Aldh2 knockout mice were more sensitive to DNA damage in leukocytes due to ethyl tertiary butyl ether exposure

To clarify the genotoxicity of ethyl tertiary butyl ether (ETBE), a gasoline additive, male and female C57BL/6 mice of Aldh2+/+ and Aldh2-/- genotypes, aged 8 wk, were exposed to 0, 500, 1,750, or 5,000 ppm ETBE for 6 h/day, 5 d per week for 13 wk. DNA damage in leukocytes was measured by the alkaline comet assay and expressed quantitatively as Tail Intensity (TI). For male mice, TI was significantly higher in all three groups exposed to ETBE than in those without exposure within Aldh2-/- mice, whereas within Aldh2+/+ mice, TI increased only in those exposed to 5,000 ppm of ETBE as compared with mice without exposure. For female mice, a significant increase in TI values was observed in the group exposed to 5,000 ppm of ETBE as compared with those without exposure within Aldh2-/- mice; TI in Aldh2-/- mice exposed to 1,750 and 5,000 ppm was significantly higher than in Aldh2+/+ mice without exposure. TI did not significantly increase in any of the groups exposed to ETBE within female Aldh2+/+ mice. Based on the results we suggest that Aldh2-/- mice are more sensitive to DNA damage caused by ETBE than Aldh2+/+ mice and that males seem more susceptible to this effect than females.     

甲基叔丁基醚对大鼠脏器毒性作用

Journal of Guilin College of Aerospace Technology93-95G641H131;2;C;H;H131_2;吴江;87-89桂林航专教材使用现状的调查、分析及对策叶桂郴;罗香妹;谢国军;李瑜玲;桂林航天工业高等专科学校,桂林航天工业高等专科学校,桂林航天工业高等专科学校,桂林航天工业高等专科学校 广西 桂林 541004,广西 桂林 541004,广西 桂林 541004,广西 桂林 541004自编教材;;非自编教材;;教材的适用性文章通过调(T-SOD)、丙二醛(MDA)、还原型谷胱甘肽(GSH)活性;光镜检测各组大鼠肝、肺、肾、脑组织病理变化。结果染毒组血清LDH较对照组呈下降趋势,且M2组与对照组比较差异有统计学意义(P<0.05)。染毒组ALT较对照组明显降低(P<0.05)。与对照组比较,染毒组肝、肺、肾组织T-SOD活力均出现不同程度降低,且M2组肝组织、M1组肺组织及M1、M2组肾组织中T-SOD下降显著(P<0.05);各组织中MDA含量比较差异无统计学意义,染毒组各组织中GSH含量较对照组均呈下降趋势,且M2组肝组织中GSH与对照组比较差异有统计学意义(P<0.05)。光镜检查发现染毒组大鼠肝、肺、肾等脏器组织结构均出现不同程度的改变。结论MTBE可以影响血清酶的水平,并对大鼠的自由基清除系统造成一定损伤,还可以影响肝、肺、肾等器官的正常组织结构形态。     

甲基叔丁基醚对细胞周期及细胞凋亡的影响

目的：探讨汽油添加剂甲基叔丁基醚（ＭＴＢＥ）对细胞周期和细胞凋亡的影响。方法 采用流式细胞仪检测ＭＴＢＥ对ＮＩＨ／３Ｔ３细胞周期（染毒浓度分别为１、２、４μｌ／ｍｌ,染毒时间为２４ｈ）的影响;应用结晶紫染色法,通过检测Ｈｅｌａ细胞的存活情况,了解ＭＴＢＥ对细胞凋亡的影响。结果 流式细胞仪结果显示,ＭＴＢＥ可使ＮＩＨ／３Ｔ３细胞周期发生改变。表现为Ｓ期细胞减少,而处于Ｇ２＋Ｍ期的细胞增多,提示ＭＴＢ     

Exposure of gasoline road-tanker drivers to methyl tert-butyl ether and methyl tert-amyl ether

