2-tert-butyl-4-methoxyphenol

Endpoint summary

Description of key information

Repeated dose toxicity: Oral

 

In a 90 days repeat dose toxicity study, male Sprague-Dawley rats were exposed to the test chemical by oral gavage in the concentrations of 0 or 50 mg/kg/day. The results showed only effect in Morris Water Maze (Hidden platform MWM and Probe trial), MDA content and SOD activity when exposed to 50 mg/kg/day the test chemical alone. In combination with 2 mg/kg/day B(a)P, the results showed an improved performance in MWM compared to the rats in the B(a)P group, demonstrating that the test chemical has a protective action against the harmful effect of B(a)P. The MDA level of rats in B(a)P-test chemical-was lower, and SOD activity was higher than in the B(a)P-group, thus also showing positive effect against B(a)P damage. The activity of ATPase improved significantly in B(a)P-test chemical-treated rats, which indicates that the test chemical plays a positive role in energy metabolism. Therefore, no observed adverse effect level (NOAEL) was considered to be 50 mg/kg body weight/ day in male Sprague-Dawley rat when exposed to the test chemical by oral gavage on a daily basis for 90 days.

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Justification for type of information:

Data is from peer reviewed journal

Qualifier:

according to guideline

Guideline:

other: Refer below principle

Principles of method if other than guideline:

Repeated dose oral toxicity study was performed to determine the toxic nature of the test chemical

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

Details on test animal
TEST ANIMALS
- Source: Chongqing Medical University Lab Animal Center (Chongqing, China)
- Age at study initiation: 8 weeks
- Weight at study initiation: No data available
- Fasting period before study: No data available
- Housing: Animals were evenly distributed into 16 cages in controlled environment and marked with a number on their ears using non-toxic ink. All care and experimental procedures for the rats were conducted in accordance with guidelines published in the Guide for the Care and Use of Laboratory Animals of Chongqing Medical University.
- Diet (e.g. ad libitum): Standard laboratory rodent food, ad libitum (?)
- Water (e.g. ad libitum): Tap water, ad libitum (?)
- Acclimatization period: One week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22°C (± 2°C)
- Humidity (%): 50% (± 20%)
- Air changes (per hr): No data available
- Photoperiod (hrs dark / hrs light): 12-hr light/dark cycle

IN-LIFE DATES: From: To: No data available

Route of administration:

oral: gavage

Vehicle:

peanut oil

Details on oral exposure:

Details on oral exposure
PREPARATION OF DOSING SOLUTIONS: BHA is poorly water soluble and to make it soluble, BHA was mixed with peanut oil to provide consistent absorption and was then subjected to sonication for 30 min at 40°C. This was performed on a weekly basis. The daily reagent dosage (50 mg/kg/day) was determined individually for each rat based on body weight.

DIET PREPARATION
- Rate of preparation of diet (frequency): No data available
- Mixing appropriate amounts with (Type of food): No data available
- Storage temperature of food: No data available

VEHICLE
- Justification for use and choice of vehicle (if other than water): Peanut oil (20 mg/mL)
- Concentration in vehicle: BHA: 50 mg/kg/day, and B(a)P-BHA combination group: B(a)P 2 mg/kg/day + BHA 50 mg/kg/day.
- Amount of vehicle (if gavage): No data available
- Lot/batch no. (if required): No data available
- Purity: No data available

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

90 days

Frequency of treatment:

Daily

Remarks:

Doses / Concentrations:
0, 50 BHA or 2 B(a)P +50 BHA mg/kg/day
Basis:
no data

No. of animals per sex per dose:

Total: 72
0 mg/kg/day : 24 male
50 mg/kg/day : 24 male
2 (B(a)P) + 50 (BHA) mg/kg/day: 24 male

Control animals:

yes, concurrent vehicle

Details on study design:

No data

Positive control:

No data

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data available
- Time schedule: No data available
- Cage side observations: No data available

DETAILED CLINICAL OBSERVATIONS: Yes, swimming ability of each rat was observed.
- Time schedule: Prior to the Morris Water Maze (MWM) test.

