Anthropogenic inputs of mercury (Hg) into the environment have significantly increased in the past century. Concurrently, the availability of methylmercury (MeHg) in aquatic systems has increased to levels posing risks to ecological and human health. We use the common loon (Gavia immer) as an upper trophic level bioindicator of aquatic Hg toxicity in freshwater lakes. Multiple endpoints were selected to measure potential negative impacts from MeHg body burdens on behavior, physiology, survival and reproductive success. A robust spatio-temporal dataset was used that included nearly 5,500 loon Hg measurements over an 18-year period. We measured significant changes related to elevated MeHg body burdens, including aberrant incubation behavior, lethargy, and wing area asymmetry. Mercury body burdens in adult loons increased an average of 8.4% per year. Increasing Hg body burdens reduced the number of fledged chicks per territorial pair, with highest risk loons producing 41% fewer fledged young than our reference group. Our multiple endpoints establish adverse effect thresholds for adult loons at 3.0 ug/g (wet weight) in blood and 40.0 ug/g (fresh weight) in feathers. Mercury contamination in parts of Maine and New Hampshire is a driving stressor for creating breeding population sinks. Standardized monitoring programs are needed to determine if population sinks occur elsewhere and to track aquatic ecosystem responses to changes in Hg emissions and deposition.

We studied the spatial distribution patterns of mercury (Hg) in lake water, littoral sediments, zooplankton, crayfish, fish, and common loons in 44 lakes of the Adirondacks of New York State, USA, a region that has been characterized as a “biological Hg hotspot”. Our study confirmed this pattern, finding that a substantial fraction of the lakes studied had fish and loon samples exceeding established criteria for human and wildlife health. Factors accounting for the spatial variability of Hg in lake water and biota were lake chemistry (pH, acid neutralizing capacity (ANC), percent carbon in sediments), biology (taxa presence, trophic status) and landscape characteristics (land cover class, lake elevation). Hg concentrations in zooplankton, fish and common loons were negatively associated with the lake water acid-base status (pH, ANC). Bioaccumulation factors (BAF) for methyl Hg (MeHg) increased from crayfish (mean log10 BAF = 5.7), to zooplankton (5.9), to prey fish (6.2), to larger fish (6.3), to common loons (7.2). MeHg BAF values in zooplankton, crayfish, and fish (yellow perch equivalent) all increased with increasing lake elevation. Our findings support the hypothesis that bioaccumulation of MeHg at the base of the food chain is an important controller of Hg concentrations in taxa at higher trophic levels. The characteristics of Adirondack lake-watersheds (sensitivity to acidic deposition; significant forest and wetland land cover; and low nutrient inputs) contribute to elevated Hg concentrations in aquatic biota.Electronic supplementary materialThe online version of this article (doi:10.1007/s10646-011-0717-y) contains supplementary material, which is available to authorized users.

Much of the Laurentian Great Lakes region is a mercury-sensitive landscape, in which atmospheric deposition and waterborne sources of mercury (Hg) have led to high concentrations of bioavailable methylmercury (MeHg) in predatory fish and piscivorous wildlife. Efforts since the early 1990s have established the common loon (Gavia immer) as the primary avian indicator for evaluating the exposure and effects of MeHg in North America. A regional Hg dataset was compiled from multiple loon tissue types and yellow perch (Perca flavescens), a preferred prey fish species for loons. Hg exposure in loons and perch was modeled to develop male and female loon units (MLU and FLU, respectively), standardized metrics that represent the estimated blood Hg exposure of a male or female loon for a given loon territory or water body. Using this common endpoint approach to assess loon Hg exposure, the authors demonstrate spatial trends in biotic Hg concentrations, examine MeHg availability in aquatic ecosystems of the Great Lakes region in relation to landscape-level characteristics, and identify areas with potentially significant adverse reproductive impacts to loons and other avian piscivores. Based on 8,101 MLUs, seven biological Hg hotspots were identified in the Great Lakes region. Policy-relevant applications are presented.

Avian mortality events are common following large-scale oil spills. However, the sublethal effects of oil on birds exposed to light external oiling are not clearly understood. We found that American oystercatchers (area of potential impact n = 42, reference n = 21), black skimmers (area of potential impact n = 121, reference n = 88), brown pelicans (area of potential impact n = 91, reference n = 48), and great egrets (area of potential impact n = 57, reference n = 47) captured between 20 June 2010 and 23 February 2011 following the Deepwater Horizon oil spill experienced oxidative injury to erythrocytes, had decreased volume of circulating erythrocytes, and showed evidence of a regenerative hematological response in the form of increased reticulocytes compared with reference populations. Erythrocytic inclusions consistent with Heinz bodies were present almost exclusively in birds from sites impacted with oil, a finding pathognomonic for oxidative injury to erythrocytes. Average packed cell volumes were 4 to 19% lower and average reticulocyte counts were 27 to 40% higher in birds with visible external oil than birds from reference sites. These findings provide evidence that small amounts of external oil exposure are associated with hemolytic anemia. Furthermore, we found that some birds captured from the area impacted by the spill but with no visible oiling also had erythrocytic inclusion bodies, increased reticulocytes, and reduced packed cell volumes when compared with birds from reference sites. Thus, birds suffered hematologic injury despite no visible oil at the time of capture. Together, these findings suggest that adverse effects of oil spills on birds may be more widespread than estimates based on avian mortality or severe visible oiling. Environ Toxicol Chem 2018;37:451-461. © 2017 SETAC.

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