American Journal of Law & Medicine

The mercury's falling: the Massachusetts approach to reducing mercury in the environment.


Mercury is a persistent, bioaccumulative toxin that adversely affects human beings and wildlife. (1) Mercury, like many such toxins, is a multimedia pollutant that can readily transfer among air, water, and soils, and thus crosses the boundaries of traditional regulatory programs. (2) Mercury can also be transported long distances in the atmosphere, creating transboundary issues that are regional and global in scope. (3) Human exposure to mercury is largely attributable to the consumption of contaminated fish, with women of childbearing age, infants, and children at greatest risk. (4) Because mercury persists in the environment, the risk of neurological or other impairments can span generations. (5) Mercury, largely from anthropogenic sources, enters aquatic systems through a variety of pathways including direct deposition from the atmosphere, runoff, and wastewater discharges. (6)

The protection of public health from mercury exposure depends in large part on the willingness of government to respond through environmental law. The characteristics of mercury demand a comprehensive and aggressive approach from environmental agencies, including limits on emissions and effective programs to better manage mercury or eliminate its use. The public health threat from mercury emissions to the air and releases to water is being addressed through a number of environmental laws at international, federal and state levels. Concerned over evidence of mercury contamination in fish and the slow pace of federal regulatory efforts, some states have developed their own strategies, including regional and binational efforts to reduce mercury. Massachusetts, and the Northeast region as a whole, provide examples of state leadership where innovative regulatory and voluntary approaches to address mercury pollution and risks are being developed and implemented. (7) Already, Massachusetts has reduced emissions of mercury from facilities in the state by almost 70%, with further reductions anticipated. (8) By going beyond federal requirements, Massachusetts provides an important example of what can be accomplished within the current technological, economic and political contexts. (9)

This Article provides an overview of the Massachusetts experience, within the context of international, federal and regional initiatives. Part II provides background information on mercury, including sources, toxicity, and fate in the environment. Part III describes the legal framework for the regulation of mercury, with particular emphasis on the Clean Air Act. Part IV presents the strategy underway in Massachusetts and the Northeast to reduce mercury emissions, through assessment and goal-setting to regulatory and voluntary implementation. The Massachusetts approach illustrates the current importance of state leadership in developing effective strategies and demonstrating workable solutions.



Mercury can exist in several different chemical forms, which, because of differences in solubility, vapor pressure, and other characteristics, differ in their environmental fate and toxicity. (10) Chemical reactions in the environment can result in the inter-conversion of all forms of mercury)l Atmospheric chemistry is particularly important in determining mercury transport and deposition. Oxidizing pollutants such as ozone may serve to drive the conversion of elemental mercury to ionic forms, facilitating their deposition. (12) Thus, patterns of mercury deposition vary regionally depending on pollutant loadings, cotransport, and meteorology. (13) While mercury changes form, it does not biodegrade but instead persists in the environment. (14)

Elemental mercury, the form used in thermometers, is a liquid at room temperature and readily volatilizes. (15) It is the predominant mercury form in the atmosphere. (16) Well known characteristics of elemental mercury are its low viscosity and tendency to form mobile, sphere-shaped droplets. (17) Inorganic forms of mercury typically exhibit higher solubility in water and reduced volatility. (18) They are the most common forms found in water and soil and readily deposit from the atmosphere during rain and other wet deposition events. (19)

Mercury can also form organic compounds. These compounds were frequently used as fungicides and pesticides in the past and are still used in industrial and research applications. (20) Organic forms of mercury are typically extremely toxic. The organic compound methyl mercury, which can be generated from other types of mercury in sediments in aquatic systems, is of particular concern from an environmental perspective. (21) Methyl mercury is formed in the environment primarily through the metabolic action of microorganisms (e.g., sulfate reducing bacteria). (22) This type of mercury concentrates up the aquatic food chain and can reach levels in fish tissues that are in excess of a million times higher than in the water. (23) Unlike many other organic pollutants (e.g., polychlorinated biphenyls), methyl mercury does not partition into fats but instead is primarily found in muscle tissue. (24) Thus, trimming fat or cooking fish using methods that remove fat, which can effectively reduce exposure to many organic contaminants, do not work with mercury-contaminated fish. (25)

The methylation of mercury may occur in water, soils or sediments depending, in part, on the amount of dissolved oxygen, sulfur, pH, and other organic constituents. (26) Acid rain may increase methylation because low pH can mobilize mercury and tends to promote the formation of methyl mercury. (27) Because chemical reactions in the environment can result in inter-conversions between the forms of mercury, environmental releases of any type of mercury are of concern. (28)


