Physiologically based pharmacokinetic model for ethyl tertiary-butyl ether and tertiary-butyl alcohol in rats: Contribution of binding to α2u-globulin in male rats and high-exposure nonlinear kinetics to toxicity and cancer outcomes.

In cancer bioassays, inhalation, but not drinking water exposure to ethyl tertiary-butyl ether (ETBE), caused liver tumors in male rats, while tertiary-butyl alcohol (TBA), an ETBE metabolite, caused kidney tumors in male rats following exposure via drinking water. To understand the contribution of ETBE and TBA kinetics under varying exposure scenarios to these tumor responses, a physiologically based pharmacokinetic model was developed based on a previously published model for methyl tertiary-butyl ether, a structurally similar chemical, and verified against the literature and study report data. The model included ETBE and TBA binding to the male rat-specific protein α2u-globulin, which plays a role in the ETBE and TBA kidney response observed in male rats. Metabolism of ETBE and TBA was described as a single, saturable pathway in the liver. The model predicted similar kidney AUC0-∞ for TBA for various exposure scenarios from ETBE and TBA cancer bioassays, supporting a male-rat-specific mode of action for TBA-induced kidney tumors. The model also predicted nonlinear kinetics at ETBE inhalation exposure concentrations above ~2000 ppm, based on blood AUC0-∞ for ETBE and TBA. The shift from linear to nonlinear kinetics at exposure concentrations below the concentration associated with liver tumors in rats (5000 ppm) suggests the mode of action for liver tumors operates under nonlinear kinetics following chronic exposure and is not relevant for assessing human risk. Copyright © 2016 The Authors Journal of Applied Toxicology Published by John Wiley & Sons Ltd.

Perfusion imaging with a freely diffusible hyperpolarized contrast agent.

Contrast agents that can diffuse freely into or within tissue have numerous attractive features for perfusion imaging. Here we present preliminary data illustrating the suitability of hyperpolarized (13)C labeled 2-methylpropan-2-ol (also known as dimethylethanol, tertiary butyl alcohol and tert-butanol) as a freely diffusible contrast agent for magnetic resonance perfusion imaging. Dynamic (13)C images acquired in rat brain with a balanced steady-state free precession sequence following administration of hyperpolarized 2-methylpropan-2-ol show that this agent can be imaged with 2-4 s temporal resolution, 2 mm slice thickness, and 700 µm in-plane resolution while retaining adequate signal-to-noise ratio. (13)C relaxation measurements on 2-methylpropan-2-ol in blood at 9.4 T yield T(1) = 46 ± 4s and T(2) = 0.55 ± 0.03 s. In the rat brain at 4.7 T, analysis of the temporal dynamics of the balanced steady-state free precession image intensity in tissue and venous blood indicate that 2-methylpropan-2-ol has a T(2) of roughly 2-4s and a T(1) of 43 ± 24 s. In addition, the images indicate that 2-methylpropan-2-ol is freely diffusible in brain and hence has a long residence time in tissue; this in turn makes it possible to image the agent continuously for tens of seconds. These characteristics show that 2-methylpropan-2-ol is a promising agent for robust and quantitative perfusion imaging in the brain and body.

Tertiary-Butanol: a toxicological review.

Tert-Butanol is an important intermediate in industrial chemical synthesis, particularly of fuel oxygenates. Human exposure to tert-butanol may occur following fuel oxygenate metabolism or biodegradation. It is poorly absorbed through skin, but is rapidly absorbed upon inhalation or ingestion and distributed to tissues throughout the body. Elimination from blood is slower and the half-life increases with dose. It is largely metabolised by oxidation via 2-methyl-1,2-propanediol to 2-hydroxyisobutyrate, the dominant urinary metabolites. Conjugations also occur and acetone may be found in urine at high doses. The single-dose systemic toxicity of tert-butanol is low, but it is irritant to skin and eyes; high oral doses produce ataxia and hypoactivity and repeated exposure can induce dependence. Tert-Butanol is not definable as a genotoxin and has no effects specific for reproduction or development; developmental delay occurred only with marked maternal toxicity. Target organs for toxicity clearly identified are kidney in male rats and urinary bladder, particularly in males, of both rats and mice. Increased tumour incidences observed were renal tubule cell adenomas in male rats and thyroid follicular cell adenomas in female mice and, non-significantly, at an intermediate dose in male mice. The renal adenomas were associated with alpha(2u)-globulin nephropathy and, to a lesser extent, exacerbation of chronic progressive nephropathy. Neither of these modes of action can function in humans. The thyroid tumour response could be strain-specific. No thyroid toxicity was observed and a study of hepatic gene expression and enzyme induction and thyroid hormone status has suggested a possible mode of action.

