Biochemical effects of methyl tertiary-butyl ether in extended vapour exposure of rats

Mutagenicity evaluation of methyl tertiary- butyl ether in multiple tissues of transgenic rats following whole body inhalation exposure

Methyl tertiary-butyl ether (MTBE) is used as a component of motor vehicle fuel to enhance combustion efficiency and to reduce emissions of carbon monoxide and nitrogen oxides. Although MTBE was largely negative in the in vitro and in vivo genotoxicity studies, isolated reports of positive findings along with the observation of tumors in the rat cancer bioassays raised concern for its in vivo mutagenic potential. To investigate this, transgenic male Big Blue Fischer 344 rats were exposed to 0 (negative control), 400, 1000, and 3000 ppm MTBE via whole body inhalation for 28 consecutive days, 6 h/day. Mutant frequencies (MF) at the cII locus of the transgene in the nasal epithelium (portal of entry tissue), liver (site of primary metabolism), bone marrow (rapidly proliferating tissue), and kidney (tumor target) were analyzed (5 rats/exposure group) following a 3-day post-exposure manifestation period. MTBE did not induce a mutagenic response in any of the tissues investigated. The adequacy of the experimental conditions to detect induced mutations was confirmed by utilizing tissue samples from animals treated with the known mutagen ethyl nitrosourea. These data provide support to the conclusion that MTBE is not an in vivo mutagen and male rat kidney tumors are not likely the result of a mutagenic mode of action.

Glutaminase 1 isoform up-regulation associated with lipid metabolism disorder induced by methyl tertiary-butyl ether in male rats

Methyl tertiary-butyl ether (MTBE) is a new unleaded gasoline additive, which is considered to be associated with abnormal lipid metabolism in many studies, but the metabolic characteristics and mechanism are still unclear. To observe the characteristics of lipid metabolism induced by MTBE and possible pathways, 21 male Wistar rats got intragastric administration for 24 weeks. The serum lipid metabolism indexes and metabolites were analyzed separately by a biochemical analyzer and untargeted metabolomics. And found that serum high-density lipoprotein cholesterol (HDL-C) levels in the exposure group were significantly reduced, and serum very low-density lipoprotein (VLDL) levels were significantly increased. In untargeted metabolomics, 190 differential metabolites were obtained. Among them, 23 metabolites were found to show the same trend in MTBE exposure groups, which might play a key role in systemic energy metabolism. Further metabolic pathways analysis showed that D-Glutamine, D-glutamate metabolism, and the other three pathways were affected by MTBE significantly. Therefore, we evaluated serum glutamine and glutamate levels and found that MTBE exposure significantly reduced glutamine levels and increased glutamate levels in rat serum and L-02 cells. Further, the key regulatory gene of glutamine metabolism, glutaminase 1 isoform (GLS1), was significantly up-regulated in rat liver and L-02 cells exposed to MTBE. While the effect of glutamine and glutamate metabolism induced by MTBE could be weakened by BPTES, an antagonist of GLS1. In conclusion, our results indicated that MTBE exposure could change the level of glutamine metabolism by promoting GLS1 expression and ultimately lead to abnormal lipid metabolism.

Fourteen-and Ninety-Day Oral Toxicity Studies of Methyl Tertiary-Butyl Ether in Sprague-Dawley Rats

Male and female Sprague-Dawley rats were gavaged with methyl tertiary-butyl ether (MtBE) for 14 or 90 days to evaluate subacute and subchronic toxicity. Five daily dose levels ranged from 0 to 1428 mg/kg body weight for the 14 day study and 0 to 1200 mg/kg body weight for the 90-day exposure. Controls received the corn oil vehicle. At or above dose levels of 1200 mg/kg, MtBE-induced anesthesia lasted about 2 h, followed by uneventful recovery. Diarrhea was common in all treatment groups, but no deaths were attributed to MtBE toxicity. In the subacute study, lung weights were reduced in high-dose females. Trends in the 14-day exposure also included increased cholesterol in both females and males and decreased blood-urea nitrogen (BUN) and creatinine in females. In the 90-day study, females exhibited elevated cholesterol and decreased BUN, while creatinine was decreased in high-dose males. Microscopic findings in most organs were unremarkable, except for high-dose males where renal changes were compatible with alpha 2-globulin nephropathy and were considered to have little toxicologic significance for humans. Both studies indicated that dose levels below those which induce anesthesia (1200 mg/kg) do not result in significant pathophysiologic changes.

