CURRENT STATE OF METAL TOXICITY AND REMEDIATION IN THE TRI-STATE MINING DISTRICT, USA

Mining operations in the world-class Tri-State Mining District of Kansas, Missouri and Oklahoma (TSMD), ended by 1970. Non-ore waste rock was disposed of near production centers. Emissions from smelters dispersed metals into top soils. Post-mining subsidence associated with abandoned mine shafts disturbed the landscape. In the early 1980s, the USEPA designated Tar Creek (OK), Cherokee County (KS) and Oronogo-Duenweg (MO) as Superfund sites. Impaired stream segments, sites added to the National Priorities List and brownfield areas designations followed. Areas within the TSMD still exhibit Cd, Pb, and Zn concentrations exceeding safe levels. Data show that sediment metal contents have the following common features: (1) Pb and Zn concentrations vary by up to three orders of magnitude, (2) median values for Cd, Pb and Zn content in sediments and soils were similar among studies, (3) median metal values were at or above guidelines recommended for aquatic habitats, and (4) highest Pb and Zn concentrations spatially are associated with the former mining and smelting centers. Increased levels of contaminants within aquatic sediments has been correlated with a decrease in biodiversity, and population sizes of invertebrates, mussels and fishes from stream reaches located downstream of mining activities. Because invertebrates and fish are important food sources, the potential for biomagnification and health impacts is considered high. Accumulation of Pb and other metals is consistent with studies from other regions. Birds studied in the TSMD had increased blood, liver and kidney concentrations of Pb, Cd and Zn compared to birds from reference sites. These birds exhibited a greater than 50% decrease in ALA-D activity which, combined with blood lead concentrations warrants classifying the birds examined as having been exposed to toxic Pb levels. Zinc was noted to have the greatest impact in waterfowl. The above observations imply that mine wastes remain a problem and further remediation is needed. Through well planned remediation, these sites can be decontaminated by applying procedures such as constructed passive wetlands combined with phytoremediation and/or using an enhanced treatment, such as aerated wetlands. Continued monitoring and remedial practices are needed until affected areas recover completely.