Refined PBPK model of aggregate exposure to methyl tertiary-butyl ether.

Aggregate (multiple pathway) exposures to methyl tertiary-butyl ether (MTBE) in air and water occur via dermal, inhalation, and oral routes. Previously, physiologically based pharmacokinetic (PBPK) models have been used to quantify the kinetic behavior of MTBE and its primary metabolite, tertiary-butyl alcohol (TBA), from inhalation exposures. However, the contribution of dermal and oral exposures to the internal dose of MTBE and TBA were not characterized well. The objective of this study was to develop a multi-route PBPK model of MTBE and TBA in humans. The model was based entirely on blood MTBE and TBA measurements from controlled human exposures. The PBPK model consists of nine primary compartments representing the lungs, skin, fat, kidney, stomach, intestine, liver, rapidly perfused tissue, and slowly perfused tissue. The MTBE and TBA models are linked by a single metabolic pathway. Although the general structure of the model is similar to previously published models of volatile organic compounds, we have now developed a detailed mathematical description of the lung, skin, and gastrointestinal tract. This PBPK model represents the most comprehensive and accurate description of MTBE and TBA pharmacokinetics in humans to date. The aggregate exposure model application for MTBE can be generalized to other environmental chemicals under this framework given appropriate empirical measurement data.

Amended final report of the safety assessment of t-Butyl Alcohol as used in cosmetics.

t-Butyl Alcohol (t-BuOH) is a tertiary aliphatic alcohol that is used as a solvent or an alcohol denaturant and as a perfume carrier in cosmetics. t-BuOH was reported as an ingredient in 32 formulations of eye makeup, fragrance, and shaving preparations, at concentrations ranging from 0.00001% and 0.3%. There is little acute oral toxicity in animals; e.g., the acute oral LD(50) in rats was 3.0 to 3.7 g/kg. In short-term oral studies in rats, t-BuOH at 2% (w/v) or less in drinking water did not cause gross organ or tissue damage in mice, although weight loss was reported and microscopic damage to livers and kidney and alterations such as centrilobular necrosis, vacuolation in hepatocytes, and loss of hepatic architecture were noted. Subchronic oral dosing with t-BuOH increased the mineralization of the kidney, nephropathy, and urinary bladder transitional cell epithelial hyperplasia in rats; and liver damage, chronic inflammation, hyperplasia of transitional cell epithelium urinary, and proliferative changes including hyperplasia and neoplasia in the thyroid in mice. Male rats exposed to t-BuOH were susceptible to alpha 2mu-globulin nephropathy. t-BuOH (99.9%) was a moderate to severe ocular irritant to rabbits and caused mild to moderate dermal irritation to rabbits. It was not considered to be a primary dermal irritant to rabbits. In animal studies, fetotoxicity generally increased with concentration, and fetal weights were slightly depressed at concentrations of 0.5% to 1% t-BuOH. t-BuOH produced a significant increase in the number of resorptions per litter. There was also a significant decrease in the number of live fetuses per litter. t-BuOH reduced maternal weight gain, litter sizes, birth weights, and weights at weaning, and increased perinatal and postnatal mortality. t-BuOH was not mutagenic in several bacterial and mammalian test systems. The principal effects from 2 years of exposure to t-BuOH in drinking water (up to 10 mg/ml for rats and 20 mg/ml for mice) were proliferative lesions (hyperplasia, adenoma, and carcinoma) in the kidneys of exposed male rats, and nephropathy in all exposed groups of female rats. There was some evidence of carcinogenic activity, but it was not consistent between species, sexes, or doses. A repeat-insult patch test (RIPT) test showed no potential for eliciting either dermal irritation or sensitization by 100% t-BuOH. Dermatitis can result from dermal exposure of humans to t-BuOH. In consideration of these data, it was concluded that t-BuOH was (at most) a weak carcinogen and unlikely to have significant carcinogenic potential as currently used in cosmetic formulations. In addition, the renal tubule effects found in male rats were likely an effect of alpha 2mu-globulin. In consideration of the reproductive and developmental toxicity data, the increased incidence of still births occurred at high exposure levels and was likely secondary to maternal toxicity. Based on the available animal and clinical data in this report, it was concluded that t-BuOH is safe as used in cosmetic products.

