Biological monitoring of workers exposed to ethylbenzene and co-exposed toxylene

Objective: Ethylbenzene is an important constituent of widely used solvent mixtures in industry. The objective of the present study was to provide inf ormation about biological monitoring of occupational exposure to ethylbenze ne, and to review the biological limit values corresponding to the threshol d limit value of ethylbenzene. Methods: A total of 20 male workers who had been exposed to a mixture of ethylbenzene and xylene, through painting and solvent mixing with commercial xylene in a metal industry, were recruited i nto this study. Environmental and biological monitoring were performed duri ng an entire week. The urinary metabolites monitored were mandelic acid for ethylbenzene and methylhippuric acid for xylene. Correlations were analyze d between urinary metabolites and environmental exposure for ethylbenzene a nd xylene. The interaction effects of a binary exposure to ethylbenzene and xylene were also investigated using a physiologically based pharmacokineti c (PBPK) model. Results: The average environmental concentration of organic solvents was 12.77 ppm for xylene, and 3.42 ppm for ethylbenzene. A signif icant correlation (R-2 = 0.503) was found between environmental xylene and urinary methylhippuric acid. Urinary level of methylhippuric acid correspon ding to 100 ppm of xylene was 1.96 g/g creatinine in the worker study, wher eas it was calculated as 1.55 g/g creatinine by the PBPK model. Urinary lev el of mandelic acid corresponding to 100 ppm of ethylbenzene was found to b e 0.7 g/g creatinine. PBPK results showed that the metabolism of ethylbenze ne was highly depressed by co-exposure to high concentrations of xylene lea ding to a non-linear behavior. Conclusions: At low exposures, both methylhi ppuric acid and mandelic acid can be used as indicators of commercial xylen e exposures. However at higher concentrations mandelic acid cannot be recom mended as a biological indicator due to the saturation of mandelic acid pro duced by the co-exposure to xylene.