dichloromethane; methylene chloride

Endpoint summary

Description of key information

No evidence of adverse effects on health has been found at the workplace following occupational exposure concentrations of about 100 ppm DCM (353 mg/m3) over several years. Therefore, 100 ppm (353 mg/m3) is considered to be a clear no-observed-adverse-effect concentration for repeated dose toxicity of dichloromethane in humans. This concentration is also set as 8 h TWA by the SCOEL. Experimental inhalation studies in rats appear consistent with this figure (NOAEC of 706 mg/m3).

Regarding the oral route of exposure a chronic NOAEL of 6 mg/kg bw/day based on liver effects (LOAEL of 52 mg/kg bw/day) in rats is selected as most critical one.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: oral

Remarks:

combined repeated dose and carcinogenicity

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 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

no

GLP compliance:

not specified

Limit test:

no

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, Portage, MI
- Age at study initiation: ca. 7 weeks old
- Housing: individually in stainless-steel hanging wire-mesh cages
- Diet (e.g. ad libitum): Purina Rodent Laboratory Chow (No. 5001), ad libitum
- Water (e.g. ad libitum): deionized water provide from water bottles with stainless steel ballpoints, ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature: 70.5 +/- 1.75 F
- Humidity (%): 53.9 +/- 5.82
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: drinking water

Vehicle:

water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
An appropriate amount of DCM was added to deionized water on a volume/volume basis to yeld a 1% stock solution. A sample was analysed prospectively to ensure that the concentration was within +/- 5% of the desired target level. Volumes of the stock solution were added to glass carboys and diluted with deionized water to yield the desired concentratios of DCM. During the first 13 weeks, dosage formulations were adjusted to the most recently recorded body weight and water consumption data; thereafter, they were adhysted every 4 weeks. Fresh dilutions were prepared and presented four times/week, twice for each sex. Samples from three randomly selevted bottles, which had been on the animal cages for a 4-day period, were anlyzed for DCM concentration weekly for the first 12 weeks and at least every 4 weeks thereafter.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

In order to ensure that the animals received the proper dosages of the test material, samples of the drinking-water administered to all groups were routinely analysed throughout the course of the study. Quantitative measurements of DCM concentrations in the aqueous delivery system were made utilizing headspace analysis by gas chromatography (Perkin-Elmer Sigma II gas chromatograph using a glass column, 6 ft x 4 mm ID packed with 0.2% Carbowas 1500 on Carbopack C, 00/80 mesh). All standards and test-solution analyses were averaged from at least duplicate injections.

Duration of treatment / exposure:

104 weeks

Frequency of treatment:

daily

Remarks:

Doses / Concentrations:
0, 6, 52, 125, 235, 232 (recovery, 18 months exposure) mg/kg bw/day (males)
Basis:
actual ingested

Remarks:

Doses / Concentrations:
0, 6, 58, 136, 263, 269 (recovery, 18 months exposure) mg/kg bw/day (females)
Basis:
actual ingested

No. of animals per sex per dose:

85 (main experiment), 25 (high dose, recovery), 50 (recovery control group)

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: dose levels were selected on the basis of findings from subchronic and pharmacokinetic studies of DCM as described by Kirschmanm, Brown, Coots and Margareidge (1986). The findings from a 90-day drking-water study in ratws revealed histopathological effects on the livers of males and females dosed at levels of 166 and 209 mg/kg/day, respectively. Pharmacokinetic studies revealed a significant change in the slope of DCM equivalents expired as carbonmonoxied and carbon dioxide at dose levels of approx. 1000 mg/kg/day, indicating a saturation of the metabolic process at higher dose levels. Therefore, the dose levels for this study were selected to induce liver toxicity at the highest level and to have two dose levels above and two below the apparent metabolic saturation point.

- Rationale for selecting satellite groups: an additional group of rats (the recovery group) was exposed to 250 mg/kg bw/day for 78 weeks followed by 26 weeks without DCM treatment, to determine whether any toxicity was reversible with time.

- Section schedule rationale (if not random): after treatment for 26, 52 and 78 weeks, 5, 10 and 20 animals, respectively, of each sex, preselected prior to initiation of the study, were killed from control group 1 and from each of the DCM-treated groups (except the recovery group) to monitor the effects of DCM treatment over time.

Positive control:

Not used.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily throughout the study for deaths and signs of moribund condition. During the second year of the study, a late-night observation was also performed on 5 nights/week.

DETAILED CLINICAL OBSERVATIONS: Yes
Detailed clinical observations were recorded on all rats weekly throughout the study.

BODY WEIGHT: Yes
- Time schedule for examinations: prior to treatment and weekly throughout the study. Fasted body weights were also recorded on all rats killed as scheduled for organ/body weight ration determinations.

