title: Complexation of arsenite with humic acid in the presence of ferric iron.
abstract: In the presence of iron (Fe), dissolved organic matter (DOM) may bind considerable amounts of arsenic (As), through formation of Fe-bridged As-Fe-DOM complexes and surface complexation of As on DOM-stabilized Fe-colloids (collectively referred to as As-Fe-DOM complexation). However, direct (e.g., chromatographic and spectroscopic) evidence and fundamental kinetic and stability constants have been rarely reported for this As-Fe-DOM complexation. Using a size exclusion chromatography (SEC)-UV-inductively coupled plasma mass spectrometry (ICP-MS) technique, arsenite (As(III))-Fe-DOM complexation was investigated after adding As(III) into the priorly prepared Fe-DOM. A series of evidence, including coelution of As, Fe, and DOM from the SEC column and coretention of As, Fe, and DOM by 3 kDa MWCO centrifugal filtration membrane, demonstrated the occurrence of As(III)-Fe-DOM complexation. The kinetic data of As(III)-Fe-DOM complexation were well described by a pseudofirst order rate equation (R(2) = 0.95), with the rate constant (k') being 0.17 ± 0.04 1/h. Stability of As(III)-Fe-DOM complexation was characterized by apparent stability constant (K(s)) derived from two-site ligand binding model, with log K(s) ranging from 4.4 ± 0.2 to 5.6 ± 0.4. Considering the kinetics (within hours) and stability (similar to typical metal-humates) of As(III)-Fe-DOM complexation, this complexation needs to be included when evaluating As mobility in Fe and DOM rich environments.
authors.affiliation: Department of Chemistry & Biochemistry and Southeast Environmental Research Center, Florida International University , Miami, Florida 33199, United States.
authors.forename: Guangliang
authors.initials: G
authors.lastname: Liu
authors.forename: Aymara
authors.initials: A
authors.lastname: Fernandez
authors.forename: Yong
authors.initials: Y
authors.lastname: Cai
mesh_terms: D018053:Arsenites / Q000737:chemistry*; D004785:Environmental Pollutants / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis*; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical
chemical_list: D018053:Arsenites; D004785:Environmental Pollutants; D006812:Humic Substances; D007501:Iron; C015001:arsenite