Assessment of heavy metal and metalloid concentrations at Horicon National Wildlife Refuge

Anthropogenic inputs of heavy metals and metalloids pose a risk to wetlands due to their long retention time in sediment, high toxicity at low concentrations, and biological accumulation. This study aimed to assess risk from seven heavy metals (cadmium:Cd, chromium:Cr, copper:Cu, mercury:Hg, nickel:Ni, lead:Pb, zinc:Zn) and one metalloid (arsenic:As) along a trophic pathway by quantifying contaminant loads in muskrat livers, roots of invasive hybrid cattail (Typha x glauca), and in sediment at Horicon National Wildlife Refuge, a wetland of international importance in southeastern Wisconsin, United States. Overall, comparison to literature and thresholds from the Environmental Protection Agency led us to conclude that heavy metals and metalloids pose a low risk to refuge biota with maximum concentrations as follows in sediment, T. x glauca roots, and muskrat livers in mg/kg dry weight: Zn—82, 54, 111, Pb—42, 43, 0.06, Cu—26, 59, 13, Ni—22, 5, 0.7, Cr—20, 3, 0.5, As—6, 11, 0.08, Cd—3, 1, 0.08, Hg—0.1, 0.02, 0.08, a finding which was further supported by low bioconcentration factors between sample types. A spatial analysis using GIS revealed hotspots for Cd, Cr, Cu, Ni, and Zn in sediment in one subplot. However, even in hotspots concentrations mostly fell below protective thresholds and were similar to or lower than concentrations found in a prior survey from 1990 (α < 0.05). Overall, while anthropogenic influences are undoubtedly present, we interpret the concentrations found here to be relatively low and present them as points of comparison regarding risk to plants and mammals for others conducting similar surveys on wetlands.