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

Lessons learned from a case of tert-butyl glucuronide excretion in urine - "New" psychoactive alcohols knocking on the back door?

BACKGROUND

Ethyl glucuronide (EtG) in urine is considered a marker of recent ethanol consumption or ethanol exposition. tert-Butanol is primarily used as a solvent and intermediate chemical. Like tert-amyl alcohol, tert-butanol is discussed in Internet forums as ethanol replacement. We discuss false-positive immunological EtG screenings by excretion of different alcohol glucuronides (EtG homologs), mainly tert-butyl glucuronide in urine of a polytoxikomanic in-patient.

METHODS

Three consecutive urine samples from an in-patient with a long history of multiple substance abuse including solvents were analyzed by DRI EtG enzyme immunoassay (ThermoFisher Scientific Microgenics) on a Beckman Coulter AU680 analyzer, an in-house LC-MS/MS for EtG, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert-butyl glucuronide, and an in-house headspace GC-FID of free congener substances methanol, 1-propanol, 2-butanone, 2-butanol, isobutanol, 1-butanol, 3-methyl-1-butanol, 2-methyl-1-butanol, and additionally for ethanol, acetone, 2-propanol, tert-butanol and 2-methyl-2-butanol.

RESULTS

EtG immunoassay yielded two positive urine samples (0.2 and 0.6mg/L or 0.1 and 0.2mg/g creatinine; cut-off 0.1mg/L) which were tested EtG negative by LC-MS/MS (cut-off 0.1mg/L) but positive for tert-butyl glucuronide (3.7 and 27.1mg/L), 2-butyl glucuronide (1.1 and 3.5mg/L), and 2-propyl glucuronide (0.1 and 0.4mg/L). Headspace GC-FID detected tert-butanol (0.97 and 4.01mg/L), methanol (0.96 and 0.62mg/L), 2-butanone (0.84 and 1.65mg/L), and 2-butanol (0.04 and 0.09mg/L), but no ethanol and no 2-methyl-2-butanol.

CONCLUSION

Cross-reaction of EtG homologs, mainly tert-butyl glucuronide after suspected tert-butanol or isobutane abuse, explains the false-positive EtG immunoassay findings. Future investigations could address the usefulness of alcohol glucuronides (EtG homologs) in urine as (a) biomarkers of an exposition to alkans or their corresponding alcohol metabolites and (b) as markers for using "old"-well known alcohols like tert-butanol or tert-amyl alcohol as easy to obtain, cheap, potent and "undetectable" ethanol replacements or "New" Psychoactive Alcohols.

Relationship between Methyl Tertiary Butyl Ether Exposure and Non-Alcoholic Fatty Liver Disease: A Cross-Sectional Study among Petrol Station Attendants in Southern China

Methyl tertiary butyl ether (MTBE)—A well known gasoline additive substituting for lead alkyls—causes lipid disorders and liver dysfunctions in animal models. However, whether MTBE exposure is a risk factor for non-alcoholic fatty liver disease (NAFLD) remains uncertain. We evaluate the possible relationship between MTBE exposure and the prevalence of NAFLD among 71 petrol station attendants in southern China. The personal exposure concentrations of MTBE were analyzed by Head Space Solid Phase Microextraction GC/MS. NAFLD was diagnosed by using abdominal ultrasonography according to the guidelines for the diagnosis and treatment of NAFLD suggested by the Chinese Hepatology Association. Demographic and clinical characteristics potentially associated with NAFLD were investigated. Mutivariate logistic regression analysis was applied to measure odds ratios and 95% confidence intervals (CI). The result showed that the total prevalence of NAFLD was 15.49% (11/71) among the study subjects. The average exposure concentrations of MTBE were 292.98 ± 154.90 μg/m³ and 286.64 ± 122.28 μg/m³ in NAFLD and non-NAFLD groups, respectively, and there was no statistically significant difference between them (p > 0.05). After adjusting for age, gender, physical exercise, body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), alanine aminotransferase (ALT), white blood cell (WBC), total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL), and high-density lipoprotein (HDL), the odds ratios were 1.31 (95% CI: 0.85–1.54; p > 0.05), 1.14 (95% CI: 0.81–1.32; p > 0.05), 1.52 (95% CI: 0.93–1.61; p > 0.05) in the groups (including men and women) with exposure concentrations of MTBE of 100–200 μg/m³, 200–300 μg/m³, and ≥300 μg/m³, respectively, as compared to the group (including men and women) ≤100 μg/m³. Our investigation indicates that exposure to MTBE does not seem to be a significant risk factor for the prevalence of NAFLD among petrol station attendants in southern China.