FOOD CONSUMPTION:
- Food consumption was measured weekly for the first 13 weeks for all rats

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations:
- Water consumption was measured twice weekly (after 3- and 4-day periods) throughout the study for all rats, adn the values were combined to yeld the weekly water consumption

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: prior to treatment and after treatment for 26, 52, 78 and 103 weeks, all rats were subjected to an ophthalmoscopic examination. Examinations were performed using an indirect ophthalmoscope after instillation of a 1% tropicamide ophthalmic solution (Mydriacyl, Alcon Kaboratories, Inc., For Worth, TX) to induce mydriasis.
- Dose groups that were examined: all

HAEMATOLOGY: Yes
- Time schedule for collection of blood: after treatment for 52 and 78 weeks, blood samples were collected from rats scheduled for the interim kill from control group 1 and from groups receiving DCM at levels of 5, 50, 125 and 250 mg/kg/day.
- Anaesthetic used for blood collection: not used
- Animals fasted: yes, overnight
- How many animals: 10 of each sex
- Parameters examined: haematocrit and haemoglobin determinations, total erythrocyte count, total and differential leucocyte counts, calculation of mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration, estimation of prothrombin time and examination of erythrocyte and leucocyte morphology.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: after treatment for 52 and 78 weeks, blood samples were collected from rats scheduled for the interim kill from control group 1 and from groups receiving DCM at levels of 5, 50, 125 and 250 mg/kg/day.
- Animals fasted: yes, overnight
- How many animals: 10 of each sex
- Parameters examined: glutamic-pyrubic transaminase, glutamic-oxalacetic transaminase, alkaline phosphatase, total cholsterol, creatinine, blood urea nitrogen, total protein and glucose.

URINALYSIS: Yes
- Time schedule for collection of urine: after treatment for 52 and 78 weeks, urine samples were collected from rats scheduled for the interim kill from control group 1 and from groups receiving DCM at levels of 5, 50, 125 and 250 mg/kg/day.
- Metabolism cages used for collection of urine: No data
- Animals fasted: Yes, overnight
- Parameters examined: protein, pH, ketones, glucose and occult blood

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
All rats received a complete necropsy.

HISTOPATHOLOGY: Yes
The following tissues were taken and preserved in 10% neutral buffered formalin: brain, spinal cord (three levels), pituitary, femur, pancrease, mesenteric lymph node, thyroid and parathyroids, adrenals, heart, lung, spreen, liver, kidneys, stomach, duodenum, jejunum, ileum, colon, caecum, rectum, sternum marrow, costochondral rib junction, tongue, Zymbal gland, testes, ovaries, prostate, urinary bladder, uterus, epididymides, seminal cesicles, salicary glands, thymus, oesophagus, trachea, larynx, aorta, thigh muscle, sciatic nerve, eyes, mammary gland, skin and lesions. In addition, the hard and soft palates, and the nasal turbinates were taken from rats killed by design after treatment for 26 and 52 weeks.

Statistics:

Body weight, food and water consumption, haem¬atology (except differential leucocyte counts), serum chemistry and organ weight data were evaluated using a preliminary test for homogeneity of variance (Bartlett, 1937) followed by a one-way classification analysis of variance-ANOVA (Winer, 1971). Fisher's least significant difference (LSD) test (Miller, 1981) was used to perform control versus treatment mean comparisons for data with homogeneous vari¬ances and significant ANOVA. In the case of significant ANOVA of data with heterogeneous vari¬ances, Wilcoxon's two-sample nonparametric rank-sum test (Hollander & Wolfe, 1973) was used for the same purpose. Linear regression analysis and lack of fit tests (Draper & Smith, 1966) were performed on all data by sex against each control group or com¬bined controls, where appropriate. A significance level of P = 0.05 was used for all tests, with the group comparisons being two-tailed. Survival was evaluated for trend and heterogeneity by the Gehan-Breslow (Generalized Kruskal-Wallis) test. Additional graph¬ical evaluation of the survival data was performed using the Kaplan-Meier method. All of the above analyses were performed with the National Cancer Institute Package (Thomas, Breslow & Gart, 1977).
All tumour data were analysed in two phases. The unadjusted tumour incidences were analysed by the Cochran-Armitage test for trend and chi-square and Fisher-Irwin exact tests for heterogeneity (Thakur, Berry & Mielke, 1985). Intercurrent mortality-adjusted tumour data (for `incidental' tumours) were analysed by the prevalence method of Dinse & Lagakis (1983). All other binary incidence data were analysed by the methods used in the case of unadjusted tumour analysis.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Food efficiency:

not examined

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

effects observed, treatment-related

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

no effects observed

Details on results:

Survival, clinical observations, body weights and food and water consumption
Overall survival rates among male and female groups were 76 and 71%, respectively, with no significant treatment-related trend or heterogeneity in
any of the groups in the study. No treatment-related clinical observations were noted. Incidental observations common to the rat were seen with similar frequency among control and treated groups of both sexes. Palpable masses were noted occasionally and were generally described as subcutaneous masses in the axillary or inguinal regions. Lower body weights and body-weight gains were observed generally throughout the study in both sexes treated with DCM at levels of 125 or 250 mg/kg/day, the differences from the controls being small but statistically significant. Small but statistically significant decreases in water consumption values were observed in both sexes treated with DCM at levels of 125 or 250 mg/kg/day generally throughout the study. Concomitant decreases in food consumption values were noted in the same groups during the first 13 wk of treatment.

Ophthalmology
No treatment-related ophthalmoscopic findings were noted during the study.

