2-methylpropan-2-ol

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1986-1988

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study was conducted according to US NTP standard study and GLP guidelines.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1995

Reference 2

Reference Type:

publication

Title:

Subchronic Toxicity Studies of t-Butyl Alcohol in Rats and Mice

Author:

Lindamood III, C. et al.

Year:

1992

Bibliographic source:

Fundamental and Applied Toxicology 19: 91-100

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: NTP standard guideline for chronic drinking water study.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-methylpropan-2-ol

EC Number:

200-889-7

EC Name:

2-methylpropan-2-ol

Cas Number:

75-65-0

Molecular formula:

C4H10O

IUPAC Name:

2-methylpropan-2-ol

Details on test material:

-Name of test material (as cited in study report): t-butyl alcohol
-Source of test material: FBC Chemical Corporation (Lancaster, NY)
-Analytical purity: >99%
-Appearance: clear, colorless liquid
-Lot No.: F112784 (used for 13-wk and 2-yr studies in rats and mice)
-Methods of analyses: identified by IR, UV-VIS and NMR spectroscopy; purity determined by elemental analyses, Karl Fischer water analysis, and gas chromatography (GC). GC indicated one major peak and one impurity with a peak area greater than or equal to 0.1% relative to the major peak. All spectra were consistent with those expected for tertiary butyl alcohol; IR and NMR spectra were consistent with literature spectra. The boiling point and density of lot F112784 were consistent with literature values.
-Stability under test conditions: Identity, purity and stability analyses were conducted by the analytical chemistry laboratory Midwest Research Institute (Kansas City, MO). Accelerated stability studies were performed on lot F112784 by the analytical chemistry laboratory. As a bulk chemical, tertiary butyl alcohol was stable when stored for 2 weeks protected from light at temperatures up to 60 °C.
-Storage condition of test material: the bulk chemical was stored at room temperature in amber glass bottles with Teflon-lined lids. Stability was monitored during the 2-year studies with gas chromatography. No degradation was detected

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS:
-Source: Taconic Laboratory Animals and Services (Germantown, NY)
-Age at receipt: approx. 5 weeks; animals were quarantined for 13 days before study initiation
-Health prior to study initiation and during study: Prior to study initiation, five male and five female rats were selected for parasite evaluation and gross observation of disease. Serology samples were collected for viral screening. The health of the animals was monitored during the studies according to the protocols of the NTP Sentinel Animal Program.
-Age at study initiation: approx. 7 weeks
-Average age at necropsy: 110 weeks
-Method of Animal Identification: toe clip
-Method of Animal Distribution: Animals randomized from weight classes into cage groups using a random numbers table; cages randomized into test groups using a random numbers table
-Housing: Animals were individually housed in solid-bottom, polycarbonate cages (Lab Products, Inc., Maywood, NJ) lined with Beta-Chips® heat-treated hardwood-chip bedding (Northeastern Products, Inc., Warrensburg, NY) or Sani-Chips® (P.J. Murphy Forest Products Corp., Montville, NJ). Cages were changed weekly and rotated every two weeks. Bedding was changed weekly. Cages were suspended on stainless steel racks (Lab Products, Inc., Maywood, NJ); racks were rotated every 2 weeks.
-Diet: NIH-07 Open Formula Meal Diet (Zeigler Brothers, Inc., Gardners, PA) was available ad libitum except during urine collection period. Food was changed weekly.
-Water: city water (filtered and deionized) was available ad libitum as plain or dosed

ENVIRONMENTAL CONDITIONS:
-Temperature (°C): 19-31°
-Relative Humidity: 52% to 59%
-Air changes per hour: minimum of 10 changes/hr
-Photoperiod (hrs dark/ hrs light): 12 hours light/dark

IN-LIFE DATES:
-Date of First Dose: 12 November 1986
-Date of Last Dose: 1 November 1988
-Duration of Dosing: 103 weeks
-Date of Necropsy: Interim (15 month) - 10 February 1988 (males); 11 February 1988 (females). Terminal - 9 to 11 November 1988

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

water

Remarks:

deionised

Details on oral exposure:

