Percent of Fish in U.S. Streams Found Contaminated with Mercury
new study conducted by the U.S. Geological Survey (USGS), every single fish
tested from 291 freshwater streams across the United States was found to
be contaminated with mercury.
study shows just how widespread mercury pollution has become in our air,
watersheds and many of our fish in freshwater streams," said Interior
Secretary Ken Salazar.
is a potent neurotoxin that builds up in the food chain at ever higher concentrations
in predators such as large fish and humans. It is especially damaging to
the developing nervous systems of fetuses and children, but can have severe
effects on adults, as well. The pollutant enters the environment almost
wholly as atmospheric emissions from industrial processes, primarily the
burning of coal for electricity. It then spreads across the plant and settles
back to the surface, eventually concentrating in rivers, lakes and oceans,
where it enters the aquatic food chain.
one cause of human mercury poisoning in the United States is the consumption
of fish and shellfish.
tested the water, sediment and fish of the 291 streams between 1998 and
2005. Fish tested were mostly larger species near the top of the food chain,
such as largemouth bass.
were contaminated with mercury, more than 66 percent of them at levels higher
than those set by the Environmental Protection agency as a "level of
concern for fish-eating mammals," according to Reuters. More than 25
percent of the fish were contaminated at levels higher than those set as
the threshold for human consumption.
is the first to focus on mercury contamination of streams, rather than lakes,
reservoirs, wetlands or oceans. The researchers found the highest mercury
concentrations in fish from the coastal blackwater streams of the Southeast.
Apparently the combination of pine forests and wooded wetlands found in
these regions transforms mercury very effectively into its more toxic organic
form (methylmercury). Mercury concentrations were also high in streams fed
from areas with a history of mining.
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