Toxicity of methyl tertiary-butyl ether on human blood lymphocytes

Methyl tertiary-butyl ether (MTBE) is a synthetic solvent widely used as oxygenate in unleaded gasoline. Few studies have addressed the cellular toxicity of MTBE on some cell lines, and so far, no comprehensive study has been conducted to investigate the probable immunotoxicity of this compound. In this study, the toxicity of MTBE on human blood lymphocytes was evaluated. Blood lymphocytes were isolated from healthy male volunteers' blood, using Ficoll polysaccharide followed by gradient centrifugation. Cell viability, reactive oxygen species (ROS) formation, lipid peroxidation, glutathione levels, and damage to mitochondria and lysosome were determined in blood lymphocytes after 6-h incubation with different concentrations of MTBE (0.1, 0.5, 1, and 2 mM). Our results showed that MTBE, in particular, decreased cell viability, which was associated with significant increase at intracellular ROS level and toxic alterations in mitochondria and lysosomes in human blood lymphocytes. Moreover, it was shown that MTBE strongly provoked lipid peroxidation and also depleted glutathione level at higher concentrations. Interestingly, MTBE exhibited its cytotoxic effects at low concentrations that may resemble to its concentrations in human blood following occupational and environmental exposure. It is therefore concluded that MTBE was capable of inducing oxidative stress and damage to mitochondria and lysosomes in human lymphocytes at concentrations ranging from 5 to 40 μg/L, which may be present in human blood as a result of environmental exposure.

Health Risk Assessment for Inhalation Exposure to Methyl Tertiary Butyl Ether at Petrol Stations in Southern China

Methyl tertiary butyl ether (MTBE), a well known gasoline additive, is used in China nationwide to enhance the octane number of gasoline and reduce harmful exhaust emissions, yet  little is known regarding the potential health risk associated with occupational exposure to MTBE in petrol stations. In this study, 97 petrol station attendants (PSAs) in southern China were recruited for an assessment of the health risk associated with inhalation exposure to MTBE. The personal exposure levels of MTBE were analyzed by Head Space Solid Phase Microextraction GC/MS, and the demographic characteristics of the PSAs were investigated. Cancer and non-cancer risks were calculated with the methods recommended by the United States Environmental Protection Agency. The results showed that the exposure levels of MTBE in operating workers were much higher than among support staff (p < 0.01) and both were lower than 50 ppm (an occupational threshold limit value). The calculated cancer risks (CRs) at the investigated petrol stations was 0.170 to 0.240 per 10⁶ for operating workers, and 0.026 to 0.049 per 10⁶ for support staff, which are below the typical target range for risk management of 1 × 10⁻⁶ to 1 × 10⁻⁴; The hazard quotients (HQs) for all subjects were <1. In conclusion, our study indicates that the MTBE exposure of PSAs in southern China is in a low range which does not seem to be a significant health risk.

Interaction of insulin with methyl tert-butyl ether promotes molten globule-like state and production of reactive oxygen species

Interaction of methyl tert-butyl ether (MTBE) with proteins is a new look at its potential adverse biological effects. When MTBE is released to the environment it enters the blood stream through inhalation, and could affect the properties of various proteins. Here we investigated the interaction of MTBE with insulin and its effect on insulin structural changes. Our results showed that insulin formed a molten globule (MG)-like structure in the presence of 8 μM MTBE under physiological pH. The insulin structural changes were studied using spectroscopy methods, viscosity calculation, dynamic light scattering and differential scanning calorimetry. To delineate the mechanisms involved in MTBE-protein interactions, the formation of reactive oxygen specious (ROS) and formation of protein aggregates were measured. The chemiluminscence experiments revealed an increase in ROS production in the presence of MTBE especially in the MG-like state. These results were further confirmed by the aggregation tests, which indicated more aggregation of insulin at 40 μM MTBE compared with 8 μM. Thus, the formation of initial aggregates and exposure of the hydrophobic patches upon formation of the MG-like state in the presence of MTBE drives protein oxidation and ROS generation.

