Comparative evaluation of blood and urine analysis as a tool for biological monitoring of n-hexane and toluene

Blood and urine samples were collected from 57 male Japanese solvent workers [exposed to n-hexane (Hex-A), ethyl acetate, and toluene (Tol-A) at 1.5, 2.3, and 2.3 ppm as GM-TWA, respectively] and also from 20 male nonexposed workers at the end of a 8-h shift, and analyzed for n-hexane (Hex-B) and toluene (Tol-B) in blood, and n-hexane (Hex-U), toluene (Tol-U), 2,5-hexanedione [both with (HD-U/cHYD) and without hydrolysis (HD-U/sHYD)] and hippuric acid (HA-U) in urine. Regression analysis showed that both Hex-B and Tol-B correlated significantly with corresponding exposure to the solvents. Solvents in urine (Hex-U and Tol-U) also correlated with solvents in air but with smaller correlation coefficients than the solvents in blood. Both HD-U/cHYD and HD-U/sHYD showed significant correlation with Hex-A, but HA-U failed to do so with Tol-A. Based on the correlation among biological exposure indicators and solvent concentration in air, sensitivity as an exposure indicator was compared between the solvent in blood and the metabolite in urine in terms of the lowest solvent concentration at which the exposed can be separated (with statistical significance) from the nonexposed (the lowest separation concentration; LSC). The LSC was 3.9 ppm for Hex-B, 1 to 2 ppm for HD-U/sHYD and 10 to 30 ppm for HD-U/cHYD, suggesting that HD-U/sHYD is superior even to Hex-B in detecting low n-hexane exposure; this high sensitivity of HD-U/sHYD is due to the absence of HD-U/sHYD in the urine from the nonexposed.