可生物降解具有螯合特性的有机酸增强土壤重金属的可溶性，促进重金属在植物中的积累和重金属-有机酸向土壤下层迁移，降低耕层土壤的生物有效态重金属含量；随着有机酸的生物降解,重金属从金属-有机酸螯合物中释放出来，并进一步转变为难溶态。本课题通过可生物降解有机酸乙二胺二琥珀酸、次氮基三乙酸和柠檬酸等处理，探讨有机酸、重金属、植物之间的相互作用，阐明有机酸促进植物积累土壤重金属的机理；探讨有机酸和重金属及其复合物在土壤中的迁移规律、有机酸在土壤中的降解过程及其影响因子，阐明有机酸生物降解后的重金属形态和生物有效性变化过程，并对施用可生物降解有机酸的环境风险和土壤修复模型的效应等进行综合评估。通过本项目的研究可以为集成高效、安全的重金属污染土壤修复技术提供理论依据。这在重金属对环境污染日趋严重的情况下，具有特别重要的理论和现实意义。

The contamination of soils by heavy metals is one of the most serious environmental problems and has significant implications for human health. Numerous efforts have been made to develop technologies for the remediation of contaminated soils, including ex-situ washing with physical-chemical methods, and the in-situ immobilization of metal pollutants.It is assumed that application of biodegradable organic acids with chelation increases the solubility of heavy metals in soils, their accumulation in plant shoots and migration of metal-chelant complexes, which may result in decrease of bioavailabilable metals in the top soils. The metals may be released from the metal-chelant complexes and transformed into insoluble forms with the biodegradation of chelants in the lower layers of soil profile. The objectives of the proposed project are to study the interactions of biodegradable organic acids (S,S-ethylenediaminedisuccinic acid, nitrilotriacetate and citric acid), heavy metals and plants in soils, and to develop a remediation technology for the cleanup of metal-contaminated soils. The detailed tasks include the following: 1) to investigate the processes of metal transformation from soil compartment to soil solution, metal leaching along soil profiles and organic acid degradation, and the factors affecting these processes. 2) to check the transformation of metal chemical forms and test the bioavailability of heavy metals after the degradation of chelants. 3) to evaluate the potential risks of metals to around soils after organic acid application. Useful information about the potential and drawbacks of this remediation technology would be drawn from the present project for possible future application in the field.