Organic oxygenates, namely, methyl tert-butyl ether (MTBE) and methyl tert-amyl ether (MTAE), are added to gasoline to reduce carbon monoxide in exhausts and to enhance the octane number. The aim of this study was to investigate road-tanker drivers' exposure to oxygenate vapors during road-tanker loading and unloading as well as to evaluate the measurements of these ethers and their metabolites in the urine as a means of assessing the uptake of the ethers. A total of 11 drivers in different parts of Finland were trained to monitor their exposure with personal samplers, to report their working conditions, and to collect their whole-day urine samples. Charcoal tubes of the air samples were analyzed for MTBE, MTAE, benzene, toluene, and aliphatic hydrocarbons. For biological monitoring purposes the two main oxygenates, tertiary ethers MTBE and MTAE, as well as their main metabolites, tertiary alcohols tert-butanol (TBA) and tert-amyl alcohol (TAA), were determined in urine specimens. On average the drivers were exposed to vapors for short periods (21 ± 14 min) three times during a work shift. The mean concentrations of MTBE and MTAE (mean ± SD) were 8.1 ± 8.4 and 0.3 ± 0.4 mg/m³. The total MTBE uptake during the shift was calculated to be an average of 106 ± 65 μmol. The mean concentrations of MTBE, TBA, MTAE and TAA detected in the first urine after the work shift were 113 ± 76, 461 ± 337, 16 ± 21, and 40 ± 38 nmol/l, and those found the next morning, 16 h later, were 18 ± 12, 322 ± 213, 9 ± 10, and 20 ± 27 nmol/l. The good relationship (r = 0.84) found between MTBE exposure and postshift excretion suggests that urinary MTBE can be used for biological monitoring of exposure, but at the present low level of exposure the corresponding metabolite TBA is not equally reliable. The determination of MTAE and its metabolite TAA in urine is sensitive enough to detect the low degree of exposure to MTAE, but in this study the data were too scarce to allow calculation of the correlations due to very low levels of MTAE exposure. Received: 10 February 1997 / Accepted: 2 July 1997     

甲基叔丁基醚对大鼠肝组织基因表达的影响

目的甲基叔丁基醚（ＭＴＢＥ）是一种新型的汽油添加剂,动物试验显示其具有一定的致癌性。为了解其动物致癌性的可能机制,我们检测了经ＭＴＢＥ亚慢性染毒的大鼠肝组织中原癌基因ｃｍｙｃ基因和功能基因谷胱甘肽Ｓ转移酶Ｐ（ＧＳＴＰ）基因的表达情况。方法４０只雄性ＳＤ大鼠,体重１８０～２００ｇ,随机分为４组。将ＭＴＢＥ溶于适量豆油中,灌胃染毒,染毒剂量分别为２００ｍｇ／ｋｇ,６００ｍｇ／ｋｇ,１０００ｍｇ／ｋｇ和对照组。每天１次,每周５天,共１３周。动物肝组织于液氮速冻后,一步法提取总ＲＮＡ。随机引物法地高辛标记ｃｍｙｃ和ＧＳＴＰ探针,与ＲＮＡ进行点杂交,图像分析仪分析结果。结果大鼠肝组织中ｃｍｙｃ基因表达水平明显增高,ＧＳＴＰ基因表达未见增强。结论ＭＴＢＥ可明显诱导ｃｍｙｃ基因的高表达,提示其具有促进细胞增殖的作用,这是其动物致癌性的可能机制之一。     

甲基叔丁基醚对原癌基因和功能基因表达的影响

甲基叔丁基醚（ＭＴＢＥ）是一种新型的汽油添加剂,被用来提高汽油燃烧效率,减少汽车尾气中有害物质的排放。ＭＴＢＥ具有一定的动物致癌性,但其机制目前并不清楚。本研究采用免疫组织化学方法,检测了ＭＴＢＥ对体外培养的ＮＩＨ３Ｔ３细胞中ｃ－ｍｙｃ和ｐ２１蛋白表达的影响;采用点杂交方法,从ＲＮＡ水平检测了ＭＴＢＥ亚慢性染毒大鼠肝组织中原癌基因ｃ－ｍｙｃ基因和功能基因ＧＳＴ－Ｐ基因的表达情况。免疫组化结果显示,ＭＴＢＥ可诱导ｃ－ｍｙｃ基因的高表达,对ｐ２１蛋白的表达未见明显影响。点杂交结果显示,ＭＴＢＥ可明显诱导大鼠肝组织中ｃ－ｍｙｃ基因的高表达,而对ＧＳＴ－Ｐ基因的表达未见明显影响。上述结果提示,ＭＴＢＥ可诱导细胞中ｃ－ｍｙｃ基因表达活性增高,可能是其动物致癌性的机制之一。     

