Kinetics of styrene urinary metabolites: a study in a low-level occupational exposure setting in Singapore.

Biological monitoring of styrene exposure commonly involves measurement of styrene metabolites, mainly mandelic acid (MA) and phenylglyoxylic acid (PGA), in the urine of exposed subjects. Previous studies on the kinetics of styrene metabolites in urine were mostly conducted in a controlled environment on subjects exposed to high concentrations of styrene. In this study, we examined subjects exposed to low levels of styrene in a fiber-reinforced plastics (FRP) plant to see whether the excretion kinetics of styrene metabolites are similar under field conditions. Eight healthy Chinese male volunteers were exposed to styrene for 4 h with a mean environmental concentration of 11 ppm. Urine samples were collected continuously for 20 h after termination of the exposure and concentrations of urinary MA and PCA were determined. The results showed that MA was rapidly excreted in urine after the exposure, with a half-life of 2.1 h or 1.9 h when corrected with urine creatinine. The excretion of PGA followed that of MA and the half-life was 8.1 h or 5.1 h after correction with creatinine. The half-lives are considerably shorter compared to those in previous reports, suggesting that environmental factors, exposure conditions, or ethnic differences may affect the excretion kinetics of styrene metabolites. The fast excretion of styrene metabolites is also consistent with the observation that urine MA and PGA levels correlated better with the half-day time-weighted average (TWA) concentration of environmental styrene than with the whole-day TWA concentration. Our findings thus underscore the need for information on excretion kinetics in order to develop an appropriate biological monitoring scheme for specific exposure settings and subjects.