BODY WEIGHT: Yes
- Time schedule for examinations: No data available

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): No data available
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data available
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No data available

FOOD EFFICIENCY: No data available
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No data available

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No data available
- Time schedule for examinations: No data available

OPHTHALMOSCOPIC EXAMINATION: Yes, visual ability was observed.
- Time schedule for examinations: Prior to the MWM test.
- Dose groups that were examined: All dose groups were examined.

HAEMATOLOGY: No data available
- Time schedule for collection of blood: No data available
- Anaesthetic used for blood collection: No data available
- Animals fasted: No data available
- How many animals: No data available
- Parameters checked in table [No.?] were examined. No data available

CLINICAL CHEMISTRY: No data available
- Time schedule for collection of blood: No data available
- Animals fasted: No data available
- How many animals: No data available
- Parameters checked: No data available

URINALYSIS: No data available
- Time schedule for collection of urine: No data available
- Metabolism cages used for collection of urine: No data available
- Animals fasted: No data available
- Parameters checked: No data available

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: Prior to the MWM test.
- Dose groups that were examined: All 72 dose groups animals were examined.
- Battery of functions tested: sensory activity / grip strength / motor activity / other: Yes, motor activity was tested.

OTHER: No data available

Sacrifice and pathology:

GROSS PATHOLOGY: No data available

HISTOPATHOLOGY: No data available

Other examinations:

Following the WMW test, malonaldehyde (MDA) content and superoxide dismutase (SOD) activity were measured to determine the oxidative damage induced by B(a)P and the protective effect of BHA.

The activity of Na+-K+-ATPase and Ca2+-Mg2+-ATPase was also measured after the MWM to determine the energy metabolism damage induced by B(a)P and the protective effect of BHA.

In addition, following the WMW test, the Ca2+-content was measured to detect the damage in the hippocampus induced by B(a)P and the protective effect of BHA.

Statistics:

All data analyses were performed with SPSS v.20.0 (SPSS, Inc., Chicago, IL, USA) and the quantitative data were expressed as mean ± S.D. The data were analyzed using analysis of variance (ANOVA). Data obtained over training days from the hidden platform trial were analyzed by ANOVA for repeated measurement. The remaining data were analyzed by one-way ANOVA. When appropriate, post hoc comparisons were assessed using the Least
Significant Difference (LSD). A probability of P < 0.05 was considered significant for all analyses.

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

not specified

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:

no effects observed

Description (incidence and severity):

No change were observed in visual ability of treated rats as compare to control.

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

No change were observed in motor activity of treated rats as compare to control.

Immunological findings:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Neuropathological findings:

not specified

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not specified

Other effects:

not specified

Details on results:

BHA was chosen to prevent the neurotoxicity on oxidative stress caused by B(a)P.
In the B(a)P-BHA-combination group, the rats had a better performance significantly in MWM compared to the rats in the B(a)P group. This demonstrates that in behavior tests BHA has protective action against the harmful effect of B(a)P.
The MDA level of rats in B(a)P-BHA-combination group is lower, and SOD activity is higher than in the B(a)P-group. This is a further sign of the positive effect against B(a)P damage.

The activity of ATPase has a significant improvement, which indicates that BHA also plays a positive role in energy metabolism.
There is no significant difference of Ca2+ content between the B(a)P group and the B(a)P-BHA-combination group.

Dose descriptor:

NOAEL

Effect level:

50 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Effect on motor activity, and levels of MDA and SOD, ATPase activity and Ca2+ concentration in rat brain.

Critical effects observed:

not specified

Conclusions:

The no observed adverse effect level (NOAEL) was considered to be 50 mg/kg body weight/ day in male Sprague-Dawley rat when exposed to the test chemical.

