There are three general kinds of hazardous
materials that contaminate fish and shellfish:
industrial toxins, biological toxins, and
disease-causing microbes and parasites.
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