Parkinsonism among Washington State Agricultural Pesticide Handlers

Previous human and animal studies suggest that some pesticides, including those typically applied by agricultural pesticide handlers, may increase the risk of parkinsonism (PS). This study assessed the feasibility of conducting neurological exams on active pesticide handlers, to determine the prevalence PS symptoms.
Epidemiological studies suggest a 49% increased risk of PS in individuals who have had chronic occupational exposure to pesticides. However, evidence of a direct association between occupational exposure to pesticides and PS is still inconclusive, and most human studies have solely looked at Parkinson’s disease, the most common cause of PS. The study assessed the feasibility of conducting neurological exams on active pesticide handlers to determine the prevalence of PS signs and symptoms and to identify any association between chronic occupational organophosphorus (OP) pesticide exposure and PS signs and symptoms.
In the 2014 spray season, we examined 38 actively working pesticide handlers ages 35-65 participating in the State of Washington’s Cholinesterase Monitoring Program in the Yakima Valley. A neurologist who specializes in movement disorders utilized the Unified Parkinson’s Disease Rating Scale motor subscore 3 (UPDRS3) and daily activities subscore 2 (UPDRS2). In addition, participants self-reported work and medical histories. The most common symptoms and signs were, respectively, excess saliva and action tremor. The UPDRS3 and UPDRS2 were unrelated to the number of years applying pesticides. Our study provided minimal evidence that this class of pesticides contributes to PS and no evidence that PS is as prevalent in this group of workers as it is in selected other occupational groups (i.e. welders, manganese miners). However, the findings of this research suggest the importance of employing additional neurological assessments to gather more sensitive measures of potential neurological health effects resulting from pesticide exposure. Future studies of this sort should focus on older or retired workers in whom symptoms of parkinsonism are expected to be more prevalent. Furthermore, the utilization of other neurological assessments may provide more objective and sensitive measures of potential neurological health effects of pesticides.
Co-Principal Investigator: Susan Searles Nielsen, PhD, MS
Assistant Professor, Neurology
Washington University in St. Louis
Co-Principal Investigator: Christopher Simpson, PhD, MSc
Professor, Environmental and Occupational Health
University of Washington
PNASH Pilot 2012-2014
Partners and Advisories
Healthy Worker Clinic
Central Washington Occupational Medicine clinic
Washington State Cholinesterase Monitoring Program
Searles Nielsen S, Hu SC, Checkoway H, Negrete M, Palmández P, Bordianu T, Racette BA, Simpson CD. Parkinsonism Signs and Symptoms in Agricultural Pesticide Handlers in Washington State. J Agromedicine. 2017;22(3):215-221. doi: 10.1080/1059924X.2017.1317684. PubMed PMID: 28418778; PubMed Central PMCID: PMC5533575.
Searles Nielsen S, Checkoway H, Zhang J, Hofmann JN, Keifer MC, Paulsen M, Farin FM, Cook TJ, Simpson CD. Blood α-synuclein in agricultural pesticide handlers in central Washington State. Environ Res. 2015 Jan;136:75-81. doi: 10.1016/j.envres.2014.10.014. Epub 2014 Nov 20. PubMed PMID: 25460623; PubMed Central PMCID: PMC4548290.