUMPTION: No data

OPHTHALMOSCOPIC EXAMINATION: No data

HAEMATOLOGY: Yes
- Time schedule for collection of blood: 42/43 days and again after 92/93 days
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: All study animals
- Parameters examined: Erythrocyte count; haemoglobin concentration; mean corpuscular volume; platelet count; leukocyte count including relative numbers of neutrophils, band neutrophils, lymphocytes, atypical lymphocytes, eosinophils, monocytes and basophils; haematocrit; mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 42/43 days and again after 92/93 days
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: All study animals
- Parameters examined: Alkaline phosphatase; alanine aminotransferase; aspartate aminotransferase; glucose; urea nitrogen; calcium; cholesterol; creatinine; total protein; albumin; sodium; potassium; globulin

URINALYSIS: Yes
- Time schedule for collection of blood: 42/43 days and again after 92/93 days
- Metabolism cages used for collection of urine: Yes
- Animals fasted: No data
- Parameters examined: .Volume; osmolality; pH; blood; sugar; protein; bilirubin; urobilinogen; ketones; colour; transparency; sediment

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes - Macroscopic examination and weighing of the brain, heart, lungs, liver, spleen, kidneys, testes and thymus. The following tissues were retained for microscopic examination: brain; spinal cord; peripheral nerve (sciatic); nasal cavity; larynx; trachea; lungs; heart; aorta; liver; pancreas; salivary glands; pharynx; oesophagus; stomach; duodenum; jejunum; ileum; caecum; colon; rectum; kidneys; urinary bladder; testes; epididymides; prostate; seminal vesicle; ovaries; uterus; cervix; vagina; pituitary; thyroid; parathyroid; adrenal; spleen; thymus; bone marrow (femur and sternum); mandibular lymph node; mesenteric lymph node; tracheobronchial lymph node; skeletal muscle; skin; mammary gland; eyes; harderian gland; exorbital lacrimal gland.


HISTOPATHOLOGY: Yes - Tissues listed above from all groups of male rats and from the control and high-dose female rats were examined microscopically. The nasal cavity from the low dose and intermediate-dose female rats were also examined.

Statistics:

One-way analysis of variance. When the F-test was significant, least significant difference (LSD) and Dunnett tests were used to compare data from the control group and treatment groups.

Clinical signs:

no effects observed

Description (incidence and severity):

Clinical signs for exposed animals were similar to those of control animals.
Animals exposed at 1.0 mg/L had wet fur during exposure due to aerosol deposition.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Males and females of the l.0 mg/L exposure group exhibited depressed rates of weight gain compared to controls.

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Males in the high-dose group showed an increased haemoglobin at the end of the treatment period. At the same time, the absolute numbers of monocytes were decreased for the 0.16 mg/L and 1.0 mg/L exposure groups. Females exposed at 0.16 mg/L exhibited a decreased mean corpuscular volume both at the mid-point of the study and at the end of the treatment period.
These statistically significant differences were seen, values were within the range of biological variability or showed no dose-response relationship and were considered unrelated to treatment.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

A slight, but statistically significant, decrease in serum sodium concentration in males and females exposed at 1.0 mg/L at the midpoint of the study (42/43 days) and near the end of the 90-day exposure period. At the same time periods there was a slight, statistically significant, increase in serum calcium in female rats exposed at 0.40 and 1.0 mg/L.

Urinalysis findings:

effects observed, non-treatment-related

Description (incidence and severity):

At the mid-point analyses, urine urobilinogen concentrations were increased in males of the 0.4 mg/L and 1.0 mg/L exposure groups. While statistically significant, these were within the range of biological variability or showed no dose-response relationship and were considered unrelated to treatment.

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

A statistically significant and dose-related decrease in absolute and relative liver weights was seen in female rats in all treatment groups, relative to controls. In addition, males exposed at 1.0 mg/L exhibited a statistically significant decrease in absolute and relative liver weight.
Other statistically significant differences in the 1.0 mg/L exposure group included slight increases in relative heart and testes weights in males and a slight decrease in absolute spleen weight in female animals. These slight organ weight changes were not accompanied by any histopathological changes and are considered of minimal biological significance.

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Squamous metaplasia was noted primarily in the olfactory epithelium in all treatment groups. The effect was minimal and seen in 3 of 20 rats exposed at 0.16 mg/L. The effect was of minimal to mild severity in 17/20 rats exposed at 0.40 mg/L, and 19/20 rats exposed at 1.0 mg/L groups. A single female in the 0.40 mg/L group showed lesions of moderate severity.
Other than these nasal lesions, examination showed no abnormal effects in exposed animals.

