PARENT SESSION
PM9 - Arsenic Fate & Effects
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P292) Prevalence and speciation of arsenic in natural water impacted by mining and agriculture.
Bednar, Anthony*,1,2, Garbarino, John2, Ranville, James1, Wildeman, Thomas1, 1 Colorado School of Mines, Department of Chemistry and Geochemistry, Golden, CO, US2 U.S. Geological Survey, National Water Quality Laboratory, Denver, CO, US
ABSTRACT- The present authors have investigated redox transformations and speciation of arsenic in various aqueous environments, including groundwater, natural surface water, agricultural runoff, and acid mine drainage (AMD). These waters can be impacted by natural sources of arsenic; however, anthropogenic sources related to mining and agricultural use of organoarsenicals can greatly influence the concentration and speciation of arsenic in water. The toxicity, mobility, and removal mechanisms of arsenic are dependent on its redox speciation. The present studies were begun in part to reconcile field and laboratory speciation method results, which often showed a discrepancy in arsenite and arsenate concentrations. Investigations of arsenic-contaminated water samples lead to development of speciation and preservation methods that were best suited to each sample matrix. Results, which show the vast speciation differences in AMD, agricultural surface water, and groundwater, are used to explain the geochemical controls on arsenic speciation in natural-water samples. Thermodynamics control arsenic redox speciation in AMD where the iron (II)/(III), however, when there is not a dominant redox couple disequilibrium can occur. Furthermore, ground and surface water in agricultural areas often have elevated arsenic levels caused by the use of organoarsenicals, which also affects speciation through the introduction of various organoarsenic species. The effects of photochemistry on arsenic speciation also was investigated.
Key words: arsenic, redox, mining, agriculture