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.

Effect of ETBE on reproductive steroids in male rats and rat Leydig cell cultures

These experiments were conducted to follow up on a report of testis seminiferous tubular degeneration in Fischer 344 rats treated with high doses of ethyl t-butyl ether (ETBE). Also, high doses of a related compound, methyl t-butyl ether (MTBE), had been shown to reduce circulating testosterone (T) in rats. Isolated rat Leydig cells were used to compare hCG-stimulated T production following exposure to ETBE, MTBE, and their common main metabolite, TBA. In addition, male Fischer 344 rats were gavaged daily with 600 mg/kg, 1200 mg/kg or 1800 mg/kg ETBE in corn oil (n=12) for 14 days, the 1200 mg/kg dose chosen for comparison with a prior 14-day MTBE gavage experiment. In cell culture experiments, TBA was more potent than either ETBE or MTBE, both of which caused similar inhibition of T production at equimolar concentrations. In the in vivo study, no significant plasma T reduction was seen 1h after the final 1200 mg/kg ETBE dose, whereas 1200 mg/kg MTBE had significantly lowered T when administered similarly to Sprague-Dawley rats. Some rats treated with 1800 mg/kg ETBE had noticeably lower T levels, and the group average T level was 66% of corn oil vehicle control (p>0.05) with high variability also evident in ETBE-treated rats. 17beta-Estradiol had been increased by 1200 mg/kg MTBE, and was elevated in the 1200 and 1800 mg/kg ETBE dose groups (p<0.05), both groups also experiencing significantly reduced body weight gain. None of these effects were seen with 600 mg/kg/day ETBE. No definitive evidence of androgen insufficiency was seen in accessory organ weights, and no testicular pathology was observed after 14 days in a small subset of 1800 mg/kg ETBE-treated animals. Like MTBE, ETBE appears to be capable of altering reproductive steroid levels in peripheral blood sampled 1h after treatment, but only with extremely high doses that inhibit body weight gain and may produce mortality.

Methyltertiary-Butyl Ether: Studies for Potential Human Health Hazards

When methyl tertiary-butyl ether (MTBE) in gasoline was first introduced to reduce vehicle exhaust emissions and comply with the Clean Air Act, in the United States, a pattern of complaints emerged characterised by seven "key symptoms." Later, carefully controlled volunteer studies did not confirm the existence of the specific key symptoms, although one study of self-reported sensitive (SRS) people did suggest that a threshold at about 11-15% MTBE in gasoline may exist for SRSs in total symptom scores. Neurobehavioral and psychophysiological studies on volunteers, including SRSs, found no adverse responses associated with MTBE at likely exposure levels. MTBE is well and rapidly absorbed following oral and inhalation exposures. Cmax values for MTBE are achieved almost immediately after oral dosing and within 2 h of continuous inhalation. It is rapidly eliminated, either by exhalation as unchanged MTBE or by urinary excretion of its less volatile metabolites. Metabolism is more rapid humans than in rats, for both MTBE and tert-butyl alcohol (TBA), its more persistent primary metabolite. The other primary metabolite, formaldehyde, is detoxified at a rate very much greater than its formation from MTBE. MTBE has no specific effects on reproduction or development, or on genetic material. Neurological effects were observed only at very high concentrations. In carcinogenicity studies of MTBE, TBA, and methanol (included as an endogenous precursor of formaldehyde, without the presence of TBA), some increases in tumor incidence have been observed, but consistency of outcome was lacking and even some degree of replication was observed in only three cases, none of which had human relevance: alpha(2u)-globulin nephropathy-related renal tubule cell adenoma in male rats; Leydig-cell adenoma in male rats, but not in mice, which provide the better model of the human disease; and B-cell-derived lymphoma/leukemia of doubtful pathogenesis that arose mainly in lungs of orally dosed female rats. In addition, hepatocellular adenomas were significantly higher in female CD-1 mice and thyroid follicular-cell adenomas were increased in female B6C3F1 mice treated with TBA, but these results lack any independent confirmation, which would have been possible from a number of other studies.

