1,2-dichloroethane

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

chronic toxicity: inhalation

Remarks:

combined repeated dose and carcinogenicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2006

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2006

Report date:

2006

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

1,2-dichloroethane

EC Number:

203-458-1

EC Name:

1,2-dichloroethane

Cas Number:

107-06-2

Molecular formula:

C2H4Cl2

IUPAC Name:

1,2-dichloroethane

Details on test material:

- Name of test material: 1,2-dichloroethane
- Analytical purity: 99 %
- Impurities: less than 0.03 % water, less than 0.0005 % chlorine, less than 0.002 % non-volatile chemicals
- Source: Wako Pure Chemical Industries, Ltd., Osaka, Japan

Each lot of test substance used in this study was analyzed for its purity and stability by gas chromatography before and after use. Neither decomposition products nor other impurities were detected.

Test animals

Species:

rat

Strain:

Fischer 344/DuCrj

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Japan, Inc., Kanagawa, Japan
- Age at study initiation: 6 weeks old
- Weight at study initiation: 120 ± 5 g
- Housing: Individually in stainless steel wire hanging cages (150 mm x 220 mm x 176 mm)
- Diet: Commercial pellet diet (CRF-1, Oriental Yeast Co., Ltd., Tokyo, Japan), ad libitum
- Water: Sterilised water, ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 23 ± 2 degree C
- Humidity: 55 ± 10 %
- Air changes: 12 ± 1 air changes/hour
- Photoperiod: 12 hours dark / 12 hours light

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: no data

Details on inhalation exposure:

Airflow containing 1,2-dichloroethane vapor at a target concentration for rats of 10, 40 or 160 ppm was prepared by a vaporization technique. The saturated vapor-air mixture was generated by bubbling clean air through liquid 1,2-dichloroethane in a temperature-regulated glass flask (25 degree C), and by cooling it through a thermostatted condenser at 18 degree C. The airflow containing the saturated vapor was diluted with clean air, and then warmed to 25 degree C in a thermostatted circulator which served to stabilize the vapor concentration by complete gasification of 1,2-dichloroethane. The flow rate of vapor-air mixture was regulated with a flow meter, further diluted with humidity- and temperature-controlled clean air in a spiraling line mixer, and then supplied to the inhalation exposure chambers. Four inhalation exposure chambers of 7600 L in volume were used in this study. Each exposure chamber accommodated 100 individual cages for 50 males and 50 females.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Chamber concentrations of 1,2-dichloroethane were monitored by gas chromatography every 15 min, and maintained constant at 10.0 ± 0.1, 39.8 ± 0.6 and 159.7 ± 2.1 ppm for the exposure of rats throughout the 2-year exposure period.

Duration of treatment / exposure:

104 weeks, 6 hours per day

Frequency of treatment:

5 days per week

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 10, 40, or 160 ppm (0, 41.1, 164.5 or 658.1 mg/m³)
Basis:
nominal conc.

No. of animals per sex per dose:

50 animals

Control animals:

yes, concurrent no treatment

Details on study design:

Groups of 50 male and 50 female rats were exposed to airflow containing 1,2-dichloroethane vapor at a target concentration of 10, 40, or 160 ppm for rats for 6 h/d, 5 d/wk and for 104 wk (2 years). Fifty rats of both sexes, serving as concurrent controls, were handled in the same manner as the 1,2-dichloroethane-exposed groups, but were exposed to clean air in the inhalation exposure chambers. The lowest exposure concentration of 10 ppm was selected in consideration of the OEL of 10 ppm for 1,2-dichloroethane. Selection of the highest concentrations of 160 ppm for rats was based on both subchronic toxicity and body weight decrement from a preliminary 13-weeks inhalation exposure study conducted at the JBRC. All rats died during the first week of 13-weeks exposure to 320 ppm, but 13-weeks exposure to 160 ppm did not cause any deaths, overt toxic signs or body weight decrements. Therefore, the highest exposure concentration of 160 ppm was predicted not to exceed the MTD from the results of the 13-weeks inhalation exposure study.

Positive control:

none

Examinations

Observations and examinations performed and frequency:

The animals were observed daily for clinical signs and mortality. Body weights and food consumption were measured once a week for the first 14 wk, and every 4 wk thereafter.