Haematology, serum chemistry and urinalysis
Increases in mean haematocrit, haemoglobin and erythrocyte count were observed in both sexes treated with DCM at levels of 50, 125 or 250 mg/kg/day for 52 or 78 wk. Approximately half of these increased mean values were determined to be statistically significant. Results of all other mean haematology and erythrocyte indices were consistent among all groups. Decreases in alkaline phosphatase, creatinine, blood urea nitrogen, total protein and cholesterol values were generally noted in both sexes of the higher-dose groups. The majority of these mean values were determined to be statistically significant at one or both of the intervals evaluated. Results of all other parameters were consistent among all groups. No treatment-related effects on urinalysis were noted during the study.

Organ weights and organ/body weight ratios
No treatment-related effects on organ weights or organ/body weight ratios were observed during the study. Instances of statistically significant positive and negative differences were noted in several organs, but were considered to be unrelated to treatment because of the lack of meaningful and distinct dose-related trends.

Pathology
Scattered incidental findings in gross pathology were noted across all groups and were considered to be unrelated to treatment. In the histopathological examinations, no treatment-related effects were noted in any of the tissues examined, with the exception of the liver. Histomorphological alterations of the liver were observed. A dose-related positive trend in the incidences of foci/areas of celIular alteration was noted in both sexes treated with
DCM. Group comparisons were statistically significant at all levels except 5 mg/kg/day. This finding was first noted after treatment for 78 wk and
progressed until wk 104. In addition, an increased incidence of fatty change in the liver was observed in tissues stained with haematoxylin and eosin, and was confirmed by staining with Oil Red O. This effect was generally observed in both sexes treated with DCM at levels of 50, 125 or 250 mg/kg/day at both wk 78 and wk 104. An increase in the incidence of foci/areas of cellular alteration, similar to that noted in the 250 mg/kg/day group, was observed in the recovery group receiving 250 mg/kg/day. However, the fatty change was less severe in the recovery group than in the group receiving 250 mg DCM/kg/day for 104 wk.

Dose descriptor:

NOAEL

Effect level:

6 mg/kg bw/day (actual dose received)

Sex:

male/female

Basis for effect level:

other: Increases in mean haematocrit, haemoglobin erythrocyte count. Increased incidences of foci/areas of cellular alteration and fatty change in the liver at 52/58 mg/kg bw.

Critical effects observed:

not specified

Table 1. Estimates of mean daily consumption of dichloromethane (DCM) by groups of rats given DCM in the drinking-water for 2 yr

Group	Target level (mg/kg/day)	Mean intake (mg/kg/day)
		Males	Females
low	5	6	6
mid 1	50	52	58
mid 2	125	125	136
high	250	235	263
high (recovery)*	250	232	269

*this group did not receive DCM after 18 months, so the mean for this group is for the first 18 months only.

Survival,clinical observations, body weights and food and water consumption

Overall survival rates among male and female groups were 76 and 71%, respectively, with no significant treatment-related trend or heterogeneity in any of the groups in the study. No treatment-related clinical observations were noted. Lower body weights and body-weight gains were observed generally throughout the study in both sexes treated with DCM at levels of 125 or 250 mg/kg/day, the differences from the controls being small but statistically significant. Small but statistically significant decreases in water consumption values were observed in both sexes treated with DCM at levels of 125 or 250 mg/kg/day generally throughout the study. Concomitant decreases in food consumption values were noted in the same groups during the first 13 wk of treatment.

 

Haematology, serum chemistry and urinalysis

Increases in mean haematocrit, haemoglobin and erythrocyte count were observed in both sexes treated with DCM at levels of 50, 125 or 250 mg/kg/day for 52 or 78 wk. Approximately half of these increased mean values were determined to be statistically significant. Results of all other mean haematology and erythrocyte indices were consistent among groups.

Decreases in alkaline phosphatase, creatinine, blood urea nitrogen, total protein and cholesterol values were generally noted in both sexes of higher-dose groups. The majority of these mean values were determined to be statistically significant at one or both of the intervals evaluated. Results for all other parameters were consistent among groups.

No treatment-related effects on urinalysis were noted during the study.

Organ weights and organ/body weight ratios

No treatment-related effects on organ weights organ/body weight ratios were observed during the study. Instances of statistically significant positive and negative differences were noted in several organs but were considered to be unrelated to treatment because of the lack of meaningful and distinct do related trends.

Pathology

Scattered incidental findings in gross pathology were noted across all groups and were considered be unrelated to treatment.

In the histopathological examinations, no treatment-related effects were noted in any of the tissues examined, with the exception of the liver. Histomorphological alterations of the liver were observed and are presented in Table 2. A dose-related positive trend in the incidences of foci/areas of cellular alteration was noted in both sexes treated with DCM. Group comparisons were statistically significant at all levels except 5 mg/kg/day. This finding was first noted after treatment for 78 wk and progressed until wk 104. In addition, an increased incidence of fatty change in the liver was observed in tissues stained with haematoxylin and eosin, and was confirmed by staining with Oil Red O. This effect was generally observed in both sexes treated with DCM levels of 50, 125 or 250 mg/kg/day at both wk 78 and wk 104. An increase in the incidence of foci/areas of cellular alteration, similar to that noted in the 50-250 mg/kg/day group, was observed in the recovery group receiving 250 mg/kg/day. However, the fatty change was less severe in the recovery group than in group receiving 250 mg DCM/kg/day for 104 wk.