Microbial adaptation to biodegradation of tert-butyl alcohol in a sequencing batch reactor.

This study demonstrates the utility of the sequencing batch reactor (SBR) to adapt microorganisms towards biological removal of tert-butyl alcohol (TBA). The reactor was inoculated with activated sludge and fed with TBA as the sole carbon source. Start-of-cycle TBA concentrations were initially set at 100 mgL(-1) with a cycle time of 24 h and a volumetric exchange ratio of 50% to maintain a TBA loading rate of not more than 100 mgL(-1)d(-1). Step increases in TBA loading rates up to 600 mgL(-1)d(-1) were achieved by first raising the start-of-cycle TBA concentration to 150 mgL(-1) on day 90 and subsequently by reducing the cycle time from 24 to 12, 8 and 6h on days 100, 121 and 199, respectively. This acclimation strategy favored the retention of increasingly higher densities of well-adapted microbial populations in the reactor. The increases in TBA loading produced better settling biomass and higher biomass concentrations with higher specific TBA biodegradation rates. Effluent TBA concentrations were consistently below the detection limit of 25 microgL(-1). The use of progressively shorter cycle times created selection pressures that fostered the self-immobilization of the reactor microorganisms into aerobic granules which first appeared on day 125. Specific TBA biodegradation rates in the granules followed the Haldane model for substrate inhibition, and peaked at 13.8 mgTBAgVSS(-1)h(-1) at a TBA concentration of 300 mgL(-1). Denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA genes from granules sampled between days 220 and 247 confirmed the existence of a highly stable microbial community with members belonging to the alpha, beta and delta subdivisions of Proteobacteria and the Cytophaga-Flavobacteria-Bacteroides (CFB) group.

Toxicokinetics of methyl tert-butyl ether and its metabolites in humans after oral exposure.

Methyl tert-butyl ether (MTBE) is widely used as an additive to gasoline, to increase oxygen content and reduce tailpipe emission of pollutants. Widespread human exposure to MTBE may occur due to leakage of gasoline storage tanks and a high stability and mobility of MTBE in ground water. To compare disposition of MTBE after different routes of exposure, its biotransformation was studied in humans after oral administration in water. Human volunteers (3 males and 3 females, identical individuals, exposures were performed 4 weeks apart) were exposed to 5 and 15 mg 13C-MTBE dissolved in 100 ml of water. Urine samples from the volunteers were collected for 96 h after administration in 6-h intervals and blood samples were taken in intervals for 24 h. In urine, MTBE and the MTBE-metabolites tert-butanol (t-butanol), 2-methyl-1,2-propane diol, and 2-hydroxyisobutyrate were quantified, MTBE and t-butanol were determined in blood samples and in exhaled air in a limited study of 3 male volunteers given 15 mg MTBE in 100 ml of water. MTBE blood concentrations were 0.69 +/- 0.25 microM after 15 mg MTBE and 0.10 +/- 0.03 microM after 5 mg MTBE. MTBE was rapidly cleared from blood with terminal half-lives of 3.7 +/- 0.9 h (15 mg MTBE) and 8.1 +/- 3.0 h (5 mg MTBE). The blood concentrations of t-butanol were 1.82 +/- 0.63 microM after 15 mg MTBE and 0.45 +/- 0.13 microM after 5 mg MTBE. Approximately 30% of the MTBE dose was cleared by exhalation as unchanged MTBE and as t-butanol. MTBE exhalation was rapid and maximal MTBE concentrations (100 nmol/l) in exhaled air were achieved within 10-20 min. Clearance of MTBE by exhalation paralleled clearance of MTBE from blood. T-butanol was cleared from blood with half-lives of 8.5 +/- 2.4 h (15 mg MTBE) and 8.1 +/- 1.6 h (5 mg MTBE). In urine samples, 2-hydroxyisobutyrate was recovered as major excretory product, t-butanol and 2-methyl-1,2-propane diol were minor metabolites. Elimination half-lives for the different urinary metabolites of MTBE were between 7.7 and 17.8 h. Approximately 50% of the administered MTBE was recovered in urine of the volunteers after both exposures, another 30% was recovered in exhaled air as unchanged MTBE and t-butanol. The obtained data indicate that MTBE-biotransformation and excretion after oral exposure is similar to inhalation exposure and suggest the absence of a significant first-pass metabolism of MTBE in the liver after oral administration.

