Coal-fired power plants are the largest source of mercury air emissions in the United States. These emissions account for 70 percent of mercury entering our oceans and inland waterways. Mercury particles released into the air fall onto oceans, lakes, and rivers, and then enter aquatic food chains. Mercury attaches to ocean sediments, where bacteria change it into highly toxic methyl mercury. Phytoplankton that feed on the organic matter in sediments then absorbs the methyl mercury.

Mercury then moves up the food chain to fish; as it does so, it becomes more concentrated. Large, long-lived carnivorous fish are likely to have more mercury in their tissues than small, short-lived species. As mercury particles are carried by air currents, they pollute waterways far from the source. Mercury is a metal element that exists as a silvery-white liquid at room temperature. It vaporizes readily and can stay suspended in the air for over a year. Mercury levels in the environment have been raising 2-5 fold over the last century and 1.5% per year since 19703 due to industrial activities, especially from burning coal and mercury-containing waste.4 The U.S. Environmental Protection Agency (EPA) lists mercury as a hazardous air pollutant under Title III of the federal Clean Air Act.

Most methylation takes place in coastal areas, and most fish consumed by humans come from or frequent coastal areas or consume other fish that do. Methyl mercury moves up the food chain from plankton to alewife to lobster, bluefish, winter flounder, and tuna and binds to the protein in fish, residing in muscles (the fillet). Although mercury has been in decline since 1970 in water, with the elimination of careless plant discharges and better sewage methods, “less” is relative. Methyl mercury is created naturally by sulfate-reducing bacteria (the sulfur smell at low tide on the coast attests to this), but industrial discharges have greatly increased it.

One of Fitzgerald’s latest projects is studying mercury depletion in five remote tundra lakes in Alaska. There, mercury is depleted from the atmosphere and deposited in the lakes. Global warming may be contributing to increased organic matter in the lakes, and this may be leading to less photodecomposition, which has in the past kept methyl mercury production in check.
The properties and behavior of mercury depend upon its physical and chemical form. When elemental mercury is released into the air it interacts with ozone to form inorganic mercury which is highly soluble. In this form, mercury returns to the earth’s surface in rain and snow and becomes transformed into organic mercury, or methylmercury, by bacteria which reside in oceans, lakes and rivers.

Methylation of mercury is a key step in the entrance of mercury into food chains, and can occur in the sediments and the water (both fresh and saltwater). Methyl mercury bioaccumulates to a greater extent than other forms of mercury. Elimination of methylmercury in living organisms takes place at a very slow rate, resulting in tissue half-lives ranging from months to years. What factors affect the methylation?

The concentration of dissolved organic carbon (DOC) and pH have a strong effect on the ultimate fate of mercury in an ecosystem. Studies have shown that for the same species of fish taken from the same region, increasing the acidity of the water (decreasing pH) and/or the DOC content generally results in higher mercury levels in fish, an indicator of greater net methylation. Higher acidity and DOC levels enhance the mobility of mercury in the environment, thus making it more likely to enter the food chain.
Mercury and methylmercury exposure to sunlight (specifically ultra-violet light) has an overall detoxifying effect. Sunlight can break down methylmercury to Hg(II) or Hg(0), which can leave the aquatic environment and reenter the atmosphere as a gas.

Organic mercury compounds, especially methylmercury, are more toxic than other forms because they easily cross cell membranes. They are most often ingested in contaminated fish. Mercury poisoning can cause severe neurological and kidney damage. Acute exposure can affect the respiratory and gastrointestinal systems. Organic mercury can cross the blood-brain barrier and cause irreversible nervous system and brain damage, e.g., loss of motor control, numbness in limbs, blindness, and inability to speak. Some studies have connected maternal mercury exposure to fetal damage. Mercury poisoning can be confirmed by urine tests. Mercury—particularly the methyl mercury that is found in fish—is toxic and poses severe health risks to developing fetuses, infants, and children. Pregnant or nursing women who eat fish contaminated with mercury may unknowingly transfer the toxins to their children. Even low levels of exposure to mercury before birth can cause serious neurological damage to developing fetuses. Studies show that mercury targets the nervous system and kidneys; infants and developing fetuses are at highest risk, because their brains and other organs are still developing. Adults, too, can become ill from mercury poisoning. Symptoms may include numbness, fatigue, irritability, loss of memory, changes in hearing and eyesight, and problems with coordination.