Interactive effects of methyl tertiary-butyl ether (MTBE) and tertiary-amyl methyl ether (TAME), ethanol and some drugs: Triglyceridemia, liver toxicity and induction of CYP (2E1, 2B1) and phase II enzymes in female Wistar rats

The abilities of the gasoline additives methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME) to cause liver damage following oral administration, dosed alone or in combination with model hepatotoxins, were investigated in the rat. Inducibility of liver drug-metabolizing enzyme activities was also studied. Exposure to these ethers (10-20mmol/kg) for 3 days resulted in hepatomegaly (13-30%) and induction of cytochrome P450 (CYP) activity towards N-nitrosodimethylamine (NDMAD), 7-pentoxyresorufin (PROD), and 7-ethoxyresorufin (EROD). Immunoinhibition assays with monoclonal antibodies showed that the ethers were equipotent as inducers of CYP2E1 activity (2-fold increase) but not of CYP2B1, which was elevated up to 260-fold in TAME-treated rats but only by 20-fold in MTBE rats. A slight or no modifying effect was observed on the NADPH:quinone oxidoreductase (NQO1), glutathione S-transferase (GST), and UDP-glucuronosyltransferase (UGT) activities. Alanine aminotransaminase (ALT) and aspartate aminotransaminase (AST) were elevated in blood plasma after administration of the ethers. No dramatic enhancement of liver damage could be detected by plasma enzyme analysis (ALT, AST, alkaline phosphatase, γ-glutamyltransferase) following ether administration (13.5mmol/kg) to rats pretreated with mildly hepatotoxic dosages of ethanol, pyrazole, phenobarbital, acetaminophen (paracetamol), or 13-cis-retinoic acid (13-cis-RA or isotretinoin). Plasma triglycerides increased in TAME-treated rats (1.7-fold) and in all 13-cis-RA-treated groups (2.1-2.8-fold). The findings that MTBE and TAME exhibited a clear but differential inducing effect on two ether-metabolizing CYP forms (2E1 and 2B1) with no marked effect on phase II activities may reflect the importance of these pathways in vivo. The observation that only TAME by itself induced hypertriglyceridemia while acetaminophen- and 13-cis-RA-induced hypertriglyceridemia were aggravated by both ethers, points to differences in their effects on lipid metabolism. TAME was clearly a more potent CNS depressant than MTBE. There was no marked potentiation of drug/chemical-induced acute liver damage either by MTBE or TAME.

The uptake, distribution, metabolism, and excretion of methyl tertiary-butyl ether inhaled alone and in combination with gasoline vapor

The purpose of these studies was to evaluate the tissue uptake, distribution, metabolism, and excretion of methyl tertiary-butyl ether (MTBE) in rats and to determine the effects of coinhalation of the volatile fraction of unleaded gasoline on these parameters. Male F344 rats were exposed nose-only once for 4 h to 4, 40, or 400 ppm 14C-MTBE and to 20 and 200 ppm of the light fraction of unleaded gasoline (LFG) containing 4 and 40 ppm 14C-MTBE, respectively. To evaluate the effects of repeated inhalation of LFG on the fate of inhaled MTBE, rats were exposed for 7 consecutive days to 20 and 200 ppm LFG followed on d 8 by exposure to LFG containing 14C-MTBE. Three subgroups of rats were included for evaluation of respiratory parameters, rates and routes of excretion, and tissue distribution and elimination. MTBE and its chief metabolite, tertiary-butyl alcohol, were quantitated in blood and kidney (immediately after exposure), and the major urinary metabolites, 2-hydroxyisobutyric acid and 2-methyl-1,2- propanediol, were identified and quantified in urine. Inhalation of MTBE alone or as a component of LFG had no concentration-dependent effect on respiratory minute volume. The initial body burdens (IBBs) of MTBE equivalents achieved after 4 h of exposure to MTBE did not increase linearly with exposure concentration. MTBE equivalents rapidly distributed to all tissues examined, with the largest percentages distributed to liver. Between 40 and 400 ppm, there was a significant reduction in percentage of the IBB present in the major organs examined, both immediately and 72 h after exposure. At 400 ppm, the elimination rates of MTBE equivalents from tissues changed significantly. Furthermore, at 400 ppm there was a significant decrease in the elimination half-time of volatile organic compounds (VOCs) in breath and a significant increase in the percentage of the IBB of MTBE equivalents eliminated as VOCs in breath. LFG coexposure significantly decreased the percentage of the MTBE equivalent IBBs in tissues and increased rates of elimination of MTBE equivalents. The study results indicate that the uptake and fate of inhaled MTBE are altered upon increasing exposure levels from 4 to 400 ppm, suggesting that toxic effects observed previously upon repeated inhalation of concentrations of 400 ppm or greater may not necessarily be linearly extrapolated to effects that might occur at lower concentrations. Furthermore, coexposure to LFG, whether acute or repeated, decreases tissue burdens of MTBE equivalents and enhances the elimination rate of MTBE and its metabolites, thereby potentially reducing the toxic effects of the MTBE compared to when it is inhaled alone.