The dose formulations were prepared by mixing tertiary butyl alcohol with deionized water for target concentrations of 0, 1.25, 2.5 and 5 mg/mL in males and 0, 2.5, 5 and 10 mg/mL in females. Tertiary butyl alcohol was mixed with approximately one-half the required volume of deionized water, diluted to the specified volume with additional deionized water, and stirred for at least 5 minutes. Formulations were stored in amber glass bottles with Teflon-lined lids in the dark at room temperature for up to 2 weeks. Animals were allowed ad libitum access to drinking water (plain or dosed) for 103 weeks. The study used target rather than actual delivered average daily doses in reporting results. Therefore, all results, discussions and conclusions in this IUCLID document have used target doses.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Stability studies were performed by the referee analytical chemistry laboratory, Midwest Research Institute (Kansas City, MO) using gas chromatography. The stability of the dose formulations was confirmed when stored in the dark for at least 3 weeks at room temperature and for at least 3 days at room temperature under normal room light.

Periodic analyses of the dose formulations were conducted at the study laboratory (Southern Research Institute) and referee analytical chemistry laboratory with gas chromatography. The formulations were analyzed approximately every 8 weeks. All of the dose formulations analyzed were within 10% of the target concentration. Results of periodic referee analyses performed by the analytical chemistry laboratory agreed with the results obtained by the study laboratory.

Duration of treatment / exposure:

103 weeks.

Frequency of treatment:

Ad libitum in the drinking water.

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
males: 1.25, 2.5, 5.0mg/mL
Basis:
nominal in water

Doses / concentrations 2

Remarks:

Doses / Concentrations:
females: 2.5, 5.0, 10mg/mL
Basis:
nominal in water

Doses / concentrations 3

Remarks:

Doses / Concentrations:
Mean for Males in mg tertiary butyl alcohol/kg bw/day: LOW DOSE: 111 (wk 1-13), 65 (wk 14-52) and 95 (wk 53-101); MID DOSE: 239 (wk 1-13), 141 (wk 14-52) and 225 (wk 53-101); HIGH DOSE:448 (wk 1-13), 288 (wk 14-52) and 516 (wk 53-101).
Basis:
actual ingested

Doses / concentrations 4

Remarks:

Doses / Concentrations:
Mean for females in mg tertiary butyl alcohol/kg bw/day: LOW DOSE: 290 (wk 1-13), 174 (wk 14-52) and 150 (wk 53-101); MID DOSE: 511 (wk 1-13), 317 (wk 14-52) and 291 (wk 53-101); HIGH DOSE: 886 (wk 1-13), 587 (wk 14-52) and 634 (wk 53-101).
Basis:
actual ingested

No. of animals per sex per dose:

60

Control animals:

yes, concurrent vehicle

Details on study design:

The doses in the study were based on findings in a 13-week study previously conducted for the NTP. In the 2-yr study, ten rats per group were evaluated after 15 months of chemical administration.

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes for mortality/morbidity.
-Time schedule: twice daily, 7 days per week.
DETAILED CLINICAL OBSERVATIONS: Yes.
-Time schedule: Clinical observations were recorded initially, weekly for 13 weeks, then every 4 weeks, at interim evaluation, and at sacrifice.
BODY WEIGHT: Yes.
-All animals were weighed initially, weekly for 13 weeks, every 4 weeks thereafter, and at interim evaluation and at terminal sacrifice.
WATER CONSUMPTION: Yes.
-Measured per animal every 2 weeks for the first 13 weeks, then every 4 weeks until the end of the study.
FOOD CONSUMPTION: no data.
OPTHALMOSCOPIC EXAMINATION: not examined.
HEMATOLOGY: Yes.
-Time schedule for collection of blood: collected from the retroorbital sinus of anesthetized (CO2) animals at the interim 15-month sacrifice.
-Number of animals: 10 rats/group.
-Parameters examined: hematocrit, hemoglobin, erythrocytes, mean cell volume, mean cell hemoglobin, mean cell hemoglobin concentration, platelets, leukocytes, segmented neutrophils, lymphocytes, atypical lymphocytes, monocytes, eosinophils.
-Method of analysis: automated hematology determinations were performed with an Ortho ELT-8 Laser Hematology Counter.
-No hematology analysis performed at study termination.
-Other: blood samples were also collected from the sentinel animals at approximately 6-month intervals and from the control groups at terminal sacrifice for serologic analysis.
CLINICAL CHEMISTRY: not examined.
URINALYSIS: Yes.
-Time schedule for collection of urine: Several days prior to the 15-month interim evaluation, urine samples were collected from previously designated rats; rats were fasted during this time but water (plain or dosed) was available ad libitum.
-Number of animals: 10 rats/group.
-Parameters evaluated: volume (mL/16 hr), specific gravity, pH, appearance, microscopic sediment.
- No urinalysis performed at study termination.
NEUROBEHAVIORAL EXAMINATION: not examined.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes. Complete necropsies were performed on all animals. At necropsy, all organs and tissues were examined for grossly visible lesions. Tissues for microscopic examination were fixed and preserved in 10% neutral buffered formalin, processed and trimmed, embedded in paraffin, sectioned to a thickness of 4 to 6 µm, and stained with hematoxylin and eosin (H&E).

