Reply #24: Exposure isn't necessarily universal though. Some land/food/air could be contaminated and some not.

[franzia99]

Plus, like with radiation exposure for example, a small percentage will get cancer and the rest won't. Some of it is random luck, some of it is the ability of your cells to deal with radiation exposure. Here, it's probably the case that not everyone has had the same exposure and that some people are just biologically better able to deal with the contamination than others.