What is Mercury?
Mercury (Hg) is a metallic element that is released naturally to the environment by volcanoes, the erosion and weathering of rocks containing mercury (e.g. cinnabar), and other processes. There are also anthropogenic sources of mercury to the atmosphere. Human beings have extracted mercury for thousands of years for use in products such as paints, lightbulbs, and thermometers, and in processes such as gold mining and the chlor-alkali industry. Prior to industrialization, most of these uses released only small amounts of mercury into the environment. Human activities in recent decades, particularly coal combustion and gold mining, are responsible for an increase in global mercury deposition.
Why are we concerned about mercury?
Mercury is persistent in the environment and does not break down or degrade. After mercury is released to the atmosphere, it is deposited to the Earth’s surface, and some eventually flows into rivers and streams. Within aquatic environments, mercury is converted by bacteria into methylmercury – a form that is more readily incorporated into living tissues and is biomagnified to high levels as it is transferred through the food web. Methylmercury binds to proteins and is not readily excreted. Most people and wildlife are exposed to methylmercury by eating fish, an important source of protein. In human populations, the most at-risk and sensitive individuals include women of childbearing age who may become pregnant, nursing mothers, and children under 12 years of age. The people with the highest exposure due to fish consumption habits include: recreational fishers and their families, some Native American populations, Asians and Pacific Islanders, and individuals who fish to meet their or their families’ nutritional needs (subsistence fishers).
(Paraphrased from Mercury Matters 2007, A Science Links Publication of the Hubbard Brook Research Foundation)
Is it Safe to Eat Fish?
People are exposed to mercury mainly through eating fish and shellfish — and 95 percent or more of the mercury in fish is the more toxic methylmercury. According to EPA, fish fillets containing more than 0.3 parts per million of methylmercury should not be eaten (Canada and the states of Maine and Minnesota suggest you avoid fish with greater than 0.2 ppm methylmercury).
Fish is an important source of protein and also has nutritional and health benefits associated with consumption. Consumers can make safer seafood choices and reduce mercury exposure by following EPA, FDA, and local and regional consumption advisories. In general, smaller fish that are low on the food chain (e.g. eat plankton) will have lower mercury concentrations than large fish that eat other fish.