The release of arsenic from contaminated sediments and muds

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Abstract
Stream muds and sediments, contaminated with As from industrial waste water were studied under laboratory conditions for release of contaminant to overlying waters. As content of muds was determined initially and simulated reservoirs were prepared from these muds and natural stream water. Systems studied were: anaerobic conditions at 25, 20, 15, 10 and 4.degree. C and aerobic conditions at 20 and 10.degree. C with dissolved O2 (DO) levels of 100, 50, 25 and 10% saturation. Distribution coefficients (dimensionless ratio of Aswater/Asmud) were determined. In aerobic and anaerboic systems, lower temperatures produced smaller distribution coefficients (those in 4-10.degree. C range were about 40% of coefficients at higher 20-25.degree. C range). Little difference was found in distribution coefficients at a given temperature between reservoirs having either 10, 25, 50 or 100% of saturation of dissolved O2. Anaerobic conditions led to levels of As, principally as As+3, about 10-fold higher than concentrations reached with aerobic conditions. Ratio of anaerobic As level/aerobic As level in reservoir waters decreased with decreasing temperature (8.3 at 25.degree. C and 5.6 at 10.degree. C). As in aerobic reservoirs was about 70% aresenate and 20% organic-As. Little pH effect was observed over a pH range of 6.0-8.5. Fe and phosphate concentrations present in the systems were significant factors in establishing As levels. Release of As was dependent on reduction of Fe+3 to Fe+2. Level of As reached in solution was controlled by more complicated phenomena than simple dissolution. Adsorption-desorption equilibria and amount of available As present in muds and sediments influence soluble As concentration found in aqueous phase.

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