"Apart from the politics, this is a nonissue," said Ellen Silbergeld, professor in Environmental Health Sciences at the Johns Hopkins School of Public Health. "It is widely known that one can have one's cake and eat it too. All it takes is to choose wisely among the fish that one consumes."
Biologically, the concept is called bioaccumulation: Mercury found either naturally or as pollution in the world's waters gets taken up initially by microorganisms. As these are eaten by small animals and subsequently by larger and larger fish, the concentration of methyl mercury increases with each successive step in the food chain.
The result is that so-called "top predators" usually have higher levels of potentially toxic chemicals.
"Due to bioaccumulation," said Silbergeld, "a top predator such as a tuna or a swordfish can have levels of mercury up to 60,000 to 80,000 times that of water."
With regards to being able to measure mercury levels in different types of fish, Silbergeld said, "The bottom line is that it is easy. There are a number of organizations that have done this. We know where the high end lies and where the low end lies."
Meanwhile, clinicians and patients are beginning to understand that one way to clear up the confusion may lie in educating themselves.
"People are not always cognizant of which fish are beneficial and which are not," said Dr. Ashlesha Dayal, assistant professor in maternal and fetal medicine at the Albert Einstein College of Medicine.
"The problem is that when something gets bad press, it will stick in patients' minds, and the immediate instinct is to back away," she said. "Until they hear that it is safe and OK, it will take a bit of education."
Multiple Web sites now have easy-to-carry cards that list "good fish" and "bad fish" with regards to omega-3 fatty acid benefits and mercury risks. For a list of such Web sites, see the links below:
Purdue University http://fn.cfs.purdue.edu/fish4health/Walletcard/walletcard.htm
National Resources Defense Council http://www.nrdc.org/health/effects/mercury/walletcard.pdf