Did you read the paper carefully? It's about pesticide use. (It's not especially plausible as epidemiological studies go, though I'm unsurprised if a better study finds a firmer correlation between pesticides and PD.)
Did you not read that the effect was directly tied to “Individuals living within water service areas” in my original comment? Yeah no shit it’s pesticides. They’re seeping into the water supply from the golf course runoff.
That play works if you are in fact a PhD in a related field, but not if we're both reading the same study as laypersons and disputing its relevance and reliability.
What I suspect happened here is that you found this study by Googling for it, and forgot that it is in fact very easy to get a capsule summary of any published study posted on HN.
