1,2,4-trichlorobenzene

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study with restrictions

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Assessment of teratogenic potential of 1,2,3-1,2,4-and 1,3,5-trichlorobenzene in rats

Author:

Black WD

Year:

1988

Bibliographic source:

Bull. Environ. Contam. Toxicol.41: 719 - 726

Reference 2

Reference Type:

publication

Title:

A teratological evaluation following oral administration of TCB and DCB isomers

Author:

Ruddick JA et al

Year:

1983

Bibliographic source:

Teratology 27, 73A - 74A

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

yes

Remarks:

Housing and feeding conditions not reported; exposure too short; numberof animals exposed too small; weight of dams recorded only at 22nd day of gestation; food consumption, number of corpora lutea , sex of each foetus not recorded.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

1,2,4-trichlorobenzene

EC Number:

204-428-0

EC Name:

1,2,4-trichlorobenzene

Cas Number:

120-82-1

Molecular formula:

C6H3Cl3

IUPAC Name:

1,2,4-trichlorobenzene

Details on test material:

- Name of test material (as cited in study report): 1,2,4-trichlorobenzene
- Analytical purity: > 99.5%

Test animals

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Woodlyn farm Laboratories, Guelph, Ontario
- Weight at study initiation: 175-122 g
- Housing: Mated females were housed in wire-top plastic cages containing cob bedding
- Acclimation period: 1 week prior mating

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Analytical verification of doses or concentrations:

no

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1/2
- Length of cohabitation: overnight
- Proof of pregnancy: vaginal swabs. The morning on which sperm was detected in the female was designed as day 1 pregnancy.
- Any other deviations from standard protocol

Duration of treatment / exposure:

day 6 to 15 of gestation

Frequency of treatment:

daily

No. of animals per sex per dose:

Each groups consisted of approximately 14 dams

Control animals:

yes, concurrent vehicle

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: No

DETAILED CLINICAL OBSERVATIONS: No


BODY WEIGHT: Yes
- Time schedule for examinations: on the 22nd day of gestation


POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 22
- Organs examined: uterus (transacted anterior to the cervix and removed with the ovaries), liver, kidney, spleen, heart and brain were removed and weighed


OTHER:
-HEMATOLOGY: maternal blood was hematologically analyzed using a Baler 700. The following parameters were measured: haemoglobin concentration, hematocrit value, erythrocyte count, total and differential counts of leucocytes, mean corpuscular volume, mean corpuscular haemoglobin concentration and mean corpuscular haemoglobin.
- BLOOD CHEMISTRY: serum from each dam was analyzed and the following parameters were analyzed: sodium, potassium, inorganic phosphorus, total bilirubin, alkaline phosphatise, glutamic oxaloacetic transaminase (GOT), total protein, calcium cholesterol, glucose, uric acid and lactic dehydrogenase (LDH).
-RESIDUE ANALYSIS: maternal tissues were selected for 1,2,4-trichlorobenzene residue analysis
-HISTOLOGICAL ANALYSIS: was performed on heart, brain, pituitary, eye, thyroid, parathyroid, trachea, bronchi, kidney, lung, thymus, stomach, small and large intestine, pancreas, liver, kidney, spleen, adrenal, skeletal muscle, peripheral nerve, skin, bone marrow, ovary, uterus, and bladder tissues.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: No
- Number of corpora lutea: No
- Number of implantations: No
- Number of resorptions: Yes

Fetal examinations:

- External examinations: Yes
- Soft tissue examinations: Yes: one third
- Skeletal examinations: Yes: two thirds of each litter
- Head examinations: No

Statistics:

The data from organ weight, body weights, haematology, and biochemistry were subjected to a simple one way analysis of variance. When significant differences (p< 0.05) were indicated, the Duncan´s Multiple Range Test (SPSS version 8.1) selected the groups that were significantly different.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Post-mortem examination showed slight liver changes (increased periportal cytoplasmic
eosinophilia and slight anisokeryosis of the cell nuclei of the hepatocytes) in dams dosed with
150 mg/kg bw/day. In addition to these effects, a significant 5.7% increase in relative liver weight was seen in the 300 mg/kg dose group; the absolute liver weight was also significantly increased, but the weights of other organs were statistically normal. Changes in the thyroid gland were also observed in the 300 mg/kg 1,2,4-TCB group. These effects are considered to be an adequate expression of maternal toxicity.
Haematological and clinical chemistry investigations showed significantly reduced haemoglobin and haematocrit values as well as a significant increase in the protein content and in the aminopyrine-N-demethylase activity in the liver at 150 mg/kg bw/day and above.

