Science Inventory

DERMAL EXPOSURE TO METHYL TERT-BUTYL ETHER (MTBE) AND DIBROMOCHLOROMETHANE (DBCM) WHILE BATHING WITH CONTAMINATED WATER

Citation:

GORDON, S. M. DERMAL EXPOSURE TO METHYL TERT-BUTYL ETHER (MTBE) AND DIBROMOCHLOROMETHANE (DBCM) WHILE BATHING WITH CONTAMINATED WATER. U.S. Environmental Protection Agency, Washington, DC, 2005.

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 help meet national ambient air quality standards in those parts of the U.S. 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, a widely used disinfection agent, reacts with humic acids to form the trihalomethanes, which are the most common and abundant byproducts in chlorinated water. Besides chloroform, which has been extensively studied, the byproduct dibromochloromethane (DBCM) occurs as a result of the chlorination process in those areas that naturally have bromide in their ground water.

Because the breath analyzer showed almost no discernible change in MTBE and DBCM breath concentrations in the shower experiments that were conducted, we abandoned all further shower exposure efforts in favor of the bath water experiments.

Three male and two female volunteers participated in the bath water study, in which each was exposed to 40 µg/L of DBCM and 150 µg/L of MTBE-d12 in water for 30 minutes. We were unable to derive meaningful results from the real-time breath analyzer data generated for DBCM, largely because of what appeared to be an interfering contaminant with mass spectral fragment ions that occurred at the same mass as the mass used to monitor for DBCM.

All of the breath concentration/time profiles obtained for the five participants, as a result of dermal exposure to MTBE-d12 and MTBE in water, showed similar small increases in breath concentrations, from levels that were roughly equal to or less than 2 - 10 µ/m3, the method detection limit, to peak levels of 7 - 15 µg/m3. After exposure ended, breath levels slowly decreased and tended toward the pre-exposure levels during the 30-minute elimination monitoring period. In all cases, except for one subject, the measured levels throughout the monitoring periods were above the limits of detection obtained with the real-time breath analyzer. This concentration range is similar to that reported for background levels of MTBE in previous studies that relied on batch collection and gas chromatographic/mass spectrometric (GC/MS) analysis for breath sample measurement.

Uptake and elimination residence times were estimated using a one-compartment linear model. The mean residence times for the decay phase were roughly twice as long as the mean residence times for the uptake phase, viz., Tuptake = 21.2 ± 13.1 min and Tdecay = 41.5 ± 26.3 min [mean 1 standard deviation]. The reasonably good agreement obtained for the residence times among the five participants suggests that our estimates of the model parameters may be fairly robust. These estimated values are much greater than the residence times obtained in our earlier study of the dermal absorption of chloroform from bath water, for which the mean uptake residence time was 8.2 ± 3.1 min and the mean decay residence time was 7.7 ± 1.0 min. This may be due to the greater solubility of MTBE in water, which is reflected by their respective Henry's Law coefficients, namely, 1.6 mole/atm for MTBE vs. 0.26 mole/atm for chloroform. These residence times also are significantly larger than the uptake and decay residence times for MTBE determined in our companion inhalation study.

The total amount of MTBE-d12 exhaled during the exposure and post-exposure periods was estimated by integrating the area under the breath uptake and elimination curve. The mean amount of MTBE-d12 exhaled at an average temperature of 39.5 °C was 3.0 ± 1.1 (SD) µg (range: 1.7 - 4.6 µg). The mean exhaled amount obtained in our earlier bath water study of chloroform absorption at roughly the same temperature was 7.0 ± 2.0 µg. This indicates that the dermal uptake of MTBE from bath water is significantly smaller than that of chloroform under similar exposure conditions.

It is interesting to note that, although dermal absorption of MTBE from water has been measured directly in the blood of human subjects in at least one earlier study, our measurements appear to be the first of the dermal uptake of MTBE using continuous breath analysis. Finally, the model parameters determined in this study may be useful to risk assessors in EPA State and Regional offices for estimating dermal exposure to this contaminant while bathing.

Record Details:

Record Type:DOCUMENT( EXTRAMURAL DOCUMENT/ CONTRACT)
Product Published Date:03/17/2005
Record Last Revised:03/14/2006
OMB Category:Other
Record ID: 131705