土壤水溶态铜对小白菜的毒害效应及其预测模型

土壤中铜(Cu)重金属的生物毒性/有效性主要取决于它们在土壤液相中含量和土壤溶液的性质。探寻土壤有效态Cu的生物毒害效应,表征量化其与土壤溶液性质关系,可为土壤Cu的环境风险评价提供参考。选取17种典型农田土壤,探讨了有效态Cu(土壤孔隙水以及CaCl_2浸提态)对小白菜生长的毒性效应及其预测模型。结果表明:土壤孔隙水中Cu对小白菜生长10%抑制的毒性阈值值(EC_(10))和50%抑制的毒性阈值(EC_(50)),最大值与最小值相差为14.7和14.6倍;同样,对于CaCl_2提取态Cu的EC_(10)和EC_(50),最大值与最小值相差12.7和7.7倍,表明土壤溶液性质对水溶性Cu对小白菜的毒性阈值影响很大。建立了土壤溶液的重要因子(溶解性有机碳、土壤溶液pH值、电导率、全硫含量、Ca~(2+)、Mg~(2+)、K~+、Na~+)和水溶性Cu阈值之间的多元回归关系,结果显示,土壤溶液性质可以较好地预测水溶性Cu对小白菜的毒性阈值。同时,土壤溶液中Mg~(2+)、K~+和S的含量是控制孔隙水中Cu对小白菜生长毒性的最重要因子,单一的S能分别解释34%的EC_(10)变异,K~+解释26%的EC_(50)变化。本研究结果可为陆地环境中水溶性Cu的风险评价提供基础。

The Toxicity Effect of Soil Soluble Copper on Bok Choy and Its Prediction Model

The phytotoxicity / bioavailability of copper (Cu) in soil mainly depends on its liable portion in soil solution and the soil solution properties. Determination of the phytotoxicity of soil soluble copper as a function of soil solution properties is helpful to develop soil environmental risk assessment guidance for China. The bioassay of bok choy plant growth was performed in 17 representative Chinese agricultural soils to investigate the phytotoxicity of soluble Cu based on soil pore water and CaCl₂ extraction in order to develop empirical models for predicting the soluble Cu phytotoxicity. When considering the toxicity thresholds for Cu in soil pore water, it was found that the effective concentrations that caused 10% biomass growth inhibition (EC₁₀) and 50% inhibition (EC₅₀) represented 14.7 to 14.6 fold differences between the maximum and minimum values. Similarly, the EC₁₀ and EC₅₀ values of Cu extracted by 0.01 mol·L^-1 CaCl₂ had 12.7 to 7.7 fold differences, respectively. These results suggested that the toxicity thresholds of soluble Cu were greatly affected by soil solution properties in a wide range of soils. Meanwhile, the relationships were developed between the important soil solution properties (dissolved organic carbon (DOC), pH, electrical conductivity (EC), S, Ca²⁺, Mg²⁺, K⁺ and Na⁺) and the toxicity thresholds for Cu in a wide range of soils, which indicated that the soluble Cu toxicity on bok choy was predicted well by soil solution properties. Moreover, the multiple regression results showed that Mg, K and S in soil pore water were more important factors controlling Cu toxicity. Single S or K was found to explain 34% (EC₁₀) or 26% (EC₅₀) of variance of the toxicity thresholds, respectively. These quantitative relationships between soluble Cu toxicity and soil solution properties can be helpful for soluble Cu toxicity risk assessment of terrestrial environment.