基于水稻根伸长的不同土壤中镉（Cd）毒性阈值（ECx）及预测模型

【目的】虽然土壤中镉（Cd）污染对水稻的生态风险受关注已久，然而大量研究集中在基于稻米中Cd限量标准的健康风险研究，而针对土壤中Cd污染的生态风险阈值研究较少。研究通过ISO11269-1根伸长毒性测试方法，测定不同性质土壤中Cd对水稻的毒性阈值（ECx，x=10，50）及其预测模型，以期为基于生态毒理效应的中国土壤Cd污染基准值的修订提供参考。【方法】采用中国8种不同性质农田土壤和3种不同Cd敏感性差异的水稻品种（T优167，T167；陆两优28，L28；湘早45，X45）为试材，每种土壤添加7个Cd浓度，通过ISO11269-1根伸长测试方法，测量水稻根的相对伸长量，并结合Log-Logistic分布函数模型测定不同土壤中水稻Cd毒性的剂量-效应关系、毒性阈值（ECx, x=10, 50）及其预测模型。【结果】随着土壤Cd浓度的增加，不同土壤中水稻的相对根长（%）逐渐减小，基于根伸长的Cd对水稻毒性的10%抑制浓度的毒性阈值（EC10）和半抑制浓度（EC50）值在不同土壤和不同Cd敏感性水稻品种间有较大差异。总体而言，在3种不同Cd敏感性（T167＞L28＞X45）水稻品种中，同一土壤中Cd的水稻毒性ECx（x=10，50）随着水稻对Cd胁迫的敏感性增强而降低；就单一品种水稻而言，不同土壤的Cd水稻毒性阈值ECx间有显著差异。其中，以Cd敏感性水稻品种T167测试的不同土壤EC10变化为1.40-5.25 mg•kg-1，最大相差275.0%，EC50变化为17.83-46.93 mg•kg-1，最大相差163.2%；以Cd非敏感性水稻品种X45测试的不同土壤EC10变化为1.72-8.22 mg•kg-1，最大相差377.9%，EC50变化为26.96-68.16 mg•kg-1，最大相差152.8%。通过水稻Cd毒性阈值ECx与土壤性质间的多元回归分析表明，土壤pH、有机碳（OC）、阳离子交换量（CEC）与水稻Cd毒性阈值间呈正相关关系，基于土壤主要性质的水稻Cd毒性预测模型表明，EC50实测值均在预测值2倍误差（±S.D）范围内。【结论】基于ISO11269-1根伸长毒性测试结果表明，不同土壤中Cd的水稻毒性阈值间有显著差异，土壤pH、OC及CEC与水稻Cd的毒性阈值间呈显著正相关关系（P＜0.05），基于上述土壤性质的预测模型可以很好预测不同土壤中Cd对水稻的毒性；不同Cd敏感性品种对测定土壤中水稻Cd毒性阈值有明显差异，因此，在制订土壤中Cd的生态基准时应充分考虑不同物种的敏感性差异特征。

The Toxicity Thresholds (ECx) of Cadmium (Cd) to Rice Cultivars as Determined by Root-Elongation Tests in Soils and Its Predicted Models

【Objective】Although the attention has been paid for decades to the ecological risk of Cd to rice in soils, most studies focused on its healthy risk in terms of the food standard instead of its ecological risk and toxicity thresholds in soils. The toxicity thresholds (ECx, x=10, 50) and its predicted models of Cd to rice cultivars in various soils in China were determined using ISO 11269-1 root-elongation endpoints with the aim of providing fundamental data for the revision of soil environmental quality standards of Cd in soils of China.【Method】Eight different soils with various properties and three rice cultivars were selected in this study, the dose-response curves and the toxicity thresholds were investigated using Log-Logistic distribution models based on the ISO 11269-1 root-elongation test in soils, the predicted models for Cd toxicity was also developed in this study. 【Result】The results indicated that the relative root elongation (%) decreased with the Cd concentrations increment in soils. The 10% (EC10) and the half inhibiting concentration (EC50) of Cd to rice cultivars varied significantly among the tested soils and the rice species. In general, the toxicity thresholds (ECx, x=10, 50) of Cd to rice species decreased with it’s sensitiveness to Cd stress in soils, i.e. the ECx followed the order of T167＞L28＞X45. The significant differences of the toxicity thresholds (ECx, x=10, 50) of Cd to rice species were also observed in this study as determined with single rice species, e.g. in terms of the Cd-stress-sensitive cultivar of T167, the 10% inhibiting concentration (EC10) of Cd to root-elongation varied form 1.40-5.25 mg•kg-1 with the maximum variety of 275.0%, the half inhibiting concentration (EC50) varied form 17.83-46.93 mg•kg-1 with the maximum variety of 163.2%, respectively. However, for the Cd-stress-tolerance cultivar of X45, the 10% inhibiting concentration (EC10) of Cd to root-elongation varied form 1.72-8.22 mg•kg-1 with the maximum variety of 377.9%, the EC50 varied form 26.96-68.16 mg•kg-1 with the maximum variety of 152.8%, respectively. The multiple regression analysis showed that there was a significant positive correlation (P＜0.05) between soil pH, organic carbon (OC), cation exchange capacity (CEC) and the toxicity thresholds (ECx, x=10, 50) of Cd to rice cultivars in soils. A predicted model was developed and validated for the toxicity thresholds (ECx, x=10, 50) of Cd to rice with the measured ECx fell within the range of predicted values±2 standard deviations. 【Conclusion】 Significant difference of the toxicity thresholds (ECx, x=10, 50) of Cd to rice cultivars was observed in soils as determined by root-elongation test, and a significant positive correlation (P＜0.05) was also observed between soil pH, OC, CEC and the toxicity thresholds. The ECx of Cd toxicity were affected by the variance of the tested rice cultivars in soils, the ecological toxicity of Cd to different test endpoints should be considered for the future revision of the soil environmental quality standards of Cd in soils of China.