Abstract
The organic constituents of exhaled human breath are representative of bloodborne concentrations through gas exchange in the blood/breath interface in the lungs. The presence of specific compounds can be an indicator of recent exposure or represent a biological response of the subject. For volatile organic compounds, sampling and analysis of breath is preferred to direct measurement from blood samples because breath collection is noninvasive, potentially infectious waste is avoided, the sample supply is essentially limitless, and the measurement of gas-phase analytes is much simpler in a gas matrix rather than in a complex biological tissue such as blood. However, to assess the distribution of a contaminant in the body requires a reasonable estimate of the blood level. We have investigated the use of noninvasive breath measurements as a surrogate for blood measurements for (high) occupational levels of trichloroethene in a controlled exposure experiment. Subjects were placed in an exposure chamber for 24 hr; they were exposed to 100 parts per million by volume trichloroethene for the initial 4 hr and to purified air for the remaining 20 hr. Matched breath and blood samples were collected periodically during the experiment. We modeled the resulting concentration data with respect to their time course and assessed the blood/breath relationship during the exposure (uptake) period and during the postexposure (elimination) period. Estimates for peak blood levels, compartmental distribution, and time constants were calculated from breath data and compared to direct blood measurements to assess the validity of the breath measurement methodology. Blood/breath partition coefficients were studied during both uptake and elimination. At equilibrium conditions at the end of the exposure, we could predict actual blood levels using breath elimination curve calculations and a literature value partition coefficient with a mean ratio of calculated:measured of 0.98 and standard error (SE) = 0.12 across all subjects. blood/breath comparisons at equilibrium resulted in calculated in vivo partition coefficients with a mean of 10.8 and SE = 0.60 across all subjects and experiments and 9.69 with SE = 0.93 for elimination-only experiments. We found that about 78% of trichloroethene entering the body during inhalation exposure is metabolized, stored, or excreted through routes other than exhalation.