Table 2. Incidence of liver foci/areas of alteration in rats given dichloromethane (DCM) in the drinking-water for up to 2 yr.

 

	Incidence of lesion* in rats given a DCM target dose (mg/kg/day) of:
Sex	0	0	5	50	125	250	250**
Wk78
Males	7/20	--	3/20	15/20	13/20	20/20	--
Females	3/20	--	11/20	14/20	16/20	17/20	--
Wk 104
Males	27/36	25/40	22/34	35/38	34/35	40/41	15/15
Females	17/31	17/36	12/29	30/41	34/38	31/34	17/20

*No. of rats affected/no. examined. **Recovery group. Bold: statistically significant differences with control group.

See for a summary on tumour data, section 7.7 (Serota et al., 1986, rat study)

Conclusions:

The 2-year NOAEL for oral toxicity was 6 mg/kg bw/day in rats, based on increased values of haematological parameters and increased foci/areas of cellular alteration and fatty changes in the liver. It was, however, noted that (a) approximately half of the increased mean values of the haematology parameters was statistically significant and no dose-response relationship was mentioned, and (b) increased foci/areas of cellular alteration and fatty acid change in the liver were based on incidence; nothing was mentioned on severity.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

6 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

Several repeated dose toxicity studies were available in rats and mice. The Serota et al. (1986) study was chosen as key study amongst others because of its relatively low NOAEL.

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Although GLP status is not known (not indicated in the publication), the study is a guideline study, published in peer reviewed literature; there are no restrictions, therefore fully adequate for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Spartan Research Animals, Inc., Haslett, Michigan
- Age at purchase: 6-8 weeks old
- Housing: 3/cage in wire-bottom stainless-steel cages
- Diet (e.g. ad libitum): Purina Laboratory Chow, Ralston-Purina Co., St. Louis, MO, ad libitum, except during exposure periods
- Water (e.g. ad libitum): ad libitum, except during exposure periods
- Acclimation period: at least 2 weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22
- Humidity (%): ca. 50
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

air

Remarks:

unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: Not applicable (vapour)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless-steel and glass chambers of 4.1 m3 volume.
- System of generating particulates/aerosols: exposure concentrations of methylene chloride were generated by metering the liquid at a constant rate with a precision pump into a warmed vaporization flask (ca. 60 C). Vapours frim the flask were swept with compressed air into the main chamber airstream where further mixing and dilution occured.
- Temperature, humidity, pressure in air chamber: 22 C, 50%
- Air flow rate: 800 l/min
- Air change rate: 12/hr

TEST ATMOSPHERE
- Brief description of analytical method used: IR spectroscopy

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration of methylene chloride in each chamber was determined 1-2 times each hour by IR spectroscopy using a Miran I IR spectrophotometer (Foxboro/Wilks, South Norwalk, CT) at a wave length of 7.95 to 13.35 microm.

Duration of treatment / exposure:

2 years

Frequency of treatment:

6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
50, 200, and 500 ppm
Basis:
other: target concentrations

Remarks:

Doses / Concentrations:
50+/-3, 199+/-5, 499+/-10 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

90 (male), 108 (female)

Control animals:

yes

Details on study design:

- Rationale for selecting satellite groups: In addition to the main experiment, 30 female rats, identified as 500con, were exposed to 500 ppm methylene chloride for the first 12 months and to room air for the last 12 months of the study. Thirty additional female rats, identified as con500, were exposed to room air for the first 12 months and 500 ppm methylene chloride for the last 12 months of the study. These animals were added to assess the temporal relationship between the initial exposure to methylene chloride and expression of the liver and mammary lesions. A subgroup of 18 female rats/exposure level was used to measure liver DNA synthesis. All remaining animals (70/sex/exposure group and 25 female rats from 500con and con500 exposure groups) were the major portion intended for oncogenic evaluation.
A separate, predesignated sub-group of 18 female rats/exposure level was used to mea­sure the rate of liver DNA synthesis. Groups of 4 female rats/exposure level were selected by a computer-derivedrandomization procedure from this subgroup after 6 and 12 months of exposure to methylene chloride. Approximately 18 hr after the last designated exposure to methylene chloride, each rat was injected ip with 0,0054 mg/kg [3H]thymidine. All rats were sacrificed 6 hr following thep injection. At the time of termination the liver was removed, the DNA was extracted, and [3H]thymidine in-corporation into the DNA was determined. All remaining animals in this subgroup were terminated without a gross examination after 12 months.

- Section schedule rationale (if not random): Subgroups of 5 rats/sex/exposure level were scheduled for interim terminations after 6, 12, 15, and 18 months of exposure to methylene chloride. Subgroups of 5 female rats from each of the 500con and con500 exposure groups were sacrificed at the 18 month interim necropsy.
Male rats were necropsied after 20 months due to the relatively limited lifespan of this substrain of male rat. All surviving female rats were necropsied after 24 months of exposure to methylene chloride.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: each day after exposure for signs of toxicity, also prior to exposure and on weekends and holidays

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: examinations of all rats for palpable masses were conducted prioir to the intial exposure to DCM, and at monthly intervals after the first 12 months, except for the subgroup designated for measuring liver DNA synthesis.

