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SPECIATION AND PRESERVATION OF INORGANIC ARSENIC IN DRINKING WATER SOURCES USING IC-ICP-MS
Citation:
Gallagher, P A., C A. Schwegel, J A. Shoemaker, J T. Creed, AND X. Wei. SPECIATION AND PRESERVATION OF INORGANIC ARSENIC IN DRINKING WATER SOURCES USING IC-ICP-MS. JOURNAL OF ENVIRONMENTAL MONITORING 3(4):371-376, (2001).
Description:
The native distribution of As(III) and As(V) in drinking water supplies can influence the treatment removal strategy. The stability of As(III) and As(V) in iron rich drinking waters can be affected by the formation of Fe precipitates (Fe oxides and/or hydroxides designated by "FeOOH"). These precipitates (PPT) can form during the transportation of the sample to the laboratory for arsenic speciation analysis. The analysis of the precipitate indicates considerable loss of the aqueous arsenic species (Asaq) to the solid phase "FeOOH" PPT. Studies of laboratory reagent water containing both As(III) and Fe(III) indicate that the reslting "FeOOH" PPT contained a mixture of As(III) and As(V) with near quantitative removal of the Asaq in 18hrs. The corresponding aqueous fraction after filtration through a 0.45u filter was composed primarily of As(V). The formation of "FeOOH" PPT and the loss of Asaq to the PPT can be virtually eliminated by the use of EDTA which sequesters the Fe(III). Reagent water fortified with Fe(III), As(III) and EDTA produced less than a 1ppb change in the As(III)aq concentration over 16 days.
The EDTA treatment was also tested on three well waters with different native As(III)/As(V) ratios. The native distribution of As(III)/As(V) was stabilized over a period of 10 days with worst case conversion of As(III) to As(V) of 2 ppb over a 30 day period. All well waters not treated with EDTA had dramatic losses (a factor of 2-5) of Asaq in less than one day. These results indicated that EDTA preservation treatment can be used to preserve Asaq in waters wherever the predominate species is the reduced form [As(III)] or in waters which the predominate species is the oxidized form [As(V)]. This preliminary investigation of EDTA to preserve As species in Fe rich waters indicates stability can be achieved for greater than 14 days.