Urinary benzene as a biomarker of exposure among occupationally exposed and unexposed subjects

Urinary benzene (UB) was investigated as a biomarker of exposure among benz ene-exposed workers and unexposed subjects in Shanghai, China, Measurements were performed via headspace solid phase microextraction of 0.5 mi of urin e specimens followed by gas chromatography-mass spectrometry, This assay is simple and more sensitive than other methods (detection limit 0.016 mug be nzene/l urine). The median daily benzene exposure was 31 p.p.m. (range 1.65 -329 p.p.m.), When subjects were divided into controls (n = 41), those expo sed to less than or equal to 31 p.p.m. benzene (n = 22) and >31 p.p.m. benz ene (n = 20), the median UB levels were 0.069, 4.95 and 46.1 mug/l, respect ively (Spearman r = 0.879, P < 0.0001), A linear relationship was observed between the logarithm of UB and the logarithm of benzene exposure in expose d subjects according to the following equation: In(UB, <mu>g/l) = 0.196 + 0 .709 In (exposure, p.p.m.) (r = 0.717, P < 0.0001), Considering all subject s, linear relationships were also observed between the logarithm of UB and the corresponding logarithms of four urinary metabolites of benzene, namely t,t-muconic acid (r = 0.938, P < 0.0001), phenol (r = 0.826, P < 0.0001), catechol (r = 0.812, P < 0.0001) and hydroquinone (r = 0.898, P < 0.0001). Ratios of individual metabolite levels to total metabolites versus UB provi de evidence of competitive inhibition of CYP450 enzymes leading to increase d production of phenol and catechol at the expense of hydroquinone and muco nic acid, Among control subjects UB was readily detected with a mean level of 0.145 <mu>g/l (range 0.027-2.06 mug/l), compared with 5.63 mug/l (range 0.837-26.38 mug/l) in workers exposed to benzene below 10 p.p.m. (P < 0.000 1), This suggests that UB is a good biomarker for exposure to low levels of benzene.