Generally speaking when it comes to health stuff, we know disappointingly little, and the stuff we do know is often from past mistakes (e.g. smoking). We don't have enough knowledge to say what the effects of something will be usually, so unless there are obvious correlations and an obvious control group (again think smoking) we might never really know.
What the FDA will do, with pesticides for example, is test an 1000x dose on a rat, and look for immediate effects. If they don't see immediate effects, then perhaps it doesn't do longterm damage to humans. It's not very convincing, but it historically things used to be much worse.
Generally speaking when it comes to health stuff, we know disappointingly little, and the stuff we do know is often from past mistakes (e.g. smoking). We don't have enough knowledge to say what the effects of something will be usually, so unless there are obvious correlations and an obvious control group (again think smoking) we might never really know.
What the FDA will do, with pesticides for example, is test an 1000x dose on a rat, and look for immediate effects. If they don't see immediate effects, then perhaps it doesn't do longterm damage to humans. It's not very convincing, but it historically things used to be much worse.