天然有机质（NOM）对土壤重金属生物有效性具有重要影响，施用含NOM的有机物料是重金属活性调控的重要措施。项目采用NOM分子量连续超滤分级和传统可溶性分级方法，结合光谱学、核磁共振、化学分析等手段，对不同来源NOM及其组分进行分离表征，以污染现象普遍、危害突出、移动性差异大的镉、铅两种元素为对象，以易累积镉大宗粮食作物水稻作为植物代表，以小鼠和蚯蚓作为试验动物，采用水稻盆栽试验、in vivo动物实验和in vitro模拟试验，结合室内化学分析，同步研究NOM及其分子组分影响土壤中镉、铅动植物生物有效性的表观效应，揭示NOM生物有效性表观效应与其分子组分的关系，探讨NOM活化或钝化土壤镉、铅的分子组成临界阈值；分析NOM对土壤性质、土壤溶液有机物分子组成、镉/铅化学行为的影响，阐释NOM调控土壤镉、铅生物有效性机理。深化对NOM生物地球化学行为的认识；为土壤镉、铅污染修复提供科学依据。

Natural organic matter (NOM), widely distribute in the environment, plays important role in regulating the bioactivity of heavy metals in soil, and application of organic substances containing NOM is an often-used and easy way to deal with soil heavy metal pollution. In this proposal the bioactivities of cadmium and lead in soils to both rice and humans as influenced by NOM are to be studied simultaneously by means of chemical analyses, rice pot experiments, in vivo and in vitro animal experiments. The separation and characterization of NOM and its components will be done by ultrafiltration, solubility classification followed by spectroscopy and NMR and chemical analyses, and influences of NOM and its components on the bioactivities of Cd and Pb to plants and humans are then studied to elucidate the overall effects of NOM in relation to its components. The threshold values of NOM composition for activation or deactivation of Cd, Pb bioactivity in soil will be established. The mechanisms of NOM in regulating soil Cd and Pb are to be elucidated through the analyses of soil properties, organic compositions, soil chemical behaviors of Cd and Pb as influenced by NOM and its different components, with the purposes for better understanding the biogeochemical behaviors of NOM and for the risk control of soil Cd, Pb pollution.