I would think the pathway (a person got exposed to lead by eating eels once per month) would be the defining link for the external exposure and the others (source, route, surface, substance) would follow from that link, but I'd need to get a better view on actual examples to be able to form an opinion.
I would think the pathway (a person got exposed to lead by eating eels once per month) would be the defining link for the external exposure and the others (source, route, surface, substance) would follow from that link, but I'd need to get a better view on actual examples to be able to form an opinion.