Effect of simultaneous exposure to toluene and xylene on their respective biological exposure indices in humans.

Studies that specifically address the influence of controlled human exposure to a combination of solvents on the biological monitoring of exposure are limited in number. The present study was undertaken to investigate whether simultaneous exposure of human volunteers to toluene and xylene could modify the respective metabolic disposition of these solvents. Five adult Caucasian men were exposed for 7 consecutive h/day over 3 consecutive days to 50 ppm toluene and 40 ppm xylene either separately or in combination in a dynamic, controlled exposure chamber (low-level exposure). The experiment was repeated three times at intervals of 2 weeks. In another experiment, three subjects were exposed to 95 ppm toluene and 80 ppm xylene or a combination of both for 4 h (high-level exposure). The concentration of unchanged solvents in blood (B) and in end-exhaled air (EA) as well as the urinary excretion of hippuric acid (HA) and methylhippuric acids (MHAs) were determined. Simultaneous exposure to the lowest level of solvents did not alter the concentration of unchanged solvents in blood or in exhaled air (average of 3-weekly means; single vs mixed exposure at 6.5 h exposure): B-toluene, 77.1 vs 78.1 micrograms/100 ml; B-xylene, 67.6 vs 77.8 micrograms/100 ml; EA-toluene, 9.9 vs 9.5 ppm; EA-xylene, 5.3 vs 4.8 ppm. Similarly, mixed exposure did not modify the excretion of urinary metabolites during the 3- to 7-h exposure period: HA, 1.11 vs 1.11 g/g creatinine: MHAs, 0.9 vs 0.87 g/g creatinine.(ABSTRACT TRUNCATED AT 250 WORDS)