Effect levels (maternal animals)

1

Dose descriptor:

NOAEL

Effect level:

75 mg/kg bw/day

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEL

Effect level:

75 mg/kg bw/day

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
Histological lesions occurred in the lenses of eyes of foetuses from the intermediate dosage group. These effects were not seen in the other two treatment groups. The ocular changes consisted of central areas of cellular disorientation and disaggregation with ballooning and granular degeneration. This finding is interpreted by the authors as possibly indicating early cataract development. However, no data on the incidence or severity of these findings are given. (Similar effects were also seen with all three groups treated with 1,3,5-TCB, when tested in the same study.) The authors draw attention to the fact that the histopathological examination of the other foetal tissues was made more difficult as a result of autolysis and insufficient conservation.
This brings into question the validity of the findings in the eye.

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Table 1.Fetal data (mean ± S.E) following oral administration of 1,2,4-trichlorobenzene congeners to pregnant rats

	1,2,4-trichlorobenzene
	Control	75	150	300
Dams at term/Inseminated	12/14	11/13	11/13	12/14
Resorption+deadfetuses	0.7±0.2	1.1±0.2	0.6±0.2	0.6±0.3
Littersize	11.5±1.2	12.1±0.9	13.1±0.5	13.3±0.66
Fetal wt(g)	5.4±0.1	5.3±0.1	5.5±0.1	5.1±0.1
Visceralobservations^a	31	28	40	42
SkeletonObservations^a	67	50	76	82^b
Sternalanomilies^c	11/3	14/6	11/4	9/7
Wavyribs^c	1/1	1/1	0	0
Centrumfusiondelay	0	0	3/2	1/1
14thrib	0	0	5/5	2/1
13thrib(short)	0	1/1	0	0

^aNo. of pups examined                                  ^cNo. of pups affected/No. of litters affected

^bone pup hasmicrognathia; others normal       ^*significant difference p=0.05

Histological lesions occurred in the lenses of eyes of foetuses from the intermediate dosage

group. These effects were not seen in the other two treatment groups. The ocular changes

consisted of central areas of cellular disorientation and disaggregation with ballooning and

granular degeneration. This finding is interpreted by the authors as possibly indicating early

cataract development. However, no data on the incidence or severity of these findings are given.

(Similar effects were also seen with all three groups treated with 1,3,5-TCB, when tested in the

same study.) The authors draw attention to the fact that the histopathological examination of the

other foetal tissues was made more difficult as a result of autolysis and insufficient conservation.

This brings into question the validity of the findings in the eye.

Applicant's summary and conclusion

Executive summary:

Black (1988):

 

14 pregnant Sprague-Dawley rats/dose group were given 0, 75, 150 and 300 mg/kg 1,2,4-TCB dissolved in corn oil by gavage from day 6 to 15 day of gestation according with a method similar to OECD guideline 414 with restrictions (Housing and feeding conditions not reported; exposure too short; numberof animals exposed too small; weight of dams recorded only at 22nd day of gestation; food consumption, number of corpora lutea , sex of each foetus not recorded).

The doses chosen for the 1,2,4-isomer were 75, 150 and 300 mg/kg.

Maternal body weight was decreased in the high-level 1,2,4-TCB dose group, but this decrease was not significant. Other external signs of maternal toxicity were not determined.

Post-mortem examination showed slight liver changes (increased periportal cytoplasmic eosinophilia and slight anisokeryosis of the cell nuclei of the hepatocytes) in dams dosed with 150 mg/kg bw/d. In addition to these effects, a significant 5.7% increase in relative liver weight was seen in the 300 mg/kg dose group; the absolute liver weight was also significantly increased, but the weights of other organs were statistically normal. Changes in the thyroid gland were also observed in the 300 mg/kg 1,2,4-TCB group. These effects are considered to be an adequate expression of maternal toxicity.

Haematological and clinical chemistry investigations showed significantly reduced haemoglobin and haematocrit values as well as a significant increase in the protein content and in the aminopyrine-N-demethylase activity in the liver at 150 mg/kg bw/d and above.

Histological lesions occurred in the lenses of eyes of foetuses from the intermediate dosage

group. These effects were not seen in the other two treatment groups. The ocular changes consisted of central areas of cellular disorientation and disaggregation with ballooning and granular degeneration. This finding is interpreted by the authors as possibly indicating early cataract development. However, no data on the incidence or severity of these findings are given.

The authors draw attention to the fact that the histopathological examination of the other foetal tissues was made more difficult as a result of autolysis and insufficient conservation.

This brings into question the validity of the findings in the eye.

The authors conclude that none of the trichlorobenzene isomers tested in this study produced teratogenic or fetotoxic effects.

The NOAEL for the dams is 75 mg/kg bw/d in this study. For the foetuses, the NOAEL depends on the significance attributed to the eye lesions seen in the foetuses in the middle dose group.

The effects seen in the eye are not considered substance related, and therefore the NOAEL for the foetuses is 300 mg/kg bw/d. However, it cannot be entirely excluded that the effects seen in the foetal eye could be substance-related, in spite of the lack of dose dependency, and that the effect is seen in the intermediate dose only. On this basis, a NOAEL of 75mg/kg bw/d can be established for both the dams and the foetuses.