Physiologically based toxicokinetic modeling of inhaled ethyl tertiary-butyl ether in humans.

A physiologically based toxicokinetic (PBTK) model was developed for evaluation of inhalation exposure in humans to the gasoline additive, ethyl tertiary-butyl ether (ETBE). PBTK models are useful tools to relate external exposure to internal doses and biological markers of exposure in humans. To describe the kinetics of ETBE, the following compartments were used: lungs (including arterial blood), liver, fat, rapidly perfused tissues, resting muscles, and working muscles. The same set of compartments and, in addition, a urinary excretion compartment were used for the metabolite tertiary-butyl alcohol (TBA). First order metabolism was assumed in the model, since linear kinetics has been shown experimentally in humans after inhalation exposure up to 50 ppm ETBE. Organ volumes and blood flows were calculated from individual body composition based on published equations, and tissue/blood partition coefficients were calculated from liquid/air partition coefficients and tissue composition. Estimates of individual metabolite parameters of 8 subjects were obtained by fitting the PBTK model to experimental data from humans (5, 25, 50 ppm ETBE, 2-h exposure; Nihlén et al., Toxicol. Sci., 1998; 46, 1-10). The PBTK model was then used to predict levels of the biomarkers ETBE and TBA in blood, urine, and exhaled air after various scenarios, such as prolonged exposure, fluctuating exposure, and exposure during physical activity. In addition, the interindividual variability in biomarker levels was predicted, in the eight experimentally exposed subjects after a working week. According to the model, raising the work load from rest to heavy exercise increases all biomarker levels by approximately 2-fold at the end of the work shift, and by 3-fold the next morning. A small accumulation of all biomarkers was seen during one week of simulated exposure. Further predictions suggested that the interindividual variability in biomarker levels would be higher the next morning than at the end of the work shift, and higher for TBA than for ETBE. Monte Carlo simulations were used to describe fluctuating exposure scenarios. These simulations suggest that ETBE levels in blood and exhaled air at the end of the working day are highly sensitive to exposure fluctuations, whereas ETBE levels the next morning and TBA in urine and blood are less sensitive. Considering these simulations, data from the previous toxicokinetic study and practical issues, we suggest that TBA in urine is a suitable biomarker for exposure to ETBE and gasoline vapor.

Biotransformation of 12C- and 2-13C-labeled methyl tert-butyl ether, ethyl tert-butyl ether, and tert-butyl alcohol in rats: identification of metabolites in urine by 13C nuclear magnetic resonance and gas chromatography/mass spectrometry.

The biotransformation of the fuel oxygenates methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) was studied in rats after inhalation exposure; the biotransformation of the initial metabolite of these ethers, tert-butyl alcohol, was studied after oral gavage. To study ether metabolism, rats were exposed for 6 h to initial concentrations of 2000 ppm of MTBE or ETBE, respectively [2-13C]MTBE and [2-13C]ETBE. Urine was collected for 48 h after the end of the exposure, and urinary metabolites were identified by 13C NMR (13C-labeled ethers) and gas chromatography/mass spectrometry (GC/MS) (12C- and 13C-labeled ethers). To study tert-butyl alcohol metabolism, rats were dosed either with tert-butyl alcohol at natural carbon isotope ratio or with 13C-enriched tert-butyl alcohol (250 mg/kg of body weight), urine was collected, and metabolites were identified by NMR and GC/MS. tert-Butyl alcohol was identified as a minor product of the biotransformation of MTBE and ETBE. In addition, small amounts of a tert-butyl alcohol conjugate, likely a glucuronide, were present in the urine of the treated animals. Moreover, the mass spectra obtained indicate the presence of small amounts of [13C]acetone in the urine of [13C]MTBE and [13C]ETBE-treated rats. 2-Methyl-1,2-propanediol, 2-hydroxyisobutyrate, and another unidentified conjugate of tert-butyl alcohol, most probably a sulfate, were major urinary metabolites of MTBE and ETBE as judged by the intensities of the NMR signals. In [13C]-tert-butyl alcohol-dosed rats, [13C]acetone, tert-butyl alcohol, and its glucuronide represented minor metabolites; as with the ethers, 2-methyl-1,2-propanediol, 2-hydroxyisobutyrate, and the presumed tert-butyl alcohol sulfate were the major metabolites present. In one human individual given 5 mg/kg [13C]-tert-butyl alcohol orally, 2-methyl-1,2-propanediol and 2-hydroxyisobutyrate were major metabolites in urine detected by 13C NMR analysis. Unconjugated tert-butyl alcohol and tert-butyl alcohol glucuronide were present as minor metabolites, and traces of the presumed tert-butyl alcohol sulfate were also present. Our results suggest that tert-butyl alcohol formed from MTBE and ETBE is intensively metabolized by further oxidation reactions. Studies to elucidate mechanisms of toxicity for these ethers to the kidney need to consider potential toxicities induced by these metabolites.

