基于薄膜扩散梯度技术的复合污染土壤镉的生物有效性研究

Diffusive Gradients in Thin Films(DGT)Technique for Evaluation of Cadmium Bioavailability in Heavy Metal Co-polluted Soils

以两种典型的陆生植物小麦和玉米为供试材料,采用盆栽实验生物富积方式,对比研究了薄膜扩散梯度(DGT)技术与5种传统的化学提取方法评价铅(Pb)复合存在下土壤镉(Cd)的生物有效性。结果表明,Cd污染土壤中Pb的存在促进两种植物对Cd的吸收,并随Pb浓度的增加其促进作用更趋明显;DGT技术测定的土壤有效态Cd含量随土壤Pb浓度的增加而显著增加,土壤溶液中Cd的浓度和4种单一提取剂(醋酸、氯化钙、醋酸钠和乙二胺四乙酸)提取的土壤有效态Cd含量均与DGT技术表现出类似的变化趋势,从动力学和静态平衡两种角度揭示了土壤Pb的存在增强Cd的生物有效性;Pearson回归分析显示,6种方法表征的土壤有效态Cd含量均与两种植物体内Cd的含量呈显著正相关,但DGT、土壤溶液和CaCl2的相关系数明显高于其他3种化学提取方法。结果显示,DGT技术与传统方法(土壤溶液法和CaCl2提取法)均可用于预测土壤Cd的生物有效性。

Diffusive gradients in thin films（DGT） technique has recently been recommended as a tool for predicating heavy metal availabili- ty in soils. However, there are still debates on its applicability. In this study, pot experiments were conducted to measure Cd bioavailability under combined pollution of Cd and Pb in soils. The Cd hioavailability was then evaluated by DGT and five chemical extraction methods in- cluding soil solution, HAc, EDTA, CaCl2 and NaAc）. Presence of Pb enhanced Cd uptake by shoots and roots of wheat and maize in Pb- and Cd-contaminated soils. Such enhancement of plant Cd uptake increased with increasing Pb concentrations. Correspondingly, bioavail- able Cd concentrations measured with DGT （CDGT）, soil solution Cd （CsoL）, and HAc, EDTA, NaAc and CaC12- extractable Cd all showed similar trends as plant Cd uptake. Pearson correlation analysis showed that significant and positive correlations existed between soil bioavailable Cd estimated by each method and Cd concentrations in two plants, but the correlation coefficients of DGT, CsoL and CaC12 were greater than those of HAc, EDTA and NaAc. These results suggest that DGT and traditional extraction methods（soil solution and CaC12） could be used to predict soil Cd bioavailability to plants.