Fuel derived pollutants and boating activity patterns in the Sea of Galilee

MTBE (Methyl tert-Butyl Ether) is a fuel additive that replaced lead as an antiknock compound in internal combustion motors. Few years after its introduction, detectable levels of MTBE were found in various water bodies. MTBE has a very low taste and odor threshold and is a potential carcinogen. Another group of fuel derived toxic compounds that has been detected in water bodies is BTEX (Benzene, Toluene, Ethylbenzene and Xylene). Boating activity and allochthonous contributions from watersheds are the major sources of fuel derived pollutants in lakes. Their concentrations in lakes thus vary as a function of boating activity intensity, lake surface area and depth, weather and wind regime, land-use in the watershed, etc. The Sea of Galilee (Lake Kinneret) is the only recreational lake in Israel and an important freshwater source. In the current study, a sampling campaign was conducted in order to quantify MTBE and BTEX concentrations in Lake Kinneret, its marinas and its main contributing streams. In addition, a boating-use survey was performed in order to estimate MTBE and BTEX contribution of recreational boating. The sampling campaign revealed that, as expected, MTBE concentrations were higher than BTEX, and that near shore (i.e., marina) concentrations were higher than in-lake concentrations. Despite the clear contribution from boating, high MTBE concentrations were found following a major inflow event in winter, indicating the importance of the allochthonous contribution. The contribution from boating during summer, as measured indirectly by in-lake concentrations, is likely underestimated due to enhanced MTBE volatilization due to strong winds and high temperatures. May-September was found to be the main recreational boating season, with continued boating year round. On average, a single boat is active 23 d/y, with 84% of the watercrafts being active only during weekends and holidays. The survey further indicated that boats stay in the lake for 4.5 h on average, which conforms to the unique winds regime that limits afternoon activity due to high winds, and have an average fuel consumption of 14 L/h. The annual load of MTBE and BTEX from recreational boating in Lake Kinneret was estimated at 4430 and 6220 kg/y respectively.

Calculating the retention of volatile organic compounds in the lung on the basis of their physicochemical properties

In the workplace, deliberate or accidental exposure to volatile organic compounds (VOCs) may occur by ingestion, but more usually through inhalation or dermal contact. The basic model of occupational exposure assumes repeated inhalation exposure during long periods of time, such as 8-h daily, 40-h per working week. Evaluation of the systemic health effects of industrial chemicals can be based on biological levels or internal doses absorbed in dermal or inhalation exposures. The lungs are the primary route of absorption in exposure to gases, vapors, and aerosols. In inhalation exposure, the dose absorbed can be calculated using the following equation: [formula in text] where C, concentration in the air; T, duration of exposure; V, lung ventilation; R, lung retention expressed as % of intake. As lung retention of VOCs has been studied on human volunteers in costly and time-consuming chamber-type experiments, available data are limited. To calculate dosage for the purpose of risk assessment, the default value of 100% is used. As the lung retention of VOCs in lungs can vary from less than 20 to more than 90%, a possibility of predicting the retention values on the basis of blood/air partition coefficients (K(B)) has been investigated. Lung retention data for 36 compounds were obtained from the existing scientific literature. These values derive from human volunteer studies lasting at least 2h. The K(B) values were either the already published experimental data or were calculated based on their physicochemical properties using a published solvation equation. The compounds under study were divided arbitrarily into two groups: water soluble (>10 g/l) and slightly soluble in water (<10 g/l) compounds. For water soluble compounds, the correlation between K(B) and lung retention was high (r=0.75 and 0.73 respectively); this referred both to K(B) values obtained experimentally or calculated in this report. For the compounds slightly soluble in water, the respective values amounted to 0.79 and 0.82. The obtained results indicate that VOC retention in the lung can be calculated solely on the basis of the partition coefficient K(B). As the descriptors used in the solvation equation can be predicted from chemical structure, this finding indicates that it is possible to assess lung retention for any chemical structure of VOC. The model described in the present report can be a practical alternative to the necessity costly and long-lasting chamber-type experiments which are also questionable on ethical grounds.

Differential toxic effects of methyl tertiary butyl ether and tert-butanol on rat fibroblasts in vitro

Methyl tertiary butyl ether (MTBE) is the most widely used motor vehicle fuel oxygenate since it reduces harmful emissions due to gasoline combustion. However, the significant increase in its use in recent years has raised new questions related to its potential toxicity. In fact, although available data are somehow conflicting, there is evidence that MTBE is a toxic substance that may have harmful effects on both animals and humans and an unresolved problem is the role played by MTBE metabolites, especially tertiary butyl alcohol (TBA), in determining toxic effects due to MTBE exposure. In this study, the toxic effects of MTBE have been analyzed on a normal diploid rat fibroblast cell line (Rat-1) and compared to the effects of TBA. The results obtained suggest that both MTBE and TBA inhibit cell growth in vitro but with different mechanisms in terms of effects on the cell cycle progression and on the modulation of cell cycle regulatory proteins. In fact, MTBE caused an accumulation of cells in the S-phase of the cell cycle, whereas TBA caused an accumulation in the G0/G1-phase with different effects on the expression of cyclin D1, p27Kip1, and p53. Moreover, both MTBE and TBA were also shown to induce DNA damage, as assessed in terms of oxidative DNA damage and nuclear DNA fragmentation, that appeared to be susceptible of repair by the cell DNA-repair machinery. In conclusion, these findings suggest that both MTBE and TBA can exert, by acting through different molecular mechanisms, important biological effects on fibroblasts in vitro. Further studies are warranted to shed light on the mechanisms responsible for the observed effects and on their potential significance for the in-vivo exposure.