甲基叔丁基醚对小鼠肝细胞周期及DNA含量的影响

目的　探讨甲基叔丁基醚 (MTBE)对小鼠肝细胞生长周期动力学及细胞DNA含量的影响。方法　昆明种小鼠经呼吸道静式染毒 ,MTBE浓度为 10 8 0 ,14 4 0 0及 4968 0mg/m3,每日 1次 ,每次 4h ,连续染毒 2 0d。流式细胞仪技术研究MTBE对小鼠肝细胞周期、细胞增殖及细胞DNA含量的结果。结果　MTBE各染毒组小鼠肝细胞的G0 /G1,S ,G2 /M期细胞数及增殖指数PI与对照组相比差异未见显著性 (P >0 0 5 ) ;MTBE 14 4 0 0与 4968 0mg/m3染毒组小鼠肝细胞DNA指数低于对照组 (P <0 0 5 )。结论　MTBE对小鼠肝细胞周期、细胞增殖无显著影响 ,可以引起小鼠肝细胞DNA含量的减少     

静态顶空-毛细管柱气相色谱法检测水中甲基叔丁基醚

目的:建立适用于水中甲基叔丁基醚的静态顶空气相色谱测定方法。方法:采用静态顶空极性毛细管柱气相色谱法测定水中甲基叔丁基醚。结果:在所建立的实验条件下水中甲基叔丁基醚的检出限为0.0163μg/L,线性范围为0.0156~120 mg/L,其相关系数r=0.9997,样品的加标回收率为92.6%~100.1%,相对标准偏差(RSD)低于1.1%。结论:此方法能够用于分析水中甲基叔丁基醚。     

甲基叔丁基醚对大鼠小脑γ-氨基丁酸影响

目的研究甲基叔丁基醚（Methyl tertiary butyl ether，MTBE）对大鼠小脑皮质神经递质γ-氨基丁酸（γ-GABA）的影响，探讨MTBE对中枢神经系统的急性系作用机制。方法54只健康成年SD大鼠，体重180～220g，随机分为9组，腹腔注射染毒，染毒剂量分别为0，700，1050，1400mg／（kg·bw）。观察各染毒剂量及染毒后0．5，1，2，4，8h时MTBE对大鼠小皮质神经递质GABA的影响。结果MTBE对小脑皮质神经递质GABA的作用其阳性产物相对灰度值结果显示，不同剂量[700，1050，1400mg／（kg·bw）]MTBE染毒后小脑皮质神经递质GABA相对灰度值随着染毒剂量增加而增加，存在剂量-效应关系；MTBE对小脑皮质GABA的影响在染毒后0．5h时GABA表达开始增加，1．0h达到高峰，2．0h时开始减弱，8．0h时GABA表达恢复到正常水平。结论MTBE对中枢神经系统急性毒作用与神经递质GABA含量的改变有关。     

Effect of vehicle use and maintenance patterns of a self-described group of sensitive individuals and nonsensitive individuals to methyl tertiary-butyl ether in gasoline.

The objective of this study was to compare the driving habits and vehicle maintenance patterns of individuals who report symptoms when exposed to methyl tertiary-butyl ether (MTBE) and those who are asymptomatic when exposed to the oxygenate. Participants were healthy volunteers (CON) and self-reported MTBE-sensitive individuals (SRS) who participated in a controlled exposure study of MTBE in gasoline. A questionnaire was developed to gather information about each participant's automobile usage, engine maintenance habits and fueling and driving patterns. Results showed that the individuals who had self-reported heightened sensitivity to the oxygenate drove their vehicles more often and fueled their vehicles more frequently than asymptomatic individuals. In addition, the self-reported symptomatic individuals in this study were shown to be more likely to drive vehicles with some form of body damage and carbureted engines.     

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.     

