基于不同测试终点的土壤锌毒性阈值及预测模型

Comparative study of Zn-toxicity thresholds in 16 Chinese soils as determined by different bioassay endpoints and its predicted models

采用基质诱导硝化(PNR)、大麦根伸长、西红柿及小白菜生长毒性测试方法,结合Log-logistic模型,对我国16种典型土壤中锌(Zn)的毒性阈值(ECx)进行了测定,同时对Zn毒性与土壤主要影响因子间的量化关系及其预测模型进行了研究.结果表明:我国土壤中Zn的毒性阈值在不同测试物种间存在较大差异,以小白菜、大麦、西红柿及土壤微生物(PNR)测试的EC10均值分别为322,356,336,297mg/kg,以土壤微生物测试最低,以大麦根伸长测定结果最高;EC50均值则分别为:846,1471,1160,768mg/kg.不同测试方法对土壤中Zn毒性的敏感性顺序为:土壤微生物(PNR)>西红柿>小白菜>大麦,而不同测试方法的稳健性顺序则相反,表明PNR法是土壤Zn毒害最敏感的测试方法,而西红柿则是对土壤Zn污染胁迫最敏感的植物品种;不同毒性测试结果显示,EC50阈值的测定结果要敏感于EC10,而EC10测定结果的变异系数普遍大于EC50的测定结果.pH值是影响土壤Zn毒性阈值最为重要的因子,而基于土壤pH值,CEC,有机碳含量的归趋化预测模型可以很好地预测土壤中Zn的生态风险阈值.

The toxicity thresholds （ECχ,χ=10,50, the effective concentration causing 10% and half inhibition） ot Zn m sixteen Chinese soils were determined using log-logistic distribution models with four different toxicity bioassay endpoints, i.e., the potential nitrification rate （PNR） test, the barley root elongation assay （BRE）, tomato （TGT） and bok choy （BGT） phytotoxicity test respectively, the quantitative relationship between the ECx of Zn in soils and the main physic-chemical （e.g. pH, CEC and org-C etc） was also quantitativety measured, and the toxicity based predicted models of Zn in soils were developed. The results indicated that toxicity thresholds of Zn varied significantly among the different bioassay endpoints. The toxicity thresholds of EC10 of bok choy growth toxicity, barley root elongation, tomato growth toxicity and potential nitrification rate test were 322, 356, 336 及 297mg/kg, respectively, the lowest EC10 was observed with potential nitrification rate test while the highest with barley root elongation test. The determined EC50 of the same order of bioassay endpoints were 846, 1471, 1160 and 768mg/kg respectively. In general, the sensitivity of the bioassay endpoints followed the order of： the potential nitrification rate test〉 tomato phytotoxicity test 〉 bok choy phytotoxicity test〉 the barley root elongation test, while the test stability reversed. The result implied that the microbe were the most sensitive organism responded to the Zn toxicity and the tomato was the most sensitive plant among the tested crops. In terms of the applicability, the ECso values were more sensitive than that of EC10, while the larger variation coefficient was observed with EC10 test. The pH value was the most important factor affecting the bioavailability of Zn in soils; the environmental risk can be well predicted by the normalization models developed on the pH, CEC and organic carbon contents of the soils.