Effects of subchronic methyl tert-butyl ether ether exposure on male Sprague-Dawley rats

Methyl tert-butyl ether (MTBE) is an additive used to oxygenate gasoline to improve air quality by reducing tailpipe emissions of carbon monoxide and ozone precursors. Although several toxicity studies in rats have been conducted to examine the acute, subchronic, and chronic toxicities by employing various routes of exposure to MTBE, few data were available on the effects of MTBE exposure on blood. In this study, MTBE was administered to rats at dose levels of 0, 400, 800, and 1600 mg/kg/day, respectively. After 2- or 4-weeks treatment period, rats were euthanized and blood was collected for the assay of hematological indicators and blood biochemistry indicators. Some organs, including brain, heart, liver, spleen, lung, kidneys, testes, epididymis, thymus, and prostate, were immediately removed and weighed. Possible subchronic health effects of MTBE exposure by gavage were evaluated on mortality, body weight, relative organ weight, hematology, and blood biochemistry indicators in male Sprague-Dawley rats. The results indicated that MTBE did not disrupt the growth rate of rats. Relative organ weight showed change in heart, liver, kidney, testes, thymus, and prostate. In the 2-week treatment, MTBE exerted toxicity on white blood cell count, including lymphocyte, granulocyte, and eosinophil. This finding was especially strong at 1600 mg/kg/day MTBE. In the 4-week treatment, hemoglobin at high dose MTBE significantly increased. The results of the assay for the biochemistry indicators and relative organ weight indicated that MTBE could impair liver and kidney functions and also have adverse effects on lipid metabolism and immune system. It was conducted that subchronic MTBE exposure induced the adverse effects occurring in the relative organ weight, the hematological indicators, and the biochemistry indicators under high MTBE dose.

Transport and Uptake of MTBE and Ethanol Vapors in a Human Upper Airway Model

Potential human exposure to vapors of methyl tertiary-butyl ether (MTBE) and ethanol is of increasing concern because these materials are widely used as gasoline additives. In this study we analyzed numerically the transport and deposition of MTBE and ethanol vapors in a model of the human upper respiratory airway, consisting of an oral airway and the first four generations of the tracheobronchial tree. Airflow characteristics and mass transfer processes were analyzed at different inspiratory flow conditions using a three-dimensional computational fluid and particle dynamics method. The deposition data were analyzed in terms of regional deposition fractions (DF = regional uptake/mouth concentration) and deposition enhancement factors (DEF = local DF/average DF) at local micro surface areas. Results show that DF in the entire upper airway model is 21.9%, 12.4%, and 6.9% for MTBE and 67.5%, 51.5%, and 38.5% for ethanol at a flow rate of 15, 30, and 60 L/min, respectively. Of the total DF, 65-70% is deposited in the oral airway for both vapors. Deposition is localized at various sites within the upper airway structure, with a maximum DEF of 1.5 for MTBE and 7.8 for ethanol. Local deposition patterns did not change with inhalation conditions, but DF and the maximum DEF increased with diffusivity, solubility, and the degree of airway wall absorption of vapors, as shown by a greater deposition of ethanol than MTBE. The vapor deposition efficiency as expressed by the dimensionless mass transfer coefficient correlated well with a product of Reynolds (Re) and Schmidt (Sc) numbers. In conclusion, MTBE and ethanol vapors deposit substantially in the upper airway structure with a marked enhancement of dose at local sites, and the deposition dose may be reasonably estimated by a functional relationship with dimensionless fluid flow and diffusion parameters.

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.

Role of exhaled breath biomarkers in environmental health science

As a discipline of public health, environmental health science is the study of the linkage from environmental pollution sources to eventual adverse health outcome. This progression may be divided into two components, (1) "exposure assessment," which deals with the source terms, environmental transport, human exposure routes, and internal dose, and (2) "health effects," which deals with metabolism, cell damage, DNA changes, pathology, and onset of disease. The primary goal of understanding the linkage from source to health outcome is to provide the most effective and efficient environmental intervention methods to reduce health risk to the population. Biomarker measurements address an individual response to a common external environmental stressor. Biomarkers are substances within an individual and are subdivided into chemical markers, exogenous metabolites, endogenous response chemicals, and complex adducts (e.g., proteins, DNA). Standard biomarker measurements are performed in blood, urine, or other biological media such as adipose tissue and lavage fluid. In general, sample collection is invasive, requires medical personnel and a controlled environment, and generates infectious waste. Exploiting exhaled breath as an alternative or supplement to established biomarker measurements is attractive primarily because it allows a simpler collection procedure in the field for numerous individuals. Furthermore, because breath is a gas-phase matrix, volatile biomarkers become more readily accessible to analysis. This article describes successful environmental health applications of exhaled breath and proposes future research directions from the perspective of U.S. Environmental Protection Agency (EPA) human exposure research.

