Mercury levels in Hawaiian Yellowfin Tuna have been rising fairly rapidly over the last few decades, according to new research from the University of Michigan and the Woods Hole Oceanographic Institution.
The work — which was done by compiling and re-analyzing three previously published reports on yellowfin tuna caught near Hawaii — found that, in keeping with old predictions that levels in predatory fish would rise fairly rapidly with rising atmospheric levels, the concentration of mercury in that species increased at least 3.8% per year from 1998 to 2008.
That’s a huge increase when you consider the relatively short timespan that the rise occurred in, and just how toxic the organic form of mercury (methylmercury) is.
Rising levels of methylmercury in the world’s oceans are primarily the result of growing levels of atmospheric deposition from human activities — in particular, from coal-fired power plants emissions, and from artisanal gold mining. The higher in the food chain a fish/animal is, the higher the expected levels of the compound are — large, predatory fish such as tuna, swordfish, etc, generally have the highest levels.
“The take-home message is that mercury in tuna appears to be increasing in lockstep with data and model predictions for mercury concentrations in water in the North Pacific,” stated researcher Paul Drevnick, an assistant research scientist at the U-M School of Natural Resources and Environment and at the U-M Biological Station. “This study confirms that mercury levels in open ocean fish are responsive to mercury emissions.”
Here’s the findings:
Drevnick and his colleagues reanalyzed data from three studies that sampled the same yellowfin tuna population near Hawaii in 1971, 1998 and 2008. In each of the three studies, muscle tissues were tested for total mercury, nearly all of which was the toxic organic form, methylmercury.
In their re-analysis, Drevnick and his colleagues included yellowfins between 48 and 167 pounds and used a computer model that controls for the effect of fish body size. Data from 229 fish were analyzed: 111 from 1971, 104 from 1998 and 14 from 2008.
The researchers found that mercury concentrations in the yellowfins did not change between the 1971 and 1998 datasets. However, concentrations were higher in 2008 than in either 1971 or 1998. Between 1998 and 2008, the mercury concentration in yellowfins increased at a rate greater than or equal to 3.8% a year, according to the new study.
“Mercury levels are increasing globally in ocean water, and our study is the first to show a consequent increase in mercury in an open-water fish,” Drevick stated. “More stringent policies are needed to reduce releases of mercury into the atmosphere. If current deposition rates are maintained, North Pacific waters will double in mercury by 2050.”
A real problem certainly. But, of course given the general overfishing of nearly all tuna species, and all fish in general, perhaps tuna won’t even be around (in notable numbers anyways) by then?
The new findings are detailed in a paper just published in the journal Environmental Toxicology and Chemistry.
Image Credit: U of M