Mercury enters the environment in various ways, such as through volcanic activity, coal combustion, and chemical manufacturing. As a toxic element, mercury 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. Fish contaminated with methylmercury may pose health threats to people who rely on fish as part of their diet. Mercury can harm fetuses and cause neurological disorders in children, resulting in, among other things, impaired cognitive abilities. The Food and Drug Administration 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. In recent years, most states have issued advisories informing the public that concentrations of mercury have been found in local fish at levels of public health concern. Coal-fired power plants burn at least one of three primary coal types— bituminous, subbituminous, and lignite—and some plants burn a blend of these coals. 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 the chemical variation within and among coal types. Coal combustion releases mercury in oxidized, elemental, or particulate-bound form. Oxidized mercury is more prevalent in the flue gas from bituminous coal combustion, and it is relatively easy to capture using some sulfur dioxide controls, such as wet scrubbers. Elemental mercury, more prevalent in the flue gas from combustion of lignite and subbituminous coal, is more difficult to capture with existing pollution controls. Particulate-bound mercury is relatively easy to capture in particulate matter control devices. In addition to mercury, coal combustion releases other harmful air pollutants, including sulfur dioxide and nitrogen oxides. EPA has regulated these pollutants since 1995 and 1996, respectively, through its program intended to control acid rain. Figure 1 shows various pollution controls that may be used at coal-fired power plants: selective catalytic reduction to control nitrogen oxides, wet or dry scrubbers to reduce sulfur dioxide, electrostatic precipitators and fabric filters to control particulate matter, and sorbent injection to reduce mercury emissions. From 2000 to 2009, DOE’s National Energy Technology Lab conducted field tests at operating power plants with different boiler configurations to develop mercury-specific control technologies capable of achieving high mercury emission reductions at the diverse fleet of U.S. coal-fired power plants. As a result, DOE now has comprehensive information on the effectiveness of sorbent injection systems using all coal types at a wide variety of boiler configurations. Most of these tests were designed to achieve mercury reductions of 50 to 70 percent while decreasing mercury reduction costs—primarily the cost of the sorbent. Thus, the results from the DOE test program may understate the mercury reductions that can be achieved by sorbent injection systems to some extent. For example, while a number of short-term tests achieved mercury reductions in excess of 90 percent, the amount of sorbent injection that achieved the reductions was often decreased during long-term tests to determine the minimum cost of achieving, on average, 70 percent mercury emission reductions. Under its mercury testing program, DOE initially tested the effectiveness of untreated carbon sorbents. On the basis of these results, we reported in 2005 that sorbent injection systems showed promising results but that they were not effective when used at boilers burning lignite and subbituminous coals. DOE went on to test the effectiveness of chemically treated sorbents—which can help convert the more difficult-to-capture mercury common in lignite and subbituminous coals to a more easily captured form—and achieved high mercury reduction across all coal types. Finally, DOE continued to test sorbent injection systems and to assess solutions to impacts on plant devices, structures, or operations that may result from operating these systems—called “balance-of-plant impacts.” In 2008, DOE reported that the high performance observed during many of its field tests at a variety of configurations has given coal-fired power pla nt operators the confidence to begin deploying these technologies. Bills have been introduced in the prior and current Congress addressing mercury emissions from power plants. The bills have proposed specific limits on mercury emissions, such as not less than 90 percent reductions, and some have specified time frames for EPA to promulgate a MACT regulation limiting mercury emissions from power plants. For example, a bill introduced in this Congress would require EPA to promulgate a MACT standard for mercury from coal-fired power plants within a year of the bill’s enactment. In addition, some bills introduced the past few years— termed multipollutant bills—would have regulated sulfur dioxide, nitrogen oxides, and carbon dioxide emissions, in addition to mercury, from coal- fired power plants. Most would have required a 90 percent reduction—or similarly stringent limit—of mercury emissions, with the compliance deadlines varying from 2011 to 2015. One such bill currently before Congress would