Details on results:

CLINICAL SIGNS AND MORTALITY: Clinical signs observed in substance exposed rats were similar to those seen in control animals. Animal exposed at 1.0 mg/L group had wet fur during exposure due to aerosol deposition, the fur drying within 2 hours after exposure ceased. One male rat of the 0.4 mg/L exposure group was killed after 35 days due to an accidentally fractured nasal septum.

BODY WEIGHT AND WEIGHT GAIN: Both males and females exposed at l.0 mg/L exhibited reduced body weight gain relative to controls.

HAEMATOLOGY: Apparent group differences seen in haematological measured parameters were regarded as being within the range of biological variability or showed no dose-response relationship and, as a result, were considered unrelated to treatment.

CLINICAL CHEMISTRY: There was a slight but statistically significant decrease in serum sodium concentration in males and females of the 1.0 mg/L exposure group at the midpoint of the study (day 42 for the males and day 43 for the females) and at the end of the study. There was a slight but statistically significant increase in serum calcium in female rats in the 0.40 and 1.0 mg/L exposure groups at the midpoint and at the end of the study.

URINALYSIS: Apparent group differences seen in those urine analysis parameters that wre measured were regarded as being within the range of biological variability or showed no dose-response relationship and were therefore considered unrelated to treatment.

ORGAN WEIGHTS: A statistically significant and dose-related reduction in both absolute and relative liver weights was seen in female rats in all treatment groups and in male rats exposed at 1.0 mg/L. Statistically significant differences between test and control animals were also apparent in animals exposed at 1.0 mg/L and included slight increases in relative heart and testes weights in males and a slight decrease in absolute spleen weight in females. These minor weight changes were not accompanied by any observed microscopic change in the tissue histopathological changes and were considered to be of minimal biological significance.

GROSS PATHOLOGY: No details available

HISTOPATHOLOGY: NON-NEOPLASTIC: Examination of the nasal areas revealed squamous metaplasia, primarily in the olfactory epithelium, in all treatment groups. The effect was minimal and noted in 3 of 20 rats exposed at 0.16 mg/L; in 17/20 animals exposed at 0.4 mg/L and in 19/20 animals exposed at 1.0 mg/L and was of minimal to mild severity. One female rat exposed at 0.40 mg/L showed lesions of moderate severity.

Dose descriptor:

LOAEC

Effect level:

0.16 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

other: histopathology: squamous metaplasia of nasal olfactory epithelium

Dose descriptor:

NOAEC

Effect level:

0.4 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Lack of significant systemic toxicity

Critical effects observed:

yes

Lowest effective dose / conc.:

0.16 mg/L air

System:

respiratory system: upper respiratory tract

Organ:

nasal cavity

Treatment related:

yes

Dose response relationship:

yes

Conclusions:

The mixture, at the concentrations examined, causes lesions of the olfactory epithelium. Other than this local effect, no significant systemic toxicity was apparent in the rat following repeated inhalation exposure over a period of at least 90 days.

Executive summary:

Groups of 10 male and 10 female rats have been exposed, by inhalation 6 hours/day/5 days/week, for approximately 14 weeks to a mixture of dibasic esters containing dimethyl succinate, dimethyl glutarate and dimethyl adipate. Animals were exposed at concentrations of 0.16, 0.40 or 1.0 mg/L.

 

Microscopic examination of the nasal areas revealed mild squamous metaplasia in the olfactory epithelium in all treated groups. Examination of other preserved tissues showed no abnormalities that could be attributed to treatment at any concentration tested. Other effects of exposure included a dose-dependent reduction in absolute and relative liver weights in female rats in all treatment groups and in male animals exposed at 1.0 mg/L. No microscopic changes were apparent in the liver and the biological significance of observed effects on liver weight is not known. A slight reduction in body weight and slightly reduced blood sodium concentrations was noted in males and females exposed at 1.0 mg/L. Slightly increased blood calcium concentrations were noted in females exposed at 0.40 or 1.0 mg/L. The slight changes in sodium and calcium concentrations were considered of minimal biological significance.

