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Harmful Mercury Found in Fish from Fresh Water


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A new study in the United States found widespread contamination of toxic mercury in fish from streams that appear to be pristine. It's the latest indication of how widespread mercury pollution is.

Mercury is poisonous to the nervous system, and it's especially harmful to young children. Exposure to a form of Mercury called methylmercury can damage children's memory, attention, language skills, and other mental abilities as they develop.

In the new report, researchers from the U.S. Geological Survey, or U-S-G-S, studied nearly 300 freshwater streams across the United States from 1998 to 2005. They examined mercury levels in fish at the top of the food chain -- the kind that fishermen prize, such as bass and trout. The study found that one-quarter of them had mercury levels above what are considered safe.

Geochemist Mark Brigham, one of the authors of the study, says some of the highest levels of contamination were in fish from relatively undisturbed streams that are surrounded by forests and wetlands. He thinks the only mercury they're getting is from atmospheric deposition or in other words, mercury falling from the sky. Brigham says it gets into the atmosphere from a variety of natural and industrial sources. The single largest man-made contributor to that pollution is burning coal for energy.

That mercury may also be coming from far outside the United States. So, any emission of mercury from one continent can affect the other continents. So, if you say there are emissions from Asia, for example, it can affect North America. Or the other way around, [emissions] from North America can also affect Africa.

That makes mercury pollution a global issue. The U.S. is the number-three mercury emitter, behind India, and well behind China. Gina Solomon with the Natural Resources Defense Council, says the U.S. needs to take the lead in reducing its mercury emissions before asking the same of developing countries

There is a compelling need, for health reasons, for all the countries of the world to reduce their mercury pollution. And this certainly applies to Asia, where the power industry is a major source of global mercury pollution.

Asia is also a major fish consumer. Not a lot of good research has been done in this area, but the U-N's Desiree Narvaez says spot checks have turned up some high levels of mercury in Asian fish.

Study author Mark Brigham says mercury accumulates up the food chain from algae to small fish to big. So the biggest fish tend to have the most mercury. Smaller fish and those lower in the food chain tend to be safer -- for example, catfish, shrimp, and pollock. Brigham notes that most of the fish his group sampled were safe to eat. And health experts recommend eating fish as part of a healthy diet -- as long as it's not contaminated with too much mercury.


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