Patterns and Interpretation of Mercury Exposure in Freshwater Avian Communities in Northeastern North America

Abstract

Abstract. A large data set of over 4,700 records of avian mercury (Hg) levels in northeastern North America was compiled and evaluated. As Hg emissions remain poorly regulated in the United States and Canada, atmospheric deposition patterns and associated ecological responses continue to elicit interest by landscape managers, conservation biologists, policy makers, and the general public. How avian Hg exposure is interpreted greatly influences decision-making practices. The geographic extent and size of this data set is valuable in understanding the factors that affect the exposure of Hg to birds. Featured are differences found among tissues, major aquatic habitats and geographic areas, between age class and gender, and among species. While Hg concentrations in egg and blood reflect short-term Hg exposure, Hg concentrations in liver and feather provide insight into long-term Hg exposure. Blood is a particularly important matrix for relating site-specific exposure to methylmercury (MeHg). The level of MeHg is generally 5-10x greater in adults compared to nestlings. Age also influences MeHg bioaccumulation, particularly for individuals where MeHg intake exceeds elimination. Gender is of interpretive concern when evaluating Hg exposure for species exhibiting sexual dimorphism and niche partitioning. Based on two indicator species, the belted kingfisher (Ceryle alcyon) and bald eagle (Haliaeetus leucocephalus), we found MeHg availability increased from marine, to estuarine and riverine systems, and was greatest in lake habitats. A large sample of >1,800 blood and egg Hg levels from the common loon (Gavia immer) facilitated a suitable comparison of geographic differences. Although some clusters of highly elevated Hg exposure (i.e., blood levels >3.0 lg/g, ww and egg levels >1.3 lg/g, ww) were associated with hydrological and biogeochemical factors known to increase MeHg production and availability, others were not. Geographic areas without a relationship between Hg exposure and biogeochemical processes were associated with emission or waterborne point sources. Differences in Hg exposure among species are primarily correlated with trophic position and availability of MeHg. Although piscivorous species were repeatedly *To whom correspondence should be addressed: Tel.: 207-839-7600; Fax: 207-839-7655; E-mail: david.evers@briloon.org Ecotoxicology, 14, 193-221, 2005 Ó 2005 shown to have some of the highest MeHg levels of the 38 species analyzed, insectivorous birds in both aquatic and terrestrial habitats (such as montane areas) were also found with elevated MeHg levels. A better understanding of the factors confounding interpretation of Hg exposure provides an effective basis for choice of indicator species and tissues according to 12 selected scenarios. This and the national need for spatiotemporal monitoring of MeHg availability require careful consideration of indicator species choice. Only then will local, regional, continental, and even global monitoring efforts be effective.

Mercury exposure affects the reproductive success of a free-living terrestrial songbird, the Carolina Wren (Thryothorus ludovicianus)

“…Methylmercury is the most bioavailable and toxic form of mercury (Wiener et al 2003); consequently, many studies investigating mercury exposure in birds have focused on fish-eating species that obtain their food from wetland or aquatic environments (Wolfe et al 2007, Scheuhammer et al 2007. Bioaccumulation of mercury also occurs in terrestrial habitats, however, and adverse effects of mercury exposure on nonpiscivorous species are increasingly apparent (Evers et al 2005, Edmonds et al 2010, Hallinger and Cristol 2011, Jackson et al 2011a, 2011b, Lane et al 2011.…”

“…Mercury concentrations in bird blood provide a measure of recent dietary exposure (Wolfe et al 1998, Evers et al 2005) and therefore represent local exposures. Feather mercury concentrations reflect exposure at the time of feather development and remobilized mercury from body burdens (Wolfe et al 1998, Evers et al 2005.…”

“…Feather mercury concentrations reflect exposure at the time of feather development and remobilized mercury from body burdens (Wolfe et al 1998, Evers et al 2005. The majority of adult shorebirds molt feathers on the wintering grounds (Holmes 1966, 1971, Pyle 2008; therefore, feather mercury concentrations reflect both exposure to mercury on the wintering areas and mercury bioaccumulated over time, especially for individuals highly exposed to mercury where not all mercury can be eliminated from the body via natural processes (depurated).…”

Comparison of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in feathers in bald eagle (Haliaeetus leucocephalus), and comparison with common eider (Somateria mollissima), glaucous-winged gull (Larus glaucescens), pigeon guillemot (Cepphus columba), and tufted puffin (Fratercula cirrhata) from the Aleutian Chain of Alaska

“…Many chemicals, such as mercury, are transported all over the world, including to relatively isolated lakes and oceanic environments (Fitzgerald 1989;Houghton et al 1992;Fitzgerald et al 2005;Hammerschmidt et al 2006). Atmospheric deposition is of particular interest for mercury because the USA and other industrialized nations are poorly regulating emissions (Evers et al 2005). Species that forage in aquatic environments are more vulnerable than terrestrial species because of the potential for rapid movement of contaminants in water, and because chemicals can be stored in bottom sediments (including the intertidal), providing a pool for years to come.…”

Status of Atmospheric Mercury Research in South Asia: A Review

“…Exposure of methylmercury has harmful effects on the growth of micro-organisms (WHO, 1990b), behavior and reproduction in birds (USEPA, 1997b;Evers et al, 2005;Scheuhammer et al, 2007), growth, development, hormonal status in fish and germination of aquatic plants (AMAP, 1998). Reproduction in fish when exposed to methylmercury in early life stages is also affected (Friedman et al, 1996;Wiener and Spry, 1996;USEPA, 1997b;Scheuhammer et al, 2007).…”