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2-Chloroprene is a high production volume chemical (> 300,000 t global per year), which is mainly used as a monomer for the production of polychloroprene. As 2-chloroprene is classified as possibly carcinogenic to humans, an effective tool for the monitoring of the individual exposure to 2-chloroprene is required.
Methods
We developed a biological monitoring strategy based on the urinary excretion of several mercapturic acids (MAs) which may derive from the conjugation of 2-chloroprene and its metabolites to glutathione. The selected biomarkers were 4-hydroxy-3-oxo-butyl-MA (HOBMA), 4-chloro-3-oxo-butyl-MA (Cl-MA I), 4-chloro-3-hydroxybutyl-MA (Cl-MA II), 3-chloro-2-hydroxy-3-butenyl-MA (Cl-MA III) and 3,4-dihydroxybutyl-MA (DHBMA). For determination of these MAs we applied an online-SPE-LC-MS/MS procedure. The detection limits ranged from 1.4 (Cl-MA III) to 4.2 µg/l (HOBMA). The method was applied to urine samples of 14 employees occupationally exposed to 2-chloroprene and of 30 subjects without any occupational exposure to 2-chloroprene (controls).
Results
Cl-MA I and Cl-MA II were not detected in any of the samples. In the urine samples of the controls Cl-MA III was also not found, but we detected this metabolite in 11 urine samples of the exposed group (median 6.1, max 25.7 µg/g creatinine). Furthermore, we discovered significantly elevated urinary levels of DHBMA (median 3,255 vs. 179 µg/g creatinine) and of HOBMA (median 214 vs. 111 µg/g creatinine) in occupationally exposed workers compared to the controls. Moreover we found a significant correlation between DHBMA and Cl-MA III for the exposed employees exposed.
Discussion
The mercapturic acids DHBMA and Cl-MA III appear to be suitable biomarkers for the assessment of occupational exposure to 2-chloroprene. DHBMA occurs as main product in 2-chloroprene metabolism and was found to be a very sensitive parameter. The determination of Cl-MA III as specific biomarker of 2-chloroprene is important as well, particularly in the case of co-exposure to 1,3-butadiene, which is metabolized to DHBMA, too.