SORPTION POTENTIAL FOR LEAD, CADMIUM, ZINC, AND ARSENIC TO SELECTED PALEOZOIC STRATA FROM CARTER AND SHANNON COUNTIES, MISSOURI

Current and potential mining exploration in Carter and Shannon Counties, Missouri, have elevated public fear concerning toxic metal contamination in both the Ozark and St. Francois regional aquifers. Data from the present study indicate that selected Paleozoic formations are natural sinks for Pb, Cd, Zn, and As dissolved in groundwater.

Rock samples from cores and/or surface outcrops were collected from the Lamotte Sandstone, Bonneterre Formation, Davis Formation (shale and limestone), Derby-Doerun Dolomite, Potosi Dolomite, and Eminence Dolomite (sandstone and dolomite). Testing consisted of the reaction of two grams of powdered rock from each sample collected with 50 mL of solution containing 10^-4M Pb, Cd, Zn, or As for three and twenty-one days. Solutions were then analyzed using ICP-AES.

Results indicate a reduction of lead from solution in all tests by three orders of magnitude. The Eminence Dolomite and Potosi Dolomite three-day tests were reduced below levels of the Environmental Protection Agency (EPA) drinking water standard (0.015 ppm for lead). Cadmium results indicate a strong correlation between rock type and sorption. In both three and twenty-one day tests, dolomite samples exhibit the highest sorption capacity, while sandstone and shale rock types demonstrate low sorption capacity for Cd. The Potosi Dolomite and Derby-Doerun Formation twenty-one day tests reduced Cd in solution to below the EPA standard of 0.005 ppm. Results from three and twenty-one day tests indicate that arsenic levels were only lowered slightly, with the exception of the Eminence Formation sandstone which lowered arsenic levels by one order of magnitude. Zinc concentrations in all tests were reduced to below the national secondary drinking water regulation of 5 ppm. This study indicates that there is minimal risk of metal contamination in the Ozark and St. Francois regional aquifers due to exploration activity.