ORGAN WEIGHTS: Yes. The following organs were weighed at the 15-month interim sacrifice: brain, right kidney, liver. No organ weights were recorded at study termination.

HISTOPATHOLOGY: Yes. A complete histopathologic examination was performed on all animals. In addition to gross lesions and tissue masses, the tissues examined included: adrenal gland, bone (marrow, femur, sternum), brain (three sections), clitoral gland, esophagus, heart, large intestine (cecum, colon, rectum), small intestine (duodenum, jejunum, ileum), kidneys, liver, lung, lymph node (mandibular, mesenteric), mammary gland, nose (three sections), ovary, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, skin, spleen, stomach (forestomach and glandular), testis (epididymis and seminal vesicle), thymus, thyroid gland, trachea, urinary bladder, uterus.

Other examinations:

Because microscopic examination of the original kidney sections showed increased proliferative lesions of the renal tubules, step sections were made from the residual kidney wet tissue from treated males. Sectioning was done in 1 mm steps throughout the kidney wet tissue that remained after the standard sections had been taken. An average of 8 additional step sections per kidney were made. The average number of sections per animal was 16 in the low- and mid-dose groups and 17 in the high-dose group. Criteria for evaluation of proliferative lesions for the kidney step sections were the same as those used in the standard evaluation. Severity grades of renal tubule epithelial hyperplasia were based on the size, complexity and disorganization of the lesion; higher severity grades reflected more progression toward adenoma.

Statistics:

Statistical analyses were used throughout the study. Dose formulations were reported as means with standard deviations. Means were calculated for body weights, water and compound consumption, and survival in days. Percent probability of survival at end of study was calculated based on the number of animals alive on the first day of terminal sacrifice. The probability of survival was estimated by the product-limit procedure of Kaplan and Meier (1958). Statistical analyses for possible dose-related effects on survival used Cox’s (1972) method for testing 2 groups for equality and Tarone’s (1975) life table test to identify dose-related trends. All reported P values for survival analyses are two sided. Means and standard deviations were used to report absolute and relative organ weights; significant differences of organ weights; organ-weight-to-body-weight ratios compared to controls were evaluated by Williams’ or Dunnett’s test. Hematology and urinalysis data were reported as means and standard deviations. Incidences of neoplasms and nonneoplastic lesions of the kidney were evaluated as significantly different (P ≤ 0.05) from the control group by the Fisher exact test (15-month interim evaluation) or by the logistic regression test (2-yr study). Severities of nephropathy were evaluated by the Mann-Whitney U test. Statistical analysis of primary neoplasms comparing controls with dosed groups used the life table test, the logistic regression test, the Cochran-Armitage test, and the Fisher exact test. The life table analysis regards neoplasms in animals dying prior to terminal kill as being (directly or indirectly) the cause of death. The logistic regression test regards these lesions as nonfatal. The Cochran-Armitage and Fisher exact tests compare directly the overall incidence rates.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

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

effects observed, treatment-related

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

not examined

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

Effects in females only.

