Aflatoxin is another one, notable for turning up nearly everywhere (including bark, sometimes).
That's the example that led me to weaken my heuristic skepticism of nontraditional agriculture. I don't have a gaian spiritual attachment to traditional food production, but I'm skeptical that the testing of pesticides and fungicides used in farming, and the drugs given to farm-raised animals, is sufficiently stringent and long-term. I am okay with those in principle, but I would like them to be introduced more conservatively than today.
At the store, the choice is between organic and regular food. So I can't buy my preferred choice of food, which would use novel drugs and chemicals but conservatively and after extensive testing. One heuristic, given that choice, is to prefer organic food. Not for the reasons most organic-food pushers are pushing it, but because organic food errs on the side of economic inefficiency, while regular food errs on the side of toxicity. Since I'm thankfully doing fairly well economically, my personal risk function prefers the first kind of error.
But sadly that doesn't work. Due to aflatoxin being everywhere, organic food can be more carcinogenic than standard food is, depending on the specific food, climate, and distribution. In some cases it may be heuristically better to ingest even insufficiently tested chemicals if the organic alternative has higher levels of aflatoxin. And that's true even if money is no object.
There are other examples, but that's the one that's common enough to have shot a hole in my purchasing heuristic. I would still prefer the in-between option, a class of food that does use pesticides and other drugs, but phases them in more conservatively, based on solid proof of their safety. Alas, there doesn't seem to be a profitable market halfway between regular and organic food.