Sources of mercury are both natural and anthropogenic. The relative contributions cannot be precisely quantified because it is not possible to determine how much of the mercury now present in the environment is attributable to historic anthropogenic releases that are being re-circulated. Studies indicate that the anthropogenic mercury released to the atmosphere exceeds natural sources, and may be as much as two to six times greater. (29) Natural sources of mercury are the ore cinnabar, which contains 86% mercury, and other rocks such as granite, which typically contain from ten to several hundred parts per billion of mercury. (30) Sedimentary rocks also contain some mercury. (31) Because of anthropogenic inputs, mercury levels are elevated in more recently deposited lake sediments. (32) While some mercury in sediments is natural in origin, human activities certainly contribute to the availability of mercury in the environment, even in remote areas removed from local point sources. (33) Mercury flux or input rates to sediments in lakes and ponds increased from two-fold to more than twelve-fold since the industrial revolution. (34)

Despite its toxicity, mercury is still used in many applications and it is traded as a commodity worldwide. (35) Although no U.S. mercury mines are currently in operation, considerable amounts of mercury are still mined annually in other countries. (36) In the United States and most of the developed world, elemental mercury supplies from such secondary sources meet or exceed demand, eliminating the need for new production. (37) Current sources of mercury in the United States include recycling of mercury-added products, recovery associated with contaminated sites and the mining of other metals, and sales from industrial stockpiles. (38) The U.S. Department of Defense has maintained a strategic mercury stockpile since the 1950s. (39) The mercury stockpile established by the Department of Defense currently consists of approximately 5,000 tons of elemental mercury, which is stored at several sites. (40) Sales of excess mercury from this stockpile were a major source of mercury from the 1970s through the early 1990s. (41) During 1993, the federal government sold more than 300 tons of mercury. (42) In 1994, net U.S. exports totaled 348 tons, suggesting these sales fueled exports. (43) In response to environmental concerns raised by many state and interstate organizations, these sales were suspended in 1994, pending an evaluation of the environmental ramifications of sales or alternate management options. (44)

Many states and organizations have urged the federal government to continue to store, rather than sell, this stockpile until long-term national strategies for its permanent retirement are developed. (45) This position springs from concerns that such sales would, by lowering prices and increasing availability, encourage unnecessary uses of mercury and ultimately contribute to global releases to the environment. (46) In response to these concerns, an Environmental Impact Statement on this issue was completed in 2003 and the federal government has concluded that the stockpile should be maintained and consolidated. (47)

Many sources of mercury pollution are associated with manmade products and activities. Table 1 summarizes recent data available on domestic U.S. uses of mercury.

Overall, mercury use has substantially declined over the past two decades, with dramatic reductions in its use in paints and batteries, attributable to state, federal and voluntary efforts. (49) Significant remaining uses include chemical and dental applications, switches, lighting, and measurement devices. (50) Mercury is still commonly found in many household products, such as thermometers, batteries, fluorescent light bulbs, thermostats, and switches. (51) Commercial or manufacturing uses include the production of chlorine and caustic soda in chemical processing. (52) Many latex paints contained mercury as a preservative and fungicide until the use was discontinued or banned in 1990. (53)

Mercury also occupies a place in many mouths as an amalgam in dental fillings. Silver amalgam fillings contain about 50% mercury, which, when placed or removed, can lead to the disposal of mercury into wastewater and solid waste. (54) Data from a variety of sources indicate that dental wastewater contributes a significant fraction of mercury loadings to sewage. (55) Mercury in amalgam, where it is chemically combined with other metals, exhibits reduced solubility and ability to vaporize when compared to elemental mercury. (56) This limits, but does not eliminate, direct exposures. Although there is no definitive scientific evidence of adverse health impacts attributable to amalgam fillings (57), they do contribute to mercury exposures. (58) Thus, some public health specialists recommend that the use of these fillings be limited in pregnant women and children. (59) Alternatives to amalgam exist but are typically more expensive, may not be as effective in some situations, and may entail other risks. (60)

Releases of mercury into the environment occur when mercury-containing products are sent for disposal in landfills, incinerated in waste combustors, or disposed of into wastewater. (61) Releases can also occur in seemingly innocent ways, such as volatilization after breakage of a thermometer or fluorescent light bulb. (62) Although individually small, these releases, in aggregate, are likely to be large. Globally, significant amounts of mercury also continue to be used in small mining operations as an amalgamating agent that enhances the recovery of gold. (63)


Mercury is toxic to human beings, with the effect depending on the dose, type of mercury and characteristics of the recipient. Mercury has been demonstrated to cause a variety of adverse health effects primarily targeting the neurological system, the kidneys, skin, and immune system. (64) Recent data suggests it may adversely affect the cardiovascular system as well. (65) Mechanistically, mercury's pleiotropic effects are likely the result of its ability to interfere with the activities and three-dimensional conformations of sulfur containing proteins. Symptoms of mercury poisoning range from loss of sensation, memory, hearing, and vision to kidney damage, paralysis and death. (66) The potent toxicity of organic forms of mercury was highlighted by the tragic death of a world-renowned research professor at Dartmouth College in 1997, who died from progressive organ failure, including brain damage, several months after accidentally spilling a few drops of dimethyl mercury on her hands during a laboratory experiment. (67)

