Biological monitoring of low level occupational xylene exposure and the role of recent exposure
Jacobson, GA and McLean, SR, Biological monitoring of low level occupational xylene exposure and the role of recent exposure, Annals of Occupational Hygiene, 47, (4) pp. 331-336. ISSN 0003-4878 (2003) [Refereed Article]
The correlation between low level time-weighted average (TWA) atmospheric xylene exposure (p.p.m.) and urinary methylhippuric acid (MHA) expressed per gram of creatinine was examined. Subjects were recruited from workplaces that utilized xylene. Ambient monitoring of o-, m- and p-xylene isomers was carried out using passive diffusion vapour monitors. Adjusted (post-shift minus pre-shift) and post-shift urinary levels of xylene metabolites (2-, 3- and 4-MHA) were determined by GC–MS. Twenty subjects were recruited into the study. Total xylene TWA exposures were 3.36 ± 3.63 p.p.m. (mean ± SD) with a range of 0.03–14.44 p.p.m. The r2 values for the regression equations between xylene exposure and individual and total adjusted MHA isomers were 0.390, 0.709, 0.677 and 0.631 for o-, m-, p- and total xylenes, respectively, which was greater than the respective correlations between non-adjusted samples. In conclusion, biological monitoring of occupational xylene exposure at levels <15 p.p.m. using urinary MHA showed a good correlation with atmospheric levels and is a valid complement to ambient monitoring. Even though occupational xylene exposure in the workplaces studied was generally low, MHA was found in the pre-shift urine of all workers and the use of adjusted values showed modest improvements in correlations. Recent exposure prior to sampling, either from occupational or non-occupational sources, should be considered when biological monitoring of xylene is undertaken. Extrapolation of data from this study predicted a MHA concentration in post-shift urine of 1.3 g/g creatinine after exposure to a TWA of 100 p.p.m. xylene.