Mercury levels in Hawaiian yellowfin tuna – that’s ahi to sushi fans – are rising by nearly 4% a year, according to a new study.

Researchers at the University of Michigan looked at earlier data that detailed concentrations of mercury in the muscles of yellowfin tuna caught near Hawaii from 1971 to 2008. They found no detectable increase in mercury between 1971 and 1998; however since 1998, the level of mercury in the tuna has taking a huge leap, rising by at least 3.8% per year.

The scientists attribute the increasing levels of mercury in the popular fish to environmental pollution, largely from burning coal, which releases mercury that moves through the air and settles into the ocean – and for that you can thank China. “Humans are responsible for a great deal of the mercury actively cycling in the environment at present,” the researchers write.

The findings were published in the journal Environmental Toxicology and Chemistry on February 2.

Mercury is toxic and affects the development and function of the nervous system, particularly the brain. It is especially dangerous for pregnant women and children. It can accumulate in high concentrations in fish, particularly predatory marine fishes such as tuna and swordfish that are at the top of the food chain.

According to the study, “Annually in the United States, approximately 300,000 to 600,000 children are born with mercury concentrations in cord blood that exceed 5.8 ?g/L, a value associated with significant loss of IQ (intelligence quotient), the economic consequence of which is estimated to be $8.7 billion annually in lost income.”

And things are only going to get worse. Even if pollution levels remain the same as they are now, “North Pacific Ocean intermediate waters are expected to double in mercury concentration by 2050,” the scientists write. “Mercury contamination of ocean fish is a serious global health issue.” The scientists call what is happening to the Pacific yellowfin a “bellwether” of things to come.

The only solution, they write, is for eastern Asian countries that rhyme with “Dinah” to stop their nonstop polluting: “Future increases in mercury in yellowfin tuna and other fishes can be avoided by reductions in atmospheric mercury emissions from point sources.” 

In the meantime, ahi is probably still fine as an occasional indulgence, but you might not want to eat it every day, or at all if you are pregnant.

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