How My Mercury Level Hit Double the Safety Limit

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Justin Guariglia / National Geographic / Getty Images

A couple of weeks ago I took a pair of scissors and clipped a thatch of hair from the back of my head. I did not do this lightly — much like petroleum, my hair is an increasingly scarce resource, and I'm doing my best to conserve it. But I was taking part in a Sierra Club–sponsored test for mercury contamination in people, and levels of the toxic metal can be detected through hair. So I taped the small sample I could spare inside an envelope and sent it off to the University of Georgia, which was doing the actual testing. And then I pretty much forgot about it.

So I was more than a bit surprised when an express letter arrived at my home from the University of Georgia a few days later, with a message from Lisa Liguori, the scientist who runs the testing lab there. It turned out that my mercury levels were more than twice the government-recommended safety limit. I wasn't exactly a walking thermometer, but I had a surprising amount of the stuff in my blood and body.

Fortunately, for a man, mercury contamination isn't considered a significant health risk — and my levels are still well below the point at which harm would likely occur. But women who are pregnant or want to get pregnant, as well as very young children, are a different story; those groups are more vulnerable to mercury contamination. The reason is that mercury is a neurotoxin that impairs brain development in young children, either directly or through a pregnant or nursing mother. According to the Environmental Protection Agency (EPA), as many as 1 in 12 American women have enough mercury in their bodies to put a baby at risk, which means that as many as 300,000 infants a year may face an increased risk of learning disabilities associated with in utero exposure to mercury. "For kids that young, their brains are developing and vulnerable to this," Liguori says.

But here's what I want to know: How was I exposed to mercury? I don't exactly handle the metal in my job, so I probably wouldn't be directly exposed to it. But I do eat seafood — a lot. I probably have a tuna sandwich twice a week for lunch, and I eat sushi — a habit I picked up during my reporting stint in Japan — almost as often. I always thought those choices were healthy — and indeed, fish like tuna are a valuable source of protein and omega-3 fatty acids, which are good for the heart. But those same fish can have high mercury levels. "Seafood is the main route of exposure for Americans," says Liguori.

But don't blame the beleaguered fish directly for the problem. We may be exposed to mercury via some seafood, but beyond naturally occurring mercury in the environment, much of the pollution begins with coal, which can contain mercury. Nearly every lump of coal we burn for energy releases some of its mercury into the atmosphere — and since we burn a lot of coal, we release a lot of the toxin. (Between 1999 and 2005 — the most recent years for data — mercury emissions from power plants increased more than 8%, from 49 tons to 53 tons.) From there, some of the mercury ends up in the aquatic environment — rivers, lakes or oceans — where bacteria transform it into organic methylmercury, which is digestible by animals but also more toxic. The methylmercury steadily moves up the food chain, bioaccumulating in large predatory fish or in especially long-lived species — which is why big hunters like the tuna or swordfish tend to have higher levels. In 2008, there were 16.8 million acres of lakes and 1.3 million miles of river under advisory for mercury levels, an increase of 19% and 42%, respectively, since 2006. "The big fish accumulate the mercury from the little fish, and then it ends up on your plate," says Mary Anne Hitt, deputy director of the Sierra Club's national coal program.

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