Effects of EDTA and low molecular weight organic acids on soil solution properties of a heavy metal polluted soil

A pot experiment was conducted to study the effects of EDTA and low molecular weight organic acids (LMWOA) on the pH, total organic carbon (TOC) and heavy metals in the soil solution in the rhizosphere of Brassica juncea grown in a paddy soil contaminated with Cu, Zn, Pb and Cd. The results show that EDTA and LMWOA have no effect on the soil solution pH. EDTA addition significantly increased the TOC concentrations in the soil solution. The TOC concentrations in treatments with EDTA were significantly higher than those in treatments with LMWOA. Adding 3 mmol kg(-1) EDTA to the soil markedly increased the total concentrations of Cu, Zn, Pb and Cd in the soil solution. Compared to EDTA, LMWOA had a very small effect on the metal concentrations. Total concentrations in the soil solution followed the sequence: EDTA much greater than citric acid (CA) approximate to oxalic acid (OA) approximate to malic acid (MA) for Cu and Pb; EDTA much greater than MA much greater than CA much greater than OA for Zn; and EDTA much greater than MA much greater than CA > OA for Cd. The labile concentrations of Cu, Zn, Pb and Cd showed similar trends to the total concentrations. (C) 2002 Elsevier Science Ltd. All rights reserved.