What's up with the mercury in tuna? Can I still eat it?

I've gotten many tuna-related questions in the wake of revelations that tuna from local grocery and restaurant sources showed surprisingly high levels of methylmercury when tested in the lab.

Methylmercury in a pregnant or nursing woman's diet can put her child at risk for neurological damage. Young children should also limit their intake, as well as women who are planning to get pregnant. Whether methylmercury poses a health risk for adults is still up in the air - some studies have indicated it might contribute to heart disease or neurological disorders, but other studies have found no effect.

The Food and Drug Administration considers fish whose methylmercury concentrations fall between 0.14 and 0.64 parts per million safe enough for the risk group to eat once a week. It was in this group that the FDA placed most tunas.

The New York Times, as well as the nonprofit research-advocacy group Oceana, found that samples of all species of tuna had significantly higher levels of methylmercury than the FDA estimates, especially bluefin tuna (the most desirable tuna for sushi), for which the FDA provides no figures. Oceana tested tuna from supermarkets all over the country and found an average methylmercury level of 0.68 ppm; tuna from sushi restaurants tested higher, an average of 0.86 ppm.

The bottom line is that for now, tuna probably should be placed alongside king mackerel, shark, swordfish and tilefish from the Gulf of Mexico as fish that children, pregnant women and nursing mothers should avoid. Adults who eat these five fish probably should do so in moderation.

Erica Marcus writes for Newsday. E-mail your queries to burningquestions@newsday.com, or send them to Erica Marcus, Food/Part 2, Newsday, 235 Pinelawn Road, Melville, NY 11747-4250.