Toxins found in seafood worldwide, study shows

Toxic chemicals are showing up in fish around the globe, according to a new analysis from the Scripps Institution of Oceanography.

While the levels vary depending on the individual fish, the study that looks at five decades of data points to a widespread pollution problem in our oceans, said researcher Stuart Sandin.

He and study co-authors compiled data from more than 300 government surveys and scientific reports. In particular, they looked at documents relating to common types of seafood like salmon, sardines, tuna and anchovies.

Next they looked at the levels pollutants in these fish, focusing on chlordanes, DDT, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and mercury. These typically come from pesticides and as byproducts of industry.

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It turns out, in every corner of the world's oceans, these chemicals turn up in fish.

(A map showing pollutants found in various bodies of water. The size of the pie charts reflects the number of data records included in the analysis for each region. The color codes represent the class of pollutants found. Image via Scripps Institution of Oceanography.)

"They are pervasive," Sandin noted. "Every family of chemicals was found in every ocean basin in fish we harvest to eat."

There was a lot of variability in the levels of these chemicals, even among a single species of fish and across multiple locations. That means it wasn't possible to make blanket statements about which fish were least toxic.

"We didn't find anything that can tell the consumer, it's very safe to eat this one species from this one region," Sandin explained.

Still, the average levels were at or below what the U.S. Environmental Protection Agency deems safe to eat.

There was good news included in the findings as well.

The data showed the overall level of toxins in fish has dropped since the 1960s, when the first environmental regulations were put in place.

"For all classes of chemicals, we watched a systematic decline through time," Sandin said.

While that's good news, many of these chemicals can last for years to decades in the ocean food web. There's also scant research on their effects to humans, especially when multiple toxins are combined, Sandin said. 

Sandin said there’s still plenty of work to do to clean up our oceans and he hopes this study will highlight the need to do more to keep our seafood healthy.

"There are ways we can be a little cleaner with our use of these chemicals," he said.

Pushing companies and regulators to try harder to avoid releasing them into the environment would help cut the pollutants in the ocean even more, he said.