A new study by the Woods Hole Oceanographic Institute has revealed massive increases in the mercury content of the world’s oceans. This is bad news for fish, but toxic news for the humans that eat them.
Mercury is a trace metal that is released into the environment in usually one of two ways: Natural volcanic emissions and man-made activities such as mining and fossil fuel combustion. It is considered by the World Health Organization to be one of the top ten chemicals of major public concern. It can be found in batteries, thermometers, electric equipment, lamps, cosmetics and pharmaceuticals.
According to the WHOI’s new report, which appeared Wednesday in the journal Nature, the amount of mercury in the Atlantic, Pacific, Southern and Arctic oceans has risen significantly since the industrial revolution. Twelve expeditions over the course of eight years recorded a threefold increase in mercury content in surface waters and a 150 percent increase in thermocline waters (the ocean layer sandwiched between the surface and deep sea) compared to pre-industrial data.
This growth in mercury levels will significantly alter the toxicity of some fish species as it circulates through the food chain. Once in the ocean environment, bacteria consume the mercury and transform it into methylmercury, which then “bioaccumulates” as the bacteria are consumed by fish and “biomagnifies” as these fish are consumed by larger fish. This is why large predatory fish – sharks, king mackerel, swordfish and tilefish – contain such high levels of mercury and why their consumption is cautioned against by the Environmental Protection Agency (EPA).
Fish contain a wide range of nutritional benefits, including high-quality protein, omega-3 fatty acids and low saturated fat content. Yet according to the EPA, “nearly all fish and shellfish contain traces of mercury.” The Food and Drug Administration (FDA) as well as the EPA advise women who are pregnant or nursing to avoid fish, as mercury can cross the blood-brain and placental barriers and cause damage to the developing nervous systems of fetuses and children.
The study notes that 5,000-8,000 tonnes of mercury are emitted by industrial processes every year.