Mercury Concentrations in Eggs of Red-Winged Blackbirds and Tree Swallows Breeding in Voyageurs National Park, Minnesota.

Most investigations of the environmental effects of mercury (Hg) have focused on aquatic food webs that include piscivorous fish or wildlife. However, recent investigations have shown that other species, including passerine songbirds, may also be at risk from exposure to methylmercury (MeHg). We quantified Hg concentrations in eggs of two species of songbirds, red-winged blackbirds (Agelaius phoeniceus) and tree swallows (Tachycineta bicolor), nesting in Voyageurs National Park, Minnesota, USA. Geometric mean concentrations of total Hg (THg) were lower in red-winged blackbird eggs [218 and 107 ng/g dry weight (dw) for 2012 and 2013, respectively] than in tree swallow eggs (228 and 300 ng/g dw for 2012 and 2013, respectively), presumably reflecting differences in the trophic positions of these two species. Concentrations of MeHg averaged 98.4 % of THg in red-winged blackbird eggs. Levels of THg observed in this study were well below critical toxicological benchmarks commonly applied to eggs of avian species, suggesting these breeding populations were not adversely affected by exposure to MeHg. In red-winged blackbirds, concentrations of THg in eggs collected in 2012 were twice those in eggs collected in 2013. Hg levels in eggs of both species increased with date of clutch initiation. In red-winged blackbirds, for example, temporal patterns showed that a 3-week delay in clutch initiation increased egg THg by 60 %. These observations indicate that in ovo exposure of wetland birds to MeHg can vary significantly within nesting season as well as between years.

Production and retention of methylmercury in inundated boreal forest soils.

The Flooded Uplands Dynamics Experiment (FLUDEX) was an ecosystem-scale study examining the production of methylmercury (MeHg) and greenhouse gases from reservoirs constructed on an upland boreal forest landscape in order to quantify their dependence upon carbon stores. We detail the within-reservoir production and storage of MeHg before, during, and nine years after the experiment. The reservoirs were net MeHg producers during the first two years of flooding, and net demethylating systems afterward. During years 1-3, a rapid pulse of MeHg and total Hg was observed in floodwater, followed by substantial increases in MeHg in seston and sediment. Resampling of the dry reservoirs nine years after the experiment ended indicated that organic soil MeHg was still 8 to 52-fold higher than preflood conditions, and averaged 86% of the levels recorded at the end of the third flooding year. Both total Hg and MeHg retention in soil were a strong function of organic carbon content. The time scale of soil MeHg retention may help explain the decadal time lag frequently observed for the decrease of piscivorous fish Hg concentrations in new reservoirs. Predicted extreme precipitation events associated with climate change may serve to make landscapes more susceptible to this process.

Burrowing dragonfly larvae as biosentinels of methylmercury in freshwater food webs.

We assessed the utility of larval burrowing dragonflies (Odonata: Anisoptera: Gomphidae) as biosentinels of methylmercury (MeHg) contamination. Gomphids were the most abundant family of dragonflies sampled during 2008-2010 from 17 lakes in four national parks of the northwestern Laurentian Great Lakes region. Ten species of burrowing gomphids were sampled; 13 lakes contained 3 or more species, and 2 species of Gomphus co-occurred in 12 lakes. Most of the total Hg (THg) in whole, late-instar larvae was MeHg, with mean percent MeHg exceeding 60% in 16 lakes. Mean MeHg in larvae of a given species varied greatly among lakes, ranging from 4 to 109 ng g(-1) dry weight. Methylmercury levels in larvae, however, were much less variable within a given lake and species. The mean concentration of MeHg in burrowing gomphids was positively correlated with mean MeHg concentration in unfiltered lake water. Mean concentrations of THg and MeHg in multispecies assemblages of Gomphus were also positively correlated with mean THg in coexisting prey fish and game fishes. We recommend-and provide guidance on-the application of burrowing gomphids as biosentinels of MeHg contamination, which can extend the bioassessment of MeHg to fishless fresh waters.

Assessment of mercury bioaccumulation within the pelagic food web of lakes in the western Great Lakes region.

While mercury is a health hazard to humans and wildlife, the biogeochemical processes responsible for its bioaccumulation in pelagic food webs are still being examined. Previous studies have indicated both "bottom-up" control of piscivorous fish Hg content through methylmercury.(MeHg) supply, as well as site-specific trophic factors. We evaluated ten studies from the western Great Lakes region to examine the similarity of MeHg trophic transfer efficiency within the pelagic food web, and assessed regional-scale spatial variability. Analyses of bioaccumulation and biomagnification factors between water, seston, zooplankton, and preyfish indicated that the largest increases in MeHg occurred at the base of the food web, and that the relative extent of trophic transfer was similar between sites. Positive correlations were observed between aqueous unfiltered MeHg, total Hg, and dissolved organic carbon, and measures of the efficiency of MeHg trophic transfer were consistent across widely disparate systems (both natural and experimentally manipulated) throughout North America. Such similarity suggests that the aqueous supply of MeHg is largely controlling bioaccumulation in pelagic food webs, while local, lake-specific variability can result from an array of trophic (biological) factors.

