The rationale for regulating air emissions of mercury from U.S. coal-fired power plants largely depends on mathematical dispersion modeling, including the atmospheric chemistry processes that affect the partitioning of Hg emissions into elemental (Hg{sub 0}) and the reactive (RGM) forms that may deposit more rapidly near sources. This paper considers and evaluates the empirical support for this paradigm. We consider the extant experimental data at three spatial scales: local (
Title 3 of the 1990 Clean Air Act Amendments (CAAA) mandated that the US Environmental Protection Agency (EPA) evaluate the need to regulate mercury emissions from electric utilities. In support of this forthcoming regulatory analysis the U.S. DOE, sponsored a risk assessment project at Brookhaven (BNL) to evaluate methylmercury (MeHg) hazards independently. In the US MeHg is the predominant way of exposure to mercury originated in the atmosphere. In the BNL study, health risks to adults resulting from Hg emissions from a hypothetical 1,000 MW coal-fired power plant were estimated using probabilistic risk assessment techniques. This study showed that the effects of emissions of a single power plant may double the background exposures to MeHg resulting from consuming fish obtained from a localized area near the power plant. Even at these more elevated exposure levels, the attributable incidence in mild neurological symptoms was estimated to be quite small, especially when compared with the estimated background incidence in the population. The current paper summarizes the basic conclusions of this assessment and highlights issues dealing with emissions control and environmental transport.
Mercury is widespread in our environment. Methylmercury, one organic form of mercury, can accumulate up the aquatic food chain and lead to high concentrations in predatory fish. When consumed by humans, contaminated fish represent a public health risk. Combustion processes, especially coal-fired power plants, are major sources of mercury contamination in the environment. The U.S. Environmental Protection Agency (EPA) is considering regulating mercury emissions from those plants. Toxicological Effects of Methylmercury reviews the health effects of methylmercury and discusses the estimation of mercury exposure from measured biomarkers, how differences between individuals affect mercury toxicity, and appropriate statistical methods for analysis of the data and thoroughly compares the epidemiological studies available on methylmercury. Included are discussions of current mercury levels on public health and a delineation of the scientific aspects and policy decisions involved in the regulation of mercury. This report is a valuable resource for individuals interested in the public health effects and regulation of mercury. The report also provides an excellent example of the implications of decisions in the risk assessment process for a larger audience.
This report presents a follow-up to previous assessments of the health risks of mercury that BNL performed for the Department of Energy. Methylmercury is an organic form of mercury that has been implicated as the form of mercury that impacts human health. A comprehensive risk assessment report was prepared (Lipfert et al., 1994) that led to several journal articles and conference presentations (Lipfert et al. 1994, 1995, 1996). In 2001, a risk assessment of mercury exposure from fish consumption was performed for 3 regions of the U.S (Northeast, Southeast, and Midwest) identified by the EPA as regions of higher impact from coal emissions (Sullivan, 2001). The risk assessment addressed the effects of in utero exposure to children through consumption of fish by their mothers. Two population groups (general population and subsistence fishers) were considered. Three mercury levels were considered in the analysis, current conditions based on measured data, and hypothetical reductions in Hg levels due to a 50% and 90% reduction in mercury emissions from coal fired power plants. The findings of the analysis suggested that a 90% reduction in coal-fired emissions would lead to a small reduction in risk to the general population (population risk reduction on the order of 10{sup -5}) and that the population risk is born by less than 1% of the population (i.e. high end fish consumers). The study conducted in 2001 focused on the health impacts arising from regional deposition patterns as determined by measured data and modeling. Health impacts were assessed on a regional scale accounting for potential percent reductions in mercury emissions from coal. However, quantitative assessment of local deposition near actual power plants has not been attempted. Generic assessments have been performed, but these are not representative of any single power plant. In this study, general background information on the mercury cycle, mercury emissions from coal plants, and risk assessment are provided to provide the basis for examining the impacts of local deposition. A section that covers modeling of local deposition of mercury emitted from coal power plants follows. The code ISCST3 was used with mercury emissions data from two power plants and local meteorological conditions to assess local deposition. The deposition modeling results were used to estimate the potential increase in mercury deposition that could occur in the vicinity of the plant. Increased deposition was assumed to lead to a linearly proportional increase in mercury concentrations in fish in local water bodies. Fish are the major pathway for human health impacts and the potential for increased mercury exposure was evaluated and the risks of such exposure estimated. Based on the findings recommendations for future work and conclusions are provided. Mercury is receiving substantial attention in a number of areas including: understanding of mercury deposition, bioaccumulation, and transport through the atmosphere, and improvements to the understanding of health impacts created by exposure to mercury. A literature review of key articles is presented as Appendix A.
