Mercury levels are going down in the Great Lakes.
But they're going up in the oceans.
Paul Drevnick, a researcher at the University of Michigan, has a new study showing that mercury levels in a specific species of tuna – yellowfin – are increasing at a rate of 3.8% a year in the Pacific.
And he thinks that's bad news for all ocean fish.
"I would expect that all the different kinds of large predatory fish like this in the ocean, if we had the measurements, we'd find the same thing," he says.
Drevnick says a related study last year showed most of the mercury showing up in the ocean is not from natural activities such as volcanic eruptions, but rather, due to an increase in electricity production globally from coal-fired power plants.
"And when we burn that coal, the impurity, the mercury, can go into the atmosphere," says Drevnick.
Consumer Reports already advises pregnant women to eat no tuna of any kind because of how much mercury it contains.
Drevnick says tuna are predatory fish, meaning they eat smaller fish, which have eaten mercury-contaminated organisms, which have eaten mercury-contaminated plants, which live in mercury-contaminated water.
The chain results in a ten-fold increase in mercury levels at each level. Large predatory ocean fish have about a million times more mercury in their bodies than the ocean water does.
Drevnick's study predicts the problem will continue to worsen as developing nations continue to increase their reliance on coal.
