ARSENIC SEQUESTRATION IN NATURALLY OCCURRING BIOGENIC PYRITE IN THE HOLOCENE FLUVIAL AQUIFERS IN UPHAPEE WATERSHED, MACON COUNTY, ALABAMA

Arsenic (As) contamination in groundwater is a major concern worldwide including the United States. Arsenic is a toxic metalloid and presence of this trace element is very common as minor constituent in pyrite (FeS₂) formed in low temperature environments. This study found pyrite crystals are forming naturally in the Holocene fluvial aquifers in Uphapee watershed, Macon County, Alabama. Results showed that the pyrite grains are mostly arsenian-pyrite and contain up to 1 weight% of arsenic. Pyrite crystals are developed as individual cube and octahedron as well as aggregates. Most of the grain’s diameter ranges 20–200 μm, whereas larger grains are visible and as large as 1 cm. Pyrite grains are often associated with lignitic wood which is organic matter and served as one of the most available electron donors. The lignitic woods are very rich in gallium (Ga) and germanium (Ge). Groundwater from the wells as well as springs showed the arsenic concentration is 1-2 μg/L indicating that arsenic was removed from groundwater while formation of the biogenic pyrite crystals.