Neurotoxicological evaluation of methyl tertiary-butyl ether in rats.

Methyl tertiary-butyl ether (MTBE) is an oxygenate that is added to gasoline to boost octane and enhance combustion, thereby reducing carbon monoxide and hydrocarbon tailpipe emissions. The acute and subchronic neurotoxicity of MTBE were evaluated in rats using a functional observation battery (FOB), measures of motor activity (MA) and a neuropathological evaluation. In the acute study, rats were exposed once to 0, 800, 4000 or 8000 ppm MTBE by inhalation for 6 h and then evaluated three times over a 24-h period. In the FOB evaluations, treatment-related effects were seen at the 1-h session immediately following exposure and were indicative of transient central nervous system (CNS) depression. Effects were most apparent in the high-dose group (8000 ppm) but were also evident to a lesser extent in the mid-dose (4000 ppm) group. Labored respiration, ataxia, duck-walk gait and decreases in muscle tone, hind-limb grip strength and treadmill performance were the most frequently noted findings. No significant effects were observed in the FOB when testing was conducted at 6 h and 24 h post-exposure. The pattern of motor activity measured in the different dose groups following exposure was also in keeping with a reversible CNS-depressant effect of MTBE. In the subchronic study, rats were exposed to 0, 800, 4000 or 8000 ppm MTBE for 6 h a day, 5 days per week, for 13 weeks. No persistent or cumulative effects on neurobehavioral function were found. Body weights and absolute brain weights were reduced in the 8000 ppm group, however there were no differences among groups when brain weight was expressed relative to body weight. No histopathological changes were noted in the brains or peripheral nervous tissues of MTBE-exposed animals. In summary, MTBE produced signs of acute reversible CNS depression following exposure to 8000 ppm and, to a lesser extent, to 4000 ppm vapor. The no-observed-adverse-effect level for these effects was 800 ppm in the present study. No persistent or cumulative neurotoxic effects were observed following exposure to MTBE at concentrations up to 8000 ppm for 13 weeks.

Health effects of inhaled tertiary amyl methyl ether and ethyl tertiary butyl ether.

Government specifications on the oxygen content of motor gasoline sold in certain areas of the USA have resulted in commercialization of the oxygenate fuel additives tertiary amyl methyl ether (TAME) and ethyl tertiary butyl ether (ETBE). TAME and ETBE were evaluated in 4-week rat inhalation studies sponsored by Amoco Corporation. Target vapor concentrations were 0, 500, 2000, or 4000 ppm for 6 h per day, 5 days per week, for 4 weeks. TAME exposure at 4000 ppm resulted in 25% mortality, apparently as a consequence of severe CNS depression. Body weight gain was decreased in the TAME high dose male rats. In contrast, no ETBE exposed animals died during the study and no changes in body weight gain were observed. Significant effects on functional observational battery (FOB) parameters were only found in the TAME high and mid-dose groups immediately after exposure. All affected FOB parameters were normal by the next day. Both TAME and ETBE exposures significantly increased relative liver weights in the high and mid-dose groups. However, no treatment-related histopathologic findings were noted for either compound. Clinical chemistry and hematology findings were absent with ETBE exposure and minimal with TAME exposure. The results indicate that 500 ppm was a NOAEL for both compounds in these studies.

Genotoxicity and twenty-eight-day subchronic toxicity studies on tertiary amyl methyl ether.

