S5 Mercury in the Laurentian Great Lakes region

Tuesday, 26 July, 2011

TS5-P1 — 11:00-12:00 and 17:30-18:30
Authors: WIENER, James G.1, SANDHEINRICH, Mark B.1, BHAVSAR, Satyendra P.2, BOHR, Joseph R.3, EVERS, David C.4, MONSON, Bruce A.5, SCHRANK, Candy S. 6
(1) University of Wisconsin-La Crosse, Wiener.jame@uwlax.edu; (2) Ontario Ministry of the Environment; (3) Michigan Department of Natural Resources; (4) BioDiversity Research Institute; (5) Minnesota Pollution Control Agency; (6) Wisconsin Department of Natural Resources.

We assessed the potential toxicological significance of methylmercury in yellow perch Perca flavescens, a fish important in the trophic transfer of methylmercury to piscivores in many lentic waters of the Laurentian Great Lakes region. Our principal objectives were (1) to compare mercury concentrations in whole yellow perch to dietary concentrations associated with reduced health and reproduction of common loons Gavia immer, a fish-eating bird that forages selectively on yellow perch, and (2) to compare concentrations of mercury in fillets of yellow perch to criteria established to protect the health of humans who eat wild fish. Data on total mercury in yellow perch were compiled from provincial and statewide monitoring programs in Ontario, Michigan, Minnesota, and Wisconsin. The data were restricted to fish collected in 1990 or later and analyzed individually as samples of axial muscle, skin-on fillet, or whole fish. The final database contained information on 6452 yellow perch, including 4340 fish from inland lakes and reservoirs and 2112 from the Great Lakes. Data for axial muscle and skin-on fillets were classified as “fillets”, and an equation derived from data on yellow perch from Kejimkujik National Park (Nova Scotia, Canada, Wyn et al. 2010) was used to derive estimates of the mercury concentration in both whole body and fillet for each fish. The database contained records for 2721 fish within the estimated size range (weight < 100 g or total length < 19 cm) of prey fish eaten by common loons; 1080 of these fish were from 110 water bodies in the US, and 1641 were from 146 waters in Ontario. Mean concentrations in whole perch (<19 cm) from 18 (7%) of these 256 waters exceeded 0.16 µg/g wet weight, an estimated dietary threshold concentration for significant reproductive effects on loons. Comparisons of mercury levels in fillets of yellow perch to criteria for human consumption were limited to fish with total length of 15 cm or greater, the minimum size of perch typically retained by anglers. Mean concentrations in fillets exceeded the US Environmental Protection Agency methylmercury criterion of 0.3 µg/g wet weight in 21 (14%) of 150 US waters. In Ontario, mean concentrations exceeded the provincial criterion of 0.26 µg/g wet weight in 34 (19%) of 176 waters. Consumption of yellow perch from many waters of the Great Lakes region could expose common loons and humans to potentially harmful levels of methylmercury.

TS5-P2 — 11:00-12:00 and 17:30-18:30
Authors: BABIARZ, Christopher1, SCHOTT, Trevor1
(1) University of Wisconsin -- Madison, cbabiarz@wisc.edu

Fifteen years have passed since the inception of the Lake Michigan Mass Balance Study (LMMB), and during that period both industrial use and atmospheric emissions of mercury (Hg) have been reduced. Given these reductions, and new information on the residence time of Hg in aquatic ecosystems, we have begun an abridged version of the tributary monitoring project to provide an interim benchmark before new caps on mercury emissions are completely met.

Our past work has shown that flow rate strongly influences the concentration of total mercury (HgT), methylmercury (MeHg), and suspended particulate matter (SPM), in rivers. Because the relative speciation of mercury also varies with flow rate the project focuses on three distinct flow regimes: base flow, storm events, and the spring melt. Measurements of HgT and MeHg concentration in the unfiltered and filtered phases, and important ancillary chemistry (DOC, pH, specific conductivity, and temperature) are being quantified.

By establishing the current condition of these tributaries, the project provides two important outcomes: (a) the data will be an important longitudinal benchmark to assess the impact of recent and future emissions reductions, and (b) the premise that tributaries can be used as sentinels will be tested by comparing the current data to those collected during the LMMB. By laying this groundwork, we hope to quantify the regional impact of current Hg emission rules and provide a scientific basis for future decisions about implementing additional control programs in the region.

