Estimation of absorption of environmental contaminants in low-level exposure by pharmacokinetic analysis

Inhalation pharmacokinetics of the environmental contaminants 1,1,1-trichloroethane, tetrachloroethylene, trichloroethylene, benzene, and p-dichlorobenzene were determined in male Sprague-Dawley rats, and data generated were used to obtain fundamental data for risk assessment of chronic low-level exposures to these substances. Measured amounts of the substances were injected into a closed chamber system in which a rat had been placed, and the concentration changes in the chamber air were examined. The pharmacokinetics of the substances were evaluated using linear or nonlinear compartment models. The metabolic elimination amounts at various exposure concentrations were extrapolated using the estimated pharmacokinetic parameters. At low (1 ppb) concentration exposure to benzene or trichloroethylene the fraction of elimination of these substances was 1.6 and 1.5 times higher, respectively, than that seen at high (10 ppm) concentration exposure. Extrapolation kinetics of low-exposure data showed more trichloroethylene (0.0016 micromol/h/kg), benzene (0.0014 micromol/h/kg), and p-dichlorobenzene (0.00052 micromol/h/kg) was absorbed by the rats than 1,1,1-trichloroethane (0.000019 micromol/h/kg) and tetrachloroethylene (0.000029 micromol/h/kg). Although the exposure concentrations for all chemicals were equal, the differences in absorption quantities need to be considered in evaluation of potential risk assessment.