Pesticides and solvents linked to Parkinson's

The research record

This is the project's file for this landmark, as written and checked. Sources are listed at the end; anything not yet confirmed is marked "Not yet verified".

Who

Caroline Tanner, Freya Kamel, G. Webster Ross, Jane Hoppin, Samuel Goldman and colleagues (Parkinson's Institute, NIEHS, Agricultural Health Study; NIH intramural, NIEHS and NCI funding listed). Goldman and colleagues for the twin study (NINDS) and, with Tanner, the Camp Lejeune study. Kimberly Paul, Beate Ritz and colleagues for the California study (NIEHS).

What happened

• 2011: A case-control study nested in the Agricultural Health Study compared 110 Parkinson's cases, diagnosed by movement-disorder specialists, with 358 controls. Ever-use of paraquat gave an odds ratio of 2.5 (95% CI 1.4–4.7); rotenone also 2.5 (1.3–4.7); any Complex I inhibitor 1.7 (1.0–2.8). Other pesticides tested were not significant.
• 2012 (twins): In 99 twin pairs where only one twin had Parkinson's, trichloroethylene (TCE) exposure gave an odds ratio of 6.1 (1.2–33) and perchloroethylene 10.5 (0.97–113).
• 2023 (Camp Lejeune): Among 158,122 Marine and Navy veterans with health data (of 340,489 who lived at either base in 1975–85), 430 had Parkinson's (0.33% at Camp Lejeune, whose water had TCE levels far above permitted amounts, against 0.21% at Camp Pendleton). Odds ratio 1.70 (1.39–2.07). Cases were confirmed by record review.
• 2024 (California): In 829 Parkinson's patients and 824 community controls in Central California, working near paraquat applications every year since 1974 gave an odds ratio of 2.15 (1.46–3.19); living near them for the same duration 1.91 (1.30–2.83). Exposure was estimated from state pesticide-use records, not self-report.
• Regulation: The US EPA issued a final rule banning all TCE uses on 17 Dec 2024 (89 FR 102568). Court challenges followed; the Third Circuit lifted its stay on 28 Mar 2025 for all but the exemption provisions, and an EPA notice published 5 May 2026 postpones the conditions on the exemptions until judicial review ends. For paraquat, Syngenta signed a letter agreement in April 2025 to resolve thousands of US lawsuits (over 5,800 in the federal case at that time) while saying the claims have no merit and the settlement does not imply paraquat causes Parkinson's.

Why it moved us toward a cure

It was the first study of specific pesticides in people who actually used them, tied to the two mechanisms already suspected from toxin models (landmarks 2 and 13). It supports prevention, and "environment plus genes" as the cause of sporadic Parkinson's.

A 1999 twin study had found little heritability in ordinary late-onset Parkinson's, pointing to environmental causes (landmark 238).

Outcome

Open. The association has been repeated in different designs and places (farm users, twins, a military base, a California population), but causation is still argued and regulation lags. The 2011 study alone is weak (110 cases, self-reported exposure), and the twin result rests on small numbers (wide intervals); read them together. No correction or retraction was found; PubMed lists commentary on Tanner 2011, Goldman 2012 and Goldman 2023.

Sources

• Tanner et al., Environ Health Perspect 2011;119:866–872, DOI 10.1289/ehp.1002839
• Goldman et al., Ann Neurol 2012;71:776–784, DOI 10.1002/ana.22629
• Goldman et al., JAMA Neurol 2023;80:673–681, DOI 10.1001/jamaneurol.2023.1168
• Paul et al., Int J Epidemiol 2024;53:dyae004, DOI 10.1093/ije/dyae004
• EPA notice 2026-08750 on TCE exemptions, Federal Register 5 May 2026
• EPA TCE rule status, updated 13 Nov 2025
• Civil Eats on paraquat evidence and EPA, Feb 2025 · The New Lede on the Syngenta settlement, Apr 2025 (journalism; primary papers not read)
• Not yet verified: the EPA's decision on paraquat re-registration; any count of countries that ban paraquat (the earlier "more than 70" figure was removed as unsourced); the court outcome for TCE; PubPeer not checked.