We seek to understand trophic distribution and routes of exposure of mercury, methyl mercury, and lead in Lake Erie, whose food web has been dramatically modified by two exotic species, the zebra mussel Dreissena polymorpha and the round goby Neogobius melanastomus. In the current food chain, zebra mussels are consumed by round gobies, which are consumed by smallmouth bass Micropterus dolomieui. Other studies have quantified the bioaccumulation of heavy metals via food-web linkages in natural systems (Chen et. al. 2000; Francis et al. 1998). Our study will characterize how mercury and lead in sediments and zebra mussels, previously unavailable to pelagic sport fishes, are now being accumulated by round gobies and, consequently, smallmouth bass. Per the U.S. Environmental Protection Agency's Lake Erie Lakewide Management Plan (Lambert 1998), mercury and lead are considered to be pollutants of concern in Lake Erie because of elevated levels in fish tissue that may be consumed by humans.

Mercury and lead operate differently in aquatic systems. Lead biodiminishes (declines in concentration) with increasing trophic level, whereas mercury biomagnifies (increases in concentration) through the food web to top predators (Chen et al. 2000). In fact, Chen et al. (2000) found that Hg increased most dramatically from zooplankton to fish whereas, As and Pb appeared to diminish from lower to higher trophic levels.

When evaluating the impact of mercury on an ecosystem, we will focus, not only on total mercury, but also on methyl mercury, the more toxic form of mercury. Most previous studies have measured only total mercury because it is $130 less per sample to quantify than methyl mercury. Mercury in fish is primarily in the methylated form, but little is known about the ratio of methyl mercury to total mercury in lower food-web levels. Methyl mercury 1) bioaccumulates through the food web, 2) is more particle-reactive, and 3) has higher potential for transport and uptake by biota than other forms of mercury. Rates of methylation vary with concentrations of dissolved organic carbon (DOC) and pH of water (Watras et al. 1995b). High DOC and low pH, characteristics of anoxic sediments and water, increase methylation of mercury; diffusion and advection then transport the methyl mercury throughout the system. Given the impact of these abiotic factors on the availability of methyl mercury, we will be quantifying these abiotic parameters as described.

Zebra mussels accumulate heavy metals by 1) filtering contaminated water and 2) ingesting contaminated suspended solids. Little work has been done with round gobies in this context; we suspect round gobies accumulate toxins via the food (zebra mussels) it ingests. Smallmouth bass gain most metals via food (an important component of which is round goby). Mercury and lead can then be transferred to humans through smallmouth bass consumption. Because these metals accumulate in the muscle tissue of organisms, trimming fat and skin from smallmouth bass does not reduce human exposure. By quantifying concentrations of mercury and lead across trophic levels, we can assess contributions of each trophic level to metal uptake and thereby to humans.

The objectives of this study are to:
Collect sediment, water, zebra mussels, round gobies, and smallmouth bass from the Maumee River Harbor, Gibraltar Island and the Sandusky Harbor (reference site) for total mercury and lead.
Measure dissolved organic carbon, pH, and total suspended solids in water from the Maumee River Harbor, Gibraltar Island and Sandusky Harbor (reference site). The Ohio EPA, Lake Erie Protection Fund (LEPF), will fund objectives 1 and 2 of our research effort.
Analyze samples collected under objectives 1 and 2 for methyl mercury, the more toxic form of mercury. Our third objective forms the basis for our request for funds from Ohio Sea Grant. Relevant to our third objective, our samples for methyl mercury analysis will be collected simultaneously with our samples for the total mercury and lead.

A small investment of funds by the Ohio Sea Grant will allow the value of the original study to be substantially enhanced. Whereas it is valuable to assess total mercury and lead in the Lake Erie food web, quantifying methyl mercury will provide additional insight into the burden of this form (the most toxic to humans) of mercury. With this information, lake managers will be better able to assess the risk of this toxin and act accordingly. Eventually, we seek to gather sufficient information to allow us to estimate trophic-level-specific ratios of methyl to total mercury such that we can use simple measurements of total mercury to predict concentrations of methyl mercury.

