Occupational pesticide use and self-reported olfactory impairment in United States farmers

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Background: Pesticide exposure may impair human olfaction through direct damage to peripheral olfactory structures, or through neurotoxic effects on the central nervous system, but empirical evidence is largely lacking. Objective: We examined associations between occupational use of specific pesticides and olfactory impairment among 20,409 pesticide applicators (mostly farmers) in the Agricultural Health Study, an ongoing prospective study in Iowa and North Carolina. Methods: Participants provided information on ever-use and lifetime days of use of 50 specific pesticides at enrollment (1993-1997) and on self-reported olfactory impairment two decades later (2013-2016). We used logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI) for the associations, adjusting for age, sex, state of residence, education, smoking, whether involved in other activities (repairing engines, working in swine confinement areas, handling stored grain, welding, and painting), and correlated pesticides. Results: About 10% of participants reported olfactory impairment. The overall cumulative days of any pesticide use at enrollment was associated with a higher odds of reporting poor sense of smell twenty years later [OR (highest vs. lowest quartile): 1.17 (95% CI:1.02-1.34), p-trend=0.003]. In the analyses of 50 specific pesticides, ever-use of 20 pesticides showed modest associations with olfactory impairment, with ORs ranging from 1.11 to 1.33. Of these, higher lifetime days of use of 12 pesticides were associated with higher odds of olfactory impairment as compared to never use (p-trend ≤ 0.05), including five insecticides DDT, lindane (organochlorines), diazinon, malathion (organophosphates), permethrin (pyrethroid), one fungicide captan, and six herbicides (glyphosate, paraquat, petroleum distillates, 2,4-D, 2,4,5-T, and metribuzin). Conclusion: Occupational use of certain pesticides may be associated with olfactory impairment. Our findings of associations with multiple pesticides across several chemical classes may indicate that pesticides could affect olfaction through multiple pathways. Future epidemiological studies with objective measurement of olfaction are required to confirm these findings.