Influence of oxygenated fuel additives and their metabolites on the binding of a convulsant ligand of the gamma-aminobutyric acid(A) (GABA(A)) receptor in rat brain membrane preparations

As a foundation for evaluating potential mechanisms of the neurological effects (e.g. headache, nausea, dizziness) of some octane boosters, we studied the gamma-aminobutyric acid(A) (GABA(A)) receptor in a series of binding assays in membranes from rat brain. The GABA(A) receptor was probed using the radioligand [3H]t-butylbicycloorthobenzoate ([3H]TBOB) which binds to the convulsant recognition site of the receptor. The results demonstrated that the short-chain t-ethers and their t-alcohol metabolites inhibit binding at the convulsant site of the GABA(A) receptor. The potency of the inhibition tended to correlate with carbon chain length. For agents having an equal number of carbon atoms, potency of inhibition of [3H]TBOB binding was greater in magnitude for the alcohols than for the ethers. The descending rank order of potency for the ethers and alcohols were as follows, t-amyl alcohol (TAA); t-amyl-methyl ether (TAME); ethyl-t-butyl ether (ETBE)>t-butyl alcohol (TBA)>methyl-t-butyl ether (MTBE)>ethanol. In additional saturation binding assays, MTBE reduced apparent density of convulsant binding (B(max)).

Toxicokinetics of organic solvents: a review of modifying factors

This article reviews, with an emphasis on human experimental data, factors known or suspected to cause changes in the toxicokinetics of organic solvents. Such changes in the toxicokinetic pattern alters the relation between external exposure and target dose and thus may explain some of the observed individual variability in susceptibility to toxic effects. Factors shown to modify the uptake, distribution, biotransformation, or excretion of solvent include physical activity (work load), body composition, age, sex, genetic polymorphism of the biotransformation, ethnicity, diet, smoking, drug treatment, and coexposure to ethanol and other solvents. A better understanding of modifying factors is needed for several reasons. First, it may help in identifying important potential confounders and eliminating negligible ones. Second, the risk assessment process may be improved if different sources of variability between external exposures and target doses can be quantitatively assessed. Third, biological exposure monitoring may be also improved for the same reason.

Potential health effects of gasoline and its constituents: A review of current literature (1990-1997) on toxicological data

We reviewed toxicological studies, both experimental and epidemiological, that appeared in international literature in the period 1990-1997 and included both leaded and unleaded gasolines as well as their components and additives. The aim of this overview was to select, arrange, and present references of scientific papers published during the period under consideration and to summarize the data in order to give a comprehensive picture of the results of toxicological studies performed in laboratory animals (including carcinogenic, teratogenic, or embryotoxic activity), mutagenicity and genotoxic aspects in mammalian and bacterial systems, and epidemiological results obtained in humans in relation to gasoline exposure. This paper draws attention to the inherent difficulties in assessing with precision any potential adverse effects on health, that is, the risk of possible damage to man and his environment from gasoline. The difficulty of risk assessment still exists despite the fact that the studies examined are definitely more technically valid than those of earlier years. The uncertainty in overall risk determination from gasoline exposure also derives from the conflicting results of different studies, from the lack of a correct scientific approach in some studies, from the variable characteristics of the different gasoline mixtures, and from the difficulties of correctly handling potentially confounding variables related to lifestyle (e.g., cigarette smoking, drug use) or to preexisting pathological conditions. In this respect, this paper highlights the need for accurately assessing the conclusive explanations reported in scientific papers so as to avoid the spread of inaccurate or misleading information on gasoline toxicity in nonscientific papers and in mass-media messages.