For all sample collections we will strictly adhere to collection and preparation protocols for heavy metals, provided by ACZ Labs Inc., 2773 Downhill Dr., Steamboat Springs, CO 80487 (hereafter ACZ Labs) and Frontier Geosciences Inc., 414 Pontius Ave. N, Seattle, WA 98109 (hereafter Frontier Labs).

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Exotic species invasions have plagued both marine and freshwater ecosystems. For the past 150 years the Laurentian Great Lakes have been particularly susceptible to these invasions. In particular, the Lake Erie food web has been dramatically modified by introduced mussels, Dreissena spp., which are now consumed by the exotic round goby, Neogobius melanastomus, which are consumed by native smallmouth bass, Micropterus dolomieui.

The introduction and spread of exotic dreissenids and the round goby have lead to a shift in the food web from a pelagic-based food web to a benthic-based one, potentially creating a new pathway for contaminant transfer to top predators, such as smallmouth bass and humans. We sought to characterize how mercury (Hg), methyl mercury (MeHg), and lead (Pb) in sediments and dreissenids, previously unavailable to pelagic sport fishes, are now being accumulated by round gobies and consequently smallmouth bass. We collected samples during June through September 2002 and July 2003, and analyzed these metals in sediment, water, dreissenids, round gobies and smallmouth bass from Maumee Bay, Gibraltar Island, and Sandusky Bay. MeHg biomagnified through the food web to top predators with no differences among the three sites. In contrast, Pb biodiminshed (decreased in concentration with increasing trophic level), as documented in other pelagic-based freshwater food webs. Differences in Pb concentrations among sites were most likely due to lower smallmouth bass Pb concentrations in Sandusky Bay than Maumee Bay or Gibraltar Island. Although we expected differences in sediment metal concentrations among sites, neither Pb nor Hg sediment concentrations differed between sites. Historical Hg concentrations in smallmouth bass did not differ from Hg concentrations in 2002 and 2003, but total Pb concentrations were higher in smallmouth bass before the inclusion of round gobies into their diets. This study is the first to demonstrate the MeHg and Pb bioaccumulation patterns in a recently shifted benthic food web that includes exotic species. In this new food chain, dreissenids appear to have merely replaced the role of zooplankton. However with their high filtration rates and ability to resuspend bottom sediments, dreissenids have the potential to accumulate high concentrations of contaminants. Predation on dreissenids by the round goby provides a pathway for contaminants that were once confined to the benthos, to be transferred through the food chain to top predators and potentially humans.

Analysis of methyl mercury is integral to our project, given methyl mercury's toxicity and bioaccumulation potential. The funds we are seeking from Ohio Sea Grant will support a complementary portion of the original research, which is being funded by the Lake Erie Protection Fund. At present, we have a pre-proposal pending at the Great Lakes National Program Office to include an even wider range of nearshore and offshore sites in the proposed research.

Our study could potentially assist Lake Erie management agencies in accomplishing their goals in the following ways. 1) Our study will provide data on current sediment concentrations of mercury and lead in nearshore and offshore harbor sites, which will assist in prioritizing sites for remediation. 2) Our study not only will focus on contaminated sediments to assess ecological risk and human health factors, but it also will quantify mercury and lead concentrations in all levels of the recently shifted food web that includes both exotic zebra mussels and round gobies, and a popular sport fish, smallmouth bass. 3) We will better understand contaminant pathways and health impacts by examining multiple trophic levels and determining bioaccumulation rates of mercury, methyl mercury and lead through the food web to top predators. 4) This study can contribute information to evaluate current consumption advisories in the Maumee River Harbor. 5) By knowing how exotic prey types affect bioaccumulation of mercury, methyl mercury and lead through the food web, agencies can better prioritize efforts geared toward reduction or eradication of targeted exotic species. 6) Because the zebra mussel is used as an effective biomonitor in many contamination assessment studies and because of its ubiquitous distribution in Lake Erie, it could be used as an indicator species for contaminant levels. 7) Finally, because we address contaminant levels of mercury and lead in the Maumee River Harbor, one of Ohio's Areas of Concern, our results can be used to assist decision-making regarding restoration of beneficial uses such as sport fishing to this harbor.

