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Q My daughter loves tuna fish sandwiches, but I know there's mercury in fish. How much can she safely eat?

A Although nearly all fish contain traces of mercury, the most common way Americans are exposed to it is through canned tuna: We eat a lot of it. Industrial polluters release mercury into the air in a variety of ways. Coal contains mercury, so when it is burned to make electricity, the toxin is released through smokestacks. Old chlorine manufacturing plants use mercury to convert salt to chlorine gas and lye, and because mercury evaporates when exposed to air, it easily escapes from these plants. After its release, it rains down into our waterways and builds up in the aquatic food chain. Large predatory fish generally contain more mercury than small fish. Because it's made from smaller species of tuna, chunk light tuna has considerably less mercury per can than albacore, so it's best to stick with chunk light when you make your daughter's sandwiches. To find out if she's eating too much tuna, enter her weight and the amount she eats into NRDC's online mercury calculator. The results will tell you if her current consumption is safe. For example, a child who weighs 45 pounds should have no more than one can of chunk light tuna a month.

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Illustration: Mark Matcho

OnEarth. Winter 2006
Copyright 2005 by the Natural Resources Defense Council