The difficulty here is that the diseases happen years or decades after the exposer, sometimes.
The industrial setting offers the hints that there might be a problem but, as you rightly point out, also might just be a case of too much exposure.
An example of this is radiation exposure, it took an embarrassingly long time for society to link radiation to cancer, and that was a somewhat obvious link. Radioactive beverages were literally marketed as health beverages because of their radium content.
You can still find radioactive trinkets being sold for their alleged health effects. Thorium in pendants and that sort of shit. They don't disclose their radioactive nature but they market with some new age woo like "emits vitalizing energy waves using crystal technology."
Most of it comes from China, presumably from people who see waste byproducts of rare earth metal processing as a business opportunity.
The industrial setting offers the hints that there might be a problem but, as you rightly point out, also might just be a case of too much exposure.
An example of this is radiation exposure, it took an embarrassingly long time for society to link radiation to cancer, and that was a somewhat obvious link. Radioactive beverages were literally marketed as health beverages because of their radium content.