Experimental exposure to methyl tertiary-butyl ether. I. Toxicokinetics in humans

Methyl tertiary-butyl ether (MTBE) is widely used in gasoline as an oxygenate and octane enhancer. The aim of this study was to evaluate the uptake, distribution, metabolism, and elimination of MTBE in humans. Ten healthy male volunteers were exposed to MTBE vapor (5, 25, and 50 ppm) on three different occasions during 2 h of light physical exercise (50 W). MTBE and the metabolite tertiary-butyl alcohol (TBA) were monitored in exhaled air, blood, and urine. Blood and urine were collected at selected time intervals, during and up to 3 days after the exposure, and analyzed by head space gas chromatography. MTBE in exhaled air was collected with sorbent sample tubes and subsequently analyzed by gas chromatography. The respiratory uptake of MTBE was rather low (42-49%), and the respiratory exhalation was high (32-47%). A relatively low metabolic blood clearance (0.34-0.52 L/h/kg) was seen compared to many other solvents. The kinetic profile of MTBE in blood could be described by four phases, and the average half-lives were 1 min, 10 min, 1.5 h, and 19 h. The post-exposure decay curve of MTBE in urine was separated into two linear phases, with average half-lives of 20 min and 3 h. The average post-exposure half-lives of TBA in blood and urine were 10 and 8.2 h, respectively. The urinary excretion of MTBE and TBA was less than 1% of the absorbed dose, indicating further metabolism of TBA, other routes of metabolism, or excretion. The kinetics of MTBE and TBA were linear up to the highest exposure level of 50 ppm. We suggest that TBA in blood or urine is a more appropriate biological exposure marker for MTBE than the parent ether itself.

Methyl tert butyl ether systemic toxicity

In male F344 rats exposed in a chronic inhalation study to methyl tertiary butyl ether (MTBE) a treatment related increase in severity of chronic nephropathy and mortality and an increase in hyaline droplets in the kidney were noted. Liver weights were increased in both rats and mice but no histological lesions other than hypertrophy are seen. Transient CNS effects but no indications of permanent nervous system effects were noted. MTBE is not a reproductive or developmental hazard. MTBE is rapidly absorbed. MTBE with some metabolite, tertiary butyl alcohol (TBA) and a little CO2 are excreted in the air. The urinary excretion products in animals are TBA metabolites, while in humans the urinary excretion products are MTBE and TBA. A comparison of the systematic responses of the possible metabolites TBA and formaldehyde indicate that they are not responsible for toxicity associated with MTBE, except that TBA may be partially responsible for the kidney effects reported. Animals and humans are similar in the uptake and excretion though with some differences in metabolism of MTBE. This supports the use of the animal data as a surrogate for humans.

Route-to-route extrapolation of the toxic potency of MTBE

MTBE is a volatile organic compound used as an oxygenating agent in gasoline. Inhalation from fumes while refueling automobiles is the principle route of exposure for humans, and toxicity by this route has been well studied. Oral exposures to MTBE exist as well, primarily due to groundwater contamination from leaking stationary sources, such as underground storage tanks. Assessing the potential public health impacts of oral exposures to MTBE is problematic because drinking water studies do not exist for MTBE, and the few oil-gavage studies from which a risk assessment could be derived are limited. This paper evaluates the suitability of the MTBE database for conducting an inhalation route-to-oral route extrapolation of toxicity. This includes evaluating the similarity of critical effect between these two routes, quantifiable differences in absorption, distribution, metabolism, and excretion, and sufficiency of toxicity data by the inhalation route. We conclude that such an extrapolation is appropriate and have validated the extrapolation by finding comparable toxicity between a subchronic gavage oral bioassay and oral doses we extrapolate from a subchronic inhalation bioassay. Our results are extended to the 2-year inhalation toxicity study by Chun et al. (1992) in which rats were exposed to 0, 400, 3000, or 8000 ppm MTBE for 6 hr/d, 5 d/wk. We have estimated the equivalent oral doses to be 0, 130, 940, or 2700 mg/kg/d. These equivalent doses may be useful in conducting noncancer and cancer risk assessments.