Tertiary amyl methyl ether (TAME) is an oxygenate with a potential role as a component in reformulated gasolines. The genotoxic potential of TAME was assessed in an Ames assay and a mouse micronucleus assay. The Ames assay was carried out using five standard salmonella strains and doses ranging from 100 to 10,000 micrograms per plate. Tertiary amyl methyl ether was not mutagenic in any of the strains, either with or without metabolic activation. In the micronucleus assay, mice were given a single intraperitoneal injection of TAME at doses of 0.15, 0.375 or 0.75 g kg-1. Bone marrow samples were collected and evaluated for micronucleus formation at 24, 48 and 72 h after dosing. No elevation in micronucleus frequency was observed at any dose or at any of the collection times. Thus, TAME was not clastogenic to mouse bone marrow under the conditions of this study. Preliminary test data indicated that the acute oral LD50 for TAME in Sprague-Dawley rats was ca. 2.1 g kg-1. In the 28-day subchronic study, Sprague-Dawley rats of both sexes were dosed orally with vehicle, 0.125, 0.5 or 1.0 g kg-1 day-1 TAME in corn oil at a dose volume of 2 ml/kg-1. Dosing continued 7 days a week for a period of 28 days. Deaths of two out of 10 animals in the high-dose group (1 g kg-1 day-1) appeared to be compound related. Food consumption and body weights were reduced in the high-dose male group relative to controls; otherwise, clinical observations were minimal.(ABSTRACT TRUNCATED AT 250 WORDS)

Two-generation reproduction study on commercial hexane solvent.

The reproductive effects of inhalation exposure to commercial hexane vapors were evaluated in Sprague-Dawley rats. Males and females were exposed to commercial hexane vapor at target concentrations of 0, 900, 3000 or 9000 ppm for 6 h a day, 5 or 7 days a week, over two generations. In addition to pre-breed exposures of 10 weeks' duration, exposures continued through mating, gestation and lactation. At both the F0 breed to produce F1 litters and the F1 breed to produce F2 litters, reproductive parameters were unaffected by commercial hexane exposure. The mating, fertility and gestational indices, as well as litter size and postnatal survival, were not significantly different between exposure groups. However, reductions in body weight and body weight gain were observed in both F1 and F2 litters exposed to 9000 ppm. Effects on body weight were not observed in offspring exposed to the two lower concentrations of commercial hexane. Histopathological examination of selected tissues revealed hyaline droplet nephropathy in adult F0 and F1 males exposed to 9000 ppm. This finding was anticipated and is not believed to be relevant for the assessment of human health effects. No other treatment-related histopathological lesions were observed. Thus, exposure of rats to commercial hexane for two generations resulted in reduced body weight gains at 9000 ppm but no adverse effects on reproduction. These findings suggest that occupational exposure to commercial hexane vapors at currently recommended threshold limit value concentrations (i.e. TLV for n-hexane is 50 ppm and TLV for other hexane isomers is 500 ppm) should not pose a reproductive hazard.

Cytogenetic studies on commercial hexane solvent.

Commercial hexane is a solvent mixture of six-carbon isomers, consisting principally of n-hexane, 3-methylpentane, methylcyclopentane and 2-methylpentane. The potential of commercial hexane to produce chromosome aberrations was evaluated in both an in vitro assay using Chinese hamster ovary (CHO) cells and an in vivo cytogenetics assay using Sprague-Dawley rats. The CHO cells were exposed to media containing commercial hexane at concentrations of 0.014-0.42 microliters ml-1 in the presence and absence of an S-9 activation mixture. Cellular toxicity was observed at the higher dose levels, but no increase in chromosome aberrations was observed in either the non-activated or S-9-activated systems. For the in vivo cytogenetics assay, rats were exposed nose-only for 6 h per day for 5 consecutive days to commercial hexane vapor at target concentrations of 900, 3000 and 9000 ppm. Bone marrow cells were collected at 6 and 24 h after the midpoint of the last exposure. Metaphase cells were examined microscopically for chromosome aberrations. No statistically significant increases in aberrant cells were observed in the commercial hexane-exposed animals of any dose group at either of the bone marrow harvest times. In conclusion, commercial hexane did not produce chromosomal mutations under the conditions of these studies.

Toxicology update isoparaffinic hydrocarbons: a summary of physical properties, toxicity studies and human exposure data.