TS5-P3 — 11:00-12:00 and 17:30-18:30
Authors: BHAVSAR, Satyendra1, GEWURTZ, Sarah2, MCGOLDRICK, Daryl2, KEIR, Michael 2, BACKUS, Sean2
(1) Ontario Ministry of Environment, satyendra.bhavsar@ontario.ca, s.bhavsar@utoronto.ca; (2) Environment Canada;

A number of initiatives have curtailed anthropogenic mercury emissions in North America over the last two decades; however, various factors, including long range transport of global emissions, may complicate the response of fish mercury levels to remedial actions. Since the Great Lakes of North America are together the largest surface freshwater body of the world and are under the influence of many complicating factors, trends in fish from the Great Lakes can reflect the overall impact of mercury management actions at local, regional and perhaps global scales. Here we present a comprehensive view of mercury trends in Canadian Great Lakes fish using two large (total 5807 samples), different (fillet and whole fish), and long-term (1970s-2007) monitoring datasets. The spatial differences in lake trout and walleye mercury levels during this period have generally been within a factor of 2-3 with Lakes Erie and Superior having the lowest and highest concentrations, respectively. These spatial differences have diminished in the recent years (2000-2007). The concentrations have generally declined over the three decades (mid-1970s to 2007); however, in recent years, the concentrations are flat in Lake Ontario walleye and appear to be increasing in Lake Erie walleye. There was a mismatch in the Lake Ontario lake trout and walleye temporal trends, which shows the importance of considering more than one fish species for proper spatial/temporal trend assessments.

TS5-P4 — 11:00-12:00 and 17:30-18:30
Author: BHAVSAR, Satyendra1
(1)Ontario Ministry of Environment, satyendra.bhavsar@ontario.ca, s.bhavsar@utoronto.ca

Mercury is a leading cause of fish consumption advisories in North America. However, most of the fish consumption advisories issued for the Canadian Great Lakes based on the most restrictive contaminant is due to elevated levels of dioxin-like PCBs and dioxins/furans. It is not clear whether the current mercury levels would restrict fish consumption if largely anthropogenically derived PCBs/dioxins/furans were to decrease below their consumption guidelines. Using Ontario Ministry of the Environment (OMOE) fish mercury measurements and consumption guidelines, we developed consumption advisories for the Canadian Great Lakes based only on mercury levels (i.e., ignore other contaminants). Restrictions on fish consumption from this "Hg-only" scenario were compared with the current restrictions advised for the Great Lakes fish. The overall results suggest that the percentage of advisories resulting in partial or complete restrictions for the general population would decrease from 39%, 44%, 59% and 66% to 7%, 3%, <1%, and 5% for Lakes Superior, Huron, Erie and Ontario, respectively. There would be no restriction for the general population on consumption of pink, coho and Chinook salmon. For various blocks considered in the Canadian Great Lakes advisories, Peninsula Harbour would be the only block with >15% (33%) restriction.

TS5-P5 — 11:00-12:00 and 17:30-18:30
Authors: RIDAL, Jeffrey J.1, NORRIS, Kristin2, CAMPBELL, Linda M.2, HODSON, Peter V.2, LEAN, David R.S.3
(1) St. Lawrence River Institute , jridal@riverinstitute.ca; (2) Queen’s University, Kingston, ON; (3) Lean Environmental, Apsley, ON.

We examined potential geographic sources of mercury to the Lake St. Francis portion of the St. Lawrence River to investigate why concentrations in sportfish are elevated compared with upstream fish, despite controls on local industrial sources. We sampled amphipods and juvenile yellow perch as indicators of mercury bioavailability from contaminated sediments and compared concentrations in biota to sediment concentrations in solids and porewater. Amphipod mono-methyl mercury (MeHg) was strongly correlated to total mercury (THg) concentrations, and the proportion of THg that was MeHg was correlated to sediment total mercury, loss on ignition, and grain size. However, the actual concentrations of THg and MeHg in amphipods and perch were not related to any sediment parameter. THg concentrations in perch were significantly correlated to amphipod concentrations of THg (r2=0.25, p=0.03) and MeHg (r2=0.49, p<0.001). Perch were most contaminated at north shore sites in Lake St. Francis, and least on the south shore. Concentrations in perch of a common length of 14.8 cm exceeded the Ontario guidelines for sensitive consumers of 260 µg/kg w.w. only for sites near the mouths of north shore tributaries. Larger fish typically caught by recreational fisherman would contain higher concentrations on average. Overall, sediment mercury concentrations provided no basis for predicting the contamination of resident fish or the risks to human consumers, suggesting that ‘legacy’ contamination of sediments does not drive mercury contamination of fish. The geographic pattern of mercury contamination of perch suggests on-going inputs from north-shore watersheds, either due to point or diffuse sources. THg water concentrations in north shore tributaries were 2-10 times greater than is typical of the St. Lawrence River, and with relatively high proportions of MeHg (19-29%). However, similar inputs along the south shore suggest a difference in the bioavailability of the mercury discharged, perhaps related to the association of mercury with dissolved and particulate matter. The pathway of mercury from tributary inputs to perch appears to be the food web, based on strong correlations with mercury concentrations in amphipods, an important diet item of juvenile perch. These data indicate that decisions on remediating mercury contaminated sites to protect human consumers of fish should consider on-going mercury inputs before implementing sediment clean-up.

