Investigation of sequential and enzymatic extraction of arsenic from drinking water distribution solids using ICP-MS

Abstract

A sequential extraction approach was utilized to estimate the distribution of arsenite [As(III)] and arsenate [As(V)] on iron oxide/hydroxide solids obtained from drinking water distribution systems. The arsenic (As) associated with these solids can be segregated into three operationally defined categories (exchangeable, amorphous and crystalline) according to the sequential extraction literature. The exchangeable As, for the six drinking water solids evaluated, was estimated using 10 mM MgCl₂ and 10 mM NaH₂PO₄ and represented between 5–34% of the total As available from the solid. The amorphously bound As was estimated using 10 mM (NH₄)₂C₂O₄ and represented between 57–124% of the As available from the respective solid. Finally, the crystalline bound As was estimated using titanium citrate and this represented less than 1.5% of the As associated with the solids. A synthetic stomach/intestine extraction approach was also applied to the distribution solids. The stomach fluid was found to extract between 0.5–33.3 μg g⁻¹ As and 120–2360 μg g⁻¹ iron (Fe). The As concentrations in the intestine fluid were between 0.02–0.04 μg g⁻¹ while the Fe concentration ranged from 0.06–0.7 μg g⁻¹ for the first six drinking water distribution solids. The elevated Fe levels associated with the stomach fluid were found to produce Fe based precipitates when the intestinal treatment was applied. Preliminary observations indicate that most of the aqueous Fe in the stomach fluid is ferric ion and the observed precipitate produced in the intestine fluid is consistent with the decreased solubility of ferric ion at the pH associated with the intestine.