UPTAKE AND DECAY OF VOLATILE ORGANIC-COMPOUNDS AT ENVIRONMENTAL CONCENTRATIONS - APPLICATION OF A 4-COMPARTMENT MODEL TO A CHAMBER STUDY OF5 HUMAN-SUBJECTS

Five subjects were exposed to nine volatile organic compounds (VOCs) a t concentrations that can be encountered in everyday life. Breath samp les 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 f or 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 fo r two subjects in a second chamber experiment including the same nine VOCs, representing three chemical classes (aromatic, aliphatic, and ch lorinated compounds). Predicted values were generally within 25% of th ose observed suggesting that the model parameters calculated here coul d be useful in estimating exposure and body burden to other VOCs in th ese 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 fro m 0.06-0.16 for four aromatic compounds and decane; 0.22-0.23 for tric hloroethylene 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 o ver four-hour decay periods. Blood/breath ratios agreed well between t he two subjects, but were higher than human blood/air partition coeffi cients reported in subjects exposed to high concentrations. This obser vation is consistent with results from other studies at relatively low concentrations.