BODY WEIGHT: Yes
- Time schedule for examinations: all rats were weighed prior to the initial exposure, twice a month for the first 3 months of the study and monthly thereafter.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at various interim necropsies, also at multiple time intervals for determining carboxyhemoglobin levels
- How many animals: 4-5 for determining carboxyhemoglobin levels
- Parameters examined: total birubin (except at 6 months), cholesterol, triglyceride, potassium, estradiol (except at 6 months), FSH and LH levels.

Sacrifice and pathology:

All rats were subjected to a complete gross necropsy examination.
An extensive set of tissues intended to include all those collected at the interim and terminal kills were embedded in paraffin, sectioned and stained for microscopy.

Other examinations:

Liver DNA synthesis: a separate, predesignated subgroup of 18 female rats/exposure level was used to measure the rate of DNA liver synthesis.

Statistics:

Carboxyhemoglobin levels, rate of thymidine incorporation into the liver, absolute and relative organ weights, body weights, and clinical chemistry determinations were evaluated by analysis of variance and Dunnett's test (Steel and Torrie, 1960). Palpable mass data was analyzed by the Wilcoxon test (Haseman and Hoel, 1974). Gross pathologic observations and histopathologic data from interim kills lvere not evaluated statistically. Incidences of mofality and remaining histopathologic observations were evaluated by Fisher's Exact Probability Test (Siegel, 1956). Because numerous measurements were statistically compared on the same group of animals, the frequency of false positive (type I ) errors is unknown but is greater than the nominal a level of 0.05 used for Dunnett's and Fisher's Exact Probability Test. In addition to results of statistical evaluation, the final toxicologic interpretation of the data considered other factors such as dose-response relationships, biological plausibility, consistency, and historical values.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

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:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

No exposure-related gross or histopathologic changes were observed in animals from interim sacrifice groups. At terminal sacrifice, the incidences of both hepatocellular cytoplasmic vacuolization consistent with fatty changes and multinuceated hepatocytes were statistically elevated in female rats exposed to 200 and 500 ppm of methylene chloride; a slight increase in the incidence of hepatocellular vacuolization was also observed in male rats exposed to 500 ppm. Histopathological changes in the liver were not found in the male rats exposed to 50 or 200 ppm of methylene chloride. No other pathologic or histopathologic nontumor findings were reported.

Dose descriptor:

NOAEC

Effect level:

200 ppm

Sex:

male/female

Basis for effect level:

other: Histopathological changes in liver of male and female rats

Critical effects observed:

not specified

Mortality and Observations

 

The mortality rates for the various groups of male and female rats exposed to methylene chloride were comparable to control values. However, due to the early onset of geriatric changes which is characteristic of this substrain of rat and which occurred in all groups of male rats, exposure of male rats was terminated after 20 months of exposure to methylene chloride and the remaining survivors were necropsied. Exposure to 50, 200, or 500 ppm methylene chloride had no discernable adverse effect on the animals' appearance during the course of the study. Group mean body weights of male and female rats exposed to methylene chloride were not adversely affected throughout the 24-month study.

 

 

Absolute and Relative Organ Weights, Clinical Chemistry, Plasma Hormone Levels and Carboxyhaemoglobin

 

Absolute and relative organ weights, clinical chemistry values, and plasma hormone levels were not altered in rats exposed to methylene chloride (data not shown). Occasional statistically significant differences between control and exposed group mean values were considered to be sporadic occurrences unrelated to exposure. Blood carboxyhaemoglobin levels of rats exposed to methylene chloride were elevated in an apparent dose-dependent relationship above control values (Table). The percentage carboxyhaemoglobin was similar within exposure groups after 6, 12, or 20 -24 (terminal kill) months, indicating a lack of accumulation with repeated exposure.

 

Table - Carboxyhaemoglobin values° of rats exposed to methylene chloride

ppm	Sex	Time interval
		6months	12months	Terminal kill
0	male	4.8 ± 2.6°	0.3 ± 0.7	2.2 ± 1.3
50	male	8.8 ± 2.0	2.8 ± 0.3*	6.5 ± 1.1*
200	male	14.3 ± 1.3*	9.6 ± 1.2*	12.5 ± 0.8*
500	male	16.7±2.4*	12.7±1.6*	13.7±0.6*
0	female	1.1 ± 0.4	2.6 ± 1.1	5.1 ± 3.4
50	female	6.3 ± 2.7*	8.2 ± 3.1*	5.9 ± 0.7
200	female	13.9 ± 1.1*	13.1 ± 1.4*	13.8 ± 1.0*
500	female	17.9 ± 2.9*	17.5 ± 1.5*	17.6 ± 2.9*

° %, mean ± standard deviation for four to five rats/ sex/exposure level.

* Significantly different from control value by Dun­nett's or Wilcoxon's test, a < 0.05.

 

 

DNA Synthesis

 

The incorporation of [³H]thymidine into hepatic DNA of female rats exposed to 50, 200, or 500 ppm methylene chloride for either 6 or 12 months was comparable to control animals. There was no detectable alteration in the rate of DNA synthesis in the liver of rats exposed to concentrations as high as 500 ppm methylene chloride.