TS5-P6 — 11:00-12:00 and 17:30-18:30
Authors: ETHIER, Adrienne1, MELCHER, Hilary2
(1) Atomic Energy of Canada Limited, ethiera@aecl.ca; (2) Trent University.

The HERMES model uses a reduced set of inputs to predict concentrations of total mercury and methyl mercury in the water column and sediments of lakes. The model was tested on a number of lakes in Canada and has proved to be a good predictive screening-level tool.

Results from application of HERMES model to all five Great Lakes (Erie, Ontario, Huron, Superior and Michigan) will be discussed, along with scenarios to show how changes in one lake might influence mercury dynamics in downstream lakes. This model could serve as a valuable tool for risk assessment and management of mercury in the Great Lakes basin.

TS5-P7 — 11:00-12:00 and 17:30-18:30
Authors: RISCH, Martin R.1, DEWILD, John F. 1, KRABBENHOFT, David. P. 1, KOLKA, Randall K. 2, ZHANG , Leiming 3
(1) U.S. Geological Survey, mrrisch@usgs.gov; (2) U.S. Forest Service; (3) Environment Canada.

Forest canopies can accumulate more mercury from the atmosphere than other landscapes because of their relatively large leaf areas. In autumn in the eastern United States, the mercury mass in the annual litterfall of deciduous or predominantly deciduous forests represents a large portion of the atmospheric mercury dry deposition that was retained in the forest landscape that year. The Mercury Deposition Network (MDN) of the National Atmospheric Deposition Program (NADP) provided a framework for litterfall mercury monitoring because it has long-term sites, a broad geographic coverage, capacity for supplementary sample collection, and weekly mercury wet-deposition data.

A study of mercury in litterfall at selected MDN sites, which were thought to represent different forest-cover types and geographic regions in the eastern US, was completed during autumn months in 2007, 2008, and 2009. Trace-metal-free methods for collecting, processing, and analyzing litterfall samples for mercury were developed for the study. Data obtained in the study include total mercury concentrations in litterfall samples and litterfall sample-catch amounts from four passive collectors randomly deployed for approximately 2 months each autumn in study plots located near from 12 to 23 MDN sites in 15 states.

Mean mercury concentration in the samples and sample-catch amount were used to estimate annual litterfall-mercury deposition at each MDN site. Litterfall-mercury concentrations, sample catch, and litterfall-mercury deposition differed significantly among MDN sites and were highest in areas with deciduous oak-hickory forest-cover types. Annual litterfall-mercury deposition was highest at three sites near urban areas in Indiana and Maryland and two sites in the Ohio River Valley in Indiana and Ohio. Litterfall-mercury deposition was as high as 23.4 µg/m2/yr (micrograms per square meter per year) and had a median of 10.9 µg/m2/yr. The mean ratio of annual litterfall-mercury deposition to annual mercury wet deposition was 1.2 to 1.

The results of this study provide a reference for regional mercury deposition models and future litterfall-mercury monitoring plans.

TS5-P8 — 11:00-12:00 and 17:30-18:30
Authors: RISCH, Martin R.1, GAY, David A.2, FOWLER, Kathleen K.1, KEELER, Gerard J. 3, BACKUS, Sean M. 4, BLANCHARD , Pierrette 4, BARRES, James A. 3, DVONCH, J. Timothy 3
(1) U.S. Geological Survey, mrrisch@usgs.gov; (2) Illinois State Water Survey; (3) University of Michigan; (4) Environment Canada;

Data from three mercury wet-deposition-monitoring networks and two precipitation-monitoring networks in the USA and Canada, for 2002-2008, were combined to assess spatial patterns and temporal trends in 9 states and 2 provinces in the Laurentian Great Lakes Region. Spatial patterns of annual mercury wet deposition were examined by generating high resolution maps based on precipitation-weighted annual mean mercury concentrations at 37 sites and annual precipitation depths at 1,684 sites. Temporal trends in weekly data were determined with the Seasonal Kendall Trends Test and the Seasonal Kendall Slope Estimator.

