title: Different low-molecular-mass organic acids specifically control leaching of arsenic and lead from contaminated soil.
abstract: Low-molecular-mass organic acids (LMMOA) are of key importance for mobilisation and fate of metals in soil, by functioning as ligands that increase the amount of dissolved metal in solution or by dissociation of metal binding minerals. Column leaching experiments were performed on soil polluted with As and Pb, in order to determine the specificity of LMMOA related release for individual elements, at varying organic acid concentrations. Acetic, citric and oxalic acids were applied in 12h leaching experiments over a concentration range (0.5-25 mM) to soil samples that represent organic and mineral horizons. The leaching of As followed the order: oxalic>citric>acetic acid in both soils. Arsenic leaching was attributed primarily to ligand-enhanced dissolution of mineral oxides followed by As released into solution, as shown by significant correlation between oxalic and citric acids and content of Al and Fe in leaching solutions. Results suggest that subsurface mineral soil layers are more vulnerable to As toxicity. Leaching of Pb from both soils followed the order: citric>oxalic>acetic acid. Mineral soil samples were shown to be more susceptible to leaching of Pb than samples characterised by a high content of organic matter. The leaching efficiency of citric acid was attributed to formation of stable complexes with Pb ions, which other acids are not capable of. Results obtained in the study are evidence that the extent of As and Pb leaching in contaminated surface and subsurface soil depends significantly on the types of carboxylic acid involved. The implications of the type of acid and the specific element that can be mobilised become increasingly significant where LMMOA concentrations are highest, such as in rhizosphere soil.
authors: Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Czech Republic. Electronic address: ash@af.czu.cz.
authors: Christopher
authors: C
authors: Ash
authors: Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Czech Republic.
authors: Václav
authors: V
authors: Tejnecký
authors: Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Czech Republic.
authors: Luboš
authors: L
authors: Borůvka
authors: Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Czech Republic.
authors: Ondřej
authors: O
authors: Drábek
mesh_terms: D019342:Acetic Acid / Q000737:chemistry; D000144:Acids, Acyclic / Q000737:chemistry*; D001151:Arsenic / Q000737:chemistry*; D019343:Citric Acid / Q000737:chemistry; D018153:Czech Republic; D007854:Lead / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry; D019815:Oxalic Acid / Q000737:chemistry; D058441:Rhizosphere; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000737:chemistry*; D012996:Solutions
chemical_list: D000144:Acids, Acyclic; D008903:Minerals; D012987:Soil; D012989:Soil Pollutants; D012996:Solutions; D019343:Citric Acid; D007854:Lead; D019815:Oxalic Acid; D001151:Arsenic; D019342:Acetic Acid
keywords: Carboxylic acid; Column leaching experiment; Heavy metal; Metalloid; Soil contamination