KINETICS OF STYRENE URINARY METABOLITES - A STUDY IN A LOW-LEVEL OCCUPATIONAL EXPOSURE SETTING IN SINGAPORE

Biological monitoring of styrene exposure commonly involves measuremen t of styrene metabolites, mainly mandelic acid (MA) and phenylglyoxyli c acid (PGA), in the urine of exposed subjects. Previous studies on th e kinetics of styrene metabolites in urine were mostly conducted in a controlled environment on subjects exposed to high concentrations of s tyrene. In this study, we examined subjects exposed to low levels of s tyrene in a fiber-reinforced plastics (FRP) plant to see whether the e xcretion kinetics of styrene metabolites are similar under field condi tions. Eight healthy Chinese male volunteers were exposed to styrene f or 4 h with a mean environmental concentration of 11 ppm. Urine sample s were collected continuously for 20 h after termination of the exposu re and concentrations of urinary MA and PCA were determined. The resul ts showed that MA was rapidly excreted in urine after the exposure, wi th 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 consider ably shorter compared to those in previous reports, suggesting that en vironmental factors, exposure conditions, or ethnic differences may af fect the excretion kinetics of styrene metabolites. The fast excretion of styrene metabolites is also consistent with the observation that u rine MA and PGA levels correlated better with the half-day time-weight ed 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 subjec ts.