Adding to the growing list of Bush-era environmental policies that it has reversed, the Obama administration announced yesterday that it would support a treaty to limit global mercury emissions. This means that the U.S. will join 140 other nations as a party to upcoming negotiations on a treaty to control the pollutant, which can cause serious damage to the human nervous system, especially in fetuses and infants. But why didn’t the Bush administration support the treaty in the first place? After all, it’s not like anyone is arguing that neurologically-damaged babies, or annoying limits on how often you should eat tuna sandwiches, are a good thing. (Except, perhaps, for the peanut-butter-sandwich lobby, which may be acting more nefariously than anyone suspects.)

In fairness, Bush did sign a bill on October 15, 2008 to ban the export of elemental mercury from the United States. It was a non-controversial ban aimed at drying up the shadowy global market for concentrated mercury, which small-scale gold miners in the developing world use to separate gold from other materials, at great risk to themselves and anyone living nearby. At the same time, the Bush administration has had a history of trying to protect coal-fired power plants from mercury-emissions limits.

Coal-fired power plants produce about 40 percent of all mercury emissions nationwide, making them the largest source of mercury pollution. Because it’s possible to reduce (though not eliminate) these emissions with improved smokestack scrubbers, a disproportionate amount of this mercury pollution comes from the nation’s oldest, dirtiest coal plants. In 2000, the EPA determined that mercury was a hazardous substance under the Clean Air Act, a move that obligated the agency to come up with regulations to reduce mercury emissions. But the Bush administration stalled on implementing mercury-emissions regulations, waiting until 2004 to propose an industry-friendly cap-and-trade system for mercury that was ultimately rejected in court.

So the best explanation for why the Bush administration didn’t want a global mercury treaty is that they were worried about its potential impacts on coal power plants. As it turns out, the coal lobby, not the peanut butter lobby, is the real enemy of the tuna sandwich.

 Update: As commenter markbenl points out, the mercury content of canned tuna, while deeply offensive to hungry environmental journalists for whom tuna is a major source of protein, is actually a good bit lower than the mercury content of the high-end tuna used for steaks or sushi. Interestingly, the cheaper "chunk light" tuna has significantly less mercury than canned albacore. But the best idea, if you're in the market for canned fish, is to take a step down the food chain and eat sardines, which have low levels of mercury and are in relatively little danger of being overfished.

--Rob Inglis