 

 

Pathology and Palpable Mass Data

 

No gross or histopathological lesions were observed in rats from the interim kill groups which were attributed to exposure to methylene chloride. Exposure-related histopathological changes observed in rats that died spontaneously or at the terminal kill were confined to the liver and mammary tissue. For the liver, the incidence of both hepatocellular cytoplasmic vacuolization (consistent with fatty change) and multinucleated hepatocytes was statistically increased in female rats exposed to 500 ppm methylene chloride. A slight increase in the incidence of hepatocellular vacuolization was observed in malerats exposed to 500 ppm methylene chloride (22 of 70 control animals vs. 28 of 70 animals exposed to 500 ppm methylene chloride). However, these liver effects were not observed in male or female rats exposed to 50 or 200 ppm methylene chloride. In female rats exposed to 200 ppm methylene chloride, the incidence of multinucleated hepatocytes was numerically but not statistically increased above the rate for control animals; this effect was considered to be of doubtful biologic significance.

See for a summary on palpable masses and tumours section 7.7 (Nitschke et al., 1988).

Conclusions:

Histopathological changes were seen in liver of male and female rats at 500 ppm. The NOAEC was 200 ppm.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

695 mg/m³

Study duration:

chronic

Species:

rat

Quality of whole database:

Several repeated inhalation toxicity studies were available in rats and mice. The Nitschke et al. (1988) study was chosen as key study.

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Although GLP status is not known (not indicated in the publication), the study is a guideline study, published in peer reviewed literature; there are no restrictions, therefore fully adequate for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Spartan Research Animals, Inc., Haslett, Michigan
- Age at purchase: 6-8 weeks old
- Housing: 3/cage in wire-bottom stainless-steel cages
- Diet (e.g. ad libitum): Purina Laboratory Chow, Ralston-Purina Co., St. Louis, MO, ad libitum, except during exposure periods
- Water (e.g. ad libitum): ad libitum, except during exposure periods
- Acclimation period: at least 2 weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22
- Humidity (%): ca. 50
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

air

Remarks:

unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: Not applicable (vapour)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless-steel and glass chambers of 4.1 m3 volume.
- System of generating particulates/aerosols: exposure concentrations of methylene chloride were generated by metering the liquid at a constant rate with a precision pump into a warmed vaporization flask (ca. 60 C). Vapours frim the flask were swept with compressed air into the main chamber airstream where further mixing and dilution occured.
- Temperature, humidity, pressure in air chamber: 22 C, 50%
- Air flow rate: 800 l/min
- Air change rate: 12/hr

TEST ATMOSPHERE
- Brief description of analytical method used: IR spectroscopy

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration of methylene chloride in each chamber was determined 1-2 times each hour by IR spectroscopy using a Miran I IR spectrophotometer (Foxboro/Wilks, South Norwalk, CT) at a wave length of 7.95 to 13.35 microm.

Duration of treatment / exposure:

2 years

Frequency of treatment:

6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
50, 200, and 500 ppm
Basis:
other: target concentrations

Remarks:

Doses / Concentrations:
50+/-3, 199+/-5, 499+/-10 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

90 (male), 108 (female)

Control animals:

yes

Details on study design:

- Rationale for selecting satellite groups: In addition to the main experiment, 30 female rats, identified as 500con, were exposed to 500 ppm methylene chloride for the first 12 months and to room air for the last 12 months of the study. Thirty additional female rats, identified as con500, were exposed to room air for the first 12 months and 500 ppm methylene chloride for the last 12 months of the study. These animals were added to assess the temporal relationship between the initial exposure to methylene chloride and expression of the liver and mammary lesions. A subgroup of 18 female rats/exposure level was used to measure liver DNA synthesis. All remaining animals (70/sex/exposure group and 25 female rats from 500con and con500 exposure groups) were the major portion intended for oncogenic evaluation.
A separate, predesignated sub-group of 18 female rats/exposure level was used to mea­sure the rate of liver DNA synthesis. Groups of 4 female rats/exposure level were selected by a computer-derivedrandomization procedure from this subgroup after 6 and 12 months of exposure to methylene chloride. Approximately 18 hr after the last designated exposure to methylene chloride, each rat was injected ip with 0,0054 mg/kg [3H]thymidine. All rats were sacrificed 6 hr following thep injection. At the time of termination the liver was removed, the DNA was extracted, and [3H]thymidine in-corporation into the DNA was determined. All remaining animals in this subgroup were terminated without a gross examination after 12 months.

- Section schedule rationale (if not random): Subgroups of 5 rats/sex/exposure level were scheduled for interim terminations after 6, 12, 15, and 18 months of exposure to methylene chloride. Subgroups of 5 female rats from each of the 500con and con500 exposure groups were sacrificed at the 18 month interim necropsy.
Male rats were necropsied after 20 months due to the relatively limited lifespan of this substrain of male rat. All surviving female rats were necropsied after 24 months of exposure to methylene chloride.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: each day after exposure for signs of toxicity, also prior to exposure and on weekends and holidays

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: examinations of all rats for palpable masses were conducted prioir to the intial exposure to DCM, and at monthly intervals after the first 12 months, except for the subgroup designated for measuring liver DNA synthesis.

