Excretion of mercapturic acids in human urine after occupational exposure to 2-chloroprene.

A pilot study was conducted for human biomonitoring of the suspected carcinogen 2-chloroprene. For this purpose, urine samples of 14 individuals occupationally exposed to 2-chloroprene (exposed group) and of 30 individuals without occupational exposure to alkylating substances (control group) were analysed for six potential mercapturic acids of 2-chloroprene: 4-chloro-3-oxobutyl mercapturic acid (Cl-MA-I), 4-chloro-3-hydroxybutyl mercapturic acid (Cl-MA-II), 3-chloro-2-hydroxy-3-butenyl mercapturic acid (Cl-MA-III), 4-hydroxy-3-oxobutyl mercapturic acid (HOBMA), 3,4-dihydroxybutyl mercapturic acid (DHBMA) and 2-hydroxy-3-butenyl mercapturic acid (MHBMA). In direct comparison with the control group, elevated levels of the mercapturic acids Cl-MA-III, MHBMA, HOBMA and DHBMA were found in the urine samples of the exposed group. Cl-MA-I and Cl-MA-II were not detected in any of the samples, whereas HOBMA and DHBMA were found in all analysed urine samples. Thus, for the first time, it was possible to detect HOBMA and Cl-MA-III in human urine. The mercapturic acid Cl-MA-III could be confirmed as a specific metabolite of 2-chloroprene in humans providing evidence for the intermediate formation of a reactive epoxide during biotransformation. The main metabolite, however, was found to be DHBMA showing a distinct and significant correlation with the urinary Cl-MA-III levels in the exposed group. The obtained results give new scientific insight into the course of biotransformation of 2-chloroprene in humans.