Quantification of Urinary Metabolites of Toluene and Xylene Isomers as Biological Indices of Occupational Exposure in Printing Industry Workers

Background: In the printing industry, workers are occupationally exposed to an extensive variety of chemical solvents, including toluene and xylene. Biological monitoring is an essential tool for assessing occupational health risk. Objectives: The aim of the present study was to evaluate occupational exposure to toluene and xylene, as well as the biomarkers of exposure, in workers of the printing industry. Methods: The hippuric acid (HA) and o-, m- and p-methyl hippuric acids (o-, m-, p- MHAs) as the biomarkers of occupational exposure to toluene and each of the three xylene isomers, respectively, were determined in the urine samples of 84 subjects, including 44 printing workers and 40 non-exposed subjects. Results: The mean concentrations of toluene (37.64 ± 24.09 ppm) in the breathing zone of workers were higher, and the mean level of each of the three isomers of xylene (o-, m-, and p-xylene) was less than the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLVs). In addition, the levels of urinary HA, o-MHA, and m- and p-MHA in the exposed group were 0.15 ± 0.04, 0.11 ± 0.01, and 0.19 ± 0.07 g g-1 creatinine, respectively. Printing workers showed a significant increase in the levels of urinary HA compared to the non-exposed subjects (P < 0.001). The correlation analysis demonstrated significant correlations between the intensity of the occupational exposure to toluene and xylene and the level of exposure biomarkers in the urine. Conclusions: The results indicated that although all the urinary biomarkers of exposure were below the Biological Exposure Indices (BEIs) recommended by ACGIH, the levels of the urinary metabolites of toluene and xylene were increased in printing workers. Therefore, monitoring of occupational exposure to toluene and xylene is helpful in the following-up of affected workers in the printing industry.