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Comparison of unchanged n-hexane in alveolar air and 2,5-hexanedione in urine for the biological monitoring of n-hexane exposure in human volunteers

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Abstract

Introduction and aim

Biological monitoring of n-hexane (HEX) is based on the measurement of urinary 2,5-hexanedione (2,5-HD). In 2001, the American Conference of Governmental Industrial Hygienists modified the biological exposure index (BEI) for HEX and suggested measuring free urinary 2,5-HD (without hydrolysis) (3.5 μmol/l) instead of total 2,5-HD (acid hydrolysis). This BEI value was derived from four field studies that involved worker exposures to variable concentrations of HEX and other solvents. This study was undertaken to characterize, for 5 consecutive days, the relationship between HEX exposure (25 ppm and 50 ppm) and (1) 2,5-HD urinary excretion and (2) HEX in alveolar air.

Methods

Five volunteers (three women, two men) were exposed to HEX in an exposure chamber for 2 non-consecutive weeks (7 h/day). They were exposed to 50 ppm HEX, during the first week and to 25 ppm during the second week. Alveolar air and urine samples were collected at different intervals before, during and after the exposures. The concentration of unchanged HEX in alveolar air and the concentration of urinary 2,5-HD under three analytical conditions (with acid, or enzymatic hydrolysis and without hydrolysis) were measured.

Results

The results show that the mean concentrations of HEX in alveolar air were 18 ppm (25 ppm) and 37 ppm (50 ppm), which indicates that approximately 73% of inspired HEX was expired unchanged in alveolar air by the volunteers. The mean (± SD) concentrations of urinary 2,5-HD for the last 4 h of exposure at the end of the week (day 5) following exposure to 50 ppm HEX were 30.4 μmol/l (±7.8 μmol/l) (acid hydrolysis); 5.8 μmol/l (±1.0 μmol/l) (enzymatic hydrolysis); 6.2 μmol/l (±0.9 µmol/l) (without hydrolysis). Following the volunteers’ exposure to 25 ppm HEX, the urinary excretion concentrations were 15.2 μmol/l ± 1.9 μmol/l, 3.1 μmol/l ± 0.7 μmol/l and 3.7 μmol/l ± 0.5 μmol/l, respectively.

Conclusion

Both free urinary 2,5-HD and HEX in alveolar air measurements could be used for the biological monitoring of HEX. Between these two indicators, HEX in alveolar air is less variable than 2,5-HD in urine, but the sampling time is more critical. Therefore, biological monitoring of HEX based on the measurement of free urinary 2,5-HD is preferable to HEX in alveolar air. Additionally, we believe that the 2,5-HD values reported in this study better reflect the actual levels of exposure to HEX alone than what has been previously reported in studies that involved co-exposure to other solvents, and that the current BEI value for HEX is most likely more protective than what has been believed up until now.

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Acknowledgements

The authors wish to thank Ginette Charest-Tardif, Suzanne Paradis and Mylène Beaudoin for their excellent technical assistance. Financial support from the Institut de recherche Robert-Sauvé en santé et en sécurité du travail is gratefully acknowledged. This work was presented at the thirty-fifth Annual Symposium of the Society of Toxicology of Canada in Montreal, Quebec, Canada, in December 2002.

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  1. Département de santé environnementale et santé au travail. Université de Montréal, 2375, Chemin de la Côte Ste-Catherine, Montréal, Québec, H3T 1A8, Canada

    G. Hamelin & R. Tardif

  2. Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), Montreal, Quebec, Canada

    G. Truchon

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  1. G. Hamelin
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Correspondence to R. Tardif.

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Hamelin, G., Truchon, G. & Tardif, R. Comparison of unchanged n-hexane in alveolar air and 2,5-hexanedione in urine for the biological monitoring of n-hexane exposure in human volunteers. Int Arch Occup Environ Health 77, 264–270 (2004). https://doi.org/10.1007/s00420-004-0506-5

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