Toxicokinetics of methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME) in humans, and implications to their biological monitoring

Healthy male volunteers were exposed via inhalation to gasoline oxygenates methyl tert-butyl ether (MTBE) or tert-amyl methyl ether (TAME). The 4-hr exposures were carried out in a dynamic chamber at 25 and 75 ppm for MTBE and at 15 and 50 ppm for TAME. The overall mean pulmonary retention of MTBE was 43 +/- 2.6%; the corresponding mean for TAME was 51 +/- 3.9%. Approximately 52% of the absorbed dose of MTBE was exhaled within 44 hr following the exposure; for TAME, the corresponding figure was 30%. MTBE and TAME in blood and exhaled air reached their highest concentrations at the end of exposure, whereas the concentrations of the metabolites tert-butanol (TBA) and tert-amyl alcohol (TAA) concentrations were highest 0.5-1 hr after the exposure and then declined slowly. Two consecutive half-times were observed for the disappearance of MTBE and TAME from blood and exhaled air. The half-times for MTBE in blood were about 1.7 and 3.8 hr and those for TAME 1.2 and 4.9 hr. For TAA, a single half-time of about 6 hr best described the disappearance from blood and exhaled air; for TBA, the disappearance was slow and seemed to follow zero-order kinetics for 24 hr. In urine, maximal concentrations of MTBE and TAME were observed toward the end of exposure or slightly (< or = 1 hr) after the exposure and showed half-times of about 4 hr and 8 hr, respectively. Urinary concentrations of TAA followed first-order kinetics with a half-time of about 8 hr, whereas the disappearance of TBA was slower and showed zero-order kinetics at concentrations above approx. 10 micro mol/L. Approximately 0.2% of the inhaled dose of MTBE and 0.1% of the dose of TAME was excreted unchanged in urine, whereas the urinary excretion of free TBA and TAA was 1.2% and 0.3% within 48 hr. The blood/air and oil/blood partition coefficients, determined in vitro, were 20 and 14 for MTBE and 20 and 37 for TAME. By intrapolation from the two experimental exposure concentrations, biomonitoring action limits corresponding to an 8-hr time-weighted average (TWA) exposure of 50 ppm was estimated to be 20 micro mol/L for post-shift urinary MTBE, 1 mu mol/L for exhaled air MTBE in a post-shift sample, and 30 micro mol/L for urinary TBA in a next-morning specimen. For TAME and TAA, concentrations corresponding to an 8-hr TWA exposure at 20 ppm were estimated to be 6 micro mol/L (TAME in post-shift urine), 0.2 micro mol/L (TAME in post-shift exhaled air), and 3 micro mol/L (TAA in next morning urine).

Review of chamber design requirements for testing of personal protective clothing ensembles

This review focuses on the physical requirements for conducting ensemble testing and describes the salient issues that organizations involved in the design, test, or certification of personal protective equipment (PPE) and protective clothing ensembles need to consider for strategic planning. Several current and proposed PPE ensemble test practices and standards were identified. The man-in-simulant test (MIST) is the primary procedure used by the military to evaluate clothing ensembles for protection against chemical and biological warfare agents. MIST has been incorporated into the current editions of protective clothing and equipment standards promulgated by the National Fire Protection Association (NFPA). ASTM has recently developed a new test method (ASTM F 2588-06) for MIST evaluation of protective ensembles. Other relevant test methods include those described in International Organization for Standardization (ISO) standards. The primary differences among the test methods were the choice of test challenge material (e.g., sulfur hexafluoride, methyl salicylate, sodium chloride particles, corn oil, fluorophore-impregnated silica) and the exercise protocol for the subject(s). Although ensemble test methods and standards provide detailed descriptions of the test procedures, none give specific requirements for chamber design. A literature survey identified 28 whole-body exposure chambers that have been or could potentially be used for testing protective clothing ensembles using human test subjects. Median chamber size, median floor space, and median volume per subject were calculated from 15 chambers (involving human test subjects), where size information is available. Based on the literature survey of existing chambers and the review of the current and proposed standards and test methods, chamber design requirements will be dictated by the test methods selected. Due to widely different test conditions for aerosol/particulate and vapor ensemble testing, it is unlikely that a single chamber could accommodate all types of ensemble testing. With increasing use of the MIST protocol by NFPA for CBRN certification of structural firefighting gear and protective ensembles for first responders, the need for MIST laboratory capability is clear. However, existing chambers can likely be adapted to accommodate MIST with some modifications.

