Toxic Metals and Pollutants

Because rain washes chemical pollution from the air to the ground, and rain and irrigation wash it from the ground, almost every kind of chemical produced on the planet ends up in the rivers and oceans, where they can be accumulated by fish and shellfish. Of the potentially hazardous substances found in fish, the most significant are heavy metals and organic (carbon-containing) pollutants, preeminently dioxins and polychlorinated biphenyls, or PCBs. The heavy metals, including mercury, lead, cadmium, and copper, interfere with oxygen absorption and the transmission of signals in the nervous system; they’re known to cause brain damage in humans. Organic pollutants cause liver damage, cancer, and hormonal disturbances in laboratory animals, and they accumulate in body fat. Fatty coho salmon and trout in the Great Lakes carry such high levels of these pollutants that government agencies advise against eating them.