Study of mixtures of organic solvent exposures and amyotrophic lateral sclerosis in Denmark

Abstract

TPS 732: Neurological effects in adults, Exhibition Hall, Ground floor, August 27, 2019, 3:00 PM - 4:30 PM Background/Aim: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by rapidly progressive loss of motor function. Previous studies of occupational solvent exposure and ALS were conflicting. However, none of these used objective, solvent-specific assessment such as job exposure matrices (JEMs) to estimate cumulative exposures. In this study, we investigate the association between occupational exposures to multiple organic solvents and odds of ALS. Methods: We conducted a nested case-control study of occupational solvent exposures - benzene, methylene chloride (MCH), toluene, trichloroethylene, perchloroethylene, and 1,1,1-trichloroethane - and ALS diagnosis using population-based data from Denmark. We identified ALS cases from 1982 to 2013 and age- and sex-matched controls. Employment history was obtained from the Danish Pension Fund. We estimated cumulative exposure to solvents based on exposure in 1639 ALS cases and 151,974 controls. We used sex-stratified conditional logistic regression to obtain adjusted odds ratios (aOR) and 95% confidence intervals (CI), for exposures categorized into quartiles and adjusting for residential location and socioeconomic status. We used weighted quantile sum (WQS) regression to further explore combined solvent exposures and risk of ALS in men with any solvent exposure. Results: Analysis for benzene and MCH exposures in men revealed higher adjusted odds for those with the highest quartile exposure unlagged: aOR=1.35 (95% CI 1.02, 1.80) and aOR=1.26 (95% CI: 1.01, 1.58), respectively, compared to those with no exposure. We observed no trends or notable results in women. Our WQS analysis revealed a significant increase for all exposure lag periods of 26 to 28% in odds of ALS for every one-unit increase in the derived solvent mixture index. Interestingly, the weights of MCH predominated the solvent mixture index for all lag periods. Conclusion: These findings support those of previously reported associations between ALS and solvent exposures and highlight the need to investigate exposure mixtures.