Ethyl tertiary-butyl ether: a toxicological review

A number of oxygenated compounds (oxygenates) are available for use in gasoline to reduce vehicle exhaust emissions, reduce the aromatic compound content, and avoid the use of organo-lead compounds, while maintaining high octane numbers. Ethyl tertiary-butyl ether (ETBE) is one such compound. The current use of ETBE in gasoline or petrol is modest but increasing, with consequently similar trends in the potential for human exposure. Inhalation is the most likely mode of exposure, with about 30% of inhaled ETBE being retained by the lungs and distributed around the body. Following cessation of exposure, the blood concentration of ETBE falls rapidly, largely as a result of its metabolism to tertiary-butyl alcohol (TBA) and acetaldehyde. TBA may be further metabolized, first to 2-methyl-1,2-propanediol and then to 2-hydroxyisobutyrate, the two dominant metabolites found in urine of volunteers and rats. The rapid oxidation of acetaldehyde suggests that its blood concentration is unlikely to rise above normal as a result of human exposure to sources of ETBE. Single-dose toxicity tests show that ETBE has low toxicity and is essentially nonirritant to eyes and skin; it did not cause sensitization in a maximization test in guinea pigs. Neurological effects have been observed only at very high exposure concentrations. There is evidence for an effect of ETBE on the kidney of rats. Increases in kidney weight were seen in both sexes, but protein droplet accumulation (with alpha(2u)-globulin involvement) and sustained increases in cell proliferation occurred only in males. In liver, centrilobular necrosis was induced in mice, but not rats, after exposure by inhalation, although this lesion was reported in some rats exposed to very high oral doses of ETBE. The proportion of liver cells engaged in S-phase DNA synthesis was increased in mice of both sexes exposed by inhalation. ETBE has no specific effects on reproduction, development, or genetic material. Carcinogenicity studies have been conducted with ETBE, TBA, and ethanol (included in this review as an endogenous precursor of acetaldehyde in the absence of TBA). A single experiment with ETBE in rats and several experiments with ethanol in rats and mice were not considered adequate for an evaluation of ETBE carcinogenicity. In male rats only, TBA induced alpha(2u)-globulin nephropathy-related renal tubule adenomas. These are generally considered to have no human relevance. In addition, increases in thyroid follicular cell adenoma incidence were associated with TBA treatment in female mice. This result lacks independent confirmation and is not supported by experiments in which similar or higher internal doses of TBA were delivered.

Biodegradability of alkylates as a sole carbon source in the presence of ethanol or BTEX

The biodegradability of alkylate compounds in serum bottles was investigated in the presence and absence of ethanol or benzene, toluene, ethylbenzene, and p-xylene (BTEX). The biomass was acclimated to three different alkylates, 2,3-dimethylpentane, 2,4-dimethylpentane and 2,2,4-trimethylpentane in porous pot reactors. The alkylates were completely mineralized in all three sets of experiments. They degraded more slowly in the presence of BTEX than in their absence because BTEX inhibited the microbial utilization of alkylates. However, in the presence of ethanol, their slower biodegradation was not related to inhibition by the ethanol. Throughout the experiments alkylates, ethanol, and BTEX concentrations did not change in the sterile controls.

Determination of low level methyl tert-butyl ether, ethyl tert-butyl ether and methyl tert-amyl ether in human urine by HS-SPME gas chromatography/mass spectrometry

Methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME) are oxygenated compounds added to gasoline to enhance octane rating and to improve combustion. They may be found as pollutants of living and working environments. In this work a robotized method for the quantification of low level MTBE, ETBE and TAME in human urine was developed and validated. The analytes were sampled in the headspace of urine by SPME in the presence of MTBE-d12 as internal standard. Different fibers were compared for their linearity and extraction efficiency: carboxen/polydimethylsiloxane, polydimethylsiloxane/divinylbenzene, and polydimethylsiloxane. The first, although highly efficient, was discarded due to deviation of linearity for competitive displacement, and the polydimethylsiloxane/divinylbenzene fiber was chosen instead. The analysis was performed by GC/MS operating in the electron impact mode. The method is very specific, with range of linearity 30-4600 ng L(-1), within- and between-run precision, as coefficient of variation, <22 and <16%, accuracy within 20% the theoretical level, and limit of detection of 6 ng L(-1) for all the analytes. The influence of the matrix on the quantification of these ethers was evaluated analysing the specimens of seven traffic policemen exposed to autovehicular emissions: using the calibration curve and the method of standard additions comparable levels of MTBE (68-528 ng L(-1)), ETBE (<6 ng L(-1)), and TAME (<6 ng L(-1)) were obtained.