BODY WEIGHT: Yes
- Time schedule for examinations: all rats were weighed prior to the initial exposure, twice a month for the first 3 months of the study and monthly thereafter.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at various interim necropsies, also at multiple time intervals for determining carboxyhemoglobin levels
- How many animals: 4-5 for determining carboxyhemoglobin levels
- Parameters examined: total birubin (except at 6 months), cholesterol, triglyceride, potassium, estradiol (except at 6 months), FSH and LH levels.

Sacrifice and pathology:

All rats were subjected to a complete gross necropsy examination.
An extensive set of tissues intended to include all those collected at the interim and terminal kills were embedded in paraffin, sectioned and stained for microscopy.

Other examinations:

Liver DNA synthesis: a separate, predesignated subgroup of 18 female rats/exposure level was used to measure the rate of DNA liver synthesis.

Statistics:

Carboxyhemoglobin levels, rate of thymidine incorporation into the liver, absolute and relative organ weights, body weights, and clinical chemistry determinations were evaluated by analysis of variance and Dunnett's test (Steel and Torrie, 1960). Palpable mass data was analyzed by the Wilcoxon test (Haseman and Hoel, 1974). Gross pathologic observations and histopathologic data from interim kills lvere not evaluated statistically. Incidences of mofality and remaining histopathologic observations were evaluated by Fisher's Exact Probability Test (Siegel, 1956). Because numerous measurements were statistically compared on the same group of animals, the frequency of false positive (type I ) errors is unknown but is greater than the nominal a level of 0.05 used for Dunnett's and Fisher's Exact Probability Test. In addition to results of statistical evaluation, the final toxicologic interpretation of the data considered other factors such as dose-response relationships, biological plausibility, consistency, and historical values.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

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:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

No exposure-related gross or histopathologic changes were observed in animals from interim sacrifice groups. At terminal sacrifice, the incidences of both hepatocellular cytoplasmic vacuolization consistent with fatty changes and multinuceated hepatocytes were statistically elevated in female rats exposed to 200 and 500 ppm of methylene chloride; a slight increase in the incidence of hepatocellular vacuolization was also observed in male rats exposed to 500 ppm. Histopathological changes in the liver were not found in the male rats exposed to 50 or 200 ppm of methylene chloride. No other pathologic or histopathologic nontumor findings were reported.

Dose descriptor:

NOAEC

Effect level:

200 ppm

Sex:

male/female

Basis for effect level:

other: Histopathological changes in liver of male and female rats

Critical effects observed:

not specified

Mortality and Observations

 

The mortality rates for the various groups of male and female rats exposed to methylene chloride were comparable to control values. However, due to the early onset of geriatric changes which is characteristic of this substrain of rat and which occurred in all groups of male rats, exposure of male rats was terminated after 20 months of exposure to methylene chloride and the remaining survivors were necropsied. Exposure to 50, 200, or 500 ppm methylene chloride had no discernable adverse effect on the animals' appearance during the course of the study. Group mean body weights of male and female rats exposed to methylene chloride were not adversely affected throughout the 24-month study.

 

 

Absolute and Relative Organ Weights, Clinical Chemistry, Plasma Hormone Levels and Carboxyhaemoglobin

 

Absolute and relative organ weights, clinical chemistry values, and plasma hormone levels were not altered in rats exposed to methylene chloride (data not shown). Occasional statistically significant differences between control and exposed group mean values were considered to be sporadic occurrences unrelated to exposure. Blood carboxyhaemoglobin levels of rats exposed to methylene chloride were elevated in an apparent dose-dependent relationship above control values (Table). The percentage carboxyhaemoglobin was similar within exposure groups after 6, 12, or 20 -24 (terminal kill) months, indicating a lack of accumulation with repeated exposure.

 

Table - Carboxyhaemoglobin values° of rats exposed to methylene chloride

ppm	Sex	Time interval
		6months	12months	Terminal kill
0	male	4.8 ± 2.6°	0.3 ± 0.7	2.2 ± 1.3
50	male	8.8 ± 2.0	2.8 ± 0.3*	6.5 ± 1.1*
200	male	14.3 ± 1.3*	9.6 ± 1.2*	12.5 ± 0.8*
500	male	16.7±2.4*	12.7±1.6*	13.7±0.6*
0	female	1.1 ± 0.4	2.6 ± 1.1	5.1 ± 3.4
50	female	6.3 ± 2.7*	8.2 ± 3.1*	5.9 ± 0.7
200	female	13.9 ± 1.1*	13.1 ± 1.4*	13.8 ± 1.0*
500	female	17.9 ± 2.9*	17.5 ± 1.5*	17.6 ± 2.9*

° %, mean ± standard deviation for four to five rats/ sex/exposure level.

* Significantly different from control value by Dun­nett's or Wilcoxon's test, a < 0.05.

 

 

DNA Synthesis

 

The incorporation of [³H]thymidine into hepatic DNA of female rats exposed to 50, 200, or 500 ppm methylene chloride for either 6 or 12 months was comparable to control animals. There was no detectable alteration in the rate of DNA synthesis in the liver of rats exposed to concentrations as high as 500 ppm methylene chloride.

