The aim of this study was twofold: on the one hand, to analyze the association between long-term exposure to environmental factors and the onset of ALS in Catalonia, Spain, and, on the other, to provide evidence of the existence of spatial clusters of ALS in relation to these environmental factors throughout the 2011-2016 period.
We found a certain geographical pattern for the risk of ALS occurrence, with three clusters characterized by their proximity to agricultural areas, the first two of which were associated with a high risk of ALS occurrence: the first located at the center of the studied region (north-south direction) and corresponding to the Vallès Oriental and Vallès Occidental regions, the second located toward the east (southwest-northeast direction) and corresponding to the Maresme region, and the third with a moderate-high risk located toward the west and corresponding to the Baix Llobregat region.
The results of this study may be in line with the findings reported in other studies, particularly those attributing a role to pesticide exposure in the onset of this condition. In this sense, all of the clusters that we identified corresponded to areas of intensive agriculture. In our case, the high-risk clusters, in addition to corresponding to agricultural areas, also corresponded to areas with an important road infrastructure and high traffic density. In fact, the results of the correlation between living less than 100 m away from an agricultural area and high levels of nitrogen oxides (deemed significant at 95%), benzopyrene, and ozone (deemed significant at 85%), as well as living less than 100 m away from highways and motorways (deemed significant at 85%), could corroborate our hypothesis.