Year-to-year variations in spatial patterns of mercury wet deposition were observed throughout the region. Generally, mean annual mercury wet deposition was highest in the southern part of the study region and lowest in the north and followed patterns of mean annual precipitation depths. Localized areas with high annual mercury wet deposition (15 to 20 micrograms per square meter) were mapped in 6 of 7 years and typically corresponded with sites having high precipitation-weighted annual mean mercury concentrations.

Seven-year temporal trends in mercury wet deposition or mercury concentration were observed in data for weekly samples from 20 monitoring sites. For sites with significant trends, the median annual decrease or increase in weekly mercury concentration was less than a nanogram per liter. For a group of monitoring sites near southern Lake Michigan, trends of decreased mercury concentrations coincided with trends of increased precipitation depths. Significant 7-year trends in weekly mercury wet deposition were not coincident with trends in weekly mercury concentration.

During the 2002-2008 study period, mercury wet deposition was unchanged in the Great Lakes region or its sub-regions. Any small decreases in mercury concentration apparently were offset by increases in precipitation. Continued monitoring could detect whether these observations are consistent over a longer time period.

TS5-P9 — 11:00-12:00 and 17:30-18:30
Authors: ROLFHUS, Kristofer R1, CHALLIS, Katie E1, LEPAK, Ryan F1, BAILEY, Sean W1, HARO, Roger J1, SANDHEINRICH, Mark B1, WIENER, James G1
(1) University of Wisconsin-La Crosse, rolfhus.kris@uwlax.edu

The majority of methylmercury (MeHg) bioaccumulation occurs between the aqueous and particulate phases in aquatic systems, yet the lower food web (both benthic and pelagic) remains under-studied in most ecosystems compared to bioaccumulation in fish. As part of a larger study examining mercury contamination within U.S. National Parks in the western Great Lakes region, we quantifed total and methylmercury content in water, surficial sediments, seston, benthic macroinvertebrates (mainly dragonfly larvae) and bulk zooplankton in relation to ancillary physical and chemical parameters in 30 water bodies across six parks. Additionally, prey fish and predatory fish from these systems are being analyzed, allowing for characterization of the lower portions of the benthic and pelagic food webs. Analyses are ongoing, and initial results indicated that aqueous fractions of MeHg (range, 0.036-2.32 ng/L) correlated most strongly with dissolved organic carbon (r2=0.42), and less so with pH and sulfate. Highest MeHg concentrations were observed in systems with watersheds dominated by wetlands. Additionally, MeHg in filtered samples (0.45 micron) averaged 67% of that in unfiltered samples. Results from the lower food web will be combined with similar measures from the past decade at several of our National Park sites to evaluate patterns of contamination and bottom-up control on the trophic transfer of methymercury within the region.

TS5-P10 — 11:00-12:00 and 17:30-18:30
Authors: ROLFHUS, Kristofer R1, HALL, Britt D2, MONSON, Bruce3, PATERSON, Michael 4, JEREMIASON, Jeff5, KNIGHTS, Brent6
(1) University of Wisconsin-La Crosse, rolfhus.kris@uwlax.edu; (2) University of Regina; (3) Minnesota Pollution Control Agency; (4) Department of Fisheries and Oceans Canada; (5) Gustavus Adolphus College; (6) US Geological Survey.

While methylmercury is a health hazard to humans and wildlife, the biogeochemical processes responsible for its bioaccumulation in pelagic food webs are still being explored and debated. Previous studies have indicated both “bottom-up” control of predatory fish Hg content through methylmercury (MeHg) supply, as well as trophic factors. We have evaluated ten studies from the western Great Lakes region as part of the Great Lakes Atmospheric Deposition (GLAD) Program’s “Integrating Multimedia Measurements of Mercury in the Great Lakes Region” Project to determine the importance of aqueous MeHg supply on trophic transfer within the lower food web, and to assess regional-scale spatial variability. Analyses of bioaccumulation and biomagnification factors (BAF, BMF) between water, seston, zooplankton, and preyfish indicated that the largest MeHg increases occur at the base of the food web, and that trophic transfer was remarkably similar in magnitude between sites (seston:water logBAF range 4.38-5.82; zooplankton:water logBAF range 5.29-6.67; preyfish:zooplankton log BMF range 0.29-0.96). Such consistency was observed in both natural and experimentally-impacted systems. We found positive correlations between aqueous unfiltered MeHg and dissolved organic carbon, and measures of food web “biomagnification power” within the western Great Lakes region were consistent with widely varying systems throughout North America. Such similarities suggest that MeHg bioaccumulation in pelagic food webs is largely a function of aqueous supply of MeHg and the factors promoting its synthesis.