The Isoparaffins covered in this manuscript are branched aliphatic hydrocarbons with a carbon skeleton length ranging from approximately C10 to C15. They are used in the manufacture of liquid imaging toners, paint formulations, charcoal lighter fluid, furniture polishes and floor clearners. Potential exposure exists in the petroleum, printing and paint industries. Isoparaffins have a very low order of acute toxicity, being practically non-toxic by oral, dermal and inhalation routes. However, aspiration of liquid isoparaffins into the lungs during oral ingestion could result in severe pulmonary injury. Dermally, isoparaffins have produced slight to moderate irritation in animals and humans under occluded patch conditions where evaporation cannot freely occur. However, they are not irritating in non-occluded tests, which are a more realistic simulation of human exposure. They have not been found to be sensitizers in guinea pig or human patch testing. However, occasional rare idiosyncratic sensitization reactions in humans have been reported. Instillation of isoparaffins into rabbit eyes produces only slight irritation. Several studies have evaluated sensory irritation in laboratory animals or odor or sensory response in humans. When evaluated by a standard procedure to assess upper airway irritation, isoparaffins did not produce sensory irritation in mice exposed to up to 400 ppm isoparaffin in air. Human volunteers were exposed for six hours to 100 ppm isoparaffin. The subjects were given a self-administered questionnaire to evaluate symptoms, which included dryness of the mucous membranes, loss of appetite, nausea, vomiting, diarrhea, fatigue, headache, dizziness, feeling of inebriation, visual disturbances, tremor, muscular weakness, impairment of coordination or paresthesia. No symptoms associated with solvent exposure were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Subchronic toxicity evaluation of tridecyl acetate in rats.

Tridecyl acetate was administered to male and female Sprague-Dawley rats by oral gavage, 5 days per week for 13 weeks (90 days). Treated rats received daily doses of 0.1, 0.5, or 1.0 g/kg/day and control rats received distilled water at a dose of 1.0 g/kg/day. After 45 days an interim termination was made to evaluate potential hematologic or hepatic effects of tridecyl acetate. Blood samples were collected for routine hematology and serum chemistry determinations and liver tissue was obtained for histological examination. After 90 days all animals were necropsied. Blood samples were obtained and selected organs were weighed and prepared for histological examination. Treatment-related effects observed in the mid and high dose groups consisted of (1) increased liver weights and/or liver/body weight ratios in both sexes at the interim and 13 week termination, (2) increased kidney weights and/or kidney/body weight ratios in both sexes at the terminal necropsy, (3) histopathologic evidence of hydrocarbon nephropathy in males, and (4) a slight decrease in serum glucose levels in male rats at both the interim and terminal necropsies. The increases in liver weight are believed to be a normal physiological response to a chemical challenge. The nephropathy produced by tridecyl acetate is characteristic of that produced by a diverse group of hydrocarbons and, to date, appears to be limited to male rats. The low dose in this study was a no observed effect level. These results are indicative of an overall low degree of systemic toxicity following subchronic oral administration of tridecyl acetate at doses up to 1 g/kg body weight.

Evaluation of the teratogenic potential of octyl acetate in rats.

Octyl acetate (CAS RN 108419-32-5) was administered via oral gavage to pregnant Sprague-Dawley rats on Gestation Days 6 through 15 at dose levels of 0, 0.1, 0.5, and 1.0 g/kg. The dams were weighed and observed for clinical signs of toxicity during pregnancy, and food consumption was measured. On Gestation Day 20 the dams were sacrificed and the fetuses were examined for external, visceral, and skeletal malformations and variations. The mid- and high-dose levels resulted in maternal toxicity as evidenced by reductions in body weight gain and food consumption. There were no statistically significant effects on embryo-fetal lethality or fetal growth for any treatment group. The number of litters with at least one malformed fetus and the mean percentage of the litter malformed were significantly (p less than 0.05) elevated in the high-dose group only. The results of the present study demonstrate that octyl acetate produced some evidence of developmental toxicity at a dose (1.0 g/kg) that was maternally toxic. Developmental toxicity was not observed at the maternally toxic 0.5 g/kg dose level or the maternally nontoxic dose level (0.1 g/kg). Therefore, these data indicate that octyl acetate is not a selective developmental toxicant in the rat.

The dermal carcinogenic potential of unrefined and hydrotreated lubricating oils.

