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

Mercury-selenium interactions in the environment

The Clean Air Act Amendments of 1990 require the U.S. Environmental Protection Agency (EPA) to consider the need to control emissions of trace elements and compounds emitted from coal combustion, including coal-fired power plants. Concern has been expressed about emissions of mercury and arsenic, for example, since health effects may be associated with exposure to some of these compounds. By and large, effects of trace element emissions have been considered individually, without regard for possible interactions. To the extent that the relevant environmental pathways and health endpoints differ, this mode of analysis is appropriate. For example, arsenic is considered a carcinogen and mercury affects the brain. However, there may be compelling reasons to consider emissions of mercury (Hg) and selenium (Se) together: (1) Both Se and Hg are emitted from power plants primarily as vapors. (2) Hg and Se are both found in fish, which is the primary pathway for Hg health effects. (3) Se has been shown to suppress Hg methylation in aqueous systems, which is a necessary step for Hg health effects at current environmental concentrations. (4) Se is a trace element that is essential for health but that can also be toxic at high concentrations; it can thus have both beneficial and adverse health effects, depending on the dosage. This paper reviews some of the salient characteristics and interactions of the Hg-Se system, to consider the hypothesis that the effects of emissions of these compounds should be considered jointly

Production mechanisms and single-spin asymmetry for kaons in high energy hadron-hadron collisions

Direct consequences on kaon production of the picture proposed in a recent Letter and subsequent publications are discussed. Further evidence supporting the proposed picture is obtained. Comparison with the data for the inclusive cross sections in unpolarized reactions is made. Quantitative results for the left-right asymmetry in single-spin processes are presented.Comment: 10 pages, 2 Postscript figure

Hyperon polarization and single spin left-right asymmetry in inclusive production processes at high energies

It is shown that the polarization of hyperons observed in high energy collisions using unpolarized hadron beams and unpolarized nucleon or nuclear targets is closely related to the left-right asymmetries observed in single spin inclusive hadron production processes. The relationship is most obvious for the production of the hyperons which have only one common valence quark with the projectile. Examples of this kind are given. Further implications of the existence of large polarization for hyperon which has two valence quarks in common with the projectile and their consequences are discussed. A comparison with the available data is made. Further tests are suggested.Comment: REVTeX, 12 pages, 2 figures embedde

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

The multiple origins of cooperativity in binding to multi-site lattices

AbstractBinding events involving the reversible association of ligands with polymeric lattices of binding sites are common in biology and frequently exhibit significant cooperativity in binding. Positive and negative cooperativity in binding may be detected by characteristic changes in binding curves for multiple binding, compared to the binding expected for simple, independent binding events that are based on combinatorial considerations only. Cooperativity arises from ligand-dependent interactions distinct from binding per se. Ligand-dependent nearest neighbor interactions may be of two types referred to as ligand-lattice (which can only occur if a bound ligand is unneighbored) and ligand-ligand (which can occur if two or more bound ligands are adjacent). The molecular mechanisms underlying these two sources of cooperativity are not the same. Identical cooperative binding curves may be produced by changes from unity in parameters representing either one or both of these interaction types. Positive cooperativity may equally result from destabilizing ligand-lattice interactions that disfavor initial, unneighbored binding, stabilizing ligand-ligand interactions that favor subsequent, neighbored binding, or both. The structural origins of these are different, and cooperativity may emerge from multiple structural interactions

Issues in the assessment of congenital health risks from mercury in coal

This paper describes a probabilistic assessment of congenital neurological risks associated with consumption of fish and shellfish containing MeHg and the effects that local coal combustion might have on those risks. Two scenarios were considered with this model: the ``baseline`` scenario (MeHg from fish consumption without local impacts), and the ``impact`` scenario (baseline plus local power-plant impact on freshwater fish). In this paper, we describe the framework and application of the model, including parameters and statistical linkages, the distributions used to represent the parameters, and the statistical methods used to characterize the inherent variability in each individual`s diet and the distribution of individuals within a hypothetical population. These factors define the baseline, which is then compared to observations of MeHg in hair in order to demonstrate the model`s validity. The incremental effect of local coal combustion is represented by augmenting the distribution of Hg in local freshwater fish by a prescribed amount, which we refer to as the ``impact factor.`` Conventional air pollution dispersion modeling is then used to relate this factor to an appropriate range of powerplant characteristics

DOE/FDA/EPA: Workshop on methylmercury and human health

In the US the general population is exposed to methylmercury (MeHg) principally through the consumption of fish. There is continuing discussion about the sources of this form of mercury (Hg), the magnitudes and trends in exposures to consumers, and the significance of the sources and their contributions to human health. In response to these discussions, the US Department of Energy, the US Food and Drug Administration, and the US Environmental Protection Agency cosponsored a two-day workshop to discuss data and methods available for characterizing the risk to human health presented by MeHg. This workshop was attended by 45 individuals representing various Federal and state organizations and interested stakeholders. The agenda covered: Agency interests; probabilistic approach to risk assessment; emission sources; atmospheric transport; biogeochemical cycling; exposure assessment; health effects of MeHg; and research needs