title: Effect of Cl-, SO4(2-), and fulvate anions on Cd2+ free ion concentrations in simulated rhizosphere soil solutions.
abstract: The binding between heavy metals and corresponding ligands affects their chemical behavior and toxicity in soil environments. The mechanisms of competitive complexation and/or chelation between Cd(2+) free cations and preferential concentrations of Cl(-), SO(4)(2-), and fulvate anions were investigated in simulated soil solutions at pH 4.00, 5.00 and 6.00. The Cd(2+) concentrations were calculated by a proposed equation, simulated by MINTEQ software, and directly determined by ion chromatography (IC). When Cl(-)/Cd or Cl(-)/Cd with SO(4)(2-)/Cd molar ratios of 3.18 and 4.05, the differences among Cd(2+) concentrations calculated by equation, simulated by MINTEQ software, and directly determined by IC were not significant, but their differences were pH independent for considering Cl(-)/Cd molar ratio and pH dependent for Cl(-)/Cd and SO(4)(2-)/Cd molar ratios. When Cl(-)/Cd, SO(4)(2-)/Cd, and additional FA/Cd molar ratios of 3.18 and 4.05, the Cd(2+) concentrations calculated by equation were significantly larger than those simulated by MINTEQ and determined by IC because in simulation and determination of Cd(2+) concentrations by IC, the complexation of Cd(2+) with ligands to form CdCl(+), CdSO(4), FACd(+) and FA(2)Cd had been considered, whereas in calculation this complexation aspect was ignored. Though IC can be used to determine Cd(2+) concentration in rhizosphere soil solutions ion chromatographic peak of Cd(2+) in 0.1M HCl saturation extract of slightly acidic soil and in deionized distilled water saturation extract of acidic soils still may be shielded by the vicinal chromatographic peaks of Mg(2+) and Mn(2+), respectively. The Cd(2+) concentrations in rhizosphere soil solutions of acidic or slightly acidic soils calculated by equation and/or simulated by Model may thus be used as potential alternatives for those determined by IC.
authors.affiliation: Department of Environmental Engineering and Management, Chaoyang University of Technology, Wufong Township, Taichung County 41349, Taiwan, ROC.
authors.forename: Shui-Wen
authors.initials: SW
authors.lastname: Chang Chien
authors.forename: Jui-Hung
authors.initials: JH
authors.lastname: Liao
authors.forename: Min-Chao
authors.initials: MC
authors.lastname: Wang
authors.forename: Madhava Rao
authors.initials: MR
authors.lastname: Mannepalli
mesh_terms: D001578:Benzopyrans / Q000737:chemistry; D001667:Binding, Competitive; D002104:Cadmium / Q000032:analysis* / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry; D002852:Chromatography, Ion Exchange; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D012987:Soil / Q000032:analysis*; D012989:Soil Pollutants; D013431:Sulfates / Q000737:chemistry
chemical_list: D001578:Benzopyrans; D002712:Chlorides; D008024:Ligands; D012987:Soil; D012989:Soil Pollutants; D013431:Sulfates; D002104:Cadmium; C005023:fulvic acid