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THE SIGNIFICANCE OF ARSENIC-BOUND SOLIDS IN DRINKING WATER DISTRIBUTION SYSTEMS
Citation:
Lytle*, D A., T J. Sorg*, AND C M. Frietch*. THE SIGNIFICANCE OF ARSENIC-BOUND SOLIDS IN DRINKING WATER DISTRIBUTION SYSTEMS. AWWA's WQTC, Seattle, WA, 11/1/2002.
Description:
Sorption, co-precipitation, and oxidation-reduction reactions of arsenic at the sorbent-water interface are importent factors affecting the fate and transport of arsenic in aqueous systems. Numerous studies have concluded that arsenite (As(III) is more soluble and mobile than arsenate (As(V), though differences exist in reactivity and stability of As(III) and As(V) at different solid-water interfaces. Iron surfaces are particularly effective at adsorping arsenic in aqueous systems. As a result, the structure of arsenate and arsenite sorption and co-precipitation on iron oxide surfaces has been extensively investigated. Results have shown that the sorption of arsenic is affected by many factors including pH, water chemistry, amount and form of iron present, and the presence of competing ions such as phosphate and silicate. It is, therefore, reasonable to assume that iron-based solids and potentially other solids that accumulate in drinking water distribution systems, such as corrosion by-products, precipitated minerals and sediment, could have a tendency to adsorb arsenic. These solids could subsequently concentrate arsenic present in water entering the distribution system. Disturbances to distribution systems brought about by water quality changes or hydraulic changes can lead to arsenic release back into the bulk water. The term "release" when used in association with arsenic is used in this manuscript to describe the introduction of arsenic (particulate or dissolved form) into the bulk water from distribution solids by any mechanism (e.g., desorption, particulate transport, dissolution, etc.). Arsenic release could result in elevated arsenic levels at the consumer's tap.