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.

Exposure to methyl tertiary-butyl ether from oxygenated gasoline in Stamford, Connecticut

In 1993, state health officials in Connecticut invited the Centers for Disease Control and Prevention (CDC) to assist in an investigation of exposure to methyl tertiary-butyl ether in oxygenated gasoline in Stamford, Connecticut. Venous blood samples were collected from 14 commuters and from 30 other persons who worked in the vicinity of traffic or automobiles, and the samples were analyzed for methyl tertiary-butyl ether, tertiary-butyl alcohol, benzene, m-/p-xylene, o-xylene, and toluene. The highest levels of methyl tertiary-butyl ether in blood were measured among gasoline service station attendants (median = 15 micrograms/l, range = 7.6-28.9 micrograms/l). Blood levels of methyl tertiary-butyl ether were highly variable among persons who worked in car-repair shops (median = 1.73 micrograms/l, range = 0.17-36.7 micrograms/l) and were generally lowest among commuters (median = 0.11 micrograms/l, range = < 0.05-2.60 micrograms/l). Blood levels of methyl tertiary-butyl ether were correlated strongly with personal-breathing-zone samples of methyl tertiary-butyl ether and blood levels of other volatile organic compounds. This exposure information should prove useful to a future risk analysis of this high-volume chemical.

Human exposure to volatile organic compounds: a comparison of organic vapor monitoring badge levels with blood levels

We undertook a study in Albany, New York, to investigate whether volatile organic compounds (VOCs) were measurable in the blood and in the breathing-zone air of people exposed to gasoline fumes and automotive exhaust. We sampled blood of 40 subjects, placed organic vapor badges on 40 subjects, and obtained personal breathing-zone samples from 24 subjects. We limited this analysis to 19 subjects who wore the organic vapor badges for at least 5 h. VOC levels, as determined by the organic vapor badges, were highly correlated with blood levels of these same compounds. Using detection in blood as the gold standard, we found the badges to be more sensitive than conventional charcoal tube samples in detecting low levels of methyl tert-butyl ether (0.60 vs 0.08), toluene (0.95 vs 0.64), and o-xylene (0.85 vs 0.64). In this study, organic vapor badges provided data on VOC exposure that correlated with blood assay results. These organic vapor badges might provide a convenient means of determining human exposure to VOCs in epidemiologic studies.

Methyl-tertiary-butyl ether (MTBE)--a gasoline additive--causes testicular and lymphohaematopoietic cancers in rats

In the framework of a series of experiments conducted to evaluate the carcinogenic effects of oxygenated gasoline additives, MTBE was analyzed in an oral lifetime carcinogenicity study using 8-week-old male and female Sprague-Dawley rats. These experiments were part of a large research project on gasoline carcinogenicity performed at the Bentivoglio (BT) Castle Cancer Research Center of the Ramazzini Foundation and of the Bologna Institute of Oncology, MTBE, dissolved in oil, was administered by stomach tube at the doses of 1000, 250, or 0 mg/kg b.w., once daily, four days weekly, for 104 weeks. The animals were maintained until natural death. The last animal died 166 weeks after the start of the experiment, i.e., at 174 weeks of age. Under the tested experimental conditions, MTBE was shown to cause an increase in Leydig interstitial cell tumors of the testes and a dose-related increase in lymphomas and leukemias in female rats.

Methyl tertiary butyl ether in human blood after exposure to oxygenated fuel in Fairbanks, Alaska

Residents of Fairbanks, Alaska reported health complaints when 15%, by volume, methyl tertiary butyl ether (MTBE) was added to gasoline during an oxygenated fuel program. We conducted an exposure survey to investigate the effect of the program on human exposure to MTBE. We studied 18 workers in December 1992 during the program and 28 workers in February 1993 after the program was suspended. All workers were heavily exposed to motor vehicle exhaust or gasoline fumes. In December, the median post-shift blood concentration of MTBE in the workers was 1.8 micrograms/l (range, 0.2-37.0 micrograms/l), and in February the median post-shift blood concentration of MTBE in the 28 workers was 0.24 micrograms/l (range, 0.05-1.44 micrograms/l; p = .0001). Blood MTBE levels were measurably higher during the oxygenated fuel program in Fairbanks than after the program was suspended.

