The greatest source of mercury in the biosphere is currently of human origin. Mercury is number three on the Agency for Toxic Substances & Disease Registry (ATSDR) 2011 Substance Priority List. Although mercury is a naturally occurring element, most of it is sequestered in subterranean rock formations and coal beds. Two-thirds of the mercury entering the biosphere comes from man-made sources, including industrial plants, coal burning and incinerators; the additional one-third is emitted from natural sources. Many former chlor-alkali facilities (for producing chlorine and sodium hydroxide) are major point sources of mercury to aquatic ecosystems and are currently designated Superfund sites. Mercury is released into the air or directly into water bodies and makes its way into lakes and estuaries, where some of it settles to the bottom. Bacteria living in the mud of lake, river and estuary bottoms helps transform mercury into methylmercury (see below).
But mercury is considered a global pollutant, as it's capable of spreading far beyond its source area. The arctic, for example, has no known sources of mercury, but it harbors mercury-contaminated fish, and recent studies indicate that whales feeding in the arctic have high levels of mercury in their tissue.
What is Methylmercury? Methylmercury is an extremely toxic form of mercury that biomagnifies in aquatic food chains. It is a potent neurotoxin and the easiest form for animals to store in their tissue. It harms the brain, affecting memory, understanding and movement. Studies have shown that mercury exposure in humans can result in developmental delays in children, motor impairment, cardiovascular effects and, in acute cases, death. Its effects have been studied in fish, whales, seals and seabirds. Methylmercury binds to proteins and easily crosses cell membranes, including the blood-brain barrier and the placenta. Affected wildlife, such as loons, develop behaviors that ultimately reduce their chances for survival and reproduction. Studies conducted on human populations have estimated that between 200,000 and 400,000 children in the United States alone are born each year with pre-natal exposure to methylmercury sufficient to put them at risk of neurologic impairment.
Mercury in fish
People are exposed to mercury mainly by eating fish and shellfish—and 95 percent or more of the mercury in fish is the more toxic methylmercury. According to the EPA, fish filets containing more than .3 parts per million (ppm) of methylmercury should not be eaten (Canada and the states of Maine and Minnesota suggest you avoid fish with .2 ppm). Fish caught in water with very low concentrations of mercury (less than 1 part per trillion) can nonetheless contain harmful levels of methylmercury. In some marine ecosystems, the concentration of methylmercury increases 10 million times as it makes its way up through the food web from microscopic algae to whales, dolphins, shark and tuna.
Mercury concentrations in fish found in lakes and rivers throughout the United States now exceed the mercury levels that cause concern for human and wildlife health. As of 2008, all 50 states and one U.S. territory have fish-consumption advisories for mercury. In addition, all states on the Atlantic and Gulf of Mexico have coastal fish advisories. Although much of the scientific research on mercury in fish has focused on freshwater ecosystems, most Americans are exposed to mercury through seafood consumption. There are many questions to be answered about where the mercury in the fish that we eat comes from and what fish are safe to eat. Solutions to the complex problem of mercury pollution have been impeded by conflicting information on the sources, transport and accumulation of mercury in the environment. Our program hopes to address these questions and, therefore, provide the scientific basis for solutions to this pressing environmental and human health issue.
There are three main forms of mercury measurable in the human body. They are all toxic. Which is why you need our mercury level test.
Methylmercury (MeHg), also known as monomethylmercury, is the most researched form of mercury present in nature. It is an organic mercury species commonly found in fish and other animal tissues. Although methylmercury is mobile and easily absorbed, it is difficult for organisms to eliminate. Instead, the methylmercury accumulates in biological tissues. For example, while digesting its prey, the predator absorbs the methylmercury contained in its victim. As a result, animals higher on the food chain tend to have more methylmercury in their tissues than those lower on the food chain. This process of methylmercury exposure is known as bioaccumulation. Bioaccumulation can result in fish having over 1 million times higher methylmercury concentrations than the water in which they swim.
Inorganic mercury is the term used to refer to mercuric ion (HgII). Inorganic mercury is highly toxic but not very mobile. Inorganic mercury in sediments, soils and food sources does not pass easily into biological tissues. However, once inside of the tissue, inorganic mercury is very difficult to remove. Inorganic mercury accumulates in tissues when a more mobile form of mercury such as elemental mercury vapor, methylmercury or ethylmercury enters the tissue and breaks down into inorganic mercury. In biological tissues, most organic forms of mercury will eventually break down into inorganic mercury.
Like methylmercury, ethylmercury is an organic form of mercury. Ethylmercury can be present in sediments or petroleum hydrocarbons. Ethylmercury is also used as a component in vaccine preservatives (thimerosal). Vaccination is the most common exposure route for this organic form of mercury. Like methylmercury, ethylmercury can move easily into biological tissues. However, ethylmercury tends to break down into inorganic mercury more rapidly than methylmercury.