Smaller panfish such as perch, sunfish, and crappie are lower on the food chain and thus safer to eat. Health officials in many states publish fish advisories which tell how safe a catch from a particular lake or stream is likely to be. Because children eat more as a percentage of their own weight, and because developing bodies may be more vulnerable to toxic chemicals, it is important to pay special attention to their exposure. Pregnant women must follow even more stringent guidelines to protect fetal development. Mercury is a naturally-occurring metal, yet it gets into the air from some consumer products, incineration of wastes, and burning of coal and other fossil fuels.
Mercury precipitates into even the most pristine of lakes.
In the water, bacteria and other processes convert it to methylmercury, which fish absorb from food and from water passing over their gills. Synthetic oils called PCBs once appeared in electrical transformers, cutting oils, and carbonless paper. Yet because they do not decompose easily, they remain in the water and in sediments. Fish absorb PCBs from water, suspended sediments, and food. Toxaphene is an insecticide mixture of over 670 chemicals.