Objective: This study describes associations of ozone and fine particulate matter with Parkinson's disease observed among farmers in North Carolina and Iowa. Methods: We used logistic regression to determine the associations of these pollutants with self-reported, doctor-diagnosed Parkinson's disease. Daily predicted pollutant concentrations were used to derive surrogates of long-term exposure and link them to study participants' geocoded addresses. Results: We observed positive associations of Parkinson's disease with ozone (odds ratio = 1.39; 95% CI: 0.98 to 1.98) and fine particulate matter (odds ratio = 1.34; 95% CI: 0.93 to 1.93) in North Carolina but not in Iowa. Conclusions: The plausibility of an effect of ambient concentrations of these pollutants on Parkinson's disease risk is supported by experimental data demonstrating damage to dopaminergic neurons at relevant concentrations. Additional studies are needed to address uncertainties related to confounding and to examine temporal aspects of the associations we observed.

In their recent article [1], Chari et al. call attention to the important subject of setting National Ambient Air Quality Standards (NAAQS) to provide requisite protection for public health, including the health of sensitive groups, as specified under the Clean Air Act (73 FR 66965) [2]. The authors focus on consideration of susceptibility to inform policy choices, using lead (Pb)-related neurocognitive effects and children from low socioeconomic status (SES) families in the context of alternative Pb standard levels. Our comments focus on the authors’ analysis of the scientific evidence and not on policy. We agree with the authors that the health effects evidence for Pb indicates a role (or roles) for SES-related factors in influencing childhood Pb exposure and associated health effects. We disagree, however, with the authors’ interpretation of the literature on SES influence on the shape of the concentration-response (C-R) relationship between children’s blood Pb and IQ (e.g., steepness of the slope). We further address aspects of the scientific evidence that are important to the consideration of sensitive populations in the context of the Pb NAAQS, and how the U.S. Environmental Protection Agency (EPA) considered this evidence in setting the Pb NAAQS in 2008.