U.S. Environmental Health Effects and Treatment of Mercury Exposure IAP 2006, 12.091 Medical Geology/Geochemistry Term Paper Sergio Navarro Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 30 January 2006 Abstract: The various methods of treatment to mercury toxicity in the human body have been studied and investigated with somewhat mixed conclusions. This paper discusses the various types of mercury, the cycle of mercury in the environment, human exposure to mercury and treatment, and methods of reducing mercury pollution and its effect in the human population in the U.S. Keywords: Methylmercury, exposure to mercury. The effect of mercury on humans has been observed for centuries now. The 80th element in the periodic table has been historically used for various purposes over the history of man, from making felt hats to thermometers and medical equipment. Dental fillings in the past were made using mercury amalagams. However, in addition to explaining and exploring the effects of mercury toxicity in the human body, it is equally vital to understand possible ways to both treat and reduce exposure of mercury to vulnerable human populations. These topics have not been well studied over time. This paper will explore these areas and include recommendations for areas where mercury exposure should be reduced. Mercury is found in nature in two main molecular forms, an organic and an inorganic form. It is manufactured by the reduction of cinnabar, which is a reaction where oxygen and cinnabar (HgS) are reacted to produce mercury (Hg) and sulfur dioxide (SO2). Both forms are dangerous and toxic in both a liquid and vapor state, however the inorganic form poses a higher risk to humans for the risk of poisoning. This is because it more easily permeates cell membranes and can accumulate in the brain. The organic form - produced from inorganic mercury by bacteria in the water system after it enters it - is a neurotoxin that can cause serious nervous system damage and the brain. This form is often caused by linking the mercury metallic ion with a methyl side group, making a methylmercury compound. This form of mercury especially poses a danger to the developing fetus and comes from the ingestion of fish. The inorganic form, commonly used in medical equipment and dental fillings, is also a neurotoxin and particularly affects the liver. Toxicity cases of this form come most commonly from inhalation during manufacturing processes or after a spill.Fig. 1. Mercury cycle in the environment. Figure 1 is pictorial representation of the production, flow, and accumulation of mercury in the atmosphere. fish with the highest concentration of mercury levels are at the top of the hydrospheric food chain. The single largest source of mercury pollution in the atmosphere is due to the burning of coal in electrical production facilities. The mercury that exists naturally in the bituminous coal and cinnabar is released into the atmosphere at a much higher concentration than background levels expected to be seen from natural geological processes. Studies estimate that close to 75% of global mercury emissions are attributable to human activity. Once mercury has been emitted into the atmosphere, it is often deposited into aqueous bodies, such as lakes and oceans. Divalent mercury, an ionic form of inorganic mercury, is more easily bonded to particles and quickly dissolves in water. Soon after being deposited into water, microorganisms transform this form into the aforementioned methylmercury. It is important to mention that methylmercury can be converted back into its elemental form and then reemitted into the atmosphere, causing this cycle to continue. Fig. 2 Sources of mercury pollution. Figure 2. indicates sources of mercury pollution. As visible, the burning of coal for both utility and industrial purposes account for 52% of total mercury emission. The ability of mercury to travel long distances through its water cycle and air cycle have an unexpected effect on areas that lack heavy industry; a particular region may have low-level contamination of mercury without any mercury-related human activity; for instance, a case in the woods of Wisconsin pose one such example, where moderate levels of mercury were found despite the lack of any possible sources of mercury pollution. Once in the hyrdrosphere, methylmercury can accumulate at extremely high concentrations in the tissues of freshwater biological creatures. These organisms eat plants that often contain mercury and are exposed to mercury in the water. The concentration of mercury in a shellfish often can be more than ten thousand times the concentration found in the water in its environment. This is due to the fact that methymercury accumulates as the organism filters water through its body and continually consumes smaller mercury-containing creatures. Larger creatures including predatory fish, birds, and humans continue to accumulate more and more amounts of mercury in their bodies as they eat these fish. One EPA report to Congress indicated that up to 30% of the male loon population in the U.S. northeast could have mercury levels high enough to cause adverse health effects. Sources of Mercury PollutionManufacturingResidential boilersHazardous wasteMedical wasteCoal, industrialMunicipal wasteCoal, utilityOther sourcesFigure 3 is the USGS map of deposition of mercury from the atmosphere in the United 2States. It is evident that the northern and eastern parts of the United States have especially higher amounts of mercury deposition. Exposure to Mercury There exist three major areas of contamination of mercury that pose serious risks to human populations. First, hospitals and health-care facilities have medical equipment that contains mercury. Secondly, manufacturing and power plants burn coal and sludge, directly producing mercury. Incineration of solid waste also is another source of mercury from this area. Lastly, the direct consumption of freshwater and seawater fish is a possible risk source. The first source of mercury contamination is most especially a risk to those with occupations in biomedical facilities. The inhalation of mercury vapors due to spills can lead to serious health consequences; as a spill can cause mercury concentrations in the indoor air to quickly become much higher than recommended levels. Biomedical experiments involving methylmercury have also been shown to be