Occupational chronic exposure to organic solvents XVII. Ambient and biological monitoring of workers exposed to xylenes

Ambient-air and biological monitoring of occupational xylene exposure were carried out on 2 groups of workers (13 and 10 men, respectively) exposed to a mixture of xylenes during the production of paints or during spraying. Methods: Personal ambient-air monitoring was performed for one complete work shift. Blood and urine samples were collected directly at the end of the shift. Biological monitoring was based on the determination of the concentration of xylenes in blood and on the quantification of the sum of the three methylhippuric acids in urine. Results: Average xylene ambient-air concentrations were 29 ppm (production) and 8 ppm (spraying), ranging from 5 to 58 ppm and from 3 to 21 ppm, respectively. The concentrations of xylenes in blood ranged from 63 to 715 μg/l and from 49 to 308 μg/l, with average values being 380 and 130 μg/l, respectively. Accordingly, the workers engaged in paint production also excreted more methylhippuric acids in their urine (average 1221 mg/l, range 194–2333 mg/l) than did the sprayers (average 485 mg/l, range 65–1633 mg/l). Discussion: Our results as well as a literature review indicate that occupational xylene exposure on average barely exceeds the threshold limit value of 100 ppm as proposed by both American and German institutions. Biological monitoring based on the determination of xylenes in blood and of methylhippuric acids in urine provides sufficient sensitivity and specificity for occupational health surveillance. The results also confirm the current limit values (BAT values) proposed by the Deutsche Forschungsgemeinschaft for xylenes in blood (1500 μg/l) and methylhippuric acids in urine (2000 mg/l).