In most of California there is both naturally occuring asbestos and manmade that has spread by wind currents. Almost every river carries a load of heavy metals and biochemicals from mining, urban or agricultural runoff, or both. Everything downwind of a significant city receives daily "rain" of toxic soup that goes into the soil and groundwater.

Fish & Game warns the young, the old, and pregnant woment not to eat more than a few ounces a month of many wild caught fish. All the courses I have attended on wild edible plant use warn us not to consume any significant quantities of plants that are downwind of a city or roadway, or near a known-polluted watersource.

People still harvest and eat plants and animals, but that provides little guidance on whether such practices are safe long-term.