Friday, October 06, 2006

What I Didn't Know About Mercury

Until I decided to write the present piece, I thought I knew as much as I needed about the risk I faced from eating mercury-laden fish. I knew, for instance, that mercury -- which passes easily from mother to child in utero and through breast milk -- is a neurotoxin that can damage the developing brain. I also thought I knew that I, personally, had nothing to worry about, as I eat very little fish that's high in mercury and don't plan to have more kids.
I have been chastened.
Surprise #1: My mercury exposure has been above the level considered safe by the Environmental Protection Agency for three of the past four weeks, according to NRDC's mercury calculator. (This is just an estimate based on averages, not a measurement of my actual exposure, which would require that I be tested.)
It wasn't that I overindulged. There was only one week when I ate fish more than once (ironically, my "safe" week), and my portions were all moderate in size.
The problem is with the fish I chose to eat -- in particular, shark and swordfish. As large, predatory species, they contain much higher levels of mercury than small fish, such as anchovies and sardines, because of the way mercury moves up the food chain. I knew this but didn't realize that a single 6-ounce portion in a week would be enough to put me over the top -- by a factor of four.
(In passing, I should note that shark was a bad choice from a sustainability standpoint, as well, as shark populations are dangerously low.)
Even the single portion of smoked bluefish I had one week was borderline. And bluefish has the added problem of contamination with PCBs.
Surprise #2: The danger from mercury is not just to developing brains. A growing body of evidence suggests an association between mercury exposure and heart disease. So even middle-aged people, like my husband and myself, should take care what they eat.
These two surprises were enough to make me shun the fish stand at the greenmarket last Saturday. But that was foolish: eating fish low in mercury is good for the heart, and low-mercury choices abound.
So, which fish are good choices? There's a longish list, including some popular fish, such as sole, tilapia, clams and oysters. When it comes to canned tuna, chunk light is much better than white albacore, as it typically has about a third of the mercury (though Consumer Reports recently found that some cans of chunk light can contain as much mercury as most albacore). Just be careful how much canned tuna you consume, as quantity matters -- even more for kids than adults because they weigh so little.
And what's bad? Well, swordfish and shark top the list, along with king mackerel, marlin, orange roughy and tilefish. Steer clear of them altogether if you are trying to become pregnant, are already pregnant or are nursing, and obviously, don't feed them to young children. Even if you aren't planning on children, if you are a woman of reproductive age, it would be wise to limit your intake in case you change your plans or become pregnant without planning -- as it takes months to shed your body of mercury.
There are many other fish besides the ones I've listed here, including many with moderate levels of mercury that are safe to eat in limited quantities. So, do yourself a favor and consult NRDC's guide to mercury in fish. Knowledge is power -- and a key to good health.
—Sheryl Eisenberg

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