Uptake and decay of volatile organic compounds at environmental concentrations: application of a four-compartment model to a chamber study of five human subjects.

Five subjects were exposed to nine volatile organic compounds (VOCs) at concentrations that can be encountered in everyday life. Breath samples were collected during a 10-h uptake phase and a 24-h decay phase. It was possible to determine four distinct slopes in the decay curve for each chemical. The distribution in the body and residence times in different tissues were calculated using a linear four-compartment mass-balance model. The model was used to predict breath concentrations for two subjects in a second chamber experiment including the same nine VOCs, representing three chemical classes (aromatic, aliphatic, and chlorinated compounds). Predicted values were generally within 25% of those observed, suggesting that the model parameters calculated here could be useful in estimating exposure and body burden to other VOCs in these three classes. Median residence times for the nine VOCs ranged from 3-12 min for compartment 1 (metabolizing); 0.3-2 h for compartment 2; 2-5 h for compartment 3; and 1-4 d for compartment 4. The fraction of the parent compound exhaled at equilibrium was estimated to range from 0.06-0.16 for four aromatic compounds and decane; 0.22-0.23 for trichloroethylene and dichloromethane; 0.35 for hexane; and 0.88 for 1,1,1-trichloroethane. Limited blood measurements were obtained for six of the nine VOCs in two subjects simultaneously with the breath samples over four-hour decay periods. Blood/breath ratios agreed well between the two subjects, but were higher than human blood/air partition coefficients reported in subjects exposed to high concentrations. This observation is consistent with results from other studies at relatively low concentrations.