GEOCHEMICAL ENVIRONMENT OF ARSENIC IN STREAM WATER AND SOIL SOLUTION

Dendrogram correlation analyses of arsenic concentrations from stream water and soil solution from two New Jersey watersheds indicate that high concentrations of arsenic in stream/soil water are generally related to a reducing environment, where concentrations of iron, manganese, and dissolved carbon tend to be high. Quantitative mineral X-ray analyses indicate that these watersheds tend to have visible amounts of pyrite and siderite in shallow aquifers. Glauconite, a common clay mineral formed in the low-oxygen marine environment, is particularly abundant at one of the studied watersheds. Our analyses of the elemental composition of the glauconite concentrated samples revealed rich arsenic in these samples on average. Further sequential extraction studies also indicate that the arsenic oxyanions are mainly bound to Fe-Mn oxyhydroxide and organic matter, and less to the carbonate and exchange sites from these samples. The explanation is that reducing environment facilitates the release of Fe²⁺ and AsS^2- from the arsenopyrite and other common arsenic minerals. Comparison of soil solution from lysimeter and stream water indicate that soil solution generally have higher arsenic concentrations (up to 7.7 ppb) than stream water due to the dilution of stream water by runoff and limited anthropogenic input of arsenic. Strong correlation between phosphorus and arsenic in the watersheds is likely due to the chemical similarity between the PO₄³⁻ and AsO­₄³⁻ anionic groups and their competitions for the anion adsorption sites on colloids.