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

Clinical signs and mortality: Until interim sacrifice at week 66, survival rates in all dose groups were similar to controls. Although the survival rate of the male rat control group was relatively low, it was similar to that observed in other concurrent control groups and reflects the general trend toward decreased survival in control F344/N rats in NTP studies. Overall survival rates of 2.5 and 5 mg/mL males were significantly lower than those of the controls (24% and 20% in the control and low-dose groups versus 8% and 4% in the mid- and high-dose groups). However, approximately 60% of the 2.5 and 5 mg/mL groups survived through week 85. Although survival among exposed female rats was lower than that of the controls at week 101, especially in the 10 mg/mL group (34% versus 58% in control group), more than 70% of the females in each group survived through week 85. Behavior and general health and appearance of exposed animals were similar to those of the controls, with the exception of an increased incidence of hyperactivity in the 10 mg/mL female group.

Body weight and weight gain: At approximately week 20, mean body weight gain of the 5 mg/mL male group was lower than that of the controls. The final mean body weight of this group was 24% less than that of the controls. Mean body weights in the 1.25 and 2.5 mg/mL male groups were similar to that of controls through about week 65 and then decreased for the remainder of the study (15% and 17% less than controls, respectively at week 101). The mean body weight of the 10 mg/mL female animals was similar to that of the controls through about week 29; with the mean body weight gain of this group was lower than that of the controls after this time. The interim mean body weight of 10 mg/mL females was 13% lower while the final body weight was 21% lower than that of the controls. Mean body weights of other exposed groups of females were similar to that of the control group throughout the study.

Water consumption: During the second year of the study, there was a dose-related increase in water consumption for male groups. Exposure levels of 1.25, 2.5 or 5 mg/mL delivered average daily doses of approximately 90, 200 or 420 mg tertiary butyl alcohol/kg bw/day. During the second year of the study, there was a dose-related decrease in water consumption for female groups. Exposure levels of 2.5, 5, or 10 mg/mL delivered average daily doses of approximately 180, 330 or 650 mg tertiary butyl alcohol/kg bw/day.

Hematology: A few minor, sporadic changes that were not considered related to exposure to tertiary butyl alcohol occurred in the hematology parameters.

Urinalysis: A few minor, sporadic changes that were not considered related to exposure to tertiary butyl alcohol occurred in the urinalysis parameters for male groups. Females given 5 or 10 mg/mL demonstrated statistically significant increased urine specific gravities and decreased urine volumes consistent with their decreased water intake. Urine volumes were decreased 56% and 37% in the 10 and 5 mg/mL female dose groups, respectively, while specific gravities were increased 3% and 1%, respectively. The pH in both female dose groups was also significantly lower than controls.

Organ weights: Brain, right kidney and liver were evaluated in 10 animals/group at the 15-month interim sacrifice. At that time, there was a statistically significant decrease in necropsy body weight in the 5 mg/mL male dose group (↓11%) and the 10 mg/mL female dose group (↓13%). Exposed male animals exhibited a slight increase in absolute kidney weights while relative kidney weights of 2.5 and 5 mg/mL males were significantly greater than controls (20%↑ and 15%↑, respectively). There was a statistically significant dose-related increase in absolute and relative kidney weights in 2.5 (8/14% ↑), 5 (18/21% ↑), and 10 mg/mL (22/42% ↑) females compared to controls. Relative brain and liver weights were significantly increased in the 5 mg/mL male group and the 10 mg/L female group.

Gross pathology: no gross lesions reported at interim or final evaluation

Histopathology (non-neoplastic): Effects were limited to the kidneys in both sexes.

At 15-months, chronic progressive nephropathy (CPN) was present in all males; severity was slightly but not statistically significantly increased in all exposed groups. Severity of CPN was significantly increased only in high-dose males at the end of the study (3.0, 3.1, 3.1, 3.3). This differed from female rats who exhibited a statistically significant increase in severity in all dose groups (see below).