prohibit existing coal-fired power plants from exceeding an emission limit of 0.6 pounds of mercury per trillion British thermal units (BTUs), a standard measure of the mercury content in coal— equivalent to approximately a 90 percent reduction—by January 2013. The managers of 14 coal-fired power plants reported to us they currently operate sorbent injection systems on 25 boilers to meet the mercury emission reduction requirements of 4 states and several consent decrees and construction permits. Preliminary data show that these boilers have achieved, on average, reductions in mercury emissions of about 90 percent. Of note, all 25 boilers currently operating sorbent injection systems have met or surpassed their relevant regulatory mercury requirements, according to plant managers. For example: A 164 megawatt bituminous-fired boiler, built in the 1960s and operating a cold-side electrostatic precipitator and wet scrubber, exceeds its 90 percent reduction requirement—achieving more than 95 percent mercury emission reductions using chemically treated carbon sorbent. A 400 megawatt subbituminous-fired boiler, built in the 1960s and operating a cold-side electrostatic precipitator and a fabric filter, achieves a 99 percent mercury reduction using untreated carbon sorbent, exceeding its 90 percent reduction regulatory requirement. A recently constructed 600 megawatt subbituminous-fired boiler operating a fabric filter, dry scrubber, and selective catalytic reduction system achieves an 85 percent mercury emission reduction using chemically treated carbon sorbent, exceeding its 83 percent reduction regulatory requirement. While mercury emissions reductions achieved with sorbent injection on a particular boiler configuration do not guarantee similar results at other boilers with the same configuration, the reductions achieved in deployments and tests provide important information for plant managers who must make decisions about pollution controls to reduce mercury emissions as more states’ mercury regulations become effective and as EPA develops its national mercury regulation. The sorbent injection systems currently used at power plants to reduce mercury emissions are operating on boiler configurations that are used at 57 percent of U.S. coal- fired power boilers. Further, when the results of 50 tests of sorbent injection systems at power plants conducted primarily as part of DOE’s or EPRI’s mercury control research and development programs are factored in, mercury reductions of at least 90 percent have been achieved at boiler configurations used at nearly three-fourths of coal-fired power boilers nationally. Some boiler configurations tested in the DOE program that are not yet included in commercial deployments follow: A 360 megawatt subbituminous-fired boiler with a fabric filter and a dry scrubber using a chemically treated carbon sorbent achieved a 93 percent mercury reduction. A 220 megawatt boiler burning lignite, equipped with a cold-side electrostatic precipitator, increased mercury reduction from 58 percent to 90 percent by changing from a combination of untreated carbon sorbent and a boiler additive to a chemically treated carbon sorbent. A 565 megawatt subbituminous-fired boiler with a fabric filter achieved mercury reductions ranging from 95 percent to 98 percent by varying the amount of chemically treated carbon sorbent injected into the system. As these examples of deployed and tested injection systems show, plants are using chemically treated sorbents and sorbent enhancement additives, as well as untreated sorbents. The DOE program initially used untreated sorbents, but during the past 6 years, the focus shifted to chemically treated sorbents and enhancement additives that were being developed. These more recent tests showed that using chemically treated sorbents and enhancement additives could achieve substantial mercury reductions for coal types that had not achieved these results in earlier tests with untreated sorbents. For example, injecting untreated sorbent reduced mercury by an average of 55 percent during a 2003 DOE test at a subbituminous-fired boiler. Recent tests using chemically treated sorbents and enhancement additives, however, have resulted in average mercury reductions of 90 percent for boilers using subbituminous coals. Similarly, recent tests on boilers using lignite reduced mercury emissions by roughly 80 percent, on average. The examples of substantial mercury reductions highlighted above also show that sorbent injection can be successful with both types of air pollution control devices that power plants use to reduce emissions of particulate matter. Specifically, regulated coal-fired power plants typically use either electrostatic precipitators or fabric filters for particulate matter control. The use of fabric filters—which are more effective at mercury emission reductions than electrostatic precipitators—at coal-fired power plants to reduce emissions of particulate matter and other pollutants is increasing, but currently less than 20 percent have them.