Proximity to residential and workplace pesticides application and the risk of progression of Parkinson's diseases in Central California.
Level 3 - non-randomized controlled study
Longitudinal observational cohort study tracking symptom progression over time.
PubMed 36526213 · doi:10.1016/j.scitotenv.2022.160851
What was done
Researchers evaluated two Parkinson's disease (PD) patient cohorts in agricultural Central California (PEG1: n = 242, mean follow-up 5.0 ± 3.5 years; PEG2: n = 259, mean follow-up 2.7 ± 1.6 years) to assess whether ambient pesticide exposure influences symptom progression. A geographic information system (GIS) linked historical California Pesticide Use Reports and land use records from 1974 to the year of PD diagnosis to estimate residential and occupational proximity (in pounds applied) for 53 pesticides previously linked to PD onset. Clinical progression was tracked via specialist-administered Unified Parkinson's Disease Rating Scale (UPDRS Part III) for motor symptoms, Mini-Mental State Examination (MMSE) for cognition, and Geriatric Depression Scale (GDS). Weighted time-to-event regression models were used to estimate hazard ratios (HRs).
What was found
Ten agricultural pesticides were associated with faster symptom progression: copper sulfate (pentahydrate), 2-methyl-4-chlorophenoxyacetic acid (MCPA) dimethylamine salt, tribufos, sodium cacodylate, methamidophos, ethephon, propargite, bromoxynil octanoate, monosodium methanearsonate (MSMA), and dicamba. Higher proximity to copper sulfate pentahydrate and MCPA dimethylamine salt was associated with faster progression across all three endpoints: copper sulfate HRs ranged from 1.22 to 1.36 (95% CIs: 1.03–1.73) and MCPA HRs ranged from 1.27 to 1.35 (95% CIs: 1.02–1.70).
Why it matters
While environmental pesticides are well-known risk factors for PD onset, this study provides longitudinal human evidence that prior ambient pesticide exposures may also drive faster post-diagnosis motor, cognitive, and affective decline.
Limits
Exposure was estimated through spatial proximity modeling rather than personal dosimeters or biological markers. The PEG2 cohort had a relatively short follow-up duration (mean 2.7 years). Multiple hypothesis testing across 53 chemical agents raises the potential for type I error, and residual confounding from unmeasured occupational or environmental exposures cannot be excluded.
Cited by
- supports Studies demonstrate that people diagnosed with Parkinson's disease who continue to be exposed to pesticides experience faster disease progression.