Tuna, marlin, even birds seeing elevated mercury levels: Asian coal plants likely to blame

Pollution from human sources—like coal plants—is impacting oceans and marine life in worrisome ways. 

A variety of research papers has reported increased levels of toxic mercury in ocean water and marine life, in Hawaiian tuna,in South Pacific Wandering albatross and in other species.

(Image: Yellowfin tuna jumping. Credit: NOAA Fisheries image by Ken Neil.)

For Hawai`i residents, reports are of increasing levels of mercury in yellowfin tuna or ahi are deeply concerning.

There did not seem to be increasing levels through the turn of the century. A 2003 study looked at mercury in Hawaiian ahi during a 27-year span from 1971 to 1998. It found no change during that period in Hawaiian-caught yellowfin, with respect to methylmercury levels. 

But studies from 1998 to 2008 saw steady increases, according to a newly published review of previous studies.

“The authors found that the concentration of mercury in these fish currently is increasing at a rate of at least 3.8% per year. This rate of increase is consistent with a model of anthropogenic forcing on the mercury cycle in the North Pacific Ocean and suggests that fish mercury concentrations are keeping pace with current loading increases to the ocean,” the authors wrote.

Where's all that mercury coming from? It has been well-tracked, and most comes from Asia--China, Japan and Korea appear to be primary sources, according to this report from 2009.

What to do about it?

“Future increases in mercury in yellowfin tuna and other fishes can be avoided by reductions in atmospheric mercury emissions from point sources,” wrote the authors of the paper that found annual 3.8 percent increases in yellowfin.

A little information about methylmercury, the most toxic form of the silver metal.

“The organic form of Hg (mercury), methylmercury, is of greatest concern because it is a potent neurotoxin and because it accounts for > 95% of the Hg in fish,” says a report, “Methylmercury in Marine Ecosystems: Spatial Patterns and Processes of Production, Bioaccumulation, and Biomagnification.”  More on human impacts later in this article.

A 2013 study in the journal Nature Geoscience, by a team that includes Hawai`i researchers, had already suggested things were changing. 

It looked at nine species of marine fish that feed at different levels. It appears that the toxic methylmercury is formed by microbes that attach themselves to particles containing regular mercury, that fall onto the ocean from the atmosphere. It is formed, the paper says, “by methylating microbes that live on sinking particles.”

In theory, as more mercury from the stacks of Chinese and other Asian coal-fired plants blows out over the Pacific, it dumps more mercury on the ocean. That mercury is converted into methylmercury by marine microbes, and is taken up in the oceanic food chain.

"This study reinforces the links between mercury emitted from Asian countries and the fish that we catch off Hawaii and consume in this country," said the paper’s lead author, Joel Blum.

Since methylmercury is more prevalent in deeper water, it makes sense that deeper-feeding fish would have higher levels. And they do.

"We found that predatory fish that feed at deeper depths in the open ocean, like opah and swordfish, have higher mercury concentrations than those that feed in waters near the surface, like mahi-mahi and yellowfin tuna," said Brian Popp, a University of Hawaii at Mānoa geology and geophysics professor. He was quoted in a 2013 report.

 What's interesting there, of course, is that ahi are comparatively shallow feeders. If they're getting higher levels of methylmercury, that is perhaps an indication that the levels are far higher than they once were.

And as you might expect, mercury levels ARE up. This US Geological Survey study found mercury levels up 30 percent in the Pacific in the past 20 years. It projects another 50 percent increase by 2050. 

There's lots of data on this. Here's a paper from the journal Global Geochemical Cycles.

A report on the Wandering albatross, the bird with the longest wingspan in the world—from 8 to nearly 12 feet—finds increasing levels of mercury, cadmium and persistent organic pollutants in the birds.

While adult survival seems to be unaffected, the paper reports that the pollutants are “negatively impacted long-term breeding probability, hatching and fledging probabilities.”

Some of the pollutants, like PCB and DDT, are long-banned but still persist in the environment. Others like mercury may be associated with coal-fired power and industrial plants.

What this means to humans who eat marine life depends on the person. Methylmercury is highly toxic, but is most toxic to fetuses and infants—individuals with developing brains. It is less of a threat to adult males and adult women who will not become pregnant and are not breastfeeding infants.

The Hawai`i Department of Health factsheet on eating marine fish can be found here.

The U.S. Environmental Protection Agency says “women of child-bearing age are the population of greatest concern. Children of women exposed to relatively high levels of methylmercury during pregnancy are at greater risk for a variety of developmental and learning disorders.”

And it’s not just ahi. Here is what the U.S. Food and DrugAdministration says about eating fish, specifically for women and children:

“Do not eat Shark, Swordfish, King Mackerel, or Tilefish because they contain high levels of mercury.

“Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury.

“Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.

“Another commonly eaten fish, albacore ("white") tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.

“Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don't consume any other fish during that week.

“Follow these same recommendations when feeding fish and shellfish to your young child, but serve smaller portions.”

© Jan TenBruggencate 2015