4-tert-butyltoluene

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

No data are available.

Additional information

In a Reproduction / Developmental Toxicity Screening Study (Nihon Bioresearch, Inc., undated), 4-tert-butyltoluene (purity 96.44%) was administered to 12 Sprague-Dawley rats/sex/dose by gavage at dose levels of 0, 1.5, 5, 15, 50 mg/kg bw/day). The study was conducted in accordance with OECD TG 421.

Parental animals:

One male given 50 mg/kg bw; one female given 15 mg/kg bw and 6 females given 50 mg/kg bw died. Hypothermia, decrease in locomotor activity, soiled fur, reddish urine hypothermia, adoption of a prone position, a staggering gait, piloerection, lacrimation, bradypnea, diarrhea, and muscle relaxation were noted at 15 and/or 50 mg/kg. Lower body weights were noted in males from 15 mg/kg upwards and in females from 5 mg/kg bw upwards. Transient lowering of food consumption was noted in males at 50 mg/kg. Lowering of food consumption was noted in females at 5 mg/kg during the lactation period.

No changes attributable to administration of the test substance were noted in the numbers of estrous cases.

On sperm examination, decreased values for the motility ratio, path velocity, straight line velocity, curvilinear velocity, viability, survivability, number of sperm, and number of sperm/g of the left caudae epididymidis and elevation of the proportion of abnormal sperm were noted at 15 and 50 mg/kg bw, and a higher value for beat cross frequency was noted at 15 mg/kg bw. On histopathological examination, changes were noted in the testes and epididymides at 15 and 50 mg/kg.

No changes attributable to administration of the test substance were noted in the numbers of estrous cases, copulation index, or number of days before copulation. The fertility index was lowered at 15 and 50 mg/kg bw. No changes attributable to compound administration were noted at 1.5, 5, or 15 mg/kg bw in terms of the numbers of corpora lutea, or implantation sites, or the implantation rate. No changes attributable to compound administration were noted at 1.5, 5, or 15 mg/kg bw regarding the gestation index.

Organ weight measurement revealed the absolute testis and epididymis weights to be or tend to be lower at 15 mg/kg bw. The absolute and relative testis and epididymis weights were lowered at 50 mg/kg bw.

At necropsy, atrophy of the testes and epididymides was noted in males at 15 and 50 mg/kg bw. On histopathological examination, atrophy of seminiferous tubules of the testes, hyperplasia of Leydig cells, and decrease in sperm in the epididymides were noted at 15 and 50 mg/kg.

Offspring:

Values for the following parameters were lowered or tended to be lower in pups of the 15 mg/kg bw group: number of pups, number of pups on day 0 of lactation, the delivery index, birth index, live birth index, number of pups on day 4 of lactation, and the viability index on day 4 of lactation. The number of stillbirths tended to be higher at 15 mg/kg bw. The number of pups on day 0 of lactation was zero at 50 mg/kg bw, since no females conceived. No external abnormalities attributable to the compound administration were noted. Pup body weights were lowered or tended to be lower in both sexes at 5 and 15 mg/kg on Days 0 and 4 of lactation.

The LOAEL is 15 mg/kg bw/day in males and females for gneral and reproductive toxicity.

The NOAEL is 5 mg/kg bw/day in males and females for general and reproductive toxicity.

The NOEL is 1.5 mg/kg bw/day in females.

This study is acceptable and satisfies the guideline requirement for a Reproduction / Developmental Toxicity Screening Study (OECD 421) in rats.

The effect of p-tert-butyl toluene (TBT) was studied in several screening studies utilizing rats, mice, guinea pigs and dogs. In each of these studies, the test substance was administered by gavage to groups of male animals once daily for 5 consecutive days.

Study	Species	Study design	Result
1 Roche (1982)	Rat	·        Dose: 12.5, 25, 50, 100 mg/kg bw/d ·        Number of animals per group: 8 males/group (dose groups); 4 control males ·        Treatment period and frequency: 5 days, daily ·        Control: vehicle (rape oil) ·        Examination endpoints: mortality, clinical symptoms, body weight, weights of liver, kidney, and testes, gross pathology, histopathology of liver, kidney and testes	·        Unspecific clinical signs (50 and 100 mg/kg), ·        Severe effects on body weight gain (50 and 100 mg/kg) ·        Gross changes in the liver (50 and 100 mg/kg) ·        Decreased testes weight (100 mg/kg) ·        Marked histological changes at the testes: severe cell-deformation in the germinal epithelium, degeneration of spermatids and spermatocytes, reduced spermatozoa, occurrence of giant cells (50 and 100 mg/kg). NOAEL = 25 mg/kg bw/d LOAEL= 50 mg/kg bw/d
2 TSCAT (1982)	Rat	·        Dose: 200 mg/kg bw/d ·        Number of animals per group: 7 males/group ·        Treatment period and frequency: 5 days, daily ·        Control: vehicle (rape oil) ·        Examination endpoints: mortality, clinical symptoms, body weight, weights of liver, kidney, and testes, gross pathology, histopathology of liver, kidney and testicles	·        Treatment-related decrease in testes weight. ·        Marked histological changes in the seminiferous tubules (such as degeneration of spermatocytes and spermatids, reduction of spermatozoa as well as appearance of giant cells) NOAEL < 200 mg/kg bw/d, the only dose level tested.
3 Roche (1984)	Mouse	·        Dose: 100 mg/kg bw/d ·        Number of animals per group: 6 males/group ·        Treatment period and frequency: 5 days, daily ·        Control: vehicle (rape oil) ·        Examination endpoints: mortality, clinical symptoms, body weight, testes weight, gross pathology, histopathology of testes	·        Slight decrease in testes weight ·        Marginal damage of the germinal epithelium in 1/6 control animals and in 3/6 test animals NOAEL> 100 mg/kg bw/d, the only dose level tested
4 Roche (1984)	Guinea pig	·        Dose: 100 mg/kg bw/d ·        Number of animals per group: 5 males/group ·        Treatment period and frequency: 5 days, daily ·        Control: vehicle (rape oil) ·        Examination endpoints: mortality, clinical symptoms, body weight, testes weight, gross pathology, histopathology of testes	·        Moderate, treatment-related damage to the germinal epithelium was noted in 1/5 dosed animal; minor damage to the germinal epithelium was seen in 1/5 dosed and 2/5 control animals. NOAEL< 100 mg/kg bw/d, the only dose level tested
5 Roche (1984)	Dog	·        Dose: 100 mg/kg bw/d ·        Number of animals per group: 2 dosed males, 1 control male ·        Treatment period and frequency: 5 days, daily ·        Control: vehicle (rape oil) ·        Examination endpoints: mortality, clinical symptoms, body weight, testes weight and histopathology of testes (after orchiectomy)	·        No testicular effect that could be clearly attributed to the test substance was seen. NOAEL> 100 mg/kg bw/d, the only dose level tested

