Edible wild plants growing in contaminated floodplains: implications for the issuance of tribal consumption advisories within the Grand Lake watershed of northeastern Oklahoma, USA.

Metal releases from the Tri-State Mining District (TSMD) that is located in southwestern Missouri, southeastern Kansas, and northeastern Oklahoma, have contaminated floodplain soils within the Neosho and Spring river watersheds of the Grand Lake watershed. Since the Oklahoma portion of the watershed lies within ten tribal jurisdictions, the potential accumulation of metals within plant species that are gathered and consumed by tribal members, as well as the resulting metal exposure risks to tribal human health, was a warranted concern for further investigation. Within this study, a total of 36 plant species that are commonly consumed by tribes were collected from floodplain areas that were previously demonstrated to have elevated soil metal concentrations relative to reference sites. A significant, positive correlation was shown for metal concentrations in plant tissues versus soil (n = 258; Cd: R = 0.72, p = 0.00; Pb: R = 0.52, p = 0.00; and Zn: R = 0.70, p = 0.00). Additionally, a significant difference in metal concentration distributions existed between reference and impacted plant samples (n = 210, p = 0.00 for all metals). These results proved that floodplain soils are a major contamination pathway for metal accumulation within plants, and the source of metal contamination is the result of mining releases from the TSMD. Metal accumulation within plants was found to vary according to specific metal and plant species. The lowest dietary exposure out of all plant organs sampled were associated with fruit, whereas the highest was associated with roots, stem/leaves, and low-lying leafy greens. Metals in plants were compared to weekly dietary intake limits established by the Joint FAO/WHO Expert Committee on Food Additives. Based on specific serving sizes established within this study for tribal children and adults, many plant species had sufficient concentrations to warrant tribal consumption restrictions within the floodplains of Elm Creek, Grand Lake, Lost Creek, Spring River, and Tar Creek. Importantly, these results highlighted the necessity for the issuance of plant consumption advisories for tribal communities in the watershed. A consumption restriction guide on the number of allowable servings of each species per week at specific streams was developed within this study for tribal children and adults. Results also demonstrated that soil metal concentrations do not need to be exceptionally elevated relative to reference sites in order for plants to accumulate sufficient metal concentrations to exceed dietary limits for one serving. Therefore, the exposure risk associated with the consumption of plants cannot be accurately predicted solely from metal concentrations within soils, but must be based on metal concentrations within specific plant tissues on a site-by-site basis. A weekly consumption scenario was created within this study in order to better understand the potential metal dietary exposures to child and adult tribal members who consume multiple servings of multiple plant species per day, as well as benthic invertebrates and fish from the watershed. These findings demonstrated that plants pose a greater consumption exposure risk for tribal members than benthic invertebrates or fish. Therefore, without the consideration of exposure risks associated with the consumption of plants within future human health risk assessments, tribal health risks will be severely underestimated.

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

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-QCd,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.