2,4-dichlorophenol

Carcinogenicity

Administrative data

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

4 MARCH 1981 to 30 JUNE 1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The study was conducted according to internationally recognised guidelines and under good laboratory practice. The following deviations from the guideline were noted: Only two dose concentrations were used. Satellite interim sacrifice groups were not included.However given the clear outcome with respect to oncogenicity those deviations from the guideline do not impact on the validity of the conclusion.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1989

Report date:

1989

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

Deviations:

yes

Remarks:

Only two dose concentrations were used. Satellite interim sacrifice groups were not included.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

2,4-dichlorophenol

EC Number:

204-429-6

EC Name:

2,4-dichlorophenol

Cas Number:

120-83-2

Molecular formula:

C6H4Cl2O

IUPAC Name:

2,4-dichlorophenol

Details on test material:

- Name of test material (as cited in study report): 2,4 Dichlorophenol
- Physical state: colourless crystalline solid
- Analytical purity: Lot number OCR-640-57, >99%; and OCR-808-125, 99.5%
- Lot/batch No.:Lot numbers OCR-640-57 and and OCR-808-125
- Expiration date of the lot/batch: None specified
- Stability under test conditions: Not stated
- Storage condition of test material: Not stated
- Other: Diets incorporating the test item were stored at 4°C for a maximum of 2 weeks

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Kingston, NY, USA
- Age at study initiation: 7 weeks
- Weight at study initiation: 121 g males, 105 g females
- Fasting period before study: None
- Housing: Polycarbonate cages (Lab Products, Inc.,Rochelle Park, NJ), 5 animals per cage
- Diet: NIH 07 Rat and Mouse Ration (Zeigler Bros., Inc., Gardners, PA); available ad libitum
- Water: Automatic watering system (Edstrom Industries,, Waterford, WI); available ad libitum
- Acclimation period: 14 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 12-28
- Humidity (%): 29-73
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12 h light / 12 h dark

IN-LIFE DATES: From: 28 February 1981 To: 3 March 1983

Administration / exposure

Route of administration:

oral: feed

Details on exposure:

DIET PREPARATION
- Rate of preparation of diet (frequency):no longer than 2 weeks
- Mixing appropriate amounts with (Type of food): NIH 07 Rat and Mouse Ration
- Storage temperature of food: 4°C

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Formulated diets were analysed at approximately 8-week intervals and were within 10% of the target concentrations approximately 82% (42/51) of the time throughout the 2-year studies. Referee analyses were periodically performed by the study and analytical chemistry laboratories; results between the laboratories varied from 1% to 6%.

Studies to determine the homogeneity of a formulated diet mixture indicated a less than 4% deviation from the target concentration for samples taken from three locations in the blender after 10 minutes of mixing; homogeneity was not improved after 15 minutes of mixing. The recovery of 2,4-dichlorophenol from formulated diets by methanol extraction, although essentially complete immediately after preparation, decreased with time to about 58% after 7 days. The addition of 1% hydrochloric acid to the methanol extracting solvent resulted in only a marginal improvement in the amount recovered. Consequently, for the study of compound stability in feed, acid digestion of the feed mixtures was carried out before extraction with ether:hexane ( l : l ) , and a recovery of 88% from feed samples stored for 2 weeks at 25°C was obtained. 2,4-DichlorophenoI at a concentration of 4,000 ppm in feed was stable for 5 weeks at -20° C. Recovery of 2,4-dichlorophenol from the feed mixture stored under these conditions was 95% relative to the zero-time recovery. For different samples of this feed mixture stored for 2 weeks at 5° C, recovery of 2,4-dichIorophenol was 93%.

Duration of treatment / exposure:

Animals were fed ad libitum diets containing the test material for 103 weeks

Frequency of treatment:

Daily ad libitum in the diet

Post exposure period:

There were no recovery groups. All animals were sacrificed post terminal dosing.

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0 ppm
Basis:
nominal in diet
Males and females

Doses / concentrations 2

Remarks:

Doses / Concentrations:
2500 ppm
Basis:
nominal in diet
Females only. Equivalent to 120 mg/kg/day

Doses / concentrations 3

Remarks:

Doses / Concentrations:
5000 ppm
Basis:
nominal in diet
Males and females. Equivalent to 210 mg/kg/day in males and 250 mg/kg/day for females

Doses / concentrations 4

Remarks:

Doses / Concentrations:
10000ppm
Basis:
nominal in diet
Males only. Equivalent to 440 mg/kg/day. Dose level not selected for females based on bone marrow atrophy observed in a 13 week study.

No. of animals per sex per dose:

50

Control animals:

yes, plain diet

Details on study design:

- Dose selection rationale: based on effects seen in preceding 90 day study
- Rationale for selecting satellite groups: There were no satellite groups
- Post-exposure recovery period in satellite groups: There were no recovery groups

Positive control:

None

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Observations made twice per day

DETAILED CLINICAL OBSERVATIONS: Yes
- made once per day

BODY WEIGHT: Yes
- Body weights were recorded once per week for the first 13 weeks and once per month thereafter.

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

COMPOUND INTAKE (if feeding study): Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: males 0, 210 and 440 mg/kg bw/day, females 0, 120 and 250 mg/kg/day.

FOOD EFFICIENCY:
No data was presented on food efficiency but estimates were made from bodyweight data and food consumption.

