Influence of organic acid and amino acid on cadmium and lead desorption from soil

A study was conducted to investigate the influence of organic acid (citric acid, oxalic acid) and amino acid (histidine) on the desorption of cadmium and lead from artificial contaminated soil in north-east China. Results showed that when the concentration of organic acid and amino acid in desorption solution was relatively low, the presence of organic ligands inhibited the desorption behaviour of Cd. When organic acid and amino acid concentrations were higher (> 2 mmol/L), the presence of organic acid and amino acid obviously promoted Cd desorption. The increment of citric acid, oxalic acid, and histidine concentration significantly (P < 0.01) accelerated the desorption of Pb. The influence of organic acid and amino acid on the desorption behaviour of Cd and Pb followed the same sequence: citric acid > oxalic acid > histidine. This revealed that the organic acids had stronger affinity with heavy metals than that of amino acids. Functional group positions and types were important in determining if an organic acid or an amino acid would complex metals and increase their potential leaching. The results of this work implicated that amendment of organic acid and amino acid would enhance conditionally the bioavailability of heavy metals adsorbed by soils, relying on the type and concentration of organic acid and amino acid in soil solution.