Personal exposure to different levels of benzene and its relationships to the urinary metabolites S-phenylmercapturic acid and trans,trans-muconic acid

Rapid determination of six urinary benzene metabolites in occupationally exposed and unexposed subjects

A gas chromatography-mass spectrometry method for measurement of the main urinary metabolites of benzene, namely, phenol, catechol, hydroquinone, 1,2,4-trihydroxybenzene (trihydroxybenzene), t,t-muconic acid (muconic acid), and S-phenylmercapturic acid (phenylmercapturic acid), is reported. The method is considerably simpler than existing assays. It was applied to urine from benzene-exposed subjects and controls from Shanghai, China. When subjects were divided into controls (n = 44), those exposed to </= 31 ppm benzene (n = 21), and those exposed to > 31 ppm benzene (n = 19), Spearman correlations with exposure category were >/= 0.728 (p < 0.0001) for all metabolites except trihydroxybenzene. When exposed subjects were compared on an individual basis, all metabolites, including trihydroxybenzene, were significantly correlated with benzene exposure (Pearson r >/= 0.472, p </= 0.002) and with each other (Pearson r >/= 0.708, p < 0.0001). Ratios of individual metabolite levels to total metabolite levels provided evidence of competitive inhibition of CYP 2E1 enzymes leading to increased production of phenol, catechol, and phenylmercapturic acid at the expense of hydroquinone, trihydroxybenzene, and muconic acid. Since all metabolites were detected in all control subjects, the method can be applied to persons exposed to environmental levels of benzene.

An electrospray ionization tandem mass spectrometry based system with an online dual-loop cleanup device for simultaneous quantitation of urinary benzene exposure biomarkers trans,trans-muconic acid and S-phenylmercapturic acid

An electrospray ionization tandem mass spectrometry (ESI-MS/MS) system with an online dual-loop cleanup device was developed for simultaneous quantitation of the urinary benzene exposure biomarkers trans,trans-muconic acid (ttMA) and S-phenylmercapturic acid (SPMA). The cleanup device was constructed from an autosampler, two electrically operated two-position switching valves, a reversed-phase C18 trap cartridge, a 200-microL loop, and two solvent-delivery pumps. The device was interfaced directly with a triple-quadrupole mass spectrometer and fully controlled by computer software and hardware. Because isotope dilution by introducing 13C-labeled ttMA and SPMA as internal standards was employed, the precision of the analytical system was high (for ttMA, intra- and inter-day CV values ranged from 3.82-4.53%; for SPMA, 2.13-7.06%). The calibration curves obtained using human urine spiked with ttMA were linear from 15.6-4000 microg/L (R = 0.9998) and SPMA at concentrations from 0.78-200 microg/L (R = 0.9993). The method detection limit (MDL) for SPMA was 0.23 microg/L. The MDL of ttMA could not be determined accurately because of unavailability of an appropriate blank urine matrix, but was estimated to be lower than 7.43 microg/L. Without tedious manual sample cleanup procedures the analytical system is fully automated and is therefore useful for high-throughput simultaneous determination of urinary ttMA and SPMA. The sample throughput is roughly 100 samples per day. With the selectivity and the sensitivity provided by MS/MS detection, the analytical system can be used for large-scale monitoring of environmental or occupational exposure of humans to benzene.