The following portion of the original study will be funded through a grant from the Ohio EPA, Lake Erie Protection Fund. We will collect samples of sediment, water, zebra mussels, round gobies, and smallmouth bass from the Maumee River Harbor and Gibraltar Island. These samples also will be collected from the Sandusky Harbor, which will be used as a reference site. We will sample six stations within each of the three sites for a total of 18 stations.

At each station, surficial sediment samples will be collected with an acid-washed piece of PVC pipe that will function as a sediment corer (Klerks et al. 1997). Upon collection, sediment will be placed in acid-washed glass containers, frozen and shipped to ACZ Labs for analysis of total mercury and lead using EPA Methods 7471 (cold vapor atomic absorption) and 6020 (ICP-MS). Water samples will be collected at each station from 1 m depth using an acid-washed tube connected to a pump; each sample will be filtered through acid-cleaned 0.45 micro meter Teflon filters into Teflon sample containers, frozen, and shipped overnight to ACZ Labs for analysis of total mercury and lead, dissolved organic carbon, and total suspended solids using EPA Methods 245.1, 200.8, 415.1 and 160.2. The following water quality parameters will be measured at each station: pH, temperature, turbidity, dissolved oxygen, and specific conductance. In addition, small (2-7 mm) and medium (8-14 mm) zebra mussels will be collected via SCUBA and ponar dredge from each station. These sizes are vulnerable to goby predation, but larger mussels are not (Carey Knight, ODW-Fairport, pers. comm.). Zebra mussels will be placed in coolers containing lake water for transport back to the lab and held for 24 h to allow for defecation, given that food and sediment particles may distort heavy metal analysis (Wiesner et al. 2001). Zebra mussels from each station will be separated into appropriate length classes and tissue will be manually removed and placed in sterile polyethylene bags, frozen at -20o C, and shipped within 48 h to ACZ Labs for analysis of total mercury and lead. Bioaccumulation rates also will be estimated based on length and age (analyzed by growth rings) of zebra mussels.

We will collect (40-90 mm and 100-150 mm) round gobies, the sizes that prey primarily on zebra mussels (Ray et al. 1997), by trawling and electrofishing at each station. Upon collection, gobies will be measured and weighed and scales from each fish will be removed for age determination. Round gobies will then be placed in polyethylene bags, frozen on dry ice, and shipped overnight to ACZ Labs for analysis of total mercury and lead. Whole body samples of round gobies will be analyzed because round gobies are consumed whole by smallmouth bass. Two size classes of smallmouth bass (200 mm and 350 mm) will be collected by trawling and electrofishing at each station. We will use data from the two length classes to estimate bioaccumulation rates. In addition, the large length class can be harvested and potentially consumed by anglers; thus, analysis of metals in these fish provides direct insight into the potential for metals to be transferred to humans. Smallmouth bass will be measured, weighed, and immediately frozen on dry ice for transport to the lab. Once there, smallmouth bass will be slowly defrosted; otoliths will be retrieved and preserved for age determination. Only filets of smallmouth bass will be analyzed as this reflects the portion consumed by humans. Scales will be removed and tissue filets will be placed in polyethylene bags, frozen at -20C, and sent to ACZ Labs for analysis of total mercury and lead. To document smallmouth bass diets, we will characterize their stomach contents. We are requesting funding from Ohio Sea Grant to support methyl mercury analysis. Samples for methyl mercury analysis will be collected simultaneously with the samples for total mercury and lead. Sediment samples will be collected in ultra clean Teflon containers, immediately frozen on dry ice and shipped to Frontier Labs. Samples of zebra mussels, round gobies and smallmouth bass for methyl mercury analysis will be collected and prepared as for total mercury and lead, and sent to Frontier Labs for analysis. To minimize sample variance in our estimate of ratios of methyl mercury to total mercury, we will measure both forms in each smallmouth bass. We will split the smallmouth bass filet in the lab and send one half for total mercury analysis and the other half for methyl mercury analysis (Carol Folt, Dartmouth, pers. comm.). All sample detection limits will be below concentrations used as consumption guidelines in the Lake Erie Lakewide Management Plan to determine human consumption advisories. The amount allocated in the Ohio Sea Grant budget for sample analysis of methyl mercury has been listed on the budget worksheet under Other Costs.