Mercury enters the environment through natural and man-made sources, including volcanoes, chemical manufacturing, and coal combustion, and poses ecological threats when it enters water bodies, where small aquatic organisms convert it into its highly toxic form—methylmercury. This form of mercury may then migrate up the food chain as predator species consume the smaller organisms. Through a process known as bioaccumulation, predator species may consume and store more mercury than they can metabolize or excrete. Fish contaminated with methylmercury may pose health threats to people that rely on fish as part of their diet. Mercury harms fetuses and can cause neurological disorders in children, including poor performance on behavioral tests, such as those measuring attention, motor and language skills, and visual-spatial abilities (such as drawing). The Food and Drug Administration (FDA) and EPA recommend that expectant or nursing mothers and young children avoid eating swordfish, king mackerel, shark, and tilefish and limit consumption of other potentially contaminated fish. These agencies also recommend checking local advisories about recreationally caught freshwater and saltwater fish. According to EPA, 45 states issued mercury advisories in 2003 (the most recent data available). According to the United Nations Environment Program, global mercury emissions are uncertain but fall within an estimated range of 4,850 to 8,267 tons per year. Of this total, EPA estimates that man-made sources in the United States emit about 115 tons per year, with about 48 tons emitted by power plants. Because mercury can circulate for long periods of time and be transported thousands of miles before it gets deposited, it is difficult to link mercury accumulation in the food chain with individual emission sources. The United States has 491 power plants that rely in whole or in part on coal for electricity generation, and these plants produced 52 percent of all electricity generated in 2004, according to DOE’s most recent data. These plants generally operate by burning coal in a boiler to convert water into steam, which in turn drives turbines that generate electricity. Figure 1 provides a general overview of a power plant’s layout. Power plants burn at least one of the three primary coal ranks— bituminous, subbituminous, and lignite—and plants may burn a blend of different coals, according to DOE. Of all coal burned by power plants in the United States in 2004, DOE estimates that about 46 percent was bituminous, 46 percent was subbituminous, and 8 percent was lignite. The amount of mercury in coal and the relative ease of its removal depend on a number of factors, including the geographic location where it was mined and chemical variation within and among coal ranks. Coal combustion releases other harmful air pollutants in addition to mercury, including sulfur dioxide and nitrogen oxides. EPA has regulated these pollutants since 1995 and 1996, respectively, through its program intended to control acid rain. In addition, the March 2005 interstate rule will require further cuts in these pollutants beginning in 2009. To comply with these and other regulations, the coal-fired power industry has installed a variety of technologies that, while intended to control nitrogen oxides, particulate matter, or sulfur dioxide, may also affect or enhance mercury capture. Examples of such technologies include selective catalytic reduction (SCR) for nitrogen oxides, electrostatic precipitators (used by about 80 percent of all facilities) and fabric filters (used by the remaining 20 percent) to control particulate matter and wet or dry scrubbers to remove sulfur dioxide. EPA estimates that power plants capture about 27 tons of mercury each year, primarily through the use of controls for other pollutants. In general, the exhaust from coal combustion (called flue gas) exits the boiler and may flow through a device intended to control nitrogen oxides before entering the particle control device and then through a scrubber prior to release from the smokestack. The combination of these devices in use at power plants differs greatly among facilities and is likely to change as a result of the interstate rule, which, according to EPA, will result in additional installations of equipment to control nitrogen oxides and sulfur dioxide. EPA believes that the steps power plants will take to control nitrogen oxides and sulfur dioxide under the interstate rule will enable them to meet the first phase mercury cap of 38 tons beginning in 2010. As noted above, EPA determined that mercury control technologies were not commercially available and that the agency could not reasonably impose requirements to use them in the near-term. Nonetheless, a number of mercury control technologies have been developed over the past several years as a result of public and private investments in research and development, and these technologies generally fall into the following categories: Sorbent (carbon-based, chemically enhanced carbon-based, and non-carbon based). This technology involves injecting a powdered substance (sorbent) into the flue gas that binds to mercury prior to collection in a particle control device. Regardless of the chemical composition of the sorbent, this technology involves adding a silo or other structure containing the sorbent and a system that injects the sorbent into ducts that carry the flue gas. Enhancements to existing controls for other pollutants to increase mercury capture. This