As shown in the table above, there are significant interspecies differences in the susceptibility of laboratory animals concerning testicular damage. Rats were most affected as evidenced by systemic changes (reduced body weight, liver changes) and marked histopathological changes in the seminiferous tubules at a dose as low as 50 mg/kg bw/d.

Guinea pigs were found to be far less susceptible than rats. A dose of 100 mg/kg bw/d produced moderate and slight damage to the germinal epithelium in 1/5 dosed rats each. However, slight damage to the germinal epithelium was also detected in 2/5 control animals.

Only marginal, if any, damage to the germinal epithelium was seen in treated mice. In dogs, no effect on testes was found that could be clearly attributed to the test substance.

These studies are acceptable. The studies have been performed to assess possible effects of the test substance on the testes of several species and have been carried out according to scientifically accepted standards. There is no guideline available for such screening studies.

Short description of key information:
In a Reproduction / Developmental Toxicity Screening Study (Nihon Bioresearch, Inc., undated), 4-tert-butyltoluene was administered to rats by gavage at dose levels of 0, 1.5, 5, 15, 50 mg/kg bw/day. The study was conducted in accordance with OECD TG 421.
The LOAEL is 15 mg/kg bw/day in males and mg/kg bw/day in females.
The NOAEL is 5 mg/kg bw/day in males and females.

Several screening studies with rats, mice, guinea pigs and dogs on testicular damage caused by 4-tert-butyltoluene revealed significant interspecies differences in susceptibility. Marked testicular effects of 4-tert-butyltoluene were reported for rats, minor effects were reported for guinea pigs. Only marginal, if any, substance-related effects were observed in mice and dogs (Roche, 1984).

Effects on developmental toxicity

Description of key information

In a developmental toxicity screening study (Hass et al., 1996), pregnant Wistar rats were exposed by inhalation to 4-tert-butyltoluene at a concentration of 0.12mg/l from days 7 through 20 of gestation (6 h/day). Learning and memory abilities of the offspring were investigated at the age of 3, 17 and 22 months in Morris water maze. 
The maternal NOAEL is > 0.12 mg/l; the only dose level used. 
A developmental NOAEL is not established, since developmental effects were seen at 0.12 mg/l, the only dose level used. 

Additional information

In a developmental toxicity screening study (Hass et al., 1996), pregnant Wistar rats were exposed by inhalation to 4-tert-butyltoluene (purity not given) at a concentration of 0.12 mg/l from days 7 through 20 of gestation (6 h/day). The aim of the study was to investigate the neurobehavioral effects of prenatal exposure to 4-tert-butyltoluene. Learning and memory abilities of the offspring were investigated at the age of 3, 17 and 22 months in Morris water maze.

The dose level used, ca. 0.12 mg/l, did not induce maternal toxicity. The dose level used did not induce decreased viability of offspring. Lowered pup body weight until day 10 and delayed ontogeny of reflexes was recorded. At the age of 3 months, increased latencies and swim length were observed in the learning period of treated female offspring. Three weeks later, indications of memory impairments were noted. However, these increases were not statistically significant. No substance-related effects were observed at 17 months. At the age of 22 months, increases in latencies and swim length indicating memory impairments were observed in the first 3 trials and in the trials following a 4-days break in testing. According to the authors, the impairment in exposed female offspring was not considered to be related to poorer swimming capability since swim lengths were increased in proportion to the increased latencies; swim speed was similar to control. The results indicated that substance-related neurobehavioral impairments could interact with the consequences of aging.

The maternal NOAEL is > 0.12 mg/l; the only dose level used.

A developmental NOAEL is not established, since developmental effects were seen at 0.12 mg/l, the only dose level used.

The study is published as an abstract only. Due to the poor documentation, the study cannot be classified as acceptable or inacceptable, and it cannot be stated if the study satisfies the requirements of current testing guidelines.

Justification for classification or non-classification

Based on the LOAELs of 15 mg/kg bw/d for male and female rats in the oral reproductive toxicity screening study, on changes of the male reproductive organs including sperm parameters and on decreased pregnancy rates, 4 -tert-butyltoluene has to be classified for impairment of fertility as follows: R 62 Possible risk of impaired fertility (according to the Directive 67/548/EC) and GHS (UN) Cat 2: suspected human reproductive toxicant.

The data available for teratogenicity are not sufficient to classify 4-tert-butyltoluene for teratogenicity according to the Directive 67/548/EC or GHS criteria.