In the dialog concerning environmental mercury contamination, little consideration has been given to the broad societal effects of mercury pollution. Consequently, applied or proposed corrective actions may be driven by technological, scientific, or narrow financial considerations, without sufficient attention to the broader sociological, economic, or cultural implications of those decisions. For example, the contamination of fish with methylmercury is a serious consequence of environmental mercury pollution because consumption of fish is the primary pathway for human exposure to this highly toxic compound. The contamination of fish, therefore, has been viewed largely from a toxicological perspective with the focus on exposure and health effects. Yet mercury pollution has also diminished the economic, recreational, nutritional, and cultural benefits derived from fishery resources. In North America, mercury contamination now accounts for more than 80 percent of all fish-consumption advisories. Almost half of the 83,000 lakes in Sweden contain game fish with mercury concentrations exceeding their national guideline. In Canada, the consequences of contaminated fishery resources for indigenous communities that abandoned subsistence fishing have been particularly severe, and include adverse effects on lifestyle, culture, social cohesion, economic status, and health. The socioeconomic losses caused by mercury contamination of fishery resources have not been quantified, but are highly relevant to policy considerations regarding the problem. The Key Question posed to this panel: What are the socioeconomic and cultural costs of mercury pollution?

Mercury contamination has degraded the quality of fishery resources in many of the world's inland, coastal, and marine waters. This has diminished the socioeconomic, nutritional, cultural, and recreational benefits derived from these resources. Nearly all of the mercury in fish is methylmercury, a highly toxic compound that readily crosses biological membranes, accumulates in exposed organisms, and biomagnifies in food webs supporting fish production. Consumption of fish is the primary pathway of human exposure to methylmercury in much of the world. Atmospheric deposition is an important source of total mercury in many surface waters, and this mercury is believed to be a substantive source for the production of methylmercury that is accumulated in fish. Analyses of dated cores from many remote and semi-remote areas have shown that most of the mercury accumulating in lake sediment, peat, and glacial ice is from human activities. Reductions in anthropogenic emissions of mercury are, therefore, being considered as a means of decreasing both mercury concentrations in fish and the associated exposures of fish eating humans and wildlife to methylmercury. The Key Question posed to this panel:How would methylmercury levels in fish respond to reduced anthropogenic emissions of mercury?

The scientific effort on environmental mercury contamination has been largely motivated by the human health risks of methylmercury exposure, which results from consumption of finfish, aquatic mammals, and shellfish. Recent toxicological research on methylmercury has focused largely on neurological effects of low level exposure, with emphasis on fetal exposure from maternal transfer. In particular, results from the epidemiological studies in the Faroe and Seychelle Islands continue to advance scientific understanding of the effects of dietary exposure to methylmercury before birth or during early childhood. Other sublethal effects of methylmercury exposure have been recently recognized, including endocrine disruption, organ dysfunction, cardiovascular disease, and immune suppression; however, the doses producing such effects and the dose response relations have not been determined. Methylmercury exposure can be substantial in biota atop aquatic food webs, and the results of recent descriptive and experimental studies imply that the reproduction and fitness of certain fish and wildlife could be adversely affected by exposure to environmentally realistic concentrations of methylmercury. The Key Question posed to this panel:What is the evidence that humans, fish, wildlife, and other biota are being adversely affected by exposure to methylmercury?

During the past two decades, researchers have generally concluded that human-related mercury emissions have increased the total amount of mercury in atmosphere about 3-5 fold over pre-industrial times, and the rate of deposition to the earth's surface is concomitantly higher. However, at any specific location the actual change in the relative rates of current to historic mercury deposition may vary widely from that range, depending strongly on the relative contributions of local, regional, and global sources. Also, although human-related emissions are reasonably well cataloged, natural and legacy emissions have been less well studied, and the "background" level impact for any particular location is difficult to estimate. Adding to this uncertainty are observations that emissions from the two largest natural sources (volatilization from the oceans and soils) are relatively under studied as net sources or sinks, and as re-emitters of previously deposited mercury. Unraveling the complexities of relating emission controls to mercury deposition rates is essential for understanding current trends and making future predictions. However, it is debatable whether we presently have the needed technical understanding for making predictions. For example, while mercury emissions in some regions of the world have decreased over the past decade (e.g., North America), emissions from the Asian continent have reportedly increased rapidly, and the overall global mercury emission budget has leveled off after decades of declines. As a result, the benefits of reducing local and regional emissions remains an active area of research and debate due to the prospect for increasing inputs of "imported mercury" from global emissions. The Key Question posed to this panel:For any given location, can we ascertain with confidence the relative contributions of local, regional, and global sources, and of natural versus anthropogenic emissions to mercury deposition?