Unrefined lubricating oils contain relatively high levels of polycyclic aromatic hydrocarbons (PAH) and have been shown to induce tumors in mouse skin. Exxon has developed a new method of refining these materials, a severe hydrotreatment process that is optimized for PAH removal. The specific objectives of the current study were to assess PAH reduction and then to evaluate directly the dermal carcinogenic potential of the materials that spanned the range of products produced by this method. The test samples included unrefined light and heavy vacuum distillates from a naphthenic crude oil, as well as the corresponding severely hydrotreated products. Two sets of samples were prepared to assess the effects of various operating parameters in the reactor. Additionally, positive (benzo[a]pyrene), negative (white mineral oil) and vehicle (toluene) control groups were included to assess the sensitivity and specificity of the bioassay. Each sample was applied in twice-weekly aliquots to the backs of 40 male C3H mice. In the analytical studies, significant reductions in the levels of several specific PAH were demonstrated. In the dermal carcinogenesis studies, the unrefined oils and the positive control induced tumors and also significantly reduced survival. None of the mice treated with severely hydrotreated oils or with the negative or vehicle controls developed skin tumors, and survival of these mice was not significantly different from the control. Thus, the data demonstrated that this new, severe hydrotreatment process was an effective means of converting carcinogenic feedstocks to non-carcinogenic products.

A subchronic toxicity study of octyl acetate in rats.

The subchronic toxicity of octyl acetate was assessed following its administration to rats via oral gavage, 5 days per week for 13 weeks. Treated rats received undiluted octyl acetate at doses of 0.1, 0.5, or 1.0 g/kg. Control rats received distilled water at a dose of 1.0 g/kg. An interim termination was made after 45 days of dosing at which time five animals per sex per group were terminated and necropsied. Blood samples were collected and liver tissues were prepared for histological examination. After 13 weeks of dosing all animals were terminated and necropsied. Blood samples were obtained and selected organs were weighed and prepared for subsequent histological examination. Several treatment-related effects were observed in the high-dose group (1.0 g/kg) animals. These effects included slight reductions in body weight and food consumption, increased liver and kidney weights, and evidence of hydrocarbon nephropathy in high-dose males only. The significance of these observations is discussed in the report. With the exception of increased liver weights in the mid-dose group, no other significant treatment-related effects were observed in the mid- or low-dose groups of animals. It is believed that the increases in liver weight which were observed are a compensatory response to an increased metabolic load, and not a reflection of true hepatotoxicity. The results of this study indicated that octyl acetate possessed an overall low degree of systemic toxicity when administered orally to rats for 13 weeks.

Forebrain damage in chick embryos exposed to carbon monoxide.

The consequences of CO-induced hypoxia to the forebrain of seven-day-old chick embryos were investigated. Exposure of embryos to CO for three hours caused hemorrhages in developing forebrain areas. Carboxyhemoglobin levels reached about 50% in the embryos. Two weeks later, about one day prior to hatching, morphology of large neurons in the paleostriatum primitivum was evaluated. In Golgi-stained sections examined under the light microscope, the CO-exposed chicks were found to have reduced branching of the dendritic tree. In addition, the nuclear size of the paleostriatum primitivum neurons was reduced in the CO-exposed chicks. These findings in chick embryos are comparable to results in previous experiments with fetal rats.

Caudate morphology and behavior of rats exposed to carbon monoxide in utero.

Postnatal morphologic damage was found in the caudate nucleus of rats exposed 2 or 3 h to carbon monoxide on gestational day 15. There were gross abnormalities in the form of ecotopic swellings of caudate tissue into the lateral ventricles. The incidence of caudate ectopias was about 20% in rats exposed 2 h as fetuses and 70% from 3 h of exposure. In addition, in the body of the caudate the number of dendritic branches was reduced in Golgi type II neurons. Postnatal behavior of the exposed rats was not significantly altered in a series of behavioral tests of motor function. Growth rate was not retarded. The failure to detect behavioral changes may be due to insensitivity of these tests detecting functional damage or to compensation by the developing brain, resulting in normal function.