 

A NOAEC was not determined as a result of the squamous metaplasia observed in the rat olfactory epithelium after exposure to the mixture of dibasic esters - a local effect thought to be an irritant response to exposure. An exposure concentration of 0.4 mg/L may be regarded as a NOAEC for systemic toxicity.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

400 mg/m³

Study duration:

subchronic

Experimental exposure time per week (hours/week):

30

Species:

rat

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

Deviations:

not specified

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:Charles River Breding Laboratories, Kingston, NY, USA
- Age at study initiation: 4 weeks
- Weight at study initiation: 57 - 100 g
- Fasting period before study: Not applicable
- Housing: Paired, in stainless steel wire mesh cages
- Diet (e.g. ad libitum): Ad libiutum except during exposure
- Water (e.g. ad libitum): Ad libitum except during exposure
- Acclimation period: Approximately 1 week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 - 25 deg C
- Humidity (%): 31 - 59%
- Photoperiod (hrs dark / hrs light): 12 / 12

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: Nitrogen

Remarks on MMAD:

MMAD / GSD: Not applicable - tested as vapour

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: NYU style inhalation chamber
- Method of holding animals in test chamber: stainless steel "modules"
- Source and rate of air: Ambient air, 300L/minute
- Method of conditioning air: Not reported
- System of generating particulates/aerosols: Vapour generation in furnace at 250-300 deg C, vapour carried to inhalation chamber by nitrogen stream at 2-3 L/minute flow rate.
- Temperature, humidity, pressure in air chamber: Measured but not reported
- Air flow rate: 300L/minute
- Air change rate: Not reported
- Method of particle size determination: Not applicable
- Treatment of exhaust air: Water scrubbing

TEST ATMOSPHERE
- Brief description of analytical method used: Identity and concentration by by GC/FID analysis of solvent traps
- Samples taken from breathing zone: yes

VEHICLE (if applicable)
- Justification for use and choice of vehicle: None used

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples were analysed by gas chromatography (GC/FID). Isothermal separation at 190 deg C on stainless steel column packed with SP-1000 on Chromosorb G 100/120 mesh. The GC response of the samples was compared with that obtained from standard samples prepared by quantitative dilution of DBE in acetone to determine chamber concentration. The method permitted separation / identification of the 3 components to determine changes in composition

Duration of treatment / exposure:

13 weeks (92 - 94) days (males and females) followed by a 6 week recovery period (satelite groups)

Frequency of treatment:

5 days / week, 6 hours / day

Dose / conc.:

0 mg/m³ air

Dose / conc.:

20 mg/m³ air

Dose / conc.:

80 mg/m³ air

Dose / conc.:

400 mg/m³ air

No. of animals per sex per dose:

40 males, 40 females - 10 males/10 females killed after 7 weeks exposure, 20 males/20 females killed after 13 weeks exposure and 10 males/10 females killed after a recovery period of 6 weeks

Control animals:

yes, sham-exposed

Details on study design:

- Dose selection rationale: Highest dose level selected based on findings from an earlier study.
- Rationale for animal assignment (if not random): Random

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule for examinations: Weekly

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No data

WATER CONSUMPTION: No data

OPHTHALMOSCOPIC EXAMINATION: No data

HAEMATOLOGY: Yes
- Time schedule for collection of blood: 46/47 days, again after 92/93 days and (recovery animals) 135/136 days
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 males / 10 females /group
- Parameters examined: Erythrocyte count; haemoglobin concentration; mean corpuscular volume; platelet count; leukocyte count including relative numbers of neutrophils, band neutrophils, lymphocytes, atypical lymphocytes, eosinophils, monocytes and basophils; haematocrit; mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 46/47 days, again after 92/93 days and (recovery animals) 135/136 days
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 males / 10 females /group
- Parameters examined: Alkaline phosphatase; alanine aminotransferase; aspartate aminotransferase; glucose; urea nitrogen; calcium; cholesterol; creatinine; total protein; albumin; sodium; potassium; globulin

URINALYSIS: Yes
- Time schedule for collection of blood: 46/47 days, again after 92/93 days and (recovery animals) 135/136 days
- Metabolism cages used for collection of urine: Yes
- Animals fasted: No data
- Parameters examined: .Volume; osmolality; pH; blood; sugar; protein; bilirubin; urobilinogen; ketones; colour; transparency; sediment

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes - Macroscopic examination and weighing of the brain, heart, lungs, liver, spleen, kidneys, testes and thymus. The following tissues were retained for microscopic examination: brain; spinal cord; peripheral nerve (sciatic); nasal cavity; larynx; trachea; lungs; heart; aorta; liver; pancreas; salivary glands; pharynx; oesophagus; stomach; duodenum; jejunum; ileum; caecum; colon; rectum; kidneys; urinary bladder; testes; epididymides; prostate; seminal vesicle; ovaries; uterus; cervix; vagina; pituitary; thyroid; parathyroid; adrenal; spleen; thymus; bone marrow (femur and sternum); mandibular lymph node; mesenteric lymph node; tracheobronchial lymph node; skeletal muscle; skin; mammary gland; eyes; harderian gland; exorbital lacrimal gland.


