Coexposure to toluene and p-xylene in man: uptake and elimination

Eight male subjects were experimentally exposed to toluene, p-xylene, and a combination of toluene and p-xylene in order to study the influence of coexposure and exposure to different levels of each solvent on their uptake and elimination. The exposures were performed for four hours at exposure levels equivalent to or lower than the Swedish threshold limit value for toluene, 300 mg/m3 (3.2 mmol/m3). During and after the exposure, solvent concentrations were measured in blood and in expired air. In addition, the pulmonary ventilation rate was measured during the exposure. Decreases in the blood/end exhaled air concentration ratio were found for both toluene and p-xylene when given in combination compared with separate exposure. The total solvent uptake relative to the exposure level was decreased after exposure to the higher solvent concentrations, and the apparent clearance was also decreased after exposure to the higher concentrations of solvent. Finally, the blood solvent concentrations were lower at the end of the exposure compared with the maximal concentration during each exposure condition. In the kinetics of toluene and p-xylene the total amount of toluene or p-xylene, or both, seems to be of major importance. The change in blood/end exhaled air concentration ratio may indicate an effect of coexposure.