Environmental factors probably play a part in the aetiology of PD. One way to investigate this is to use geographical epidemiology: map the distribution of cases, see if there is some clustering of cases, and try to find some shared factor between these.

In this forum, we have had posts in the past of the spatial distribution of PD in the US, Spain and England.

A new paper by Sade et al. [1] uses this approach in the Negev (Southern Israel). They identified 3792 cases of PD between 2001 and 2012. This number of cases was about 50% higher than expected.

They report that PD incidence rates "were higher than expected in rural localities. Furthermore, it appears that proximity to [agricultural cultivated fields] and the field size contribute to PD risk."

Reference

[1] Parkinson’s Disease
Volume 2015 (2015), Article ID 576564, 7 pages
http://dx.doi.org/10.1155/2015/576564
"Parkinson’s Disease Prevalence and Proximity to Agricultural Cultivated Fields"
Maayan Yitshak Sade, Yair Zlotnik, Itai Kloog, Victor Novack, Chava Peretz,5 and Gal Ifergane
http://www.hindawi.com/journals/pd/2015/576564/

John