title: Predicting arsenic solubility in contaminated soils using isotopic dilution techniques.
abstract: An isotopic dilution assay was developed to measure radiolabile As concentration in a diverse range of soils (pH 3.30-7.62; % C = 1.00-6.55). Soils amended with 50 mg of As kg(-1) (as Na2HAsO4 x 7H2O) were incubated for over 800 d in an aerated "microcosm" experiment. After 818 d, radiolabile As ranged from 27 to 57% of total applied As and showed a pH-dependent increase above pH 6. The radiolabile assay was also applied to three sets of soils historically contaminated with sewage sludge or mine-spoil. Results reflected the various geochemical forms in which the arsenic was present. On soils from a sewage disposal facility, radiolabile arsenate ranged from 3 to 60% of total As; mean lability was lower than in the equivalent pH range of the microcosm soils, suggesting occlusion of As into calcium phosphate compounds in the sludge-amended soils. In soils from mining areas in the U.K. and Malaysia, radiolabile As accounted for 0.44-19% of total As. The lowest levels of lability were associated with extremely large As concentrations, up to 17,000 mg kg(-1), from arsenopyrite. Soil pore water was extracted from the microcosm experiment and speciated using "GEOCHEM". The solid<==>solution equilibria of As in the microcosm soils was described by a simple model based on competition between HAsO4(2-) and HPO4(2-) for "labile" adsorption sites.
authors.affiliation: School of Life and Environmental Sciences, University of Nottingham, University Park, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Tye
authors.forename: S D
authors.initials: SD
authors.lastname: Young
authors.forename: N M J
authors.initials: NM
authors.lastname: Crout
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: S
authors.initials: S
authors.lastname: Preston
authors.forename: E H
authors.initials: EH
authors.lastname: Bailey
authors.forename: W
authors.initials: W
authors.lastname: Davison
authors.forename: S P
authors.initials: SP
authors.lastname: McGrath
authors.forename: G I
authors.initials: GI
authors.lastname: Paton
authors.forename: K
authors.initials: K
authors.lastname: Kilham
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D004784:Environmental Monitoring; D005544:Forecasting; D007554:Isotopes; D008906:Mining; D008962:Models, Theoretical; D012722:Sewage; D012989:Soil Pollutants; D012995:Solubility
chemical_list: D007554:Isotopes; D012722:Sewage; D012989:Soil Pollutants; D001151:Arsenic