2-tert-butylhydroquinone

Repeated dose toxicity: oral

Administrative data

Endpoint:

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 publication

Data source

Reference

Reference Type:

review article or handbook

Title:

Repeated dose oral toxicity study of the test chemical

Author:

DHHS

Year:

1997

Bibliographic source:

NTP

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: Refer below principle

Principles of method if other than guideline:

Male and female F344/N rats were fed diets containing 0, 2500, 5000 or 10000 ppm of the test chemical for 13 weeks after weaning to study the cumulative toxic effects of the substance.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

2-tert-butylhydroquinone

EC Number:

217-752-2

EC Name:

2-tert-butylhydroquinone

Cas Number:

1948-33-0

Molecular formula:

C10-H14-O2

IUPAC Name:

2-tert-butylbenzene-1,4-diol

Details on test material:

- Name of test material: tert-Butyl hydroquinone (TBHQ)
- IUPAC name: 2-tert-Butylhydroquinone
- Molecular formula: C10H14O2
- Molecular weight: 166.219 g/mol
- Substance type: Organic

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Male and female F344/N rats in the F0 generation were obtained from Taconic Farms (German-town, NY). Offspring (F 1 generation) of the breeders from the perinatal phase of the study.
- Age at study initiation: 34 days
- Housing: Rats were housed five per cage in polycarbonate cages with bedding
- Diet (e.g. ad libitum): NIH-07 open formula mash diet, ad libitum
- Water (e.g. ad libitum): Tap water via automatic watering system; available ad libitum
- Acclimation period: None

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18.7°C to 24.2°C
- Humidity (%): 35.8 %-79.3 %
- Air changes (per hr): minimum of 10 changes per hour
- Photoperiod (hrs dark / hrs light): 12 hours/day

Administration / exposure

Route of administration:

oral: feed

Vehicle:

other: NIH-07 open formula mash diet

Details on oral exposure:

DIET PREPARATION
- Rate of preparation of diet (frequency): Weekly
- Storage temperature of food: The dose formulations were stored in sealed containers in the dark at 5°C for no longer than 3 weeks.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Homogeneity and stability analyses of the dose formulations were conducted by the analytical chemistry laboratory using high-performance liquid chromatography.

Duration of treatment / exposure:

13 weeks after weaning

Frequency of treatment:

daily

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 2500, 5000, or 10000 ppm (0, 200, 400 or 800 mg/kg bw for males and 0, 200, 400 or 750 mg/kg bw for females)
Basis:
other: Approx 0, 200, 400 or 800 mg/kg bw for males and 0, 200, 400 or 750 mg/kg bw for females

No. of animals per sex per dose:

Control: 10 males and 10 females
2500 ppm: 10 males and 10 females
5000 ppm: 10 males and 10 females
10000 ppm: 10 males and 10 females

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: No F1 offspring resulted from F0 females fed diets containing 20000 or 40000 ppm, so these exposure levels were not used in the 13-week rat study
- Rationale for animal assignment: Animals were distributed randomly into groups of approximately equal initial mean body weights

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
Animals were observed twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
Clinical findings were recorded

BODY WEIGHT: Yes
- Time schedule for examinations: The animals were weighed initially, weekly, and at the end of the study

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
Feed consumption was recorded as an average of grams per animal per day.

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: At 13 weeks
- Parameters examined: Hematocrit level, hemoglobin concentration, erythrocyte count, reticulocyte count, nucleated erythrocyte count, mean cell volume, mean cell hemoglobin, mean cell hemoglobin concentration, platelet count, and leukocyte count and differential.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: At 13 weeks
- Parameters examined: Blood urea nitrogen, creatinine, total protein, albumin, alkaline phosphatase, creatine kinase, sorbitol dehydrogenase, and bile acids

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

OTHER:
Sperm Motility and Vaginal Cytology Evaluation:
Sperm and vaginal fluid samples were evaluated in all groups at the end of the studies. The parameters evaluated in males were sperm count and motility. The right cauda, right epididymis, and right testis were weighed. Vaginal fluid samples were collected for up to 7 consecutive days prior to the end of the studies for vaginal cytology evaluations. The parameters evaluated in females were relative frequency of estrous stages and estrous cycle length