Manual and automatic gallstone dissolution with methyl tert-butyl ether

The aim of the study was to establish the efficiency of cholesterol gallstone dissolution with methyl tert-butyl ether in a large group of patients and to compare the results of patients treated manually by a nurse or using an automatic pump. Gallbladder puncture was successful in 228 patients (99%). After 9 hr, 211 patients (91%) were stone-free; 144 (68%) of them left the hospital on the fourth day. In radiolucent stones not isodense with bile on a CT scan, dissolution rate decreased by 10%, treatment time was prolonged by 40%. Forty-two of the 228 patients were selected for the hand-syringed group, 42 patients, who matched these patients in stone size and number, were treated with an automatic pump (Baxter). Stone burden in matched pairs was comparable. Stones dissolved in 96% of the patients in both groups. Sludge remained in the gallbladder in 52% after manual treatment and 60% after automatic therapy. Side effects were identical in both groups. None of the side effects were pump-related. Automatic therapy reduced the time needed by the nurse to treat each patient by 70%.

Acute toxicity of gasoline and some additives

The acute toxicity of gasoline; its components benzene, toluene, and xylene; and the additives ethanol, methanol, and methyl tertiary butyl ether are reviewed. All of these chemicals are only moderately to mildly toxic at acute doses. Because of their volatility, these compounds are not extensively absorbed dermally unless the exposed skin is occluded. Absorption through the lungs and the gastrointestinal tract is quite efficient. After ingestion, the principal danger for a number of these chemicals, particularly gasoline, is aspiration pneumonia, which occurs mainly in children. It is currently not clear whether aspiration pneumonia would still be a problem if gasoline were diluted with ethanol or methanol. During the normal use of gasoline or mixtures of gasoline and the other solvents as a fuel, exposures would be much lower than the doses that have resulted in poisoning. No acute toxic health effects would occur during the normal course of using automotive fuels.

Systemic and local toxicity in the rat of methyl tert-butyl ether: a gallstone dissolution agent

Methyl tert-butyl ether (MTBE) is an organic solvent that has been used to dissolve gallstones via a percutaneous transhepatic catheter into the gallbladder. To test whether MTBE might cause serious tissue injury if accidentally infused outside the gallbladder, the effect of MTBE (0.2 ml/kg) injected into the hepatic parenchyma, or administered intravenously or intraperitoneally, was examined in the rat. The toxicity of isopropyl acetate (IPA), an organic solvent with a similar chemical structure, was examined similarly. Intracaval injection of MTBE caused the highest mortality (100%). Mortality was less (59%) after intrahepatic injection and still less (17%) after peripheral vein injection. Most animals died instantaneously from cardiorespiratory arrest. Almost all animals that were injected with MTBE intrahepatically or intravenously showed localized areas of congestion, hemorrhage, and interstitial edema in the lungs. These changes were more severe in rats which survived for 24 hr than in those which died sooner. In those rats receiving intrahepatic injections, most rats which survived for 24 hr had liver necrosis at the site of injection. Intraperitoneal injection of MTBE produced 100% survival with only 1/5 rats showing a mild pulmonary injury at autopsy. IPA had toxic effects similar to those evoked by MTBE. To test whether tumor necrosis factor was involved in organ injury, serum levels were measured; they remained unchanged. These experiments indicate that two organic solvents, MTBE and IPA, are cytotoxic to local tissues and cause severe, and often fatal, lung damage when infused into a central vein. Less toxicity occurred if solvents were given into a peripheral or portal vein or intraperitoneally.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of topical methyl tert-butyl ether or ethyl propionate on gallbladder histology in animals: a comparison of two solvents for contact dissolution of cholesterol gallstones

