13 September (WNN) — Bluefin tuna, which travel long distances and accumulate mercury with age, could serve as a global barometer of mercury pollution, according to a new study.
Health officials in the United States recommend eating no more than a few ounces of tuna per week, and pregnant women are advised to abstain.
This is because tuna, especially older, larger specimens, tend to accumulate methylmercury in their muscle tissue.
Exposure to significant levels of methylmercury can disrupt the nervous system. The contamination has been linked to cancer in adults and cognitive impairment in children.
In bluefin tuna, mercury contamination can reach concentrations unsafe for human consumption. However, mercury concentrations in bluefin tuna populations vary.
Unfortunately, the global distribution of mercury pollution is poorly understood.
To shed light on the problem, the scientists conducted a global survey of mercury contamination levels, revealing geographic variations, as well as the effects of age, size, gender and position in the food web on mercury concentrations.
Using data from dozens of tissue sample surveys conducted between 1998 and 2019, the researchers determined that Atlantic bluefin tuna caught in the Mediterranean Sea have the highest rates of mercury accumulation.
The scientists published the results of their survey in a new paper published online Monday in the journal PNAS.
Atlantic tuna is the most important tuna species for commercial fishing, and most are caught in the Mediterranean Sea. Atlantic tuna from the North Atlantic tend to have lower levels of mercury, as do related species, Pacific tuna and southern tuna, caught in the Pacific and Indian Oceans.
The data also showed that variations in mercury concentrations are consistent with mercury pollution levels measured in seawater and zooplankton samples.
“Our study shows that mercury accumulation rates in bluefin tuna can be used as a global pollution index that can reveal patterns of mercury pollution and bioavailability in the oceans, natural and anthropogenic emissions, and regional environmental characteristics. ,” senior author John Reinfelder, a professor of environmental science at Rutgers University, said in a press release.
Mercury naturally enters the ocean from rocks. It is also released by metal mining, the burning of fossil fuels, and other human activities.
The researchers confirmed that the geographic variation of mercury pollution reflects the distribution of mercury-emitting human activities.
Previous studies have shown that as mercury pollution levels drop, so do the concentrations in tuna and other fish populations.
Unfortunately, mercury levels continue to rise in some places, increasing concentrations in local tuna populations.
“Overall, mercury accumulation rates among geographically distinct populations of upper trophic level marine fish in ocean sub-basins to investigate the trophic dynamics of mercury in marine food webs and improve public health risk assessments of mercury exposure.” Mercury provides a means of comparing bioavailability of seafood,” Reinfelder said.