A Field Evaluation of Mandelic Acid in Urine as a Compliance Monitor for Styrene Exposure

Abstract

The Special Studies Unit of Cal/OSHA monitored mandelic acid in urine and styrene exposure in a survey of 324 workers in the fiberglass-reinforced plastics industry. The urine was sampled at the end of the shift, and the mandelic acid was analyzed by high-performance liquid chromatography. A stepwise regression analysis shows that the mandelic acid (MA) concentration is affected by the styrene concentration, the urine's specific gravity, effective respirator usage, work rate, and sampling on Friday; it is unaffected by skin exposure to styrene or exposure to other solvents. The regression model supports the Biological Exposure Index (BEI) of 1 g/L if the MA concentration is standardized for specific gravity. In a comparison of styrene and MA compliance decision, 7 percent of the subjects were false positives, i.e., violating the BEI while in compliance with the styrene threshold limit value. Since one of the false positives was using an organic vapor respirator, the MA monitoring did demonstrate that the respirator cartridge had become overloaded. The problematic interpretation of the remaining false positives, the wide confidence limits around the MA measurements, quality control problems with the MA analysis, and the difficulties in obtaining urine samples caused Cal/OSHA to recommend against the monitoring of urinary MA for determining compliance with health standards. The false positives also indicate that MA monitoring can potentially detect disease risks which are not found by air exposure monitoring for styrene.