Methylmercury risk assessment issues

This paper reviews the general background of health risks associated with mercury (Hg), primarily methylmercury (MeHg), with a view towards application to advanced technologies that could reduce any contributions from coal combustion. The need for accurate assessment of such risks is discussed, since Hg is now widely dispersed in the environment and cannot easily be eliminated. The primary pathway of MeHg intake is through eating contaminated fish. The issues of concern include identification of critical health outcomes (various neurological indices) and their confounding factors, accurate assessment of MeHg intake rates, and appropriate use of dose-response functions. Ultimately, such information will be used to evaluate alternative coal combustion systems

THE COMPETITION BETWEEN METHYLMERCURY RISKS AND OMEGA-3 POLYUNSATURATED FATTY ACID BENEFITS: A REVIEW OF CONFLICTING EVIDENCE ON FISH CONSUMPTION AND CARDIOVASCULAR HEALTH.

The health concerns of methylmercury (MeHg) contamination of seafood have recently been extended to include cardiovascular effects, especially premature mortality. Although the fatty acids (fish oils) found in most species are thought to confer a wide range of health benefits, especially to the cardiovascular system, some epidemiological studies have suggested that such benefits may be offset by adverse effects of MeHg. This comprehensive review is based on searches of the NIH MEDLINE database and compares and contrasts 145 published studies involving cardiovascular effects and exposures to mercury and other fish contaminants, intake of fatty acids including dietary supplements of fish oils, and rates of seafood consumption. Since few of these studies include adequate simultaneous measurements of all of these potential predictor variables, we summarized their effects separately, across the available studies of each, and then drew conclusions based on the aggregated findings. It is important to realize that studies of seafood consumption encompass the net effects of all of these predictor variables, but that seafood intake studies are rarely supported by human biomarker measurements that reflect the actual uptake of harmful as well as beneficial fish ingredients. As a result, exposure measurement error is an issue when comparing studies and predictor variables. It is also possible that the observed benefits of eating fish may relate more to the characteristics of the consumers than to those of the fish. We found the evidence for adverse cardiovascular effects of MeHg to be sparse and unconvincing. Studies of cardiovascular mortality show net benefits, and the findings of adverse effects are mainly limited to studies Finland at high mercury exposure levels. By contrast, a very consistent picture of beneficial effects is seen for fatty acids, after recognizing the effects of exposure uncertainties and the presence of threshold effects. Studies based on measured biomarker levels are seen to be the most reliable and present a convincing picture of strong beneficial effects, especially for those causes of death involving cardiac arrhythmia. This conclusion also extends to studies of fish-oil supplementation. Studies based on fish consumption show mainly benefits from increased consumption. This finding is supported by an ecological study at the national population level, for which the lifestyle effects that might be correlated with fish consumption within a given population would be expected to ''average out'' across nations. Finally, the net survival benefits resulting from eating fish are consistent with studies involving complete diets, although benefits are also seen to accrue from reduced consumption of red meat and saturated fats

Technical comments on EPA`s proposed revisions to the National Ambient Air Quality Standard for particulate matter

The US Environmental Protection Agency (EPA) has proposed new ambient air quality standards specifically for fine particulate matter, regulating concentrations of particles with median aerodynamic diameters less than 2.5 {mu}m (PM{sub 2.5}). Two new standards have been proposed: a maximum 24-hr concentration that is intended to protect against acute health effects, and an annual concentration limit that is intended to protect against longer-term health effects. EPA has also proposed a slight relaxation of the 24-hr standard for inhalable particles (PM{sub 10}), by allowing additional exceedances each year. Fine particles are currently being indirectly controlled by means of regulations for PM{sub 10} and TSP, under the Clean Air Act of 1970 and subsequent amendments. Although routine monitoring of PM{sub 2.5} is rare and data are sparse, the available data indicate that ambient concentrations have been declining at about 6% per year under existing regulations

Mortality and air pollution: lessons from statistics. [1959 to 1974 data review]

