WA4 Metals in the Environment: Chemistry and Fate Issues
Room 16A/B, Level 4
8:00 AM - 12:00 PM, Wednesday, 12 November 2003
Chair: Bell, Russell ,
Co-chair: Campbell, Peter ,
(352) Speciation of inorganic arsenic in natural and synthetic waters: redox transformations and ligand-metal complexation.
Redman, A1, Macalady, D2, 1 HydroQual, Inc, Camillus, NY2 Colorado School of Mines, Golden, CO
ABSTRACT- Arsenic toxicity and mobility is controlled by its speciation in aquatic environments. In laboratory studies with natural and synthetic waters that were open to the atmosphere, reduction of arsenate (As(V)) to arsenite (As(III)) was observed during 96 hour batch tests. Filtered, NOM-rich (20 mg/L DOC) raw natural water samples from a stock solution of Black River water in upper peninsula Michigan demonstrated variable reactivity towards arsenic reduction along with variable DOC characteristics during a 6-month study period. Filter sterilization, the presence of AgCl(s) and the addition of strongly complexing ligands (EDTA and phosphate) inhibited As(V) reduction, implying a microbial component to the observed arsenate reduction. In contrast, oxidation of As(III) to As(V) was not observed in these open systems. In addition to arsenic redox transformations, this study focused on complexation of inorganic arsenic to hydrous aluminum(III) in DOC-rich systems. In Black River water, NOM-aluminum-arsenate complexes were present as particulate and colloidal phases whereas, in synthetic waters with model ligands (5-sulfosalycilate, EDTA, and citrate) both soluble and colloidal phases were observed using analytical chemistry and spectroscopic techniques at pH 5 and 7. Phosphate formed citrate-aluminum-phosphate complexes to a much greater extent than arsenate in 1:1:1 solutions at pH 7 and arsenite did not form complexes with NOM-aluminum systems. Dissolved NOM-metal-arsenic complexes are not expected to be a major soluble arsenic species in NOM-rich waters. Future research should be conducted to determine the extent of these complexes in natural and synthetic waters under a wider range of conditions and the subsequent bioavailability of inorganic arsenic and phosphate in these systems.
Key words: Aluminum, Arsenic, Phosphate, Speciation