Correlation of xylene exposure and methyl hippuric acid excretion in urine among paint industry workers

Different calculations of methyl hippuric acid excretion in urine were correlated to the time-weighted average (TWA) of the xylene exposure of a complete workday for 40 paint industry workers exposed to 12 different solvents. The 8-h TWA xylene exposure varied between 0 and 865 (median 69) mg/m3. The amount of methyl hippuric acid excreted in about 24 h showed only a slightly higher linear correlation to the xylene exposure than the amount of methyl hippuric acid excreted per hour during the latter part of the workshift among the 37 subjects exposed to TWA xylene air concentrations of 0-200 mg/m3. It was concluded that the methyl hippuric acid excretion rate during the latter part of the workshift can be used for crude xylene exposure categorizations.