Relation of occupational exposure to respiratory symptoms and asthma in a general population sample: self-reported versus interview-based exposure data

The objective of this study was to examine how the consistency of self-reported exposure to dust or gas, asbestos, and quartz varied between subjects with and those without respiratory symptoms and asthma in a Norwegian community sample () in 1987-1988. Exposure characterization obtained in a structured work history interview was used as the "gold standard." The authors also wanted to assess how the exposure-disease relation differed when the exposure was based on self-reported versus interview-obtained data. The prevalence of self-reported exposure to dust or gas, asbestos, and quartz was 28%, 5%, and 4%, respectively. The sensitivity of the self-reported exposure data varied from 21% to 64% and was higher in those with than in those without the respiratory disorders. The specificity varied from 78% to 100% and was lower in those with than in those without the respiratory disorders. The sex-, age-, and smoking-adjusted odds ratios of the respiratory disorders in those with exposure to dust or gas and to asbestos were only slightly reduced when misclassification was taken into account. The corresponding numbers for exposure to quartz were halved and lost their statistical significance when the misclassification was allowed for. In this general population sample, the self-reported occupational, airborne exposure data were differentially misclassified by disease status.     

Long-term neurobehavioral health effects of methyl parathion exposure in children in Mississippi and Ohio

Methyl parathion (MP), an organophosphate pesticide licensed only for agricultural uses, was sprayed illegally for pest control in Mississippi and Ohio residences. To evaluate the association between MP exposure and neurobehavioral development, we assessed children 6 years or younger at the time of the spraying and local comparison groups of unexposed children using the Pediatric Environmental Neurobehavioral Test Battery (PENTB). The PENTB is composed of informant-based procedures (parent interview and questionnaires) and performance-based procedures (neurobehavioral tests for children 4 years or older) that evaluate cognitive, motor, sensory, and affect domains essential to neurobehavioral assessment. Children were classified as exposed or unexposed on the basis of urinary para-nitrophenol levels and environmental wipe samples for MP. Exposed children had more difficulties with tasks involving short-term memory and attention. Additionally, parents of exposed children reported that their children had more behavioral and motor skill problems than did parents of unexposed children. However, these effects were not consistently seen at both sites. There were no differences between exposed and unexposed children in tests for general intelligence, the integration of visual and motor skills, and multistep processing. Our findings suggest that MP might be associated with subtle changes to short-term memory and attention and contribute to problems with motor skills and some behaviors, but the results of the study are not conclusive.     

Customer exposure to MTBE, TAME, C6 alkyl methyl ethers, and benzene during gasoline refueling.

We studied customer exposure during refueling by collecting air samples from customers' breathing zone. The measurements were carried out during 4 days in summer 1996 at two Finnish self-service gasoline stations with "stage I" vapor recovery systems. The 95-RON (research octane number) gasoline contained approximately 2.7% methyl tert-butyl ether (MTBE), approximately 8.5% tert-amyl methyl ether (TAME), approximately 3.2% C6 alkyl methyl ethers (C6 AMEs), and 0.75% benzene. The individual exposure concentrations showed a wide log-normal distribution, with low exposures being the most frequent. In over 90% of the samples, the concentration of MTBE was higher (range <0.02-51 mg/m3) than that of TAME. The MTBE values were well below the short-term (15 min) threshold limits set for occupational exposure (250-360 mg/m3). At station A, the geometric mean concentrations in individual samples were 3.9 mg/m3 MTBE and 2. 2 mg/m3 TAME. The corresponding values at station B were 2.4 and 1.7 mg/m3, respectively. The average refueling (sampling) time was 63 sec at station A and 74 sec at station B. No statistically significant difference was observed in customer exposures between the two service stations. The overall geometric means (n = 167) for an adjusted 1-min refueling time were 3.3 mg/m3 MTBE and 1.9 mg/m3 TAME. Each day an integrated breathing zone sample was also collected, corresponding to an arithmetic mean of 20-21 refuelings. The overall arithmetic mean concentrations in the integrated samples (n = 8) were 0.90 mg/m3 for benzene and 0.56 mg/m3 for C6 AMEs calculated as a group. Mean MTBE concentrations in ambient air (a stationary point in the middle of the pump island) were 0.16 mg/m3 for station A and 0.07 mg/m3 for station B. The mean ambient concentrations of TAME, C6 AMEs, and benzene were 0.031 mg/m3, approximately 0.005 mg/m3, and approximately 0.01 mg/m3, respectively, at both stations. The mean wind speed was 1.4 m/sec and mean air temperature was 21 degreesC. Of the gasoline refueled during the study, 75% was 95 grade and 25% was 98/99 grade, with an oxygenate (MTBE) content of 12.2%.     

