METALS - Marine Pollution: What Everyone Needs to Know - page 82

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METALS
What are the major sources of metal pollutants?
Metals are naturally occurring elements in the earth's crust
that can become contaminants when industrial activity con-
centrates them at higher than normal levels. Since they are
elements, they cannot break down into anything else. Metals
released from mining and industrial processes are among the
major contaminants of concern in coastal environments, where
they accumulate in sediments and coastal organisms. Mercury,
cadmium, copper, zinc, chromium, and silver are major con-
taminants from industrial processes, including power plants.
Since coal contains mercury, when it is burned the mercury
enters the atmosphere where it can be transported long dis-
tances before being deposited far from its source. Mercury
(Hg) deposited from the atmosphere is a significant fraction of
the mercury entering coastal waters and approximately 90% of
the Hg in the open ocean. It contaminates seafood commonly
eaten by people in the United States and globally. Over the past
century, Hg in the surface ocean has more than doubled as a
result of human activities. While some metals such as copper
(Cu) and zinc (Zn) are essential for life at low concentrations,
other metals (Hg for example) play no normal biological role.
While most metal contamination originates from land-based
industrial sources, metals also are used in antifouling paints
for ships. Since fouling (attached) organisms such as barnacles
and algae can accumulate on ship bottoms (increasing drag,
thus increasing fuel consumption), antifoulant coatings have