But do the risks of eating fish outweigh the benefits? For most, fish can still safely be considered a health food. In November, the American Heart Association said that it’s better to eat fish than to avoid it, especially since there are still plenty of seafoods like cod, farmed tilapia and shellfish that remain pure. And while the fish richest in omega-3s often have the highest levels of contaminants, they are still safe, to a point. There’s little solid evidence that low levels of contaminants like mercury in fish can harm healthy adults. The only groups that might need to worry are young children and expectant mothers who might be exposed to mercury–and they can still eat most fish in moderation.
Mercury contamination starts at the bottom of the food chain and the bottom of the ocean, where small aquatic organisms take up the chemical from contaminated silt as they feed. When they themselves become prey, they pass the mercury on to the fish that eat them. The pollutant is never metabolized and builds up in the fatty tissues of large animals. The result is that top predators–the fatty fish most prized by gourmets and health nuts alike–have the highest levels, gained from eating so many meals of mercury themselves. The fish typically highest in mercury are swordfish, shark, tilefish and king mackerel, but tuna isn’t far behind.
Expectant mothers, who were singled out as a risk group by the FDA, should be particularly wary of the big fish because mercury is widely believed to harm developing brains in utero. According to an April CDC study, 8 percent of American women have levels of mercury in their blood potentially hazardous to fetuses, and the EPA says 300,000 infants each year could be at risk. But a study of 779 pregnant women released in May could find no link between mercury in fish and fetal neurological problems. The study’s authors, who continue to look for a connection, say the FDA’s guidelines–which allow pregnant women to eat various types of fish in moderation–are reasonable.
Mercury isn’t the only toxin that has fish fans worried. PCBs, formerly used in electrical equipment and plastics, were banned in 1977, but they linger in the environment. Like mercury, they build up in the tissues of fatty fish, particularly farm-raised salmon, which are often fed smaller fish from contaminated areas. There’s a reason PCBs were outlawed–they may be carcinogenic and have been loosely linked to reproductive and immune problems. But, as with mercury, it’s unclear if eating PCB-contaminated fish is truly risky for adults. Although the chemicals cause cancer in lab animals, few human studies have been conducted. And fish consumption probably doesn’t expose people to levels high enough to be harmful. Data released by the FDA in June show that butter can carry PCB levels three times as high as those in salmon. (Cows that eat contaminated grass excrete PCBs into their milk.) But the FDA isn’t warning anyone off butter. Actually, it isn’t warning anyone off salmon, either; it has no injunction against PCB-laden fish, nor any plans to release one. “It’s bad to scare people about PCBs in their food,” says Dun Gifford, president of Oldways, a food think tank. “I think the omega-3s outweigh anything else in fish. The benefits are proven. The dangers aren’t.” Not yet, anyway.