Chelation therapy is used for poisoning with elemental mercury and mercury salts; there is no treatment for organic mercury poisoning. Mercury has become an environmental pollutant in areas where eroding mercury-bearing rock or agricultural and industrial wastes containing the metal escape or are discharged into waterways. Mercury has long been known to be toxic;

In several areas of the United States, concentrations of mercury in fish and wildlife are high enough to be a risk to wildlife. It is difficult to prove cause and effect in field studies, however, because other factors that may contribute to the biological effect under study (for example, reproductive success) are often impossible to control. Scientists have discovered toxic effects in the field at concentrations of mercury that are toxic in the lab, and controlled lab studies have found toxic effects at concentrations that are common in certain environments. In studies in Wisconsin, reductions in loon chick production has been found in lakes where mercury concentrations in eggs exceed concentrations that are toxic in laboratory studies. At dietary mercury concentrations that are typical of parts of the Everglades, the behavior of juvenile great egrets can be affected. Studies with mallards, great egrets, and other aquatic birds have shown that protective enzymes are less effective following exposure to mercury. Analyses of such biochemical indicators indicate that mercury is adversely affecting diving ducks from the San Francisco Bay, herons and egrets from the Carson River, Nevada, and heron embryos from colonies along the Mississippi River. Finally, other contaminants also affect the toxicity of mercury. Methylmercury can be more harmful to bird embryos when selenium, another potentially toxic element, is present in the diet.

Mercury Contamination - Past, Present, and Future

In highly polluted areas where mercury has accumulated through industrial or mining activities, natural processes may bury, dilute, or erode the mercury deposits, resulting in declines in concentration. In many relatively pristine areas, however, mercury concentrations have actually increased because atmospheric deposition has increased. For instance, concentrations of mercury in feathers of fish-eating seabirds from the northeastern Atlantic Ocean have steadily increased for more than a century. In North American sediment cores, sediments deposited since industrialization have mercury concentrations about 3-5 times those found in older sediments. Some sites may have become methylmercury hot spots inadvertently through human activities. Lake acidification, addition of substances like sulfur that stimulate methylation, and mobilization of mercury in soils in newly flooded reservoirs or constructed wetlands have been shown to increase the likelihood that mercury will become a problem in fish. Although scientists from USGS and elsewhere are beginning to unravel the complex interactions between mercury and the environment, a lack of information on the sources, behavior, and effects of mercury in the environment has impeded identification of effective management responses to the Nation's growing mercury problem.

Mild mercury poisoning causes tingling in the lips, tongue, fingers, and toes. But in some cases, these signs do not appear until long after exposure. Severe mercury poisoning causes headaches, memory loss, difficulty coordinating movement and vision, dizziness, metal taste in the mouth, muscle spasms, pain and stiffness in joints and muscles, nervous heart, very weak or very strong pulse, and even death. In pregnant women, exposure to small amounts of methyl mercury can interfere with normal brain development of their children, causing permanent learning disabilities. It may cause coordination problems, delayed walking, attention problems, memory impairments and problems with language skills. Higher exposures can cause birth defects and mental retardation in their children.
In sites where a whole system has been affected, evaluation of remedial alternatives may need to be based on an understanding of the system-specific processes that lead to increased methylation and the pathways to resources of concern. In water, very low concentrations need to be measured; the separation of the
different forms of mercury requires special analytical techniques. Matrix effects in
the extraction of mercury from tissue may interfere with accurate analyses for
methyl and total mercury. When analyzing mercury in water, sediment, and tissue,
analysis of certified standards for the appropriate matrix must be included as part of
the quality control plan.

Most mercury pesticides have been withdrawn from the U.S. market, and many countries banned ocean dumping of mercury and other pollutants in 1972. Production of mercury-containing interior and exterior paints in the United States was phased out in 1991. Mercury, which has been used in medicines for hundreds of years, continues to be used in dental amalgams and various medicaments that deliver minimal exposures. Most other medical uses have been banned or are being phased out, but mercury use in industry is increasing.