A physiologically-based pharmacokinetic model assessment of methyl t-butyl ether in groundwater for a bathing and showering determination.

Methyl t-butyl ether (MTBE) is a gasoline additive that has appeared in private wells as a result of leaking underground storage tanks. Neurological symptoms (headache, dizziness) have been reported from household use of MTBE-affected water, consistent with animal studies showing acute CNS depression from MTBE exposure. The current research evaluates acute CNS effects during bathing/showering by application of physiologically-based pharmacokinetic (PBPK) techniques to compare internal doses in animal toxicity studies to human exposure scenarios. An additional reference point was the delivered dose associated with the acute Minimum Risk Level (MRL) for MTBE established by the Agency for Toxic Substances and Disease Registry. A PBPK model for MTBE and its principal metabolite, t-butyl alcohol (TBA) was developed and validated against published data in rats and humans. PBPK analysis of animal studies showed that acute CNS toxicity after MTBE exposure can be attributed principally to the parent compound since the metabolite (TBA) internal dose was below that needed for CNS effects. The PBPK model was combined with an exposure model for bathing and showering which integrates inhalation and dermal exposures. This modeling indicated that bathing or showering in water containing MTBE at 1 mg/L would produce brain concentrations approximately 1000-fold below the animal effects level and twofold below brain concentrations associated with the acute MRL. These findings indicate that MTBE water concentrations of 1 mg/L or below are unlikely to trigger acute CNS effects during bathing and showering. However, MTBE's strong odor may be a secondary but deciding factor regarding the suitability of such water for domestic uses.

Pharmacokinetics of tertiary butyl alcohol in male and female Fischer 344 rats.

Tertiary butyl alcohol (TBA) is a small aliphatic alcohol with multiple industrial and scientific uses. A comprehensive pharmacokinetic profile for TBA has not been determined in rats. The purpose of this study was to fully characterize the pharmacokinetics of TBA in male and female F-344 rats following intravenous administration of 37.5, 75, 150 and 300 mg/kg TBA. TBA was observed to undergo a rapid distribution phase followed by a slower elimination phase. The steady-state volume of distribution for TBA was roughly 4.5 times greater than total body water, and the clearance was lower than the estimated glomerular filtration rate. The elimination of TBA appears to saturate at higher doses, as evidenced by a disproportional increase in area under the concentration-time curve and decreased rate of clearance.

NTP technical report on toxicity studies of t-butyl alcohol (CAS No. 75-65-0). Administered by inhalation to F344/N rats and B6C3F1 mice.