Executive summary:

In a 90 days repeat dose toxicity study, male Sprague-Dawley rats were exposed to the test chemical by oral gavage in the concentrations of 0 or 50 mg/kg/day. The results showed only effect in Morris Water Maze (Hidden platform MWM and Probe trial), MDA content and SOD activity when exposed to 50 mg/kg/day the test chemical alone. In combination with 2 mg/kg/day B(a)P, the results showed an improved performance in MWM compared to the rats in the B(a)P group, demonstrating that the test chemical has a protective action against the harmful effect of B(a)P. The MDA level of rats in B(a)P-test chemical-was lower, and SOD activity was higher than in the B(a)P-group, thus also showing positive effect against B(a)P damage. The activity of ATPase improved significantly in B(a)P-test chemical-treated rats, which indicates that the test chemical plays a positive role in energy metabolism. Therefore, no observed adverse effect level (NOAEL) was considered to be 50 mg/kg body weight/ day in male Sprague-Dawley rat when exposed to the test chemical by oral gavage on a daily basis for 90 days.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

50 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

Data is from peer reviewed publication

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

repeated dose toxicity: inhalation, other

Data waiving:

other justification

Justification for data waiving:

other:

Endpoint conclusion

Endpoint conclusion:

no study available

Quality of whole database:

Waiver

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Link to relevant study records

Reference

Endpoint:

repeated dose toxicity: dermal

Data waiving:

other justification

Justification for data waiving:

other:

Critical effects observed:

not specified

Endpoint conclusion

Endpoint conclusion:

no study available

Quality of whole database:

Waiver

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Data available for the test chemicals was reviewed to determine the toxic nature of the test chemical. The studies are mentioned below:

 

Repeated dose toxicity: Oral

 

In a 90 days repeat dose toxicity study, male Sprague-Dawley rats were exposed to the test chemical by oral gavage in the concentrations of 0 or 50 mg/kg/day. The results showed only effect in Morris Water Maze (Hidden platform MWM and Probe trial), MDA content and SOD activity when exposed to 50 mg/kg/day the test chemical alone. In combination with 2 mg/kg/day B(a)P, the results showed an improved performance in MWM compared to the rats in the B(a)P group, demonstrating that the test chemical has a protective action against the harmful effect of B(a)P. The MDA level of rats in B(a)P-test chemical-was lower, and SOD activity was higher than in the B(a)P-group, thus also showing positive effect against B(a)P damage. The activity of ATPase improved significantly in B(a)P-test chemical-treated rats, which indicates that the test chemical plays a positive role in energy metabolism. Therefore, no observed adverse effect level (NOAEL) was considered to be 50 mg/kg body weight/ day in male Sprague-Dawley rat when exposed to the test chemical by oral gavage on a daily basis for 90 days.

 

 

In another repeated dose toxicity study, male Crj:CD (SD)rat were exposed to the test chemical by oral gavage route of exposure in the concentrations of 0, 50, 100, 250 or 500 mg/kg/day. Toxic changes were observed as decreased body weight gain when male rats were treated with of TP and TP with the test chemical 250 mg/kg/day. No change in food consumption were observed in treated rats. Relative liver weight, right and left adrenal gland weight were significantly increased when treated with 500 mg/kg/day. Treatment with TP or TP with test chemical 250 mg/kg/day in male rat resulted in significantly decreased right and left adrenal gland weights, while the relative and absolute weights of androgen-dependent accessory sex organs were not affected by the treatment of test chemical alone. The relative TP-stimulated ventral prostate weight was significantly increased by the test chemical 250 mg/kg, but the absolute and formalin-fixed weight was not significantly changed. The absolute and relative weights of LABC, seminal vesicle with coagulating glands, glans penis, Cowper’s gland were not changed. Therefore, no observed adverse effect level (NOAEL) was considered to be 50 mg/kg/day when male rat were exposed to the test chemical by gavage route of exposure for 10 days.

