Free and total 2,5-hexanedione in biological monitoring of workers exposed to n-hexane in the shoe industry

Abstract

Objectives: To analyse the role of total 2,5-hexanedione (2,5-HD) compared with free 2,5-HD as a biological indicator of exposure to n-hexane at work.

Methods: One-hundred and thirty two workers in contact with this solvent during their occupation in the shoe industry in the province of Alicante (Spain) were studied. Environmental and biological tests were carried out analysing variations of the concentration of the metabolite in urine corresponding to different working conditions. Environmental exposure was evaluated in each work place using active personal monitors and measured by gas chromatography (GC). Dichloromethane extracts of the urine samples collected at the end of the working shifts were analysed, before (determining free 2,5-HD, the toxic metabolite) and after acid hydrolysis (pH 0.1) (yielding the total 2,5-HD) and also by GC. The concentration of conjugated metabolite 4,5-dihydroxy-2-hexanone was calculated from the difference between total and free 2,5-HD.

Results: Free 2,5-HD represented an average of 14.2% of the total 2,5-HD determined in urine, and this percentage increased significantly (P<0.01) with higher environmental levels of acetone. Other factors, such as absorption through the skin (depending on the use of gloves) and the day on which samples were taken also significantly affected the relation between the two indicators and their respective relationships with environmental concentrations of n-hexane.

Conclusion: Although analyses of the relationship between the levels of atmospheric n-hexane and those of metabolites in urine show a greater correlation for total 2,5-HD than for free 2,5-HD, our results suggest that free 2,5-HD could be a better indicator in evaluating risk of exposure to n-hexane, since the concentration is directly related to the neurotoxic effect.