TS5-P11 — 11:00-12:00 and 17:30-18:30
Authors: TURNQUIST, Madeline A.1, SCHLAEPFER, Martin A.2, DRISCOLL, Charles T.3
(1) State University of New York - College of Environmental Science and Forestry, mturn704@gmail.com; (2) INRA - Ecology and Ecosystem Health Research Unit; (3) Department of Civil and Environmental Engineering, Syracuse University.

There have been numerous studies examining the relationship of mercury (Hg) concentrations in fish with environmental factors. In this study, we used landscape features depicted through GIS data layers and atmospheric Hg deposition to increase predictability over New York State. The objective of this study was to construct spatial models which consider water chemistry and landscape features to empirically predict Hg concentrations in four fish species; yellow perch (YP, Perca flavescens), smallmouth bass (SMB, Micropterus dolomieu), largemouth bass (LMB, Micropterus salmoides), and walleye (WEYE, Sander vitreus), and then apply the models to lakes within New York State. We used 37 landscape GIS characteristics and 24 water chemistry variables as potential model parameters. The variables were selected based on previous studies that have shown that pH, acid neutralizing capacity (ANC), dissolved organic carbon (DOC), abundance of wetlands, % forest cover, and lake to watershed ratio to be correlated with fish Hg concentrations. A total of 185 independent sample sites were available with both fish Hg measurements and environmental parameters. Regression models were built for standardized fish lengths [YP=229mm (9in), SMB and LMB = 356mm (14in), WEYE = 457mm (18in)] removing the influence of size as a covariate in the models. Akaike’s information criterion (AIC) was used to determine the most suitable model for each species. The three most prominent parameters in the models were the mean gaseous elemental Hg deposition in the watershed, the % wet area (open water and wetlands) relative to the lake area, and ANC, resulting in coefficients of determination (R2) as follows, YP R2 = 0.56, SMB R2 = 0.61, LMB R2 = 0.41, and WEYE R2 = 0.24, allowing at least for YP and SMB a high predictability to the model. Since the parameters selected were readily available either through GIS calculations or statewide water chemistry databases, we were able to apply the derived models to an additional 180 lakes in New York to predict the Hg concentration of a standard size fish for each species. The potential risk was assessed by applying prediction intervals and the results were displayed on maps. The models highlight areas of New York State where fish Hg concentrations could be elevated beyond safe consumption advisory limits, thus assisting resource managers in focusing their fish Hg sampling efforts.

TS5-P13 — 11:00-12:00 and 17:30-18:30
Authors: POULOPOULOS, John1, CAMPBELL, Linda M1
(1) Queen’s University, 5jp37@queensu.ca

In the Great Lakes region, scientific consensus is that fish Hg concentrations were generally greatest in the mid-20th century, when anthropogenic Hg emissions peaked. However, most monitoring programs began in the 1970s, and there are few records of pre-1970s fish Hg concentrations with which to determine earlier contamination levels. We used archived ichthyology collections from museums to measure concentrations in fish captured as early as the 1920s, long before the presumed peak in contamination. Our study lakes, Lakes Nipigon, Simcoe and Champlain, are among the largest inland lakes in the region (744-4848 km2) and range from remote to urban. For each lake, we collected fish from many trophic levels in both historical (1920s-60s) and modern (2006-7) time periods. We measured stable C and N isotopes to determine food web structure, and related these to Hg concentrations. Using results from a separate study, we applied correction factors to the data to account for tissue preservation effects. We determined the historical and modern Hg vs. d15N regressions of Lake Nipigon had the same slopes, as did those of Lake Champlain. This indicates long-term stability in the biomagnification rate of Hg. Correlations between Hg and d15N in historical and modern Lake Simcoe food webs were not significant, possibly due to small sample size. In both Lakes Simcoe and Champlain, historical fish tended to have higher Hg concentrations than modern ones. This is consistent with the declines in fish Hg concentrations observed in urban or semi-urban areas throughout the Great Lakes region in recent decades. In contrast, historical and modern Hg concentrations in Lake Nipigon broadly overlapped, as expected for this remote and relatively unimpacted lake. Our results provide a historical target for Hg abatement efforts throughout the Great Lakes region, and highlight the power of retrospective analyses using archival material.