Sacrifice and pathology:

All the rats which died or were killed in a moribund state during the 2-year exposure period, or survived to the end of the 2-year period received complete necropsy. Urinary parameters were measured from urine sampled with Ames Reagent Strips in the last week of the 2-year exposure period. For haematology and blood biochemistry, the surviving animals were bled under ether anaesthesia at terminal necropsy after they were fasted overnight. The blood samples were analyzed on an automatic blood cell analyzer for haematology, and an automatic analyzer Hitachi 705 and a flame analyzer Hitachi 750 for blood biochemistry. Organs were removed, weighed, and examined for macroscopic lesions at the necropsy. Tissues for microscopic examinations were fixed in 10 % neutral buffered formalin and embedded in paraffin. Tissue sections 5 µm thick were prepared and stained with haematoxylin and eosin.

Other examinations:

none

Statistics:

Incidences of neoplastic lesions were analyzed for a dose response relationship indicated by a significant positive trend by Peto’s test, and for a significant difference from the concurrent control group by Fisher’s exact test. Incidences of non-neoplastic lesions and urinary parameters were analyzed by Chi-square test. Survival curves were plotted according to the Kaplan- Meier method, and the log-rank test was used to test statistical significance of the difference between any 1,2-dichloroethane-exposed rat group of either sex and the respective control. Body weight, organ weight, haematological and blood biochemical parameters were analyzed by Dunnett’s test. When tumor incidences were increased in a dose-related manner as indicated by Peto’s test and when the tumor incidence in each of the exposed groups was increased but not statistically significant as compared with the concurrent, matched-control group by Fisher’s exact test, the borderline increase in the tumor incidence was tested as to whether or not it was biologically meaningful, using a range of minimum and maximum tumor incidences in the JBRC historical control data.

Results and discussion

Results of examinations

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):

no effects observed

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:

no effects observed

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

MORTALITY, BODY WEIGHT, FOOD CONSUMPTION AND CLINICAL OBSERVATIONS:
There was no significant difference in the survival rate at any time point of the 2- year exposure period between any exposed group of either sex and the respective control. At the end of the 2-year exposure period, the survival rates of the 0 (clean air as control), 10, 40 and 160 ppm exposure groups were 74, 70, 64 and 74 % for males, and 70, 82, 74 and 76 % for females, respectively. Neither growth rate nor food consumption was suppressed in any exposed group of either sex as compared with the respective control. The body weights of the 0, 10, 40 and 160 ppm exposure groups at the end of 2-year exposure period were 434 ± 46, 459 ± 59, 448 ± 41 and 467 ± 85 g for males, and 317 ± 46, 329 ± 41, 33 ± 45 and 336 ± 56 g for females, respectively. Incidences of subcutaneous masses, which were found in the breast, back, and abdominal and perigenital areas by clinical observation, tended to increase in the exposed groups of both sexes. No exposure-related change in any haematological, blood biochemical or urinary parameter was found in any exposed group of either sex.

HISTOPATHOLOGY:
For carcinogenicity please refer to IUCLID5 chapter 7.7
No exposure-related, non-neoplastic lesions were observed in any exposed group of either sex.

Effect levels

Dose descriptor:

NOAEL

Effect level:

658.1 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: no adverse effects observed except of carcinogenicity

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

1,2-dichloroethane was shown to be carcinogenic after inhalation exposure to rats for a period of 2 years.

Executive summary:

Carcinogenicity and chronic toxicity of 1,2- dichloroethane were examined by inhalation exposure of groups of 50 F344/sex/dose to 1,2- dichloroethane vapor or clean air as control for 6 h/d, 5 d/wk and 104 wk. The rats were exposed to 0, 10, 40 or 160 ppm (v/v) ( equivalent to 0, 41.1, 164.5 or 658.1 mg/m³) 1,2- dichloroethane. The 2-year exposure produced a dose-dependent increase in incidences of benign and malignant tumors, including subcutaneous fibroma, mammary gland fibroadenoma and peritoneal mesothelioma in male rats; subcutaneous fibroma and mammary gland adenoma, fibroadenoma and adenocarcinoma in female rats. No exposure-related change in the incidence of non-neoplastic lesions or in any haematological, blood biochemical or urinary parameter occurred in any exposed rat group. The types of tumors and their target organs found in this study were consistent with those observed in rats and mice administered 1,2 - dichloroethane by gavage in a NCI study. Selection of the exposure concentrations was considered appropriate with reference to the maximum tolerated dose for the highest doses and an occupational exposure limit of 1,2- dichloroethane for the lowest dose.