外源铅在4种土壤中的老化特征及对土壤化学性质的影响

采用化学提取和梯度薄膜扩散技术(DGT)探究外源铅(Pb)在不同类型土壤中老化的形态变化规律,考察了外源Pb添加对土壤pH、阳离子交换量(CEC)和可溶性有机质(DOC)等的影响,初步建立了土壤Pb生物有效性的预测模型.结果表明:EDTA提取态Pb含量随老化时间的延长而降低;准二级动力学方程可较好地表达有效态Pb在老化过程中的动力学特征,方程的参数反映了Pb处理浓度的增加延长了老化达平衡的时间,所有供试土壤的EDTA提取态Pb含量在3个月后基本达到老化平衡;不同提取态Pb含量和变化不同,CaCl_2提取态Pb含量最少、变化最大,HNO_3提取态Pb含量变化最小;外源Pb添加会降低土壤pH,但对CEC和DOC无明显影响;随着老化时间的延长,土壤pH升高,CEC无明显变化,DOC显著降低;土壤水溶态Pb和DOC可用来预测DGT测定的有效态Pb含量,预测效果较好.

Aging process of Pb affects the chemical properties of four types of soil

Chemical single extraction methods and diffusive gradients in thin-films technique (DGT) were coupled to investigate the change of Pb speciation in different aging soils. And the influence of exogenous Pb on the soil pH value, cation exchange capacity (CEC) and dissolved organic carbon (DOC) was examined. Also, a regression prediction model of Pb bioavailability was built. The results showed that the concentration of EDTA extractable Pb decreased with aging time. Pseudo-second-order model fitted the dynamic process of available Pb well, of which the parameters showed that the increase of exogenous Pb concentration would prolong the time to reach equilibrium, and the concentration of EDTA extractable Pb in all treatments could reach equilibrium after 3 months. Moreover, different extracts showed different effects. The concentration of CaCl₂ extractable Pb was the lowest among all the extractable Pb, which also changed fastest, while the concentration of HNO₃ extractable Pb changed slowest. Besides, the addition of exogenous Pb reduced soil pH, but had no effect on CEC and DOC. The pH value decreased with aging time. Meanwhile, no significant differences were found for the CEC value, but DOC decreased significantly with aging time. Also, the concentration of H₂O extractable Pb and DOC can predict available Pb measured by DGT.