Do two fish contaminants create greater health threat than the worst one?

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By Jack Nissen

A new study published in the Journal of Environmental Health Perspectives questions if advice on eating Great Lakes fish is restrictive enough.

Ken Drouillard, a professor at the University of Windsor, looked at whether the Great Lakes region placed sufficient restrictions on monthly meals of sport fish.

The results are in and while they say no, they weren’t as restrictive as Drouillard expected.

Consumption advisories are used to limit human exposure to harmful substances that fish may contain.

Drouillard found that 60 percent of advisories would provide more restrictive advice under a method that takes into account multiple chemicals in a fish. That’s contrary to the current practice of basing fish advisories on just a single contaminant.

The decision to use a contaminant-mixture process is based on an assumption that when consuming PCBs and mercury–common contaminants involved in fish advisories– they compound each others’ response in the body.

“Assuming those results are reasonable, and there has been a lot of research on the potential risk to human health from PCBs and mercury exposure through fish consumption, then it makes sense there are a lot of advisories that need to be revisited,” said Michael Murray, a staff scientist with the Great Lakes Regional Center at the National Wildlife Federation in Ann Arbor, Michigan.

While the researchers predicted the number of restrictions would be much higher with the mixture method, they didn’t increase as much as they expected, Drouillard said.

Fish advisories depend on factors like the size of the fish, its species and where it is caught. Recommendations are based on monthly consumption rates, with 31 not being very restrictive and zero being the most restrictive.

“They’re typically developed on an individual contaminant basis, so we’ll develop an advisory for just mercury alone, then we’ll look at possible advisories for PCBs by themselves,” Murray said. “It’s typical then they’ll base an advisory on whatever is more restrictive.”

The system has been used by the Ontario Ministry of Environment and Climate Change since the 1970s. Drouillard wanted to study its effectiveness.

Instead of looking at what contaminant was most prevalent, he considered a combination of contaminants. While both mercury and PCBs have different origins, they share a similar toxicological response.

“Because particularly the two major compounds, mercury and PCBs, have a similar toxicological endpoint, we might consider treating them as a mixture,” Drouillard said. “But we would certainly say there should be follow up research to basically document whether for example combined exposures to the two contaminants have an additive effect on the toxicity.”

The single-contaminant process is typically used for non-carcinogens because of their different end-responses,

PCBs are byproducts of industrial sources, said Jennifer Gray, a toxicologist with the Michigan Department of Health and Human Services. While the electric coolant and insulator was banned in 1979, it still persists in the environment today. The EPA’s National Coastal Assessment says it is the most common contaminant in the Great Lakes.

Mercury, however, comes from natural sources like coal, Gray said. A study found that burning coal is the largest source of mercury emissions in the United States. Mercury is the number one driver of advisories in inland lakes in the region, Drouillard said.

“Ultimately the reason why we’re worried about exposures to PCBs and mercury by humans, particularly the sensitive population, which is women of childbearing age and children under the age of 15, is because they basically contribute to disorders in the nervous system,” Drouillard said.

Revising restrictions is tricky. The concern is to make them sufficient but not scare the public from consuming fish, he said.

The study only wanted to produce more accurate advisories without unnecessarily frightening anyone from eating fish, Drouillard said.

Fish is good source of minerals like iron, zinc and magnesium. They also carry protein, omega 2 and 3 fatty acids, which help keep the heart and brain healthy.

The Great Lakes were chosen for the study due to their chemical complexity, Drouillard said. A former industrial hub, legacy chemicals like PCBs and mercury were common byproducts of industry and continue to accumulate in fish today.

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