Fishing News

Fishermen unload their catch on April 16, 2015 in the Baja California town of San Felipe. / photo by Misael Virgen * U-T

Fish in today’s oceans contain far lower levels of mercury, DDT and other toxins than at any time in the past four decades, according to a major review by scientists at the Scripps Institution of Oceanography in La Jolla.

In what’s billed as the first analysis of its kind, the researchers looked at nearly 2,700 studies of pollutants found in fish samples taken from all over the world between 1969 and 2012. They saw steady, significant drops in the concentrations of a wide range of contaminants known to accumulate in fish — from about 50 percent for mercury to more than 90 percent for polychlorinated biphenyls, or PCBs.

At high enough concentrations, these toxins can cause cancer, neurological disorders, birth defects, thyroid problems and other ailments in people who consume tainted fish.

Echoing what marine experts have said over the years, the Scripps scientists conclude that clean-water regulations, lawsuits and other forms of public pressure have led to bans or sharp reductions in the use of industrial and agricultural contaminants that end up in creeks, rivers and oceans.

But they also tempered the good news with a sobering reminder: Many fish in the wild still have pollutants at levels considered unsafe for frequent human consumption.

And forget the longstanding belief that smaller fish — those lower on the food chain — generally contain fewer toxins than large predator fish, or that fish caught in certain areas of the world are safer than those harvested in other zones.

“Maybe there’s a little pattern of those predators through bioaccumulation having more [contamination], but it wasn’t a common pattern. So it doesn’t mean you’re safe as long as you eat a halibut,” said Stuart Sandin, a marine biologist at Scripps and co-author of the new analysis.

“There’s just a lot more complexity out there that washes away that very clean and easy signal of, ‘Eat something that’s not a predator and you’ll be OK,’” he added.

The new report found no predictable pattern of contamination.

Some mackerel and sardines had far greater pollution than some swordfish and shark. In addition, oceanographers have come to realize that an unexpectedly high number of fish species migrate for thousands of miles. Even within a school of fish caught in the same location, the degree of toxins can vary greatly from one individual fish to another.

To further complicate matters, today’s increasingly international seafood market means that U.S. stores typically sell fish shipped from Southeast Asia, South America and elsewhere.

“Some fish [surprisingly] showed low concentrations and some showed very high concentrations” of toxins, Sandin said. “So it’s a little bit of a gamble.”

Rita Kampalath, science and policy director for the environmental group Heal the Bay, said while the decrease in contaminant levels is welcomed news, it isn’t particularly surprising. “It’s great that that’s documented. I would hope that they would drop since many of these contaminants haven’t been produced for a long time,” she said.

The report, published Thursday in the journal PeerJ, focused on five contaminants or classes of contaminants that are widespread in the oceans: chlordane, DDT, mercury, PCBs and polybrominated diphenyl ethers, or PBDEs.

Sandin and his colleagues didn’t try to assess the health effects of these chemicals because that field of science has long been established. Instead, they sought to identify geographic and other patterns in the chemical contamination of fish worldwide.

Their analysis showed that on average, pollutant concentrations now meet federal safety guidelines in the United States for occasional fish consumption — two or three servings per week, based on various marine groups’ standards. For example, mercury and PCBs were found at levels acceptable for occasional human consumption and DDT was consistently below the established threshold for concern.

Still, with millions of people worldwide relying on fish as their main source of protein, the threat of contamination continues to loom large.

“We label a lot of things like whether it’s sustainable or whether it’s wild-caught or farmed, but one of the things that we still haven’t figured out how to do is to address whether it’s contaminated or not. I think that’s something most people want to know,” said Amro Hamdoun, a biology professor at Scripps and co-author of the new report.

Attempts to track contamination by species, geographic region and other factors revealed a complex set of circumstances that researchers have yet to fully understand.

“The pollution does not stay in one place,” Sandin said. “We thought that we would find something like that. But when you start increasing the scale, that predictability goes away. We didn’t find any evidence that when you’re near shore versus 100 miles off shore that you had more or less chemicals in the seafood.”

Currently, chemical testing for seafood is limited and expensive.

“One of the things that we’re working on right now in the lab is new technologies that could be used to rapidly screen fish and other types of food for these different types of contaminants,” Hamdoun said.

He and his Scripps colleagues also are collecting data about yellowfin tuna from around the world, in part to develop techniques for studying how various contaminants interact with one another. They said such testing is needed because one specimen of fish often contains several types of pollutants.

“For a consumer, if you’re eating something that has a high chemical concentration of one you’re getting a bunch, you’re getting a cocktail of these chemicals,” Sandin said. “And we’ve yet to explore the health consequences of mixing these chemicals.”

Kampalath of Heal the Bay agreed with the Scripps team that further research is needed.

“I think the authors acknowledged there are confounding factors that would make the conclusions less clean,” Kampalath said. “The coarseness of the scale presents a challenge in identifying patterns in [pollutant] concentration levels.”

CONSUMPTION GUIDELINES

• Some recommendations from California’s Office of Environmental Health Hazard Assessment:

• In the same location, some fish species can have higher chemical levels than others. If possible, eat smaller amounts of several types of fish rather than a large amount of one type.

• Eat only the fillet portions. Don’t eat the guts and liver because chemicals usually concentrate in those parts. Also, avoid frequent consumption of any reproductive parts such as eggs and roe.

• Many contaminants are stored in fish fat, so skin the fish when possible and trim any visible fat.

• Use a cooking method that allows juices to drain away from the fish — baking, broiling, grilling or steaming. The juices contain chemicals from fish fat and should be thrown away. If you make stews or chowders, use fillet parts.

• Raw fish may be infested by parasites, so cook fish thoroughly to destroy them. This also helps to reduce the level of many contaminants.

• Pregnant women should talk with their doctors about fish-consumption warnings given by the U.S. Food and Drug Administration and the U.S. Environmental Protection Agency.

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