Researchers at Scripps Institute of Oceanography at UCSD found that though the amount of persistent, bioaccumulative and toxic pollutants in fish has declined 15 to 30 percent per decade over the last 30 years, it remains highly variable across species and locations.

Corresponding Author and Associate Professor at Scripps Stuart Sandin explained that the variability in PBT concentration meant that species of fish in different parts of the world were equally likely to contain significant amount of pollutants.

“I expected to see fishes caught near coastlines to have higher concentrations [of pollutants] than those caught in the middle of the ocean; instead, there was still a lot of variation at each of those locations,” Sandid told the UCSD Guardian. “Every group of fish from the top of the predators down to those that eat lower on the food chain all showed possibility of having very high concentrations.”

Contributing Author and Associate Professor of biology at Scripps Amro Hamdoun said that the variability in pollutant concentration could result in more toxic fish being sold at the supermarket.

“The huge variation means that it’s very hard to generalize what amount of pollutants you’re going to be exposed to when you buy a piece of fish,” Hamoun told the Guardian. “When you go to the supermarket to buy a piece of fish, you can potentially have 180 times more pollutants in one fish than another fish.”

The team published their findings in PeerJ on Jan. 28, basing them on review research of approximately 2,500 different academic literature and governmental reports. They aimed to learn more about the distribution of these pollutants by looking for patterns across species, geography and five suites of chemicals that make up the PBT designation.

Hamdoun added that the variability problem does not have an immediate solution as it is difficult to differentiate between types of seafood.

“This is going to pose a new challenge for us in how we label seafood,” Hamdoun said. “We label all kinds of things about seafood — whether it’s farmed or wild, sustainable or not sustainable — and of the things we haven’t yet figured out how to do is to designate clean or dirty.”

The Stockholm Convention — a global treaty established in 2004 by the Governing Council of the United Nations Environment Programme — intends to eliminate release of persistent organic pollutants, a subset of PBTs, into the environment. Although Sandid finds it encouraging that international policies like the Stockholm Convention have been effective in lowering concentration of pollutants, the pollutants will still remain for some time.

“The average concentration of pollutants has been systematically decreasing — the average in the 1980s were anywhere from twice to three times as high as the average we saw in studies as of the 2000s,” Sandid said. “It’s encouraging to see things like the Stockholm Convention and [other] international efforts to limit our use being successful, but the [pollutants] are still persistent in the environment and they’re going to last for decades more.”

Sandid describes the review paper as a reactionary approach to dealing with environmental consequences when it should be more preventative.

“I feel like there’s a very good opportunity for applied chemistry to be thoughtful about potential environmental consequences so we can prevent a new suite of chemicals from getting into the environment,” Sandid said. “I’m hoping this study shows sure, we can react and manage, but we should be a little more proactive and think about our design of chemicals that are not likely to persist in the environment.”