HISTOPATHOLOGY: Yes - Nasal tissues only..

Statistics:

One-way analysis of variance and Dunnett's test

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

reduced at 390 mg/m3

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Increased Na in females at 76 and 390 mg/m3;

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Reduced liver weight in females at 390 mg/m3

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Degeneration of olfactory epithelium in females at all concentrations and in males at 76 and 390 mg/m3

Details on results:

CLINICAL SIGNS AND MORTALITY: One female at 76 mg/m3 was accidentally killed on test Day 25. One male at 76 mg/m3 was killed on test Day 32 because of a severely distended urinary bladder. Necropsy revealed calculi in the urinary bladder and kidneys. Clinical signs of exposed animals were similar to those of the controls.

BODY WEIGHT AND WEIGHT GAIN: Females at 390 mg/m3 exhibited reduced rates of weight gain compared to controls during the exposure period. During the subsequent 6-week recovery period the rate of weight gain was similar to that of the controls.

HAEMATOLOGY: No significant treatment-related differences were reported in measured haematology parameters. Those statistically significant differences that were seen showed no dose-response relationship and were considered unrelated to treatment.

CLINICAL CHEMISTRY: Slightly reduced serum sodium concentration was noted all exposed male rats and in females exposed at 76 and 390 mg/m3 relative to controls at the end of the 13-week exposure period. Concentrations in males and females exposed at 390 mg/m3 remained slightly low but the sodium concentrations in the other affected groups were no longer different from those of the control group at the end of the 6-week recovery period. Those statistically significant differences that were seen in other measured parameters showed no dose-response relationship and were considered unrelated to treatment.

URINALYSIS: Those statistically significant differences that were seen showed no dose-response relationship and were considered unrelated to treatment.

ORGAN WEIGHTS: Reduced absolute liver weights were observed in female rats treated at 390 mg/m3 at the end of the I3-week exposure period. Relative (to body weight) liver weights in these animals were not different from those of the controls. The absolute liver weights females of this treatment group were slightly decreased after approximately 7 weeks of exposure but the decrease was not statistically siignificant. Relative lung and brain weights in females treated at 390mg/m3 were increased at the end of the exposure period, this considered related to the observed body weight depression and was considered not to be a direct effect of exposure to the substance. Slight but statistically significant decreases were observed in relative brain weights of females after 7 weeks of exposure at 20 mg/m3 and in absolute brain weights of females after 13 weeks exposure at 390 mg/m3. These changes were considered to be of no biological significance. No organ weight effects seen at the end of the 6-week recovery period.

GROSS PATHOLOGY: No details available

HISTOPATHOLOGY: NON-NEOPLASTIC: Examination of the nasal tissue after 7 weeks of exposure revealed degeneration of the olfactory epithelium in both male and female rats exposed at 76 or 390 mg/m3. One male rat exposed at 20 mg/m3 showed a small focal area of olfactory epithelial degeneration. Degeneration of the olfactory epithelium was apparent at all exposure concentrations in the female rats and in male rats exposed 76 and 390 mg/m3 at the end of the 13-week exposure period. At the end of the 6-week recovery period, effects seen in exposed rats included disorganisation of the olfactory epithelium, reduced numbers of neuronal cells and respiratory metaplasia. These findings were considered related to tissue repair and regenerative processes and were noted in males and females of all exposure groups.

Dose descriptor:

NOAEC

Effect level:

20 mg/m³ air

Based on:

test mat.

Sex:

male

Basis for effect level:

histopathology: non-neoplastic

other: Histopathology: degeneration of nasal olfactory epithelium

Dose descriptor:

LOAEC

Effect level:

20 mg/m³ air

Based on:

test mat.