Cross sectional studies which attempt to link persistent geographic differences in mortality rates with air pollution are reviewed. Some early studies are mentioned and detailed results are given for seven major contemporary studies, two of which are still in the publication process. Differences among the studies are discussed with regard to statistical techniques, trends in the results over time (1959 to 1974), and interpretation and use of the results. The analysis concludes that there are far too many problems with this technique to allow causality to be firmly established, and thus the results should not be used for cost benefit or policy analysis

Regional Issue Identification and Assessment program (RIIA). Environmental impacts and issues of the EIA MID-MID scenario: Federal Region III (mid-Atlantic)

The EIA MID-MID scenario generally reinforces existing environmental concerns in the mid-Atlantic region. This results in part from the emphasis on existing rather than new energy technologies. The widespread public opposition to nuclear power in the region is likely to impede realization of the nuclear goals of the scenario. About 50% improvement in sulfur oxides air quality is projected for the region (all states), based on emissions reductions both within the region and in neighboring regions. Even though strip mine production is projected to decrease by 1990, coal production levels hypothesized by the scenario may be significantly constrained by the impact of new Federal regulations on reclamation (Pennsylvania, Virginia, and West Virginia). In the event that offshore oil and gas exploration becomes successful, development may be constrained by continuing opposition on environmental grounds in Maryland and Delaware, relating to protection of coastal environmental resources. Given the abandonment of several recent dam projects in the Delaware, water availability constraints may be important for inland sites where low flow augmentation is required. The health and safety impacts of the scenario are dominated by the coal fuel cycle. By 1990, mining related injuries and deaths are projected to increase by about 25% over current levels, while public health impacts due to sulfur oxides air pollution are projected to decrease by about 40%. Impacts due to other air pollutants, however, were not quantified. Although health and safety impacts due to nuclear power plants in Pennsylvania and Virginia are projected to increase, the numbers are quite small and are likely to constrain the scenario only because of public perception rather than actual risk. Pennsylvania has non-attainment areas (air pollution standards have not been met) which may constrain the siting of new energy-related facilities

National estimates of residential firewood and air pollution emissions

Estimates are presented for the distribution and quantity of recent (1978-1979) use of residential firewood in the United States, based on a correlation of survey data from 64 New England counties. The available survey data from other states are in agreement with the relationship derived from New England; no constraints due to wood supply are apparent. This relationship indicates that the highest density of wood usage (Kg/ha) occurs in urban areas; thus exacerbation of urban air quality problems is a matter of some concern. The data presentation used here gives an upper limit to this density of firewood usage which will allow realistic estimates of air quality impact to be made

A systems approach to risk assessment: Application to methylmercury from coal combustion

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

Efficiencies of free-air gas fumigation devices

One of the key uncertainties relative to future increases in atmospheric CO{sub 2} is the extent to which growth in future emissions will be accommodated by increased uptake by terrestrial vegetation, the so-called fertilization'' effect. Research on this issue is currently pursued by many research groups around the world, using various experimental protocols and devices. These range from leaf cuvettes to various types of enclosures and glass-houses to various types of open-field gas enrichment or fumigation systems. As research priorities move from crops to forests and natural ecosystems, these experimental devices tend to become large and enrichment gas (i.e., CO{sub 2}) requirements and costs become a major factor in experimental design. This paper considers the relative efficiencies of gas usage for different types of systems currently in use. One of these is the Free Air CO{sub 2} Enrichment System (FACE) designed and developed at Brookhaven National Laboratory (BNL). In this paper, we develop some nondimensional groups of parameters for the purpose of characterizing performance, i.e., enrichment gas usage. These nondimensional groups are then used as figures of merit and basically allow the required flow rates of CO{sub 2} to be predicted based on the geometry of the device, wind speed, and the incremental gas concentration desired. The parameters chosen to comprise a useful nondimensional group must not only have the correct dimensions, they must also represent an appropriate physical relationship