Environmental mercury (Hg) contamination is an urgent global health threat. The complexity of Hg in the environment can hinder accurate determination of ecological and human health risks, particularly within the context of the rapid global changes that are altering many ecological processes, socioeconomic patterns, and other factors like infectious disease incidence, which can affect Hg exposures and health outcomes. However, the success of global Hg-reduction efforts depends on accurate assessments of their effectiveness in reducing health risks. In this paper, we examine the role that key extrinsic and intrinsic drivers play on several aspects of Hg risk to humans and organisms in the environment. We do so within three key domains of ecological and human health risk. First, we examine how extrinsic global change drivers influence pathways of Hg bioaccumulation and biomagnification through food webs. Next, we describe how extrinsic socioeconomic drivers at a global scale, and intrinsic individual-level drivers, influence human Hg exposure. Finally, we address how the adverse health effects of Hg in humans and wildlife are modulated by a range of extrinsic and intrinsic drivers within the context of rapid global change. Incorporating components of these three domains into research and monitoring will facilitate a more holistic understanding of how ecological and societal drivers interact to influence Hg health risks.

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Cooper Ornithological Society and can be found at: http://www.bioone.org/loi/cond.Lead (Pb) is a metabolic poison that can negatively influence biological processes, leading to illness and mortality\ud across a large spectrum of North American avifauna (>120 species) and other organisms. Pb poisoning can result from\ud numerous sources, including ingestion of bullet fragments and shot pellets left in animal carcasses, spent ammunition\ud left in the field, lost fishing tackle, Pb-based paints, large-scale mining, and Pb smelting activities. Although Pb shot has\ud been banned for waterfowl hunting in the United States (since 1991) and Canada (since 1999), Pb exposure remains a\ud problem for many avian species. Despite a large body of scientific literature on exposure to Pb and its toxicological\ud effects on birds, controversy still exists regarding its impacts at a population level. We explore these issues and\ud highlight areas in need of investigation: (1) variation in sensitivity to Pb exposure among bird species; (2) spatial extent\ud and sources of Pb contamination in habitats in relation to bird exposure in those same locations; and (3) interactions\ud between avian Pb exposure and other landscape-level stressors that synergistically affect bird demography. We\ud explore multiple paths taken to reduce Pb exposure in birds that (1) recognize common ground among a range of\ud affected interests; (2) have been applied at local to national scales; and (3) engage governmental agencies, interest\ud groups, and professional societies to communicate the impacts of Pb ammunition and fishing tackle, and to describe\ud approaches for reducing their availability to birds. As they have in previous times, users of fish and wildlife will play a\ud key role in resolving the Pb poisoning issue

Despite a large body of research concerning mercury (Hg) in birds, no single tissue has been used consistently to assess Hg exposure, and this has hampered comparisons across studies. We evaluated the relationships of Hg concentrations among tissues in four species of waterbirds (American avocets [Recurvirostra americana], black-necked stilts [Himantopus mexicanus], Caspian terns [Hydroprogne caspia; formerly Sterna caspia], and Forster's terns [Sterna forsteri]) and across three life stages (prebreeding adults, breeding adults, and chicks) in San Francisco Bay, California, USA. Across species and life stages, Hg concentrations (least square mean ± standard error) were highest in head feathers (6.45 ± 0.31 μg/g dry wt) and breast feathers (5.76 ± 0.28 μg/g dry wt), followed by kidney (4.54 ± 0.22 μg/g dry wt), liver (4.43 ± 0.21 μg/g dry wt), blood (3.10 ± 0.15 μg/g dry wt), and muscle (1.67 ± 0.08 μg/g dry wt). Relative Hg distribution among tissues, however, differed by species and life stage. Mercury concentrations were highly correlated among internal tissues (r2 ≥ 0.89). Conversely, the relationships between Hg in feathers and internal tissues were substantially weaker (r2 ≤ 0.42). Regression slopes sometimes differed among species and life stages, indicating that care must be used when predicting Hg concentrations in one tissue based on those in another. However, we found good agreement between predictions made using a general tissue-prediction equation and more specific equations developed for each species and life stage. Finally, our results suggest that blood is an excellent, nonlethal predictor of Hg concentrations in internal tissues but that feathers are relatively poor indicators of Hg concentrations in internal tissues.