Background: Persistent organic pollutants (POPs) are toxic chemicals that bioaccumulate and were used in pesticides and industrial products/processes. POP-exposed occupations and environmental exposure to POPs have been associated with amyotrophic lateral sclerosis (ALS), but no study has evaluated the association with ALS when measuring POPs in samples collected before ALS onset.
Objectives: This study examined the relationship between pre-disease POP exposure and ALS risk.
Methods: We conducted a nested case-control study pooling three Finnish cohorts (n=56,862). During a median follow-up of 27 years, 97 incident ALS cases were identified (mean age at ALS=68). Within each cohort, two controls per case were selected by individual matching for age, sex, municipality, and serum freeze-thaw cycles. Thirteen polychlorinated biphenyls (PCB) and nine organochlorine pesticides (OCP) were determined in serum samples collected at baseline and stored at -20C. We considered these POPs both in groups (similar congener, isomer, metabolite groups) and separately. Odds ratios and 95% confidence intervals were estimated using a conditional logistic model in a two-stage approach, further adjusting for smoking, occupation, marital status, BMI, and serum cholesterol level in primary models.
Results: In the main model hexachlorobenzene (HCB) showed a positive association with ALS occurrence. In contrast, Σnon-dioxin-like (NDL) PCB and ΣDDT were significantly inversely associated with ALS incidence. Most other POP groups were non-significantly inversely associated with ALS risk. In co-pollutant models, the only notable changes were that Σdioxin-like PCB and ΣHCH showed large non-significant, elevated, ORs, suggesting some negative co-pollutant confounding. There were some suggestions of stronger findings when limiting to some subgroups.
Discussion: We found little evidence that POPs were associated with ALS, but we identified a suggestive positive association with HCB and HCH. ΣNDL PCB and ΣDDT were inversely associated with ALS. This could suggest protective mechanisms or uncontrolled confounding by neuroprotective factors (e.g. fish oils). https://doi.org/10.1289/EHP16539.