Occupational exposure to water-based paints and self-reported asthma,lower airway symptoms,bronchial hyperresponsiveness,and lung function

The associations between occupational exposure to water-based paints and the prevalence of self-reported asthma, other lower airway symptoms, bronchial hyperresponsiveness (BHR), and lung function were studied in house painters. Symptom prevalences were obtained from a self-administered questionnaire sent to 415 male painters during 1989–1992. Clinical investigations were carried out in three selected groups: 23 painters with asthmatic symptoms, nine painters with other lower airway symptoms, and 12 painters without airway symptoms. The clinical studies included lung function test, methacholine provocation test, and occurrence of atopy, confirmed by skin prick test to common allergens. In addition, a group of 18 young male painters with no occupational exposure to solvent-based paints were followed with dynamic spirometry before and after a workshift, when only water-based paints were used. The prevalence of self-reported asthma (7%) was somewhat, but not statistically, increased compared to an industrial population without exposure to water-based paints or other airway irritants. A decrease in FEV₁ and FVC during the workday was observed in the young painters. In the clinical studies the painters exhibited increased BHR compared to the referents and a decreased FEV₁. The number of years working as a painter was related to a decrease in FEV₁, which was most pronounced in subjects with atopy who also reported lower airway symptoms in relation to the degree of work with water-based paints, but not to the degree of use of solvent-based paints. Our results indicate that house painters have an increased risk of airway problems. A contributory cause could be exposure to volatile organic compounds or other volatile compounds emitted from water-based paints. It is also concluded that painters with atopy should be informed about the increased risk of airway illness. This would be an important task for occupational health services in their aim of preventing the adverse effects of occupational exposures.     

Controlled exposure to a mixture of SO2, NO2, and particulate air pollutants: effects on human pulmonary function and respiratory symptoms

Exposure of 20 volunteers to sodium chloride (NaCl) aerosol or to a mixture containing NaCl plus irritant particles (zinc ammonium sulfate) and irritant gases (nitrogen dioxide and sulfur dioxide) produced no significant decrements in pulmonary function. There was a slight tendency for respiratory symptoms to be greater during the exposure to the mixture than during exposure to the NaCl aerosol alone; the differences were not statistically significant. The pollutant concentrations studied approximated worst-case ambient levels observed in the Los Angeles basin.     

Prenatal exposure to mercury and neurobehavioral development of neonates in Zhoushan City, China

Exposure to hazardous Hg can adversely affect children's neurodevelopment. However, few data are available on either Hg levels in neonates and their mothers or the impact of prenatal exposure to Hg on neonates' neurobehavioral development in the Chinese population. Therefore, this study examined Hg levels in neonates and their mothers and the relationship between prenatal exposure to Hg and neonates' neurobehavioral development in Zhoushan City, Zhejiang Province, China. Between August and October 2004, 417 women who delivered their babies at Zhoushan Women's and Children's Health Hospital, an island city in east China were invited to take part in this study. A total of 408 complete questionnaires, 405 maternal hair samples, and 406 umbilical cord samples were collected. Neonatal behavioral neurological assessments (NBNA) were conducted for 384 neonates. The geometric mean (GM) of Hg level in cord blood was 5.58 microg/L (interquartile range: 3.96-7.82 microg/L), and the GM of maternal hair Hg level was 1246.56 microg/kg (interquartile range: 927.34-1684.67 microg/kg), a level much lower than other reported fish-eating populations, indicating Hg exposure in Zhoushan city is generally below those considered hazardous. However, according to the reference dose of Hg levels (RfD 5.8 microg/L) derived by EPA, 69.9% of newborns had levels at or above the RfD, an estimated level assumed to be without appreciable harm. There was a strong correlation between maternal hair and cord blood Hg levels (r = 0.82, P < 0.01). Frequency of fish consumption was associated with hair Hg (r = 0.48, P < 0.01) and cord blood Hg levels (r = 0.54, P < 0.01). Increased prenatal Hg exposure was associated with decreased behavioral ability for males (OR = 1.235, 95%CI of OR = 1.078-1.414, P < 0.001), but not for females. Our results provide some support for the hypothesis that there is neurodevelopmental risk for males from prenatal MeHg exposure resulting from fish consumption. But the findings of this study may be due to chance, and long-term follow-up research is needed to evaluate cumulative effects of exposure to mercury.     

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).