t-Butyl alcohol is widely used in the manufacture of perfumes and a variety of cosmetics. It is also used as a raw material in the production of isobutylene, which may be used to produce methyl tertiary butyl ether, a common gasoline additive, or to produce butyl elastomers used in the production of automobile tires. The National Cancer Institute nominated t-butyl alcohol to the NTP for study as a result of a review of chemicals found in drinking water. In addition to the high annual production and the potential for occupational exposure, there is also a potential for human exposure to t-butyl alcohol by the inhalation route from its use as an additive in unleaded gasoline. Therefore, toxicity studies of t-butyl alcohol were conducted in male and female F344/N rats and B6C3F1 mice by whole-body inhalation. Animals were evaluated for hematology, clinical chemistry, urinalysis, reproductive toxicity, and histopathology. The genetic toxicity of t-butyl alcohol was assessed by testing the ability of the chemical to induce mutations in various strains of Salmonella typhimurium and L5178Y mouse lymphoma cells or sister chromatid exchanges and chromosomal aberrations in cultured Chinese hamster ovary cells, and by measuring the frequency of micronucleated erythrocytes in rat bone marrow and mouse peripheral blood. In the 18-day inhalation studies, groups of five male and five female rats and mice were exposed to t-butyl alcohol by inhalation at concentrations of 450, 900, 1,750, 3,500, and 7, 000 ppm for 6 hours per day, 5 days per week, for 12 exposure days. All rats and mice exposed to 7,000 ppm were killed moribund following a single 6-hour exposure. One 3,500 ppm male mouse died on day 3. Final mean body weights of 3,500 ppm male and female rats were significantly lower than those of the controls. Final mean body weights and body weight gains of all other exposed groups were similar to those of the controls. In animals exposed to 3.500 ppm, the thymus weights of male and female rats and female mice were less than those of the controls. The liver weights of male and female mice exposed to 3,500 ppm were greater than those of the controls. No grss or microscopic lesion were present in rats or mice. In the 13-week inhalation studies, groups of 10 male and 10 female rats and mice were exposed to t-butyl alcohol at concentrations of 0, 135, 270, 540, 1,080, and 2,100 ppm for 6 hours per day, 5 days per week, for 13 weeks. One 2,100 ppm and five 1,080 ppm male mice died before the end of the studies. The final mean body weight of 2,100 ppm female mice and the mean body weight gains of 1,080 and 2,100 ppm female mice were significantly lower than those of the controls. Clinical findings of toxicity in the 1,080 ppm male mice died during the studies included rough coats and emaciated appearance, hypoactivity, and prostration. Minimal decreases in hematocrit values, hemoglobin concentrations, and erythrocyte counts occurred in the 1,080 and 2,100 ppm male rats at week 13. Hemoglobin concentrations and/or hematocrit values were also minimally decreased in male rats in the lower exposure groups. At week 13, a minimal decrease in urine pH occurred in the 1,080 ppm female and 2,100 ppm male and female rats. Neutrophilia occurred in the 2,100 ppm male mice. Organ weight differences in exposed rats included increased absolute and relative kidney weights of 1,080 ppm males and 2,100 ppm males and females and increased relative liver weights of 1,080 and 2,100 ppm females. There were no treatment-related gross findings in male or female rats or mice; no microscopic lesion occurred in female rats or male or female mice that survived to the end of the study. In male rats, there was an exposure concentration-related increase in the severity of chronic nephropathy. Splenic lymphoid depletion was present in male mice that died during the studies; this lesion was presumed to be secondary to stress. t-butyl alcohol produced no adverse effects on reproductive parameters in male or female rats or mice. The results of all tests of t-butyl alcohol for induction of genetic damage in vitro and in vivo were negative. In vitro, t-butyl alcohol was negative in Salmonella typhimurium and mouse lymphoma cell mutation test, and it did not induce sister chromatid exchanges or chromosomal aberrations in cultured Chinese hamster ovary cells. These in vitro studies were conducted with and without metabolic activation (S9). In vivo, no increase in the frequency of micronucleated erythrocytes was observed in peripheral blood samples from mice administered t-butyl alcohol in drinking water for 13 weeks. Also, induction or micronucleated erythrocytes was noted in bone marrow cells of rats administered t-butyl alcohol by intraperitoneal injection. In summary, inhalation exposure of rats and mice to t-butyl alcohol resulted in deaths following a single 7,000 ppm exposure and clinical findings of alcohol toxicity (hyper- and hypoactivity, ataxia) at concentrations of 900 ppm and greater in rats and 1,750 ppm and greater in mice. In 13-week studies at concentrations up to 2,100 ppm, only one death (that of a 2,100 ppm mouse) was attributed to chemical exposure. The most notable evidence of toxicity at the end of 13 weeks was limited to males and consisted of increased kidney weights, which correlated microscopically to increased severity of chronic nephropathy. Reproductive parameters in male and female rats and mice were unaffected after 13 weeks of exposure, and the results of all tests for genetic toxicity were negative.