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes, all organs and tissues were examined
HISTOPATHOLOGY: Yes
The following tissues were examined histologically for control and high dose groups: adrenal glands, blood smear, brain, colon, oesophagus, eyes, gross lesions, heart, kidneys, liver, lungs and mainstem bronchi, mammary gland, mandibular or mesenteric lymph nodes, pancreas, parathyroid glands, pituitary gland, prostate/testes or ovaries/uterus, regional lymph nodes, salivary glands, skin, small intestine, spleen, sternum or femur or vertebrae including marrow, stomach, thymus, thyroid gland, tissue masses, trachea, and urinary bladder. Tissues examined from low dose groups included liver, nose, pituitary gland, and thyroid gland for male rats; adrenal glands, lymph nodes, pancreas, and spleen for female rats.

Peripheral nerves were not examined.

Statistics:

Three statistical methods are used to analyse tumor incidence data: life table tests, logistic regression and Fisher exact/Cochran-Armitage trend analyses. Tests of significance include pair-wise comparisons of high dose and low dose groups with controls and tests for overall dose-response trends. For studies in which administration of the study compound has little effect on survival, the results of the three alternative analyses will generally be similar. When differing results are obtained by the three methods, the final interpretation of the data will depend on the extent to which the tumor under consideration is regarded as being the cause of death. Continuity-corrected tests are used in the analysis of tumor incidence, and reported P values are one-sided.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Body weight gain was depressed in both sexes, resulting in bodyweight reductions of ca. 10% compared to controls in top dose in males (10000 ppm) and females (5000 ppm).

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

The average daily feed consumption by rats in the low dose and high dose groups was 95% of that by the controls for males and 94-97% for females.

Food efficiency:

not examined

Description (incidence and severity):

Calculations performed on data in the report indicate no consistent discernible effect of treatment on food efficiency in males or females.

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

No remarkable findings

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

In males – dose-related increase in the incidence of multifocal degeneration of the respiratory epithelium compared with controls, and a significant decrease in incidence of mononuclear cell leukemia in low and high dosed animals (34%) compared with contr

Histopathological findings: neoplastic:

effects observed, treatment-related

Description (incidence and severity):

No treatment related increase in any tumor incidence was noted.

Details on results:

SURVIVAL
Survival was unaffected by treatment. Survival of animals was greater than 50% at termination giving validity to the negative carcinogenicity result.

BODY WEIGHT AND WEIGHT GAIN

Mean body weights of high dose male rats were generally 5%-11% lower than those of controls from week 3 to the end of the study. Mean body weights of high dose female rats were 6%-12% lower than those of controls from week 31 to the end of the study.

FOOD CONSUMPTION AND COMPOUND INTAKE

Food consumption was reduced in both sexes in treated groups. The average daily feed consumption by rats in the low dose and high dose groups was 95% of that by the controls for males and 97% and 94% for females.

FOOD EFFICIENCY
Not calculated. However decreased body weights and bodyweight gains are likely to be due to reduced food consumption, compounded by diets consisting of 0.25 to 1% test material.

HISTOPATHOLOGY: NON-NEOPLASTIC

Nose: The incidences of multifocal degeneration of the respiratory epithelium were increased in dosed male rats (control, 25/45; low dose, 38/48; high dose, 42/46). This lesion was characterized by the formation of small cysts and increased numbers of goblet cells within the epithelium and was located in the arch of the dorsal nasal meatus.

Relevance of carcinogenic effects / potential:

No treatment related oncogenicity was seen in the study.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

> 10 000 ppm (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: No test material related oncogenicity was observed

Remarks on result:

other: Effect type: carcinogenicity (migrated information)

2

Dose descriptor:

NOAEL

Effect level:

> 5 000 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: No test material oncogenicity was observed.

Remarks on result:

other: Effect type: carcinogenicity (migrated information)

Applicant's summary and conclusion

Conclusions:

Under the conditions of this 2-year feeding study, there was no evidence of carcinogenic activity for male F344/N rats fed diets containing 5,000 or 10,000 ppm 2,4-dichlorophenol or for female F344/N rats fed diets containing 2,500 or 5,000 ppm 2,4-dichlorophenol.

Executive summary:

In a carcinogenicity study (NTP TR 353 ), 2,4-dichlorophenol was administered to 50 F344 rats/sex/dose in the diet at dose levels of 0, 5000, and 10,000 ppm (0, 210 and 440 mg/kg bw/day) in males and 0, 2,500, and 5,000 ppm (0, 120 and 250 mg/kg bw/day) in females for 2 years.

There were no compound-related effects on mortality, and there were no clinical signs of toxicity observed. Body weights in top dose males and females were depressed by ca. 10% compared to the controls. Food consumption,was reduced by 5% in males at both dose levels and by 3% and 6% at the low and high dose levels respectively in females. The NOAEL for carcinogenicity is 440 mg/kg bw/day in males and 250 mg/kg bw/day in females, which were the highest dose levels tested, based on the absence of any treatment related tumorigenicity/oncogencity.

At the doses tested, there were no treatment related increase in tumor incidences of any type when compared to controls. Dosing was considered adequate based on the reduction in bodyweight gain and analysis of diets.

This carcinogenicity study in the rat is acceptable and satisfies the major points of the guideline requirements for a chronic/carcinogenicity study; OECD 451 in the rat with the exception that no interim sacrifice satellite groups were included, and only two dose levels were investigated. However given the clear outcome with respect to oncogenicity those deviations from the guideline do not impact on the validity of the conclusion.