I would generally agree, except in wonder what the aquifers/groundwater looks like in that region and also the sea water along that coast (likely more of a biological source than an industrial one in that case, I think).
Well water contamination is common and people are increasingly neglecting to test on a regular schedule. One of the symptoms listed is gastrointestinal upset which makes me think it could be something that was ingested. They mention that Roger’s condition has stabilized now that he’s in a care home, tenuous but it seems location change resulted in change in progression of symptoms. By agricultural I mean waste from livestock.
