梯度薄膜扩散技术(DGT)与传统化学方法评估黑麦草吸收Cd的对比

Comparison of the method of diffusive gradients in thin films with traditional chemical extraction techniques for evaluating cadmium bioavailability in ryegrass

为研究不同方法评估黑麦草吸收Cd的效果,采集了16个不同理化性质实际Cd污染土壤,盆栽试验种植黑麦草,采用梯度薄膜扩散技术(DGT)测定黑麦草根际土Cd的生物有效性,并与离心法采集土壤溶液、乙酸(HAc)和乙二胺四乙酸二钠(EDTANa2)3种传统提取方法所提取土壤有效态Cd含量进行比较,研究其与黑麦草地上部和地下部Cd含量的相关关系.结果表明,DGT提取的土壤有效态Cd含量与黑麦草中Cd含量的相关性显著高于化学提取法.运用多元统计分析研究土壤pH、阳离子交换量(CEC)、有机质(OM)和土壤颗粒组成等理化指标的影响,提取出两种主成分因子,建立了多元回归模型.第一主成分与OM和黏粒(clay)之间呈显著相关,定义为土壤中影响重金属生物有效性的"有机指标",第二主成分则与土壤pH和CEC相关程度较高,定义为土壤中影响重金属生物有效性的"无机指标".研究表明,第二主成分显著影响了3种化学方法构建的预测模型,而DGT技术综合了两种主成分对土壤有效态Cd含量的影响,所构建的模型几乎不受土壤基本理化性质的影响,说明DGT分析法是一种预测黑麦草吸收Cd的较好方法.

To test the predictive capabilities of different methods with regard to cadmium accumulation in ryegrass, 16 natural Cd contaminated soils with diverse properties were collected, and ryegrass was grown on these soils by pot experiment. Rhizosphere soils of ryegrass were collected and Cd bioavailable concentrations were determined in soil solution, acetic acid （HAc） extraction, ethylenediaminetetraacetic acid disodium salt （EDTANa2 ） extraction, and by diffusive gradients in thin films （DGT）. Correlation analyses were performed to study the relationship between Cd bioavailable concentrations and Cd in shoots and roots of ryegrass. Simple linear regression analyses showed that the correlation coefficients between DGT measured Cd bioavailable concentrations and Cd in shoots and roots of ryegrass were significantly higher than those obtained by other techniques. Multivariate analyses were used to assess the impact of pH, cation exchanged capacity （ CEC）, soil organic materials （OM） and texture. Two principal components were extracted and the linear regression models were established. The first was well correlated with OM and clay, which was defined as the representative of ＂organic matter＂. The second primarily correlated with pH and CEC, which was defined as the representative of ＂inorganic ions＂. Results showed that the second principal component had significant effects on prediction models built by 3 chemistry methods, but there was little effect on the prediction model based on DGT technique. DGT measurement incorporated the main factors affected bioavailability, and could better predict the potential runoff of Cd from soil and the accumulation of Cd in ryegrass than traditional chemical methods.