Sex:

female

Basis for effect level:

histopathology: non-neoplastic

other: Histopathology: degeneration of the olfactory epithelium

Dose descriptor:

NOAEC

Effect level:

400 mg/m³ air

Sex:

male/female

Basis for effect level:

other: Lack of significant systemic toxicity

Critical effects observed:

yes

Lowest effective dose / conc.:

20 mg/m³ air

System:

respiratory system: upper respiratory tract

Organ:

nasal cavity

Treatment related:

yes

Dose response relationship:

yes

Conclusions:

The mixture, at the concentrations examined, causes lesions of the olfactory epithelium. Other than this local effect, no significant systemic toxicity was apparent in the rat following repeated inhalation exposure over a period of at least 90 days.

Executive summary:

Groups of 20 male and 20 female rats have been exposed, by inhalation 6 hours/day/5 days/week, for 13 weeks to a mixture of dibasic esters containing dimethyl succinate, dimethyl glutarate and dimethyl adipate. Animals were exposed at concentrations of 20, 76 and 390 mg/m3.

 

Microscopic examination of the nasal areas revealed degeneration of the olfactory epithelium in allexposure concentrations inthe female rats and in male rats exposed 76 and 390 mg/m3 at the end of the 13-week exposure period. At the end of the 6-week recovery period, effects seen in exposed rats included disorganisation of the olfactory epithelium, reduced numbers of neuronal cells and respiratory metaplasia. These findings were considered related to tissue repair and regenerative processes and were noted in males and females of all exposure groups.Other effects of exposure included a reduction in absolute liver weights in female rats treated at 390 mg/m3. A slight reduction in body weight was noted in males and females exposed at 390mg/m3.Slightly reduced serum sodium concentration was noted all exposed male rats and in females exposed at 76 and 390 mg/m3 at the end of the 13-week exposure period. Concentrations in males and females exposed at 390 mg/m3 remained slightly low at the end of the 6-week recovery period.

 

A NOAEC was not determined as a result of the degeneration observed in the rat olfactory epithelium after exposure to the mixture of dibasic esters - a local effect, possibly an irritant effect. A NOAEC or LOAEC for systemic effects may be regarded as 76 mg/m3.

 

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEC

20 mg/m³

Study duration:

subchronic

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

Groups of 10 male and 10 female rats have been exposed, by inhalation 6 hours/day/5 days/week, for approximately 14 weeks to a mixture of dibasic esters containing dimethyl succinate, dimethyl glutarate and dimethyl adipate. Animals were exposed at concentrations of 0.16, 0.40 or 1.0 mg/L (160, 400 or 1000 mg/m³). Microscopic examination of the nasal areas revealed mild squamous metaplasia in the olfactory epithelium in all treated groups. Examination of other preserved tissues showed no abnormalities that could be attributed to treatment at any concentration tested. Other effects of exposure included a dose-dependent reduction in absolute and relative liver weights in female rats in all treatment groups and in male animals exposed at 1.0 mg/L (1000 mg/m³). No microscopic changes were apparent in the liver and the biological significance of observed effects on liver weight is not known. A slight reduction in body weight and slightly reduced blood sodium concentrations was noted in males and females exposed at 1.0 mg/L (1000 mg/m³). Slightly increased blood calcium concentrations were noted in females exposed at 0.40 or 1.0 mg/L (400 or 1000 mg/m³). The slight changes in sodium and calcium concentrations were considered of minimal biological significance. A NOAEC was not determined as a result of the squamous metaplasia observed in the rat olfactory epithelium after exposure to the mixture of dibasic esters although the lowest dose investigated may be regarded as a LOAEC for local effects. An exposure concentration of 0.4 mg/L (400 mg/m³) may be regarded as a NOAEC for systemic toxicity.

 

A second study has been described by Keenan et.al. (Fund Appl Toxicol 15: 381-393, 1990) in which groups of 20 male and 20 female rats were exposed, by inhalation, 6 hours/day/5 days/week, for 13 weeks to a mixture of dibasic esters containing dimethyl succinate, dimethyl glutarate and dimethyl adipate. Animals were exposed at concentrations of 20, 76 and 390 mg/m³. Again degeneration was observed in the rat olfactory epithelium and a NOAEC could not be determined as a result.

Repeated dose toxicity: inhalation - local effects (target organ) respiratory: nose

Justification for classification or non-classification

Based on the results of a repeated dose toxicity study on a mixture of dibasic esters containing dimethyl succinate, classification and labelling according to Directive 67/548/EEC or Regulation 1272/2008 is not required. The local effects observed in sub-chronic studies in rats have limited relevance to humans and thus STOT - repeated exposure classification is not warranted.