Dose-response relationships in human experimental exposure to solvents

Previous studies carried out in the field of experimental toxicology have shown evidence of biphasic dose-response relationships for different experimental models, endpoints and chemicals tested. As these studies excluded humans as the experimental model, we have examined the literature of the last three decades in order to verify data concerning human experimental exposure with the aim of highlighting possible biphasic dose-response relationships. The substances used for experimental exposures included hydrocarbons, esters, alcohols, ketones, ethers, glycoethers, halogenated hydrocarbons, and carbon sulphide; the absorption route was inhalation. We did not detect any biphasic dose-response relationship and, in the studies reviewed, our examination revealed major methodological limitations that prevented us making a more detailed examination of experimental data. We concluded that the experimental data available did not allow us to support evidence of biphasic dose-response relationships in human experimental exposure to the above-mentioned chemical substances.

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 ethers used as fuel oxygenates

The toxicokinetics and biotransformation of methyl-tert.butyl ether (MTBE), ethyl-tert.butyl ether (ETBE) and tert.amyl-methyl ether (TAME) in rats and humans are summarized. These ethers are used as gasoline additives in large amounts, and thus, a considerable potential for human exposure exists. After inhalation exposure MTBE, ETBE and TAME are rapidly taken up by both rats and humans; after termination of exposure, clearance by exhalation and biotransformation to urinary metabolites is rapid in rats. In humans, clearance by exhalation is slower in comparison to rats. Biotransformation of MTBE and ETBE is both qualitatively and quantitatively similar in humans and rats after inhalation exposure under identical conditions. The extent of biotransformation of TAME is also quantitatively similar in rats and humans; the metabolic pathways, however, are different. The results suggest that reactive and potentially toxic metabolites are not formed during biotransformation of these ethers and that toxic effects of these compounds initiated by covalent binding to cellular macromolecules are unlikely.

Toxicokinetics of human exposure to methyl tertiary-butyl ether (MTBE) following short-term controlled exposures

Methyl tertiary-butyl ether (MTBE) is an oxygenated compound added to gasoline to improve air quality as part of the US Federal Clean Air Act. Due to the increasing and widespread use of MTBE and suspected health effects, a controlled, short-term MTBE inhalation exposure kinetics study was conducted using breath and blood analyses to evaluate the metabolic kinetics of MTBE and its metabolite, tertiary-butyl alcohol (TBA), in the human body. In order to simulate common exposure situations such as gasoline pumping, subjects were exposed to vapors from MTBE in gasoline rather than pure MTBE. Six subjects (three females, three males) were exposed to 1.7 ppm of MTBE generated by vaporizing 15 LV% MTBE gasoline mixture for 15 min. The mean percentage of MTBE absorbed was 65.8 +/- 5.6% following exposures to MTBE. The mean accumulated percentages expired through inhalation for 1 and 8 h after exposure for all subjects were 40.1% and 69.4%, respectively. The three elimination half-lives of the triphasic exponential breath decay curves for the first compartment was 1-4 min, for the second compartment 9-53 min, and for the third compartment 2-8 h. The half-lives data set for the breath second and blood first compartments suggested that the second breath compartment rather than the first breath compartment is associated with a blood compartment. Possible locations for the very short breath half-life observed are in the lungs or mucous membranes. The third compartment calculated for the blood data represent the vessel poor tissues or adipose tissues. A strong correlation between blood MTBE and breath MTBE was found with mean blood-to-breath ratio of 23.5. The peak blood TBA levels occurred after the MTBE peak concentration and reached the highest levels around 2-4 h after exposures. Following the exposures, immediate increases in MTBE urinary excretion rates were observed with lags in the TBA excretion rate. The TBA concentrations reached their highest levels around 6-8 h, and then gradually returned to background levels around 20 h after exposure. Approximately 0.7-1.5% of the inhaled MTBE dose was excreted as unchange urinary MTBE, and 1-3% was excreted as unconjugated urinary TBA within 24 h after exposure.

METHYL tert-BUTYL ETHER AS A GASOLINE OXYGENATE: Lessons for Environmental Public Policy

