Lead bioavailability from contaminated wetland sediments at a former shooting range

Background/Question/Methods

Legacy lead contamination from past shooting range activities poses a potential threat to ecosystem  and public health. Between 1932 and 1963, the La Crosse Gun Club discharged large quantities of lead shot into the La Crosse River Marsh, an urban wetland located at the confluence of the Mississippi and La Crosse Rivers in La Crosse, Wisconsin. Recent research found 3.5 hectares of surface sediment above the EPA contamination threshold of 400 ppm, with a maximum value of 31,100 ppm. In humans and wildlife, high concentrations of lead are known to cause physical deformities, behavioral changes, and reproductive dysfunctions. It is therefore essential that we determine the potential transfer of lead from sediments to plants and animals in the marsh. To test whether the lead is transferring to biota from the contaminated sediments, we collected duckweed (Lemna sp.), bethic invertebrates (Leptocerus americanus), fish species from multiple trophic levels, and water for lead analysis. Samples were collected in areas with low (200-1000 ppm), medium (1,000 -4,000 ppm) and high (>4,000) lead contaminated surface sediments. All samples were analyzed for lead by using inductively coupled plasma mass spectroscopy (ICP-MS) and atomic absorption spectroscopy (AAS).

Results/Conclusions

Findings show lead from the contaminated sediments is bioavailable after 50 years of shooting inactivity at the site. Lead levels were as high as 6 ppm in fish samples, 268 ppm in duckweed samples, and 170 ppm in invertebrate samples. Surface water had total lead levels of up to 7 ppm and dissolved lead reached 2 ppm. Significant correlations exist between lead concentrations within biota, water, and surface sediments indicating that the regions with the highest sediment lead concentrations pose the greatest threat to biota. Ongoing malformation analyses of zooplankton and invertebrates, and laboratory toxicity assays using zebrafish larvae will determine if lead contaminated sediments pose a toxicological risk. Results from this study will provide the framework for deciding whether remediation and/or long-term monitoring is required at the site.