That arsenic is harmful to human health was never in dispute. When I worked as a database administrator in the basement of Memorial Sloan-Kettering in the mid 1980s, I could never get used to the sight of all the patients who appeared to be under ten years old or so.
Cancer is the quintessential disease of late capitalism.
This would require a breakthrough in molecular biochemistry that would by its very nature lead to a cure for cancer. All we can do is point to overwhelming circumstantial evidence linking tobacco, PCB's, DDT, arsenic, etc. to cancer. But these sorts of substances are essential to capital accumulation in its decadent mature phase. Joel Kovel once analogized capitalist growth with metastizing tumors. He was correct.