Experiments were performed in anesthetized rabbits and piglets to assess gallbladder mucosal injury during irrigation with methyl tert-butyl ether, a C5 ether, or ethyl propionate, a C5 ester--two organic solvents used in the contact dissolution of cholesterol gallstones. In 44 New Zealand White rabbits, the gallbladder was exposed to individual solvents or saline solution through a transhepatic catheter for 2 hr. Gallbladders were then harvested and fixed immediately or after a recovery period of 1, 4 or 8 days. Tissue sections were examined under light microscopy, and severity of injury was graded with predefined criteria by two pathologists blinded to the animals' treatment regimens. Histological assessment showed severe mucosal injury such as necrosis of the cells at the villus tips immediately after 2 hr of exposure to either solvent. After 4 days, injury had decreased significantly; after 8 days, complete mucosal healing had taken place. A similar study was performed in 32 piglets. Solvent or saline solution was oscillated in and out of the gallbladders of these piglets with a computer-controlled syringe pump at a pressure less than the leakage pressure of the gallbladder. Histological assessment was performed on tissue samples obtained immediately after the procedure or 8 days later. Both solvents caused severe mucosal injury; however, after 8 days complete mucosal healing had occurred, so that gallbladders exposed to solvent were indistinguishable from gallbladders exposed to saline solution, which was used as control. We conclude that both methyl tert-butyl ether and ethyl propionate cause moderate to severe epithelial injury but that the gallbladder epithelium regenerates within a few days.(ABSTRACT TRUNCATED AT 250 WORDS)

Percutaneous dissolution of gallstones

Contact dissolution with MTBE is an effective and safe method to treat symptomatic patients with cholesterol gallstones. Personnel, time, and safety factors have limited widespread use of the procedure. With current competing methods to treat gallstones, it is likely that MTBE use will be reserved for those patients who elect percutaneous therapy due to fear of surgery or anesthesia and in those elderly patients who are compromised by underlying medical conditions.

Gallstone dissolution with methyl tert-butyl ether in 120 patients--efficacy and safety

Of 612 patients with cholesterol gallbladder stones, 120 were eligible for percutaneous transhepatic litholysis with methyl tert-butyl ether (MTBE). Puncture of the gallbladder was successful in 117/120 (97.5%). In 113/117 (96.6%) the stones dissolved. With solitary stones, treatment lasted for an average of 4 hr, with multiple stones 10 hr. Mean hospitalization was 3.6 days. In 3/117 (2.6%) patients a bile leakage developed; 33% reported mild complaints. After the end of treatment 34% had some residue in the gallbladder; two of these patients developed recurrent stones. MTBE is exhaled, is distributed in fatty tissue, and is excreted renally together with its metabolite tert-butanol. Methanol was found only in traces. Gallbladder histology of six patients showed chronic cholecystitis. Since these findings were independent of treatment time and the interval between treatment end and operation, they are most consistent with stone-related changes rather than caused by MTBE.

Metabolism of methyl tertiary-butyl ether by rat hepatic microsomes

Exposure to methyl tertiary-butyl ether (MTBE), a commonly used octane booster in gasoline, has previously been shown to alter various muscle, kidney, and liver metabolic activities. In the present study, the metabolism of MTBE by liver microsomes from acetone- or phenobarbital-treated Sprague-Dawley rats was studied at concentrations of up to 5 mM MTBE. Equimolar amounts of tertiary-butanol, as measured by head-space gas chromatography, and formaldehyde were formed. The Vmax for the demethylation increased by 4-fold and 5.5-fold after acetone and phenobarbital treatments, respectively. The apparent Km value of 0.70 mM using control microsomes was decreased slightly after acetone treatment, but was increased by 2-fold after phenobarbital treatment. The metabolism of MTBE (1 mM) was inhibited by 35% by monoclonal antibodies against P450IIE1, the acetone/ethanol inducible form of cytochrome P450, suggesting a partial contribution by this isozyme. A single 18-h pretreatment of rats with 1 or 5 ml/kg MTBE (i.p.) resulted in a 50-fold induction of liver microsomal pentoxyresorufin dealkylase activity but no change in N-nitrosodimethylamine demethylase activity. These trends in activity agreed with immunoblot analysis which showed an elevation in P450IIB1 but no change in P450IIE1 levels.