▪ Abstract  We assess the environmental health impact and policy implications of the widespread addition of methyl tert-butyl ether (MTBE) as a chemical that is used as an oxygenate to much of the gasoline supply in the United States. Initial concerns about short-term and long-term adverse health consequences following the substantial increase in MTBE use in the winter of 1992–1993 have been supplemented by the discovery in 1996 of what is now relatively widespread contamination of groundwater. We identify 14 governmental initiatives during the 10-year period 1989–1999 in which the potential adverse consequences of MTBE were considered and a nearly identical research agenda was proposed. The lessons from the ongoing MTBE episode show that: (a) research should precede rather than follow environmental health policy decisions; (b) the extent of potential human and environmental exposure should be an important criterion in determining the amount of information needed before making an environmental policy decision; (c) a better understanding of nonspecific human symptoms associated with environmental exposures is needed; (d) the boundaries between the US Environmental Protection Agency program offices should be as porous as the boundaries between environmental media; (e) the US Environmental Protection Agency needs to focus more on public health rather than on legal approaches to environmental management; (f) it is more difficult to remove a chemical once it is in commerce than it is to prevent its use; (g) resolution of uncertainty is best accomplished through research rather than through repetitive review; and (h) better tools are needed to evaluate risk/risk trade-offs. The ongoing replacement of MTBE by other, less well studied oxygenates such as tertiary amyl methyl ether indicates that these environmental public policy lessons have not been learned.

Mutagenicity studies of methyl-tert-butylether using the Ames tester strain TA102

Methyl-tert-butylether (MTBE) is an oxygenate widely used in the United States as a motor vehicle fuel additive to reduce emissions and as an octane booster [National Research Council, Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fules, National Academy Press, Washington, DC, 1996]. But it is the potential for MTBE to enter drinking water supplies that has become an area of public concern. MTBE has been shown to induce liver and kidney tumors in rodents but the biochemical process leading to carcinogenesis is unknown. MTBE was previously shown to be non-mutagenic in the standard Ames plate incorporation test with tester strains that detect frame shift (TA98) and point mutations (TA100) and in a suspension assay using TA104, a strain that detects oxidative damage, suggesting a non-genotoxic mechanism accounts for its carcinogenic potential. These strains are deficient in excision repair due to deletion of the uvrB gene. We hypothesized that the carcinogenic activity of MTBE may be dependent upon a functional excision repair system that attempts to remove alkyl adducts and/or oxidative base damage caused by direct interaction of MTBE with DNA or by its metabolites, formaldehyde and tert-butyl alcohol (TBA), established carcinogens that are mutagenic in some Ames strains. To test our hypothesis, the genotoxicity of MTBE-induced DNA alterations was assayed using the standard Ames test with TA102, a strain similar to TA104 in the damage it detects but uvrB + and, therefore, excision repair proficient. The assay was performed (1) with and without Aroclor-induced rat S-9, (2) with and without the addition of formaldehyde dehydrogenase (FDH), and (3) with human S-9 homogenate. MTBE was weakly mutagenic when tested directly and moderately mutagenic with S-9 activation producing between 80 and 200 TA102 revertants/mg of compound. Mutagenicity was inhibited 25%-30% by FDH. TA102 revertants were also induced by TBA and by MTBE when human S-9 was substituted for rat S-9. We conclude that MTBE and its metabolites induce a mutagenic pathway involving oxidation of DNA bases and an intact repair system. These data are significant in view of the controversy surrounding public safety and the environmental release of MTBE and similar fuel additives.

Experimental exposure to methyl tertiary-butyl ether. II. Acute effects in humans

Methyl tertiary-butyl ether (MTBE) is widely used in gasoline as an oxygenate and octane enhancer. Acute effects, such as headache, nausea, and nasal and ocular irritation, have been associated with the exposure to gasoline containing MTBE. The aim of this study was to assess acute health effects up to the Swedish occupational exposure limit value, both with objective methods and a questionnaire. Ten healthy male volunteers were exposed to MTBE vapor for 2 h at three levels (5, 25, and 50 ppm), during light physical work (50 W). All subjects rated the degree of irritative symptoms, discomfort, and CNS effects before, during, and after all three exposure occasions using a questionnaire. Answers were given on a 100-mm visual analog scale, graded from "not at all" to "almost unbearable." Ocular (redness, tear film break-up time, self-reported tear film break-up time, conjunctival epithelial damage, and blinking frequency) and nasal (mouth and nasal peak expiratory flow, acoustic rhinometry, biochemical inflammatory markers, and cells in nasal lavage) measurements were performed mainly at the highest exposure level. The ratings of solvent smell increased dramatically (ratings up to 50% of the scale) as the volunteers entered the chamber and declined slowly with time (p < 0.05, repeated-measures ANOVA). All other questions were rated from "not at all" to "hardly at all" (0-10% of the scale) with no significant relation to exposure. The eye measurements showed no effects of MTBE exposure. Blockage index, a measure of nasal airway resistance calculated from the peak expiratory flows, increased significantly after exposure; however, the effect was not related to exposure level. In addition, a nonsignificant tendency of decreased nasal volume was seen in the acoustic rhinometry measurements, but with no clear dose-effect relationship. In conclusion, our study suggests no or minimal acute effects of MTBE vapor upon short-term exposure at relatively high levels.