title: Effects of pH, organic acids, and competitive cations on mercury desorption in soils.
abstract: The effects of pH, organic acids, and competitive cations on Hg(2+) desorption were studied. Three representative soils for rice production in China, locally referred to as a yellowish red soil (YRS), purplish clayey soil (PCS), and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were, respectively, collected from Jiaxin County, Deqing County, and Xiasha District of Hangzhou City, Zhejiang Province. Most of the added Hg(2+) was adsorbed at low initial concentrations (<2 mg l(-1)). Desorption of the adsorbed Hg(2+) in 0.01M KCl (simulating soil solution) was minimal, but was significantly enhanced by the change of pH, and the presence of organic acids or competitive cations. The desorption of Hg(2+) in the soils decreased with pH from 3.0 to 5.0, leveled off at pH 5.0-8.0, but increased with pH from 7.0 to 9.0. The presence of organic ligands enhanced Hg(2+) desorption in the soils except for YRS, in which the addition of tartaric, malic, or oxalic acid reduced Hg(2+) desorption at low concentrations (<10(-4)M), but Hg(2+) desorption generally increased with organic acid concentration. Citric acid was most effective in increasing Hg(2+) desorption, followed by tartaric acid and malic acid; and oxalic acid was the least effective. Desorption of adsorbed Hg(2+) increased with increasing concentrations of added Cu(2+) or Zn(2+). Applied Cu(2+) increased Hg(2+) desorption more than Zn(2+) at the same loading rate.
  The effects of organic acids and competitive cations on Hg desorption in soil-water system are related to their concentrations, basic chemical properties, and soil properties.
authors.affiliation: MOE Key Laboratory of Environmental, Remediation and Ecosystem Health, College of Natural Resources and Environmental Sciences, Zhejiang University, Hangzhou 310029, Zhejiang, China.
authors.forename: Y D
authors.initials: YD
authors.lastname: Jing
authors.forename: Z L
authors.initials: ZL
authors.lastname: He
authors.forename: X E
authors.initials: XE
authors.lastname: Yang
mesh_terms: D000327:Adsorption; D000383:Agriculture / Q000592:standards; D002264:Carboxylic Acids / Q000737:chemistry*; D002413:Cations, Divalent / Q000737:chemistry; D002681:China; D003300:Copper / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008628:Mercury / Q000032:analysis*; D011786:Quality Control; D012987:Soil / Q000032:analysis* / Q000592:standards; D012989:Soil Pollutants / Q000032:analysis*; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D002413:Cations, Divalent; D012987:Soil; D012989:Soil Pollutants; D003300:Copper; D008628:Mercury; D015032:Zinc