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CONTROLLED, SHORT-TERM DERMAL AND INHALATION EXPOSURE TO MTBE AND DIBROMOCHLOROMETHANE
Citation:
Gordon, S. M., M. C. Brinkman, J. Satola, L A. Wallace, C. E. Weisel, AND J. Y. Shin. CONTROLLED, SHORT-TERM DERMAL AND INHALATION EXPOSURE TO MTBE AND DIBROMOCHLOROMETHANE. Presented at International Society of Exposure Analysis 2002 Conference, Vancouver, Canada, August 11-15, 2002.
Impact/Purpose:
The primary study objectives are:
1.To quantify personal exposures and indoor air concentrations for PM/gases for potentially sensitive individuals (cross sectional, inter- and intrapersonal).
2.To describe (magnitude and variability) the relationships between personal exposure, and indoor, outdoor and ambient air concentrations for PM/gases for different sensitive cohorts. These cohorts represent subjects of opportunity and relationships established will not be used to extrapolate to the general population.
3.To examine the inter- and intrapersonal variability in the relationship between personal exposures, and indoor, outdoor, and ambient air concentrations for PM/gases for sensitive individuals.
4.To identify and model the factors that contribute to the inter- and intrapersonal variability in the relationships between personal exposures and indoor, outdoor, and ambient air concentrations for PM/gases.
5.To determine the contribution of ambient concentrations to indoor air/personal exposures for PM/gases.
6.To examine the effects of air shed (location, season), population demographics, and residential setting (apartment vs stand-alone homes) on the relationship between personal exposure and indoor, outdoor, and ambient air concentrations for PM/gases.
Description:
The oxygenate methyl tert-butyl ether (MTBE) has been added to gasoline to meet national ambient air quality standards in those parts of the US that are non-compliant for carbon monoxide. Although MTBE has provided important health benefits in terms of reduced hazardous air pollutants, the increasing occurrence and detection of MTBE in drinking water sources in California, New Jersey, and elsewhere has raised concerns about potential exposures from water usage and resulting health effects. In addition to MTBE, disinfection byproducts can be present in the water people use for showering, bathing, or drinking, as a result of the reaction of disinfection agents with organic material already present in water. Chlorine reacts with humic acids to form the trihalomethanes, which are the most common and abundant byproducts in chlorinated water. Besides chloroform, which has been widely studied, the byproduct dibromochloromethane (DBCM) occurs as a result of the chlorination process in those areas that naturally have bromide in their ground water. Relatively little information on exposure to this chemical is available. We conducted studies to determine the uptake by humans of MTBE and DBCM as a result of controlled, short-term dermal and inhalation exposures. Our approach made use of continuous real-time breath analysis to generate exhaled-breath profiles and evaluate MTBE and DBCM kinetics in the body. In the dermal exposure study, real-time breath analysis was used to measure the absorption of MTBE and DBCM while bathing in contaminated water. Seven subjects bathed in water containing MTBE-d12 (at ~150 ug/L) and DBCM (at ~40 ug/L) at 40 degrees C for 30 minutes. The breath profiles obtained for MTBE and DBCM were qualitatively similar to those for chloroform obtained in a previous study, but the amounts of MTBE and DBCM dermally absorbed were significantly lower than in the case of chloroform. In the inhalation study, seven subjects were exposed continuously to 500 ppb MTBE-d12 and 115 ppb DBCM, except for several brief (2-min) intervals in which breath measurements were taken. Total exposure time was 30 min, followed by exposure to clean air for ~30 min. Exhaled breath was sampled and analyzed with the real-time breath technology; blood samples were simultaneously collected from the subjects (3-4 samples during exposure; 2-5 samples post-exposure). The real-time technology was specially modified with a biofeedback exposure control system to allow us to make uptake measurements during the exposure period; breath measurements were continuous throughout the post-exposure period. The uptake and decay of the target chemicals in the blood was estimated by fitting the exposure and post-exposure breath and blood data to a multi-compartmental model that estimated residence times. The measurements also provided information on blood:breath concentration ratios, as well as the fraction of breath MTBE and DBCM exhaled unchanged at equilibrium.
This abstract has been reviewed in accordance with US Environmental Protection Agency's peer and administrative review policies and approved for publication.