 

 

Pathology and Palpable Mass Data

 

No gross or histopathological lesions were observed in rats from the interim kill groups which were attributed to exposure to methylene chloride. Exposure-related histopathological changes observed in rats that died spontaneously or at the terminal kill were confined to the liver and mammary tissue. For the liver, the incidence of both hepatocellular cytoplasmic vacuolization (consistent with fatty change) and multinucleated hepatocytes was statistically increased in female rats exposed to 500 ppm methylene chloride. A slight increase in the incidence of hepatocellular vacuolization was observed in malerats exposed to 500 ppm methylene chloride (22 of 70 control animals vs. 28 of 70 animals exposed to 500 ppm methylene chloride). However, these liver effects were not observed in male or female rats exposed to 50 or 200 ppm methylene chloride. In female rats exposed to 200 ppm methylene chloride, the incidence of multinucleated hepatocytes was numerically but not statistically increased above the rate for control animals; this effect was considered to be of doubtful biologic significance.

See for a summary on palpable masses and tumours section 7.7 (Nitschke et al., 1988).

Conclusions:

Histopathological changes were seen in liver of male and female rats at 500 ppm. The NOAEC was 200 ppm.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Study duration:

chronic

Species:

rat

Quality of whole database:

Several repeated inhalation toxicity studies were available in rats and mice. The Nitschke et al. (1988) study was chosen as key study. At the NOAEC of 695 mg/m3 (200 ppm) and at 500 ppm no local effects were observed.

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

Human data (see also section 7.10)

Oral

No human data on repeated dermal exposure to DCM are available.

 

Dermal

No human data on repeated dermal exposure to DCM are available.

 

Inhalation

There was no evidence of any adverse effect on liver function in 150 workers who had been occupationally exposed for at least 10 years to 1677 mg/m3 dichloromethane. Neurological tests revealed no abnormalities in 29 workers that had been exposed for several years to levels of dichloromethane ranging from 260 to 347 mg/m or in 25 workers with over 22 years of exposure at 781 mg/m3. Humans exposed to 50, 100, 150 and 200 ppm (174, 347, 520 and 694 mg/m3) dichloromethane for 7.5 hours for 5 days, showed no difference from pre-exposure values in the post-exposure levels of glucose, blood urea nitrogen, uric acid, cholesterol, triglyceride, aspartate aminotransferase, ornithine carbamyltransferase, haematocrit, haemoglobin, and differential cell count and electrocardiogram. Peak blood carboxyhaemoglobin saturations of 1.9 -6.8% were measured.

Studies of possible morbidity associated with workplace exposure to dichloromethane have all been small scale and not all included control groups. The data suggest that no adverse effects on health are associated with workplace exposure up to concentrations of about 100 ppm (353 mg/m3) over several years. Irritation of the eyes and respiratory tract, subtle neurotoxic effects and minor effects on blood were observed at higher levels of exposure.

Animal data

Oral

Several chronic and subchronic oral repeated dose studies were performed in rats and mice, as well as one subacute study in rats. The 2 -year NOAEL for oral toxicity was 6 mg/kg bw/day in rats, based on increased incidence of foci/areas of cellular alteration and fatty changes in the liver. A 2 -year NOAEL for oral toxicity in mice was set at 185 mg/kg bw/d based on liver changes.

 

Dermal

No toxicity studies addressing the dermal route of exposure are available.

 

Inhalation

The 2 -year NOAEC for inhalation toxicity in rats was 200 ppm (695 mg/m3) based on histopathological changes in the liver.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:

Well performed chronic study; taken as key study. Lower effect levels were reported in rats than in mice.

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:

Well performed chronic study.

Justification for selection of repeated dose toxicity inhalation - local effects endpoint:

Well performed chronic study.

Repeated dose toxicity: via oral route - systemic effects (target organ) digestive: liver

Repeated dose toxicity: inhalation - systemic effects (target organ) digestive: liver

Justification for classification or non-classification

The 2-year oral toxicity study in mice shows a NOAEL of 185 mg/kg bw/day, the same 2 -year study in rats shows a NOAEL of 6 mg/kg bwday. The levels tested in rats were 0, 6, 52, 125 and 235 mg/kg bw/day in males, and 0, 6, 58, 136 and 263 mg/kg bw/day in females. In rats the changes consisted of increases in mean haematocrit, haemoglobin and erythrocyte count and were observed in both sexes at levels of 52/58, 125/136 and 235/263 mg/kg bw. Approximately half of these increased mean values were determined to be statistically significant, and there was no mentioning of dose-response relationships. In the liver, a dose-related positive trend was seen in the incidences of foci/areas of cellular alteration and an increased incidence of fatty change in the liver was observed. However, there was no indication for a dose-response relationship on severity, only on incidence. In addition, no changes in organ weight were reported. Therefore, it can be concluded that the histopathological liver changes observed at 52/58, 125/136 and 235/263 mg/kg bw appear more or less similar, and although severity is not reported, together with the absence of liver weight changes, GHS classification does not seem warranted.

In addition, the ranges of <10 and 10-100 mg/kg bw are indications for a 90-day study. It is advised to multiply these figures with a factor 3 in case of a 28 -day study. However, in this case results of a 2 -year study in rats were reported, so in this case multiplication with a factor 0.5 could also be advised (because normally a factor 2 is used for extrapolation from subchronic to chronic) which would result in ranges of < 5 and 5-50 mg/kg bw. As such the LOAEL of 52/58 mg/kg bw would not be in this range.

Regarding inhalation exposure, the available animal and human data do not warrant classification.