Thinking about why things do or don't belong on your list, and I think they basically have to be very harmful. If they're good we do an experiment and find out, but if they're bad we just declare it established with a correlation. For example I think Thalidomide could go on your list, in that the evidence was basically "people who took Thalidomide were far more likely to have babies with major birth defects." Probably lead (paint, fuel)? Our sense of what's a safe dose of radiation?