Mercury in streams at Grand Portage National Monument (Minnesota, USA): assessment of ecosystem sensitivity and ecological risk.

Mercury (Hg) in water, sediment, soils, seston, and biota were quantified for three streams in the Grand Portage National Monument (GRPO) in far northeastern Minnesota to assess ecosystem contamination and the potential for harmful exposure of piscivorous fish, wildlife, and humans to methylmercury (MeHg). Concentrations of total Hg in water, sediment, and soil were typical of those in forest ecosystems within the region, whereas MeHg concentrations and percent MeHg in these ecosystem components were markedly higher than values reported elsewhere in the western Great Lakes Region. Soils and sediment were Hg-enriched, containing approximately 4-fold more total Hg per unit of organic matter. We hypothesized that localized Hg enrichment was due in part to anthropogenic pollution associated with historic fur-trading activity. Bottom-up forcing of bioaccumulation was evidenced by MeHg concentrations in larval dragonflies, which were near the maxima for dragonflies sampled concurrently from five other national park units in the region. Despite its semi-remote location, GRPO is a Hg-sensitive landscape in which MeHg is produced and bioaccumulated in aquatic food webs to concentrations that pose ecological risks to MeHg-sensitive piscivores, including predatory fish, belted kingfisher, and mink.

Spatial and temporal patterns of mercury accumulation in lacustrine sediments across the Laurentian Great Lakes region.

Data from 104 sediment cores from the Great Lakes and "inland lakes" in the region were compiled to assess historical and recent changes in mercury (Hg) deposition. The lower Great Lakes showed sharp increases in Hg loading c. 1850-1950 from point-source water dischargers, with marked decreases during the past half century associated with effluent controls and decreases in the industrial use of Hg. In contrast, Lake Superior and inland lakes exhibited a pattern of Hg loading consistent with an atmospheric source - gradual increases followed by recent (post-1980) decreases. Variation in sedimentary Hg flux among inland lakes was primarily attributed to the ratio of watershed area:lake area, and secondarily to a lake's proximity to emission sources. A consistent region-wide decrease (∼20%) of sediment-Hg flux suggests that controls on local and regional atmospheric Hg emissions have been effective in decreasing the supply of Hg to Lake Superior and inland lakes.

Cardiovascular effects of consumption of black versus English walnuts.

English walnuts have been shown to decrease cardiovascular disease risk; however, black walnuts do not appear to have not been studied for their cardioprotective effects. The purpose of this study was to determine the effects of English versus black walnut consumption on blood lipids, body weight, fatty-acid composition of red blood cell (RBC) membranes, and endothelial function. Consumption of 30 g of English walnuts per day for 30 days, by 36 human participants, improved blood lipids; the effects of black walnuts were dependent on the participant's sex. Addition of either nut to the diet did not result in weight gain. The fatty-acid composition of RBC membranes was favorably affected by walnut consumption. RBC polyunsaturated fatty acids increased after consumption of either type of nut; however, eicosapentaenoic acid increased significantly more after English walnut consumption. Endothelial function of 6 unmedicated humans with hypercholesterolemia was maintained after consumption of English walnuts with a meal high in high saturated fats; however, consumption of black walnuts with the same meal did not maintain endothelial function. Overall, these results support the recommendation that consumption of 1 oz of English walnuts per day may decrease cardiovascular risk, but more research on black walnut consumption is necessary before an appropriate recommendation can be made.

Analysis of fin clips as a nonlethal method for monitoring mercury in fish.

Monitoring of mercury in fish typically involves removal of individuals from the sampled population and subsequent analysis of fillets. This study assessed whether the analysis of fins, structures routinely clipped to mark released fish in population studies, could provide a nonlethal approach for estimating mercury concentrations in axial muscle (fillets). We analyzed fillets and selected fins from 401 northern pike (Esox lucius) and 79 walleye (Sander vitreus) from 21 lakes in Minnesota and Wisconsin, 19 Arctic grayling (Thymallus arcticus) from Toolik Lake, Alaska, and 14 winter flounder (Pseudopleuronectes americanus) from Long Island Sound, New York. On average, 83% of mercury in fins was methylmercury, and concentrations in the proximal portion were about half-those in the distal portion in pelvic fins. Mean concentrations of mercury in fins, averaged by species and fin type, ranged from 2.7 to 8.9% of those in fillets. Coefficients of determination (r2) for linear regressions of mercury concentrations in fillets against those in fins of individual fish ranged from 0.04 to 0.96 among species and water bodies (median r2 = 0.52). The concentration in fin clips was a better predictor of mercury in fillets for individual Arctic grayling (r2 = 0.65, n = 12 and r2 = 0.84, n = 8) and winter flounder (r2 = 0.94, n = 14) than for individual northern pike (median r2 = 0.56) or walleye (median r2 = 0.22) from a given lake. In northern pike in the 400-500 mm total-length interval, the mean concentrations of total mercury in caudal fins and fillets, averaged by lake (n = 12), were strongly correlated (r2 = 0.95). The analysis of composited samples of fin clips from fish within a restricted length interval could, therefore, be a useful screening tool for assessing the relative mercury contamination of fish among different water bodies.