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 mumol. 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.