class of technologies focuses on retrofitting existing controls for other pollutants to improve their ability to capture mercury. Examples of enhancements include adding sorbents to wet scrubbers used for sulfur dioxide removal or modifying selective catalytic reduction devices used to reduce nitrogen oxides. Multipollutant controls. This class of technologies is designed from the outset to simultaneously control or enhance the removal of multiple pollutants, such as mercury, nitrogen oxides, or sulfur dioxide. These technologies may also use sorbents. Oxidation technologies. This class includes methods, chemicals, or equipment designed to oxidize mercury into a form that is more readily captured. Other technologies. This category includes other technologies that capture mercury using approaches such as removing mercury from coal prior to combustion and fixed adsorption devices that rely on precious metals such as gold to separate mercury from flue gas. The intended location of these technologies in a power plant’s overall layout may vary. As shown in figure 2, some may be located between the boiler and the particulate matter collection device, while others may be located further downstream in a plant’s process. This figure also shows that some plants can either install sorbent injection upstream of the existing particulate matter removal device or downstream of the device using a supplemental filter to collect the spent sorbent, keeping it separate from the fly ash collected in the particulate matter collection device. The latter configuration may be relevant for those facilities that sell their fly ash as a raw material for use in other applications, such as cement manufacturing, because carbon-based sorbent can render fly ash unsuitable for some of these applications. According to EPA, power plants sell about 35 percent of their fly ash for use in other applications, with 15 percent going to uses, such as cement manufacturing, where carbon contamination could pose a problem. The Department of Energy’s (DOE) National Energy Technology Laboratory partners with the private sector to evaluate the use of mercury control technologies at power plants in tests lasting up to 5 months. The testing program focuses on mercury controls, such as sorbent injection, and ways to better and more consistently capture mercury with technologies for other pollutants. Participants in DOE’s program evaluate concepts in laboratories and develop promising technologies in progressively larger-scale applications, including actual power plants. The duration of the tests that have been completed has varied from several hours to 5 months, with most of the completed DOE-funded tests lasting between 1 week and several months. The most recent phase of DOE testing has focused on the longer-term performance of mercury control technologies. Appendix III provides more information on the DOE tests completed, ongoing, or planned as of February 2005. Power plants in the United States do not currently use mercury controls, but some technologies are available for purchase and have shown promising results in full-scale tests in power plants. These tests have shown that mercury controls known as sorbent technologies—which involve injection of a powdered material that binds to mercury in the plant’s exhaust—have shown the greatest effectiveness in removing mercury during tests at power plants. However, long-term test data are limited because most of these tests have lasted less than 3 months. According to all 40 survey respondents, coal-fired power plants were not, as of November 2004, using mercury controls, although several plants have subsequently announced plans to install them. The coal-fired power industry has not used mercury controls because, prior to EPA’s March 2005 rule, federal law had not required mercury emissions reductions at power plants. In fact, most of the power industry survey respondents (13 of 14) cited uncertainty about future regulations as one of the top three reasons for not installing mercury controls. Thus, in the absence of federal requirements to reduce mercury emissions, limited demand existed for mercury controls. We found that although some mercury controls, such as activated carbon injection, are currently available for purchase from vendors, perceptions about their availability vary widely among stakeholders, primarily because stakeholders do not consistently define “availability.” That is, some stakeholders believe that mercury controls become available when they have been demonstrated in long-term tests under normal commercial operations, rather than when they are available for purchase. Thus, some stakeholders’ views on availability reflect more of a judgment about the proven effectiveness of a control technology than their availability for purchase. In this context, we found that views regarding the availability of mercury controls generally varied by stakeholder group and by the type of control. A greater portion of the vendors described mercury controls as available than either of the other two groups we surveyed, with the power industry group citing these controls as available least frequently. As shown in figure 3, the stakeholders were overall most optimistic about the availability of activated carbon injection technologies, followed by multipollutant controls and enhancements to existing controls for other pollutants. Appendix IV provides more detailed information on stakeholder perceptions of the availability of mercury controls.