Screening Level Assessment of Metal Concentrations in Streambed Sediments and Floodplain Soils within the Grand Lake Watershed in Northeastern Oklahoma, USA

Abstract

Metal releases have been received by the Grand Lake watershed from the Tri-State Mining District (TSMD) since the mid 1800s. To address data gaps in metal distributions in the Oklahoma portion of the watershed, streambed sediment and floodplain soil was sampled on various streams. The <63-µm fraction was analyzed for Cd, Pb, and Zn concentrations by portable X-ray fluorescence spectroscopy and inductively coupled plasma-mass spectrometry. Mean metal concentration results at reference transects indicated that background sediment/soil concentrations for Cd, Pb, and Zn within the watershed were 0.5, 19, and 68 mg/kg, respectively. A significant difference in the distributions of metal concentrations was found between reference and impacted transects (Cd, Pb, Zn: p = 0.00; Cd: n = 29; Pb, Zn: n = 283). These results demonstrated that concentrations of metals in streambed sediments and floodplain soils were significantly higher in areas downstream of major mining influences relative to upstream reference sites, and the source of metal contamination within these media was the result of mining releases from the TSMD. Toxicity risks to benthic macroinvertebrates were evaluated using a TSMD-specific sediment mixture model (∑PEC-Q_Cd,Pb,Zn) for metals (MacDonald et al. in Development and evaluation of sediment and pore-water toxicity thresholds to support sediment quality assessments in the Tri-State Mining District (TSMD), Missouri, Oklahoma, and Kansas. Draft Final Technical Report. Volume I: Text. Prepared for the U.S. Environmental Protection Agency and the U.S. Fish and Wildlife Service. Prepared by MacDonald Environmental Sciences Ltd., U.S. Geological Survey, and CH2M Hill, Nanaimo, 2009). Toxicity risks to plant populations were also assessed by comparing soil metal concentrations to Ecological Soil Screening Levels (Eco-SSLs). It was found that the survival and/or biomass of benthic invertebrates was highly impacted at Tar Creek, highly to moderately impacted at Spring River and Elm Creek, and unimpacted at Lost Creek and Grand Lake as a result of sediment metal concentrations. It also was found that soil metal concentrations were likely sufficient to impact plant populations at all streams. Within the Oklahoma portion of the watershed, the majority of environmental studies, remediation, and restoration efforts by local, state, and federal agencies have been primarily focused within the Tar Creek Superfund Site (TCSS) boundary. Importantly, the findings of this study highlighted the downstream extent of metals contamination as well as the resulting potential toxicities to benthic invertebrates and plants that is present outside of the TCSS boundary. Because the Oklahoma portion of the watershed comprises the jurisdictional lands of ten tribes, these results emphasized the potential tribal loss of use of benthic invertebrates and plants due to their decline in population as a result of metal toxicity. These overall findings provide an important basis for future data needs in assessing metal concentrations in aquatic and terrestrial biota that are consumed by tribal communities within the watershed to determine if certain organisms are unsafe to consume or warrant consumption advisories. This will allow risk assessors and risk managers to better understand the potential loss of use of tribal biological resources as well as improving risk-based decision making to be protective of these resources and tribal human health.