4 March 2004 | Scripps Howard News Service
by Joan Lowy
You are what you eat, even if you’re a fish. And fish that thrive on veggies tend to be less toxic than flesh eaters.
With new studies showing PCBs, dioxin, and pesticides in salmon and mercury in canned tuna, consumers who find themselves struggling to figure out what’s safe to eat will find some species of fish are high in contaminants, while others are generally low.
The reason is usually diet — some fish eat smaller fish, but other fish eat veggies and tiny organisms.
Fish-chow hazard
Contaminants like PCBs and dioxin accumulate in the fatty tissue of fish. These contaminants become more concentrated with each step in the food chain.
So the fatty carnivores at the top of the food chain — salmon — have the highest levels.
A recent study published in Science magazine found contaminant levels were significantly higher in farmed salmon than in wild salmon caught in the ocean. That’s because farmed salmon are fed diets of ground fish and fish oil, and wild salmon have a more varied diet.
“Fish-chow pellets are made up of ground trash fish and fish oil,” said Jeff Foran, a toxicology professor at the University of Michigan and a co-author of the study. “From day one, a farmed fish is getting this pellet with a concentrated dose of contaminants.”
The farmed salmon industry has been gradually shifting its feed to include more soy protein and vegetable oil, said Alex Trent, a spokesman for Salmon of the Americas, a trade association for the industry.
“It’s complicated by the fact that salmon are carnivores and not vegetarians,” Trent said. “To get them to switch from eating fish meal and fish oil to a diet of vegetable protein and vegetable oil takes a lot of research, including for palatability — first you have to get them to eat it.”
Guessing game
Even among wild salmon, contaminant levels can vary widely depending on the species.
Pink and chum salmon, which are smaller species, feed on critters that are low on the food chain and thus are usually lower in contaminants. Coho salmon are in the middle, and big Chinook and sockeye salmon dine on larger fish and are usually higher.
Consumers may be able to reduce their exposure to some contaminants by trimming fat and grilling, broiling or baking, rather than frying.
“It’s prudent health advice to take those actions,” Foran said, “but the scientific literature is inconclusive about how much reduction you really get using those techniques.”
Mercury, unlike PCBs, accumulates in the flesh of fish and cannot be reduced in cooking or preparation. Fish species with the highest mercury concentrations also tend to be at the top of the food chain — shark, swordfish and some species of tuna.
However, even fish species that are generally lower in mercury can have elevated levels if the filet comes from a larger, older fish.
“A consumer really has no way to know when they are buying a filet at a store whether that filet came from an older, bigger fish, so it leaves consumers with very little power,” said Jane Houlihan, a scientist with the Environmental Working Group, an advocacy group that studies toxic exposures.
Alternatives
The Environmental Protection Agency’s safety level for mercury, which can interfere with brain development in the fetus, is 5.8 parts per billion per deciliter in human blood.
By comparison, the safety level for lead, another established neurotoxin, is 100 ppb. PCBs and dioxins are also potent neurotoxins.
“We’re talking about chemicals that pose a risk to the human brain at very, very low levels,” Houlihan said. “It’s a real risk, but the flip side is that it’s really important for women to get omega-3 fatty acids in their diet.”
Some fish, particularly salmon, are high in omega-3 fatty acids, which have been shown to reduce the risk of heart disease.
There are alternatives that are low in contaminants. Tilapia, for example, is a hardy fish native to Africa that has been farmed in the area that is now Israel for about 2,500 years. It’s an efficient “filter feeder” that dines primarily on plankton, small invertebrates and plants.
Tilapia produces mild, white filets with a slightly sweet taste. Farmed catfish, another vegetarian, is also generally low in contaminants.
Consumers will get some help this fall when seafood sold in U.S. supermarkets starts to carry labels stating where it was caught and processed and whether it is wild or farmed. The labeling doesn’t include fish sold in restaurants.
Fish pregnant women can eat, and how much
Fish are an excellent source of protein, vitamin D and omega-3 fatty acids, which help prevent heart disease. But elevated levels of mercury, PCBs, dioxin, pesticides and flame-retardants have been found in some species of fish, making it difficult for consumers to know what’s safe and what’s not.
Deciding which fish are safe to eat is especially important to pregnant women because some contaminants accumulate in the human body over time and can affect the developing fetus.
Here’s what some experts advise pregnant women and women who plan to have children:
Fish OK to eat 2-3 meals per week, assuming each meal is about 8 ounces — Farmed catfish, farmed trout (rainbow), anchovies, clams, Mid-Atlantic blue crab, fish sticks (usually made from Pacific pollock), flounder (Pacific and Atlantic), wild Pacific salmon, wild Alaskan salmon, canned Alaskan salmon.
Fish OK to eat 1 meal per week — Pacific cod, Atlantic cod, crab (Dungeness, blue, Stone), king crab, imitation crab, haddock, hake (Pacific and Atlantic), herring, mahi mahi, mussels, oysters, Pacific pollock, pompano, sardines, scallops, tilapia (farmed in the U.S.), canned chunk light tuna.
Fish OK to 1 meal per month — Bluefish, crab (Gulf Coast blue), grouper, Pacific and Atlantic halibut (Alaskan halibut can be eaten more frequently), lobster, Atlantic pollock, rockfish, tuna steaks.
Do not eat: King mackerel, orange roughy, shark, red snapper, swordfish, tilefish (sometimes sold as “white snapper” or “golden snapper”), canned white albacore tuna.
Canned white albacore tuna is on average three times higher in mercury than canned chunk light tuna. To more precisely gauge how much canned tuna it’s safe for you to eat based on your weight, try the tuna calculator at www.ewg.org/issues/mercury/20031209/calculator.php.
Missing fish: Shrimp, the most popularly consumed seafood in the United States, are generally low in mercury, but data on other contaminants are lacking. For advice on locally caught freshwater fish, check with your state health department, environmental protection agency, or fish and game commission.
This advice is based on an average-sized woman who is pregnant or plans to have children. Men and some women may eat more fish; children should generally eat smaller servings.
Sources: Institute for Agriculture and Trade Policy, Environmental Working Group
How to decrease exposure to fish toxins
Consumers might be able to significantly reduce their exposure to PCBs, dioxin, pesticides and other contaminants in fish by keeping a few basic guidelines in mind:
Eat smaller fish, sometimes called “panfish,” rather than fillets from larger and older predator fish.
Eat smaller portions of fish that might be contaminated. A typical serving size is 6 to 8 ounces, but if you cut that to 3 ounces — about the size of a deck of cards — you are also decreasing your exposure.
Carefully remove skin and trim fat along the back, belly and sides of the fish before cooking. This might reduce exposure since some toxins concentrate in fat. However, trimming will not get rid of mercury, which accumulates in the flesh of the fish.
Broil, bake or grill fish. These methods let fat drip away, reducing the levels of some contaminants. Do not deep-fry or pan-fry fish.
Source: Institute for Agriculture & Trade Policy
