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Understanding Sources and Cycling of Mercury in the St Louis River using Stable Isotope Approaches
Citation:
Janssen, S., J. Hoffman, G. Peterson, M. Pearson, R. Lepak, A. Cotter, AND D. Krabbenhoft. Understanding Sources and Cycling of Mercury in the St Louis River using Stable Isotope Approaches. SETAC North America, Fort Worth, TX, November 15 - 19, 2020. https://doi.org/10.23645/epacomptox.13171757
Impact/Purpose:
Mercury (Hg) contamination within the St. Louis River estuary (SLRE) is of long-term concern because fish Hg concentrations are elevated above human health guidelines, contributing to an existing Beneficial Use Impairment under the Area of Concern program. Our goal was to determine whether legacy sediment Hg contamination is bioaccumulating in fish, and the major source of Hg in fish. We found that the Hg concentrations and isotopic measurements of sediment and fish from the SLRE indicate that legacy Hg is actively cycling within the ecosystem, and strongly contributing to fish Hg bioaccumulation.
Description:
Mercury (Hg) contamination within the St. Louis River estuary (SLRE) is of long-term concern because fish Hg concentrations are elevated above human health and wildlife guidelines. In addition, it is known that Hg concentrations in SLRE sediments are higher than those observed elsewhere in the region, and that game fish Hg concentrations in the estuary are double that of Lake Superior. However, it is unclear whether industrial Hg, from legacy contamination, within the SLRE contributes to these high Hg concentrations in fish and sediments. The aim of this study was to address that specific understanding gap, as well as to compare Hg concentrations in sediment, and biota to a reference site, the Bad River. To understand the relative contributions of legacy versus contemporary Hg contributions, we included the use of Hg stable isotopes as tracers of Hg sources within the SLRE food web. Stable isotope analysis showed that sediments within SLRE with the highest Hg concentrations were associated with an enrichment in 202Hg, which is commonly observed in legacy contaminated sites. Most of the sediments collected within 5 distinct regions of SLRE had industrial Hg sources, often representing >50% of the total Hg source. This signature was also observed in benthic invertebrates and prey fish from SLRE, indicating that industrial Hg is an important Hg source that is bioaccumulating into the food web. Corresponding samples from the Bad River were absent of this signature and indicative of signatures derived from atmospheric Hg. The isotopic Hg source to game fish was shown to be dependent on fish migration and feeding habits, with individuals feeding in Lake Superior displaying a source signature similar to precipitation. The Hg concentrations and isotopic measurements of sediment and biota from the SLRE suggest the presence and active cycling of industrial Hg within the system as well as the contribution of offshore Hg sources in migratory fish.
URLs/Downloads:
DOI: Understanding Sources and Cycling of Mercury in the St Louis River using Stable Isotope Approaches