Isn't LD50 only relevant to acute exposure?[0] Just because you can eat 5 grams of something and survive doesn't mean repeated exposure to it in smaller quantities or in other ways won't hurt you (obviously). E.g. acute inhalation of asbestos has no recorded mortality. I think I'm missing something in your post.

[0] https://en.wikipedia.org/wiki/Median_lethal_dose