The U.S. Environmental Protection Agency (EPA) has announced plans to regulate mercury (Hg) emissions from coal-fired power plants. EPA has not prepared a quantitative assessment of the reduction in risk that could be achieved through reduction in coal plant emissions of Hg. To address this issue, Brookhaven National Laboratory (BNL) with support from the U.S. Department of Energy Office of Fossil Energy (DOE FE) prepared a quantitative assessment of the reduction in human health risk that could be achieved through reduction in coal plant emissions of Hg. The primary pathway for Hg exposure is through consumption of fish. The most susceptible population to Hg exposure is the fetus. Therefore the risk assessment focused on consumption of fish by women of child-bearing age. Dose response factors were generated from studies on loss of cognitive abilities (language skills, motor skills, etc.) by young children whose mothers consumed large amounts of fish with high Hg levels. Population risks were estimated for the general population in three regions of the country, (the Midwest, Northeast, and Southeast) that were identified by EPA as being heavily impacted by coal emissions. Three scenarios for reducing Hg emissions from coal plants were considered: (1) A base case using current conditions; (2) A 50% reduction; and, (3) A 90% reduction. These reductions in emissions were assumed to translate linearly into a reduction in fish Hg levels of 8.6% and 15.5%, respectively. Population risk estimates were also calculated for two subsistence fisher populations. These groups of people consume substantially more fish than the general public and, depending on location, the fish may contain higher Hg levels than average. Risk estimates for these groups were calculated for the three Hg levels used for the general population analyses. Analysis shows that the general population risks for exposure of the fetus to Hg are small. Estimated risks under current conditions (i.e., no specific Hg controls) ranged from 5.7 x 10−6 in the Midwest to 2 x 10−5 in the Southeast. Reducing emissions from coal plants by 90% reduced the estimated range in risk to 5 x 10−6 in the Midwest and 1.5 x 10−5 in Southeast, respectively. The population risk for the subsistence fisher using the Southeast regional fish Hg levels was 3.8 x 10−3, a factor of 200 greater than the general population risk. For the subsistence fishers and the Savannah River Hg levels, the population risk was 4.3 x 10−5, a factor of 2 greater than for the general population. The estimated risk reductions from a 90% reduction in coal plant Hg emissions ranged from 25%-68%, which is greater than the assumed reduction in Hg levels in fish, (15.5%). To place this risk in perspective, there are approximately 4 x 106 births/year in the U.S (National Vital Statistics Report, 2000). Assuming that the Southeast risk level (the highest of the regions) is appropriate for the entire U.S., an estimate of 80 newborn children per year have a 5% chance of realizing any of the 16 adverse effects used to generate the DRF. If Hg emissions from power plants are reduced 90%, the number of children at risk is reduced to 60.
This report is the fifth in a series dealing with the human health risks of toxic substances emitted by coal-fired power plants. It summarizes two earlier studies that examined selenium and beryllium discharges from a power plant in Pennsylvania (the Montour Steam Electric Station operated by Pennsylvania Power and Light Company). The authors extend the earlier analysis to include calculation of pollutant exposure associated with consumption of animal and vegetable products raised in the region surrounding the Montour plant. Specifically, they calculate how much the incidence of cancer and selenosis might increase in the regional population that consumes drinking water or fish from the Susquehanna River or any of several animal or vegetable products raised in the region. The results indicate that Montour selenium and beryllium discharges should have a negligible effect on the incidence of selenosis and cancer in the regional population.
The Department of Energy (DOE) asked Brookhaven National Laboratory (BNL) to perform a probabilistic assessment of the health risks associated with Hg from coal-fired power plants. The objective of the assessment is to estimate the incremental health risks that might ensue from a typical coal-fired power plant, together with their uncertainties, taking into account existing background levels and the actual adverse health effects that have previously been associated with exposure to various Hg species. Mercury has a long history of association with adverse neurological effects at high exposure levels. The most important current exposure pathway has been found to be ingestion of fish containing methylmercury (MeHg), which is the end product of bioconcentration moving up the aquatic food chain. Mercury can enter natural waters from either industrial discharges or from atmospheric deposition of various inorganic Ho. compounds. Because of the worldwide background and the existence of local emissions sources, Hg deposition must be considered on local, regional and global scales. The regulatory technical challenge presented by methy1mercury is to protect public health without foreclosing an appreciable a portion of the food supply or impacting on the lifestyles of North American native populations. This paper presents an abbreviated account of the DOE/BNL risk assessment, as viewed from a systems perspective. We review the structure of the model, the sources of data used, the assumptions that were made, and the interpretation of the findings. Since publication of the first risk assessment report, we have refined our estimates of local atmospheric dispersion and deposition and {open_quotes}calibrated{close_quotes} the pharmacokinetic portion of the model against observations.
