北京城近郊区土壤中Cd的释放、形态转化与演变趋势

Release,form transformation and evolutionary trend of Cd in soils in the suburbs of Beijing China.

在对北京城近郊区主要类型土壤(潮土和褐土)中Cd形态分析的基础上,研究pH与土壤中Cd的释放量及其形态转化的关系。结果表明:潮土和褐土中Cd的释放量曲线都呈下凹的弧形,在pH=6～7之间释放量最低。pH对土壤中Cd释放的影响,其本质是土壤中Cd的化学形态发生了变化,各形态间的转化以水溶态为中介体。所有的形态转化中,pH对交换态和碳酸盐结合态影响最大,且这两者之间的转化对生物有效量起决定性作用。进而根据北京城近郊区土壤中生物有效Cd的分布状况,结合北京市近12年监测的大气pH值,对北京城近郊区土壤Cd污染进行预警。

On the basis of an analysis of the chemical forms of Cd in the main types of soil （fluvo-aquic soil and cinnamon soil） in the suburbs of Beijing, the relations of pH values to the release rate of Cd in fluvo-aquic soil and cinnamon soil and its form transformation are studied. The results show that the Cd release curve of fluvo-aquic soil and cinnamon soil always occurs as an arc concave downward and that the Cd release rate is lowest at pH=6-7. The essence of the influence of pH on Cd release from soils is the change in chemical form of Cd in soils. The water-soluble phase is taken as a mediator in the transformation of various chemical forms of Cd. In all the transformations of Cd chemical forms, the influences of pH on the exchange state and carbonate binding state are greatest, and transformation between the two states plays a decisive role in the bioavailable dose. And according to the distribution of bioavailable Cd in soils in the suburbs of Beijing, combined with the atmospheric pH values that have been monitored in Beijing in the past 12 years, early-warning of Cd pollution of soils in the suburbs of Beijing have been carried out.