 

 

In yet another repeated dose study for 12-weeks, cynomolgus monkeys were exposed to the test chemical at a dose concentration of 0, 125 or 500 mg/kg/day. Several parameters were analyzed and included body weight, organ weight, serum chemistry and hematology, liver size and hepatic monooxygenase activity. At 250 mg/kg/day, no significant changes were noted in blood urea and other enzyme levels. Histological examination of stomach epithelial tissues showed no unusual proliferation or hyperplasia of epithelial cells, and no thickening of the epithelial layers was shown. Terminal observations revealed decreased hepatic monooxygenase activity and an increase in the mitotic index of the oesophageal epithelium. Gastroscopic evaluation of the stomach and oesophagus at monthly intervals and extensive gross and histopathological examination failed to reveal the proliferative effects. Therefore, the low observed adverse effect level (LOAEL) was considered to be ≤250 mg/kg/day when cynomolgus monkeys were exposed to the test chemical.

 

 

In a toxicity study on the test chemical, male F344 were exposed to the test chemical on a daily basis of 0 or 12000 ppm of the test chemical in their diet for 110 weeks. Survival of rats in all groups gradually decreased after 84 weeks. The test chemical did not affect body weight or liver weight, and a mild hyperplasia and moderate, but significant, incidence of gastric squamous cell papillomas were observed. Therefore, the low observed adverse effect level (LOEAL) was considered to be 12000 ppm per day (900 mg/Kg/day) when male F344 rats are exposed to the test chemical on a daily basis through their diet.

 

The above studies are further supported by data from various other publications as-

 

In a repeated dose oral toxicity study, Norway hooded rats were exposed to the test chemical at the concentration of 0, 0.0004, 0.001, 0.01 or 0.5 p.c. per day,( 0, 0.2, 0.5, 5 or 250 mg/kg) depending on the level of dietary fat. A diet containing 0.5 p.c. test chemical produced only a relatively small reduction in the initial growth rate and small reduction in the mature weight. BHA had no effect on the condition of the rat hair. Increased kidney weights were observed. No histopathological differences were observed between control and test specimens of the spleens, testes, kidneys or livers. However, the test chemical produced increased liver weight when exposed to 0.5 p.c. per day, at the 0.1 p.c. and below had no effect on the relative liver weight and no histopatholgical changes observed at this dosage. Therefore, the low observed adverse effect level (LOAEL) was considered to be 0.5 p.c. per day (250 mg/kg)while and the no observed adverse effect level (NOAEL) was considered to be 0.1 p.c. per day (50 mg/kg) when Norway hooded rats were exposed to the test chemical on a daily basis by diet for 8 months.

 

 

Toxicity by the test chemical in female Sprague-Dawley rats was also studied at dose level of 0, 200, 500 mg/kg/day. The test chemical (500 mg/kg/day) in corn oil was administered orally for 3 days to one group of rats followed by 200 mg/kg/day for 9 additional days. There was a decrease in hepatic lipid peroxidation occurred when compared to the corn oil treated control group, the test chemical treatment resulted in over a 50% increase in hepatic GSH content. The body weights of animals receiving the test chemical daily were not significantly different than body weights of rats receiving only the corn oil vehicle. The test chemical treated animals showed an increase in liver weight. Thus from above findings it is concluded that the low observed adverse effect level (LOAEL) for the test chemical when exposed to female Sprague-Dawley rat by the oral route was observed at dose concentration of 500 mg/kg bw .

 

 

In 6 months repeated dose oral toxicity study, male and female dogs were exposed to the test chemical by oral feed in the concentrations of 0, 1.0 and 1.3 % . The results showed that the test chemical was toxic. Toxic changes were observed in body weight and food consumption. In addition, significant histopathological changes were observed in gastric mucosa epithelium, stomach, thyroid and liver in 1.0 and 1.3 % dose group. Increase in mixed function oxidase, UDP- glucuronyl transferase, glutathione -S- transferase, epoxide hydratase was observed in clinical chemistry. Liver and thyroid weight was increased in 1.0 and 1.3% dose group. Therefore, the low observed adverse effect level (LOAEL) is considered to be 1.0% (250 mg/kg bw/day) dose group when male and female dogs are exposed to the test chemical by oral feed on a daily basis for 6 months.

