BLUE HILL – Cutting the skin off salmon before cooking it will do little to minimize the threat of exposure to toxic chemicals in the fish, according to a recent study published by Dr. Susan Shaw, founder and executive director of the Marine Environmental Research Institute.

The study supported previous research that indicated farmed salmon contain higher levels of cancer-causing chemicals than found in wild salmon, according to Shaw, who spoke about the research at MERI headquarters Wednesday. The common practice of removing the skin from the salmon to eliminate some of the chemical risk is ineffective because the chemicals are stored in the fat cells which accumulate between the layers of meat.

“It has been generally accepted almost as dogma, that if you take the skin off, you can reduce contamination levels by 50 percent,” Shaw said. “We did not find any reduction of contamination by removing the skin.”

Shaw was the lead author of the study published this summer by the American Chemical Society in its journal Environmental Science and Technology.

The findings are important, Shaw said, because people are consuming more fish, including salmon, in their diets. The study noted that between 1987 and 2000, consumption of salmon in the United States increased by more than 26 percent annually. Currently, more than half the salmon consumed around the world is farmed salmon.

“Most people know more about the benefits of eating fish than they do about the risks,” Shaw said.

Although fish are a good source for omega-3 fatty acids, the fish, including salmon, can contain PCBs and dioxins which are immune suppressants and carcinogens, she said.

“So the benefits of omega-3 fatty acids in fish must be balanced against the increased risks from the contaminants,” she said.

Shaw noted that, because of the levels of chemicals in both farmed and wild salmon, the U.S. Environmental Protection Agency has published a consumption advisory for fish, including the different types of salmon. It recommends just one meal every five months for European farmed salmon, and two meals every five months for U.S. farmed salmon.

The study looked at farmed Atlantic salmon from Norway, eastern Canada and Maine, as well as wild salmon from Alaska. All samples showed elevated levels of contaminants including DDT.

“We see DDT, PCBs and chlorinated pesticides,” Shaw said. “They were all banned in the ’70s, but they are so pervasive in the environment, they are still recycling in the food chain.”

It is through the food chain that salmon are exposed to the carcinogens, according to Shaw. It is an indication of the level of pollution that exists in the oceans, she said. The small forage fish that salmon eat are contaminated, and they pass that contamination on to the salmon.

Shaw noted that farmed salmon show higher levels of contaminants because of the way they are fed. Farmed salmon are fed a combination of fish meal with fish oils added. The fish oil is a byproduct of the fish meal. Contaminants accumulate in the forage fish, which can contain complex mixtures of chemicals.

Their feed is so fortified with fish oil that the farmed salmon consume large amounts of fat and retain that fat, along with any contaminants that might be in the fish oils, she said. The chemicals accumulate in salmon over a lifetime, Shaw said, as they also do in humans.

The fat builds up in layers that are clearly visible in the skinned salmon. Shaw and Daniel Sweimler from Wescott Forge, a Blue Hill restaurant, displayed samples of the two types of salmon during a press conference Wednesday. The wild salmon, she said, is a much tighter fish and a drier meat because there is less of a fatty layer between the muscle layers. In the farmed salmon, the fatty layers are noticeably thicker and whiter.

“You can see the difference,” said Sweimler. “You can see the sheen because of the extra fat.”

The difference in cooking farmed and wild salmon is primarily in the flavor and ease of cooking, Sweimler said. Some customers have complained about the taste and dryness when eating wild salmon, he said.

The study, he said, causes a dilemma because he does have to meet the customers’ demand, which is often for the more flavorful farmed salmon.

“So we have to educate as well as provide a service,” he said. “People’s tastes can be changed.”

The study recommended that, because of the higher levels of contaminants in the farmed salmon, it should be labeled as farmed salmon. It also notes that there is a need for a reassessment of human health risks associated with eating farmed salmon and recommends that health agencies develop consistent consumption advisories.