The effects of mercury depend significantly on its chemical speciation, which determines the degree of absorption into, and distribution within, the body's organs. (68) For example, organic forms are readily absorbed through the skin while elemental mercury is not. (69) Both elemental and organic mercury can pass through the blood-brain barrier and pass across the placenta, while inorganic mercury cannot. (70) Mercury is retained in the kidneys and can trigger immune responses that lead to kidney damage. (71) Methyl mercury from consumption of fish, where it has bioaccumulated, is very well absorbed into the bloodstream. (72) From the blood, methyl mercury can be transferred to the brain and fetus. (73) Mercury may also be transferred to milk and into hair, which can serve a biomarker of past exposure. (74) Loss of methyl mercury from the body after it has been absorbed typically takes about two months. (75) Chelation therapy can be used to accelerate clearance of mercury from the body, but these therapies entail other risks. (76)

The health effects database for mercury is among the best available for any environmental toxicant. Substantial health effects data on mercury are available from a number of laboratory studies as well as studies on large populations of people. (77) These include epidemic poisonings as well as exposures to lower levels of mercury through the diet. (78) In an infamous event in Japan in the late 1950s, many residents near Minamata and Nigata Bays were severely poisoned by eating fish contaminated by industrial discharges of mercury. (79) Many deaths occurred and many children exposed in utero developed serious birth defects and neurological impairments. (80) Another epidemic poisoning occurred in 1972 in Iraq when seed grain treated with a mercurial fungicide was accidentally used to make bread. (81) Again, in addition to numerous deaths, those exposed suffered from a range of adverse affects including neurological symptoms. (82) Several studies of lower dose exposures attributable to dietary sources have also demonstrated adverse effects.(83) The risks from low levels of mercury exposure from fish consumption continue to be the subject of a great deal of research.

Ongoing studies of human populations include studies in the Seychelles Islands and Faroe Islands. (84) In the Seychelles study, no association between mercury and developmental effects in children has been detected. (85) In contrast, a number of adverse neurodevelopmental effects associated with dietary exposures to mercury in whale and fish have been observed in the Faroe Islands work. (86) Recent data from these studies demonstrates persistent changes in brain function in children exposed to mercury in utero as well as additional effects associated with ongoing exposures to mercury post-birth. (87)

The reasons for the different results in the Faroe and Seychelles studies are not known but may relate to a number of factors, possibly including: different sensitivities of the populations studied; different dose patterns; confounding; differences in measures of exposure; and/or differences in the ability of the different tests used to detect an effect. (88) The National Academy of Sciences and the U.S. Environmental Protection Agency ("EPA") have concluded, in light of the weight of the evidence available from numerous other positive human and laboratory studies, that the results of the Faroe Island study provide a preferential basis for evaluating mercury risk. (89) Although some uncertainty exists as to the precise level of risk associated with lower level exposures to methyl mercury, a broad consensus exists that exposures to this toxin should be limited. (90)


Currently in the United States, much of the public health concern about mercury is focused on the consumption of fish containing methyl mercury. (91) The exposure depends on the amount of fish consumed and the concentrations of mercury in the fish. In general, larger predatory fish have higher amounts of mercury. (92) Forty-five states, including Massachusetts and the other Northeast states, now have advisories on the consumption of freshwater fish from some waterbodies due to concentrations of methyl mercury. (93) Several states, as well as the U.S. Food and Drug Administration ("FDA"), have also issued consumption advisories for saltwater fish including shark, swordfish, tuna, tilefish and king mackerel. (94) Exposures of pregnant women and children are of particular concern. Even when pregnant women show no indication of effects from mercury ingestion from eating fish, the fetus may be affected with symptoms at birth or during childhood. (95) Neurodevelopmental effects in children of mothers exposed to mercury are one of the most sensitive endpoints of mercury toxicity. Effects range from severe problems such as overt mental retardation and cerebral palsy at high doses (like those in the epidemic poisoning in Japan and Iraq) to more subtle, yet significant, decrements in various measures of central nervous system function and delays in attaining developmental milestones at lower doses. (96) Exposures to mercury are more than an academic concern. A survey of mercury levels in the blood of U.S. citizens by the Centers for Disease Control indicates that about 8% of women of childbearing age in the United States have mercury levels that exceed those recommended by EPA and the National Academy of Sciences. (97) At current birth rates, this information equates to over 300,000 newborns per year at risk of mercury toxicity. (98) The actual number may be considerably higher. A recent EPA assessment indicates that the fetus is likely to be exposed to levels of mercury higher than the mother, which would raise the estimated number of newborns at risk to over 600,000. (99) In another recent study in California, frequent consumers of fish, particularly swordfish, were shown to have high levels of mercury exposure. (100)

In addition to fish consumption, individuals may also be exposed to mercury from other sources, increasing potential risks. Although the concentration of mercury in ambient outdoor air is typically very low, because of its volatility, indoor air concentrations can exceed recommended levels if mercury is spilled, for example from a broken mercury thermometer, and not properly cleaned up. …

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