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Organs weighed were the heart, right kidney, liver, lungs, right testis, and thymus
HISTOPATHOLOGY: Yes
Complete histopathologic examinations were performed. In addition to gross lesions, tissue masses, and associated lymph nodes, the tissues examined included: adrenal gland, bone and marrow, brain, clitoral gland, esophagus, heart (with aorta), large intestine (cecum, colon, rectum), kidneys, liver, lungs and main stem bronchi, lymph nodes (mandibular and mesenteric), mammary gland, nasal cavity and turbinates, ovaries, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, skeletal muscle, skin, small intestine (duodenum, jejunum, ileum), spinal cord and sciatic nerve, spleen, stomach (fore stomach and glandular stomach), testis with epididymis and seminal vesicle, thymus, thyroid gland, trachea, urinary bladder, and uterus.

Statistics:

Williams' or Dunnett' s test (organ and body weights) or Dunn's test (spermatid and epididymal spermatozoal parameters)

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):

The final mean body weights of males and females in the 5000 and 10000 ppm groups were significantly lower than those of the controls

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Feed consumption by exposed groups was lower than that by controls at week 2, and, feed consumption by 5000 and 10000 ppm males and 10000 ppm females was slightly lower than that consumed by controls at the end of the study

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

The increases observed in the Serum bile acid levels and Serum alanine aminotransferase activity were marginal, and as histopathologic evaluation did not reveal evidence of liver toxicity, these increases were not considered to be biologically significant

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not specified

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

The organ weight differences were associated with histopathologic lesions and in many cases were secondary to lower body weights of exposed groups. Therefore, they were not considered clearly related to t-butylhydroquinone exposure

Gross pathological findings:

no effects observed

Neuropathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Increased incidences of splenic pigmentation were observed in males and females exposed to 5000 or 10000 ppm, and incidences of atrophy of the red pulp were observed in these groups of females

Histopathological findings: neoplastic:

not examined

Other effects:

not specified

Details on results:

The mean spermatid count, spermatid heads per testis, and spermatid heads per gram of testis were significantly decreased in males exposed to 5000 ppm. The estrous cycles of females exposed to 2500 or 5000 ppm were significantly longer than that of the controls. There were no biologically significant changes in clinical pathology parameters or in organ weights.

Effect levels

1

Dose descriptor:

LOAEL

Effect level:

200 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: Significantly longer estrous cycles

2

Dose descriptor:

NOAEL

Effect level:

200 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Body weight, feed consumption, sperm analysis

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

The LOAEL value of the test chemical when administered in diet was found to be 200 mg/kg/day in female rats, as significantly longer estrous cycles were observed at this dose as compared to controls. The NOAEL value in male rats was determined to be 200 mg/kg/day, based on no effects observed during analysis of body weight, feed consumption and sperm parameters.

Executive summary:

The cumulative toxic effects of the test chemical in rats were evaluated in the 13 week study. The test substance was administered in diet to male and female F344/N rats at a dose level of 0, 2500, 5000 or 10000 ppm for 13 weeks after weaning. This dose level is equivalent to a daily dose of approximately 0, 200, 400 or 800 mg/kg bw for males and 0, 200, 400 or 750 mg/kg bw for females.

 

The following parameters were evaluated: body weight and feed consumption, hematology, clinical chemistry and coagulation analysis, sperm motility and vaginal cytology. A complete histopathological examination was conducted. The LOAEL value of 2-tert-butylhydroquinone was found to be 200 mg/kg/day in female rats due to effect on length ofestrous cycles. The NOAEL value in male rats was determined to be 200 mg/kg/day,based on no effects observed during analysis of body weight, feed consumption and sperm parameters.

 

At various time points there were increases in serum bile acid levels and serum alanine aminotransferase activity levels in male and female rats exposed to the test chemical. Such increases are generally associated with liver toxicity and since histopathologic evaluation did not reveal any evidence of liver toxicity, these marginal increases were not considered to be biologically significant. The effect of the test chemical on reproductive parameters in male rats were observed only at dose level of 5000 ppm. Histopathologic changes were observed in rats exposed to 5000 or 10000 ppm the test chemical which included increased incidences of nasal respiratory epithelial hyperplasia, nasal exudate (males only), splenic pigmentation, splenic atrophy of the red pulp (females only), and kidney mineralization (females only).