Your tuna is getting more toxic

The rate of mercury contamination in tuna and other Pacific fish has increased 30% since about 1990, and is expected to increase another 50% if China continues to build more coal-fired power plants to fuel its industrial revolution.

The data comes from a new federal study by the U.S. Geologic Survey that was published in the peer-reviewed scientific journal Global Biogeochemical Cycles.

Mercury levels in the Northern Pacific have already increased a staggering 30% in about 15 years, and are expected to rise another 50% by 2050. This stunning increase is a direct result of China's rapid industrialization, which has included the construction of as many as one new coal-fired power plant a week, by some estimates.

About 40% of all U.S. exposure to mercury comes from eating contaminated tuna from the Pacific, and roughly 75% of all human exposure to mercury comes from eating fish, according to U.S. officials. Mercury poisoning, even very small amounts, early in life can lead to permanent developmental effects. That's why the government has warned since 2004 that women who are pregnant, and young children, should not eat many species of fish. That's why the Environmental Protection Agency has been fighting to retain those strong public cautions against efforts by the fishing industry and the Food and Drug Administration to weaken or confuse them.

Mercury becomes toxic when it is converted by bacteria into a form called methylmercury. Scientists have long known how this conversion takes place in freshwater lakes, reservoirs and rivers. Health advisories caution people -- particularly young children and pregnant or nursing women -- against eating many fish caught recreationally in many U.S. waters. But this study is the first to document how that conversion takes place in the ocean, according to the authors:

"This study documents for the first time the formation of methylmercury in the North Pacific Ocean. It shows that methylmercury is produced in mid-depth ocean waters by processes linked to the ocean rain. Algae, which are produced in sunlit waters near the surface, die quickly and rain downward to greater water depths. At depth, the settling algae are decomposed by bacteria and the interaction of this decomposition process in the presence of mercury results in the formation of methylmercury. Many steps up the food chain later, predators like tuna receive methylmercury from the fish they consume."

Asia is an important source of mercury in the Pacific not only because prevailing winds carry air pollution over the ocean, where it rains down, but also because ocean currents carry the pollution throughout the basin, according to the study.

The U.S., more than 100 years into its industrial revolution, has only begun to crack down on mercury pollution from coal-fired power plants. The Bush Administration enacted the first-ever mercury control limits on coal-fired power plants, but they were struck down in court because they would have allowed local pollution levels around some plants to increase; many states have enacted their own regulations in the meantime. After years of delay under the Bush Administration, the EPA has also recently announced plans to regulate mercury emissions from another major source: cement plants.

Chinese coal-fired power plants have been a growing concern not because of mercury, but because of carbon dioxide emissions, which have helped China catapult ahead of the U.S. as the world's top emitter of the greenhouse gases that fuel global warming. For that reason, Secretary of State Hillary Clinton recently told China that it . The Obama Administration has also strongly supported an international treaty on mercury -- but the bottom line is that China will need technological help to achieve a low-mercury/low-carbon industrialization. Which means we'll need renewable energy breakthroughs as well as pollution control breakthroughs that make coal either clean or obsolete ... Which means solving the American tuna problem will probably mean solving the global warming problem.

About Mercury Pollution

Mercury is a naturally occurring element, but it's a food supply contaminant because of industry. Mercury is spewed from the smokestacks of coal-fired power plants (coal has trace amounts of mercury), cement kilns (which burn coal, and use limestone, both of which can contain mercury) and certain types of mining (gold mining uses mercury to process the rock). Mercury has been used to make a variety of manufactured goods, from compact fluorescent light bulbs to thermostats.

When mercury enters the air, it eventually rains down and is incorporated into aquatic food chains. Larger predatory fish like tuna, swordfish and shark, can accumulate potentially unhealthy doses because they spend a lifetime eating smaller fish and aquatic creatures. Women who are pregnant or nursing, and young children, are most at risk of mercury poisoning, because it can lead to permanent brain damage.

You can still eat fish if you are careful. The Environmental Defense Fund's Seafood Selector is the best one-stop source for information about eating only fish that are low in contaminants and harvested sustainably. It's been helping people abide by the "Piven Principle" since before Piven's sushi habits made news. The Seafood Selector is among The Daily Green's 10 Food Visionaries Nominated for a 2009 Heart of Green Award.

The Daily Green has compiled several recipes for uncontaminated, sustainable fish, and tips for greening your diet, including how to decipher labels at the fish counter.

Map of mercury advisories in game fish in this article is courtesy Earthjustice, which is currently running a fish naming contest for some of the most contaminated species.

More from The Daily Green

• 7 Recipes for Eco-Friendly Fish
• The Dirty Dozen: 12 Foods to Eat Organic
• The Clean 15: Foods Low in Pesticide Residue
• 18 Ways to Green Your Diet
• What's Your Organic Food IQ? Take the Quiz!

Reprinted with permission of Hearst Communications, Inc