Humans may be to blame for rising mercury levels in a species of fish that's very popular as food, according to a news study published this week. Levels of a potentially poisonous form of the element have been creeping up in Pacific yellowfin tuna 3.8 percent every year since 1998, according to a report discussed an article by the Los Angeles Times.
Methyl Mercury levels in tuna and other large fish have been a public health concern for some time. Health authorities such as the Food and Drug Administration recommend that young children, as well as women who are either pregnant or nursing limit their intake of tuna, and avoid other large species entirely, including swordfish and tilefish.
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The study adds to evidence suggesting that human activity—particularly the burning of coal—is causing a buildup of the element in the air and water that is subsequently making its way into the food chain, according to an article in the Los Angeles Times discussing the research. Some fishing industry groups have long maintained that mercury levels in tuna and large fish are stable and come from natural sources, such as deep ocean vents.
Yellowfin—sometimes called ahi tuna—is sold in steaks and eaten in sushi, and can be sometimes found in small amounts in canned light tuna. The fact that the fish are not top-level predators could indicate that a broader swath of ocean life may be accumulating mercury levels that would make them hazardous to human health, if eaten.
"What this number is saying is that the amount of mercury in fish is getting higher and higher all the time, and if it keeps going like that, at some point, most every kind of fish is going to be potentially hazardous," study coauthor Carl Lamborg told the Los Angeles Times. "Where that point is, I don't know."