TS5-P14 — 11:00-12:00 and 17:30-18:30
Authors: KRABBENHOFT, David1, AIKEN, George1, DEWILD, John1, SABIN, Thomas1, THOMPSON, Charles1, TATE, Michael1
(1) U.S. Geological Survey, dpkrabbe@usgs.gov

In 2006, mercury (Hg) was responsible for 80 percent, or 3,080, of the fish consumption advisories posted in the 48 United States. The seemingly ubiquitous nature of Hg-contaminated fish, and daunting task of monitoring and mapping such widespread and complex problem, has caused some states to issue statewide advisories in order to warn their citizens. While statewide advisories may be effective for warning the public of possible unsafe exposure levels of Hg in fish, this strategy does little to indentify whether areas of greater or lesser concern may exist and what the controlling factors are. The goal of this study was to evaluate regional trends in Hg and methylmercury (MeHg) for lakes in the Upper Midwest (US) states of Minnesota, Wisconsin, Michigan and Illinois, and to ascertain whether we can infer the controlling factors.

the summer of 2007 the USEPA sponsored a nationwide of more than 1000 lakes across the coterminous United States. The sampling design for the survey was a probability-based network intended to provide statistically-valid estimates of the condition of all lakes with known confidence. In the original design of the project the only mercury-related work component was the acquisition of a single sediment core from the center of each lake, and the top two centimeters was sectioned off for HgT and MeHg analyses. Shortly before the initiation of the field sampling, the USGS Mercury Research Lab contacted the sampling teams in Minnesota, Wisconsin, Michigan and Illinois to invite the collection of water samples for HgT and MeHg analyses. In all, 234 lakes were sampled in the four-state area. Results from the study show clear spatial trends across the sampling domain. First, Hg in Illinois lakes was about 2-3 times greater than lakes sampled from the other three states (2.24 ng/L, Illinois; 1.13 ng/L, Michigan; 0.68 ng/L, Wisconsin; and, 0.93 ng/L, Minnesota). Methylmercury concentrations showed different spatial trends with the greatest mean values observed in Michigan and Minnesota (0.09 ng/L); Illinois lakes had many very low MeHg lakes, and an overall mean of 0.07 ng/L; and, the sampled lakes from Wisconsin were more moderate with a mean concentration of 0.06 ng/L. Third, the methylation capacity (as estimated by the MeHg/Hg ratio) were comparatively low for Illinois lakes (3%); greatest in Minnesota and Michigan lakes (12 and 11%, respectively); and Illinois was relatively low (3 percent); and, Wisconsin lakes were moderate (8%). The key factor controlling MeHg levels and the MeHg/HgT ratio appears to be DOC concentrations.

TS5-P15 — 11:00-12:00 and 17:30-18:30
Author: RUTKIEWICZ, Jennifer1
(1) University of Michigan, rutkiewj@umich.edu

In this study, we assessed mercury (Hg) exposure in several tissues (brain, liver, and breast and primary feathers) in bald eagles (Haliaeetus leucocephalus) (n=135) collected from across five Great Lakes states (Iowa, Michigan, Minnesota, Ohio, and Wisconsin) and assessed relationships between brain Hg and neurochemical receptors (NMDA and GABAA) and enzymes (glutamine synthetase (GS) and glutamic acid decarboxylase (GAD)). Brain total Hg (THg) levels averaged 2.8 µg/g (range:0.2-34.0), and levels were highest in Michigan birds. THg levels in liver (rp=0.81) and breast feathers (rp=0.61) significantly correlated with those in brain. Brain Hg was not associated with binding to the GABAA receptor. Brain THg and inorganic Hg (IHg) were significantly positively correlated with GS activity (THg rp=0.19; IHg rp=0.19) and negatively correlated with NMDA receptor levels (THg rp=-025; IHg rp=-0.28), and IHg was negatively correlated with GAD activity (rs=-0.20). We also report upon Hg demethylation and relationships between Hg and Se in brain and liver. These results suggest that bald eagles in the Great Lakes region are exposed to Hg at levels capable of causing subclinical neurological damage, and that when tissue burdens are related to proposed avian thresholds approximately 14-27% of eagles studied here may be at risk.

Tuesday, 26 July, 2011