The existence and feasibility of styrene (100425) control measures were investigated. Among the secondary objectives was to monitor the mandelic-acid (90642) (MA) in worker urine samples. Industrial hygienists performed unannounced inspections in 141 of over 300 large mold fiberglass reinforced plastics (FRP) firms in California. Fifty of the inspected facilities were judged to have airborne styrene levels above the NIOSH recommended limit of 50 parts per million (ppm). Of the 378 employees who were monitored for organic vapor exposure, 324 (85%) provided end of shift urine samples for MA analysis. The maximum styrene exposure exceeded 100ppm. A stepwise regression analysis showed that the MA concentration was affected by the styrene concentration, the urine specific gravity, effective respirator usage, work rate, and sampling on Friday and was unaffected by skin exposure to styrene or exposure to other solvents. The regression model supported the Biological Exposure Index (BEI) of 1 gram/liter if the MA concentration was standardized for specific gravity. The styrene/mandelic-acid relationship showed very wide confidence limits, both in the regression analysis and in a comparison between styrene and MA compliance decisions. The compliance decisions also showed a 6% bias toward false positives. A regulatory agency would have difficulty justifying legal action with these false positives. For compliance determinations by other parties, the false positives suggest a role for urine monitoring to supplement air exposure monitoring of styrene. A direct dose response relationship between neurological symptoms and MA monitored according to the BEI procedures would be most helpful.
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