Two types of mineralization occurred during the study. Focal tubular mineralization at the corticomedullary junction was observed in control males and some exposed males (versus all females). Incidences were significantly increased in high-dose (26/50, 28/50, 35/50, 48/50) males. Linear papillary mineralization occurred only in exposed male rats, showing a clear dose-response with statistically significant increased incidences of 10%, 48% and 92% in the 1.25, 2.5 and 5 mg/mL groups, respectively. A dose-related increase in incidences and severities in mineralization was also seen at the 15-month sacrifice in the mid- and high-dose (statistically significant at high-dose) group males but no distinction was made for mineralization type.

Renal tubule hyperplasia (synonymous with atypical tubule hyperplasia; ATH, a sequential, preneoplastic stage in the continuum leading to renal tubule adenoma and carcinoma) was found in all male rat groups. Standard evaluation of the original single kidney sections demonstrated a non-statistically significant distribution of ATH of 3/50, 7/50, 6/50 and 6/50 for the 0, 1.25, 2.5 and 5 mg/mL dose-groups, respectively. When results from the single and step sections of kidneys from male rats were combined, the incidence of ATH was 14/50, 20/50, 17/50 and 25/50 for the 0, 1.25, 2.5 and 5 mg/mL doses, respectively; the high-dose was statistically significantly different from controls. By comparison, only a single ATH lesion was observed in one high-dose female.

Other lesions associated with nephropathy at the end of the study included hyperplasia of the transitional cell lining of the renal pelvis in all male groups, which was significantly increased in 2.5 and 5 mg/mL animals (incidences were 25/50, 32/50, 36/50, and 40/50 for the 0, 1.25, 2.5 and 5 mg/mL dose-groups, respectively). There was no progression of transitional epithelial hyperplasia to benign or malignant neoplasms.

Focal tubule mineralization at the “corticomedullary” junction was present in all groups of female rats. There was no significant increase in mineralization over controls, either numbers of animals affected or degree of severity. A second and distinct form of mineralization, linear papillary mineralization, occurred in male rats only. At 15-months, chronic progressive nephropathy (CPN) was present in all females and the severity of nephropathy was slightly increased at higher doses. There was a statistically significant exacerbation of the severity of CPN in all exposed groups of females at the end of the study (1.6, 1.9, 2.3, 2.9). At study termination, renal tubule hyperplasia (synonymous with atypical tubule hyperplasia; ATH), widely accepted as a sequential, preneoplastic stage in the continuum leading to renal tubule adenoma and carcinoma, was limited to minimal severity in one high-dose female. Microscopically, lesions consistent with CPN were thickened tubule and glomerular basement membranes, basophilic foci of regenerating renal tubule epithelium, intratubule protein casts, focal mononuclear inflammatory cell aggregates within areas of interstitial fibrosis and scarring, and glomerular sclerosis. Inflammation of the kidneys, also regarded as part of the nephropathy, was significantly increased in both 5 and 10 mg/mL group female animals at the end of the study. Transitional cell hyperplasia was also significantly increased in 10 mg/mL females (incidences were 0/50, 0/50, 3/50, 17/50 in the 0, 2.5, 5 and 10 mg/mL dose-groups, respectively).

Effect levels

1

Dose descriptor:

LOAEL

Effect level:

1.25 other: mg/ml drinking water

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Under the conditions of this 2-yr drinking water study, there was a dose-dependent statistically significant increase in incidence and severity of mineralization in the kidneys of male F344/N rats in all dose groups.

2

Dose descriptor:

LOAEL

Effect level:

2.5 other: mg/ml drinking water

Based on:

test mat.

Sex:

female

Basis for effect level:

other: Under the conditions of this 2-yr drinking water study, there was a dose-dependent statistically significant exacerbation in the severity of chronic progressive nephropathy in female F344/N rats in all tertiary butyl alcohol-exposed groups.

