They studied the fish under varying
temperatures in the lab and in salt marsh pools in Maine. Fish in the
marshes ate insects, worms and other natural food sources, while the lab
fish were fed mercury-enriched food.
The results showed that fish in warmer
water ate more but grew less and had higher methylmercury levels in
their tissues, suggesting that increases in their metabolic rate caused
the increased mercury uptake.
Mercury released into the air from
industrial pollution can accumulate in streams and oceans and is turned
into methylmercury in the water.
Public Health Risks
High levels of methylmercury accumulate in
large ocean-going fish such as tuna, swordfish and marlins. Though most
people do not eat enough of these to risk mercury poisoning, pregnant
women are still advised to restrict their consumption because of
possible risk to the unborn child.
In the laboratory experiments, the highest
levels of mercury contamination occurred in the fish in the warmest
water (27°C). In the salt marsh pools on the coast of Maine the water
temperatures ranged from 18 to 22°C. Once again, the warmer pools held
fish with greater levels of mercury, even though they were feeding on
natural food sources with no added mercury.
The Dartmouth study suggests that climate
change may increase the risk to humans. Its finding that pollution
levels in the fish may increase with temperature because their
metabolism accelerates in warmer water means that as the fish eat more,
they absorb more methylmercury from the environment.
Coal-burning power plants produce most
atmospheric mercury pollution. When the
mercury falls back to Earth it lands either at sea or on land where it
can be washed into lakes, streams, and eventually the ocean,
contaminating species which find their way into human diets.
Climate News Network