 

 

In another repeat dose toxicity study, female Wistar rats were exposed to the test chemical by an oral solution in the concentration of 0 or 300 mg/kg/day. The results showed that the relative weight of liver, kidneys and spleen were not affected by the treatment with the test chemical, while the relative uterine and ovaries weights were significantly decreased as compared to the negative control. The histopathological results showed rats with minimal histopathologic changes in the uterus, and no changes in cervix or vagina. When performing a morphometric analysis, the results showed a slight thickness in the endometrial stroma, as well as increased thickness in the myometrium and endometrial endothelium as compared to control. A similar trend was observed for the uterine wall thickness, where the animals from the test chemical treated group had significantly thicker walls as compared to the control group. Endometrial epithelial hyperplasia of the uterine mucosa, stroma, myometrium and that of the uterine wall are considered histological markers of endocrine action. Therefore, the low observed adverse effect level (LOAEL) was considered to be 300 mg/kg body weight/ day when female Wistar rats are exposed to the test chemical by oral gavage on a daily basis for 3 days.

 

 

In a combined repeated dose toxicity and carcinogenicity study, female ACI rats were exposed to the test chemical by feed in the concentration of 0 or 0.7% (w/w) for up to 240 days. The results showed that no tumor nodules were developed in females treated with the test chemical alone. When exposed to E2 +test chemical, the mammary tumor incidence was 24% after 8 months of treatment. Histopathological examination of mammary tissue from the control and the test chemical groups revealed normal lobular architecture with branched ducts and normal distribution of fat tissue, whereas mammary tissues in E2+ test chemical-treated rats showed ductal hyperplasia with increased expansion of terminal lobular units accompanied by compression of and expansion into the surrounding fat tissue. It was also observed that co-treatment with the test chemical inhibited E2-mediated increases in 8-isoprostane levels as well as activities of antioxidant enzymes, thus suggesting that estrogen-mediated oxidant stress plays a critical role in the development of estrogen-dependent breast cancers where the test chemical inhibits E2dependent breast carcinogenesis by decreasing oxidant stress. Therefore, the no observed adverse effect level (NOAEL) is considered to be 0.7% (w/w; 350 mg/kg body weight) when female ACI rats are exposed to the test chemical by feed on a daily basis for up to 240 days.

 

Repeated dose toxicity: Inhalation

 

Tert-butyl-4-methoxyphenol (CAS No.25013-16-5) has very a low vapor pressure of 0.0023326915 mm Hg at 25°C. The particle size distribution was determined to be in the range of 150 micron to 106 micron. The normal conditions of use of this substance will not result in aerosols, particles or droplets of an inhalable size, so exposure to humans via the inhalatory route will be highly unlikely. Therefore this end point for repeated dose toxicity by inhalation route is considered for waiver.

 

Repeated dose toxicity: Dermal

 

The acute dermal toxicity value for Tert-butyl-4-methoxyphenol (CAS No.25013-16-5) (as provided in section 7.2.3) is >2000 mg/kg body weight. Considering this, the end point for repeated dermal toxicity is considered as waiver.

 

Repeated dose toxicity: Other route

In a repeated dose subcutaneous toxicity study, female Crj:CD (SD) rats were exposed to the test chemical by subcutaneous injection into dorsal surface, caudal to the nape of neck in the concentration of 0, 50, 100, 250 and 500 mg/kg/body weight/day. Toxic changes were observed as decrease in body weight gain of 250 and 500 mg/kg/day treated female rat. Changes were also observd in uterine weight of female rat at 50 mg/kg/day. Therefore, Low observed adverse effect level (LOAEL) is considered to be 50 mg/kg/body weight/day when female rats are exposed to the test chemical by subcutaneous injection for 3 days.

Based on the data available for the target chemical, the test chemical does not show repeated dose toxicity by oral route of exposure. Hence the test chemical is not likely to be toxic upon repeated exposure by oral route, dermal and inhalation route of exposure.

Justification for classification or non-classification

Based on the data available for the target chemical, the test chemical does not show repeated dose toxicity by oral route of exposure. Hence the test chemical is not likely to be toxic upon repeated exposure by oral route, dermal and inhalation route of exposure.