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

In the 2-year drinking water study in male rats, overall survival rates in the mid- and high-dose male groups were significantly lower than controls and mean body weights were decreased in all male exposure groups. Non-neoplastic microscopic effects in males were found only in the kidney and included a dose-dependent increase in severity of chronic progressive nephropathy (statistically significant in high-dose group), a dose-dependent statistically significant increase in linear papillary mineralization, the presence of renal tubule hyperplasia in all groups including controls (statistically significant in high-dose group), and a significant increase in hyperplasia of the transitional cell lining of the renal pelvis in the mid- and high-dose groups. The principal treatment-related effects in the 2-year drinking water study in female rats were decreased survival, decreased mean body weight gain and mean body weight, and increased incidence of hyperactivity in the high-dose group, and a dose-related decrease in water consumption during year 2 in all dose groups. At the 15-month interim sacrifice, there was a statistically significant increase in absolute and relative kidney weights in all treatment groups; chronic progressive nephropathy was present in all females and severity was significantly increased in all treatment groups by the end of the study. Average severity was not as high as that seen in similarly treated male rats.

The LOAEL for systemic toxicity following oral treatment of F344/N male rats with tertiary butyl alcohol for 2 years was 1.25 mg/mL based on greater incidence and severity of linear papillary mineralization in the kidneys in all treatment groups. The LOAEL for systemic toxicity following oral treatment of F344/N female rats with tertiary butyl alcohol for 2 years was 2.5 mg/mL based on greater severity of chronic progressive nephropathy in all treatment groups.

The only significant non-neoplastic effects observed in male rats following exposure in the drinking water at dose levels up to 288-516 mg/kg bw/day for 2 years were limited to the kidney. Adverse effects observed in all male groups, including controls, included chronic progressive nephropathy, mineralization, and renal tubule hyperplasia. The only non-neoplastic effects observed in female rats following exposure in the drinking water at dose levels up to 587-886 mg/kg bw/day for 2-years were also limited to the kidney. Chronic progressive nephropathy was observed in all female groups, including controls at the 15-month interim evaluation and severity was slightly increased at higher doses. There was a statistically significant exacerbation of severity of CPN in all female dose groups by the end of the study. Chronic progressive nephropathy is a common lesion in this strain of rat and many chemicals have been reported to exacerbate onset and severity. Based on an extensive evaluation of the available literature and their own personal observations, Hard et al. (2009) reported that chronic progressive nephropathy has not been observed in humans. It was also not observed in male or female mice exposed to dose levels of approximately 2000 mg/kg bw/day. In the absence of any other target organ toxicity following lifetime exposure, tertiary butyl alcohol is not classified in male or female rats exposed by the oral route for “Specific Target Organ Toxicity – Repeated Exposure” according to the GHS guidelines.

Executive summary:

In a 2-year chronic toxicity study, tertiary butyl alcohol was administered to 60 F344/N male rats/dose ad libitum in drinking water at dose levels of 0, 1.25, 2.5 and 5 mg/mL and to 60 F344/N female rats/dose at dose levels of 0, 2.5, 5 and 10 mg/mL for 103 weeks. Survival was decreased at the mid- and high-dose levels in males (24% and 20% in the control and low-dose group versus 8% and 4% in the mid- and high-dose groups) while survival was decreased in females at the high-dose level only (34% versus 58% in control group). In males, final mean body weight was 24% less than controls in the high-dose group; low- and mid-dose groups were decreased 15% and 17%, respectively. In females, at the 15-month interim evaluation, necropsy body weight was significantly decreased in the 10 mg/mL group; final mean body weight was 21% lower than the control in the high dose group. In females, there was a statistically significant dose-related increase in absolute and relative kidney weights at all dose levels. There were no gross lesions.

At the 15-month interim evaluation in males, incidences and severities of mineralization (type not specified) of the kidney were greater than controls in the mid- and high-dose groups, chronic progressive nephropathy was present in all males, and severity of nephropathy was slightly but not statistically significantly increased in all exposed groups. By study termination, severity of nephropathy was significantly increased in the high-dose group, incidences of linear papillary mineralization were significantly increased in all dose groups, and there was a dose-related increase in focal renal tubule hyperplasia in all dose groups. These results indicate that, in male rats, the kidney is the target organ for tertiary butyl alcohol repeated exposure toxicity.

In females, microscopic lesions included chronic progressive nephropathy in all groups at 15-months with a statistically significant increase in severity in all exposed groups by the end of the study. Kidney transitional cell hyperplasia was also significantly increased in the high-dose group. These results indicate that, in female rats, the kidney is the target organ for tertiary butyl alcohol repeated exposure toxicity