. The federal Food and Drug Administration (FDA) and the Environmental Protection Agency have issued identical mercury advisories for shark, king mackerel, tilefish, and swordfish. Both agencies warn that pregnant women and children six years and under should avoid these fish altogether. Other fish known to have high levels of mercury are grouper, halibut, amberjack, and Chilean sea bass. Although 13 U.S. states have tuna consumption guidelines, the FDA has yet to address the issue of tuna consumption.

The Bush Administration is proposing to weaken the existing laws that regulate U.S. mercury emissions. The Administration’s Clear Skies Initiative actually weakens mercury protections in the current Clean Air Act. Under the Act, coal-fired power plants must comply with” maximum achievable control technology” by 2007. This technology would reduce mercury emissions by 90 percent, from 48 to 5 tons nationwide, by 2008. The Bush plan would postpone initial reductions until 2010, and would allow 26 tons of mercury to be released in 2010, and 15 tons in 2018. The end result: the Clear Skies Initiative would actually permit five times the amount of mercury emissions from U.S. power plants through 2017than would exist law.
. The Seychelles Island study found that the ingestion of mercury by women and children at average levels normally found in marine and fresh water fish would not cause neurological impairment. Conversely, the Faroe Island study found that children who ate fish with mercury levels similar to those found in the U.S. suffered neurological damage, impairing their ability to concentrate, comprehend, and learn. This is a grave new finding and warrants application of the precautionary principle, especially when considering the development of future generations.
Given these uncertainties, policy makers are faced with making a serious decision. Should they set a policy now to prevent further contamination and exposure, or allow ongoing scientific uncertainties to justify continued delay to do what’s ultimately necessary—namely, to eliminate, to the greatest extent possible, man-made mercury releases into our environment and promote significant reductions in human exposures

The hazards posed by eating mercury-contaminated fish are well documented, however, it is impossible to know whether the mercury levels in either freshwater or marine species of fish are safe unless they are tested regularly.
It has been one year since EPA released its long-delayed, 1,500 page Mercury Study Report to Congress. Since that time, many articles have been published documenting widespread mercury contamination throughout our society, from our schools to the fish we eat to the farthest reaches of the earth.
The marine environment has often been overlooked when considering mercury contamination, although the primary exposure route for methylmercury in humans is through the consumption of marine species of fish.

It's important to note that of the approximately 20 source categories (listed below) identified by EPA as being the primary emitters of mercury, the agency has issued national standards limiting mercury emissions for only four of these sources: municipal and medical waste incinerators, sewage sludge incinerators, and chlor alkali manufacturing facilities.
EPA’s Estimated Sources of Mercury
Sources Emissions Percent Facilities
Coal-fired Power Plants 52 tons 33.54% 1043
Municipal Waste Incinerators 30 tons 18.73% 105
Commercial/Industrial Boilers 29 tons 18.35% ~2000
Medical Waste Incinerators 16 tons 10.12% ~1500
Hazardous Waste Incinerators 7 tons* 4.43%
Chlor-alkali manufacturing 7.14 tons 4.51% 14
Portland Cement 4.85 tons 3.07% 112
Other Manufacturing Sources 3.6 tons 2.28%
Residential Boilers 3.5 tons 2.21%
Area sources 3.4 tons 2.15%
Pulp and Paper Manufacturing 1.9 tons 1.2%
Geothermal Power 1.4 tons 0.9%
Other Combustion 1.2 tons 0.7%
Instrument Manufacturing 0.5 tons 0.3%
Secondary mercury production 0.4 tons 0.2%
Carbon Black 0.3 tons 0.2%
Electrical Apparatus 0.3 tons 0.2%
Primary Copper Production 0.1 tons 0.06%
Primary lead production 0.1 tons 0.06% 3
Lime Manufacturing 0.1 tons 0.06%
Other sources 6.4 tons 4.0%

[Source: Final Mercury Study Report to Congress [EPA-452/R-96-001a] Dec 1997]