| Sixteen soils were selected to obtain the toxicity thresholds of Zn in soils based on four different bioassay toxicity endpoints（i.e. the barley root elongation, tomato biomass and bok choy growth, potential nitrification rate（PNR）） by using Log-logistic dose-response models, and the predicted models of soil Zn toxicity thresholds were established in laboratory condition. In order to validate the toxicity thresholds of Zn determined in lab condition, two sites were selected for tests under field condition, i.e. the acid red soil located in Qiyang, Hunan province and the neutral paddy soil located in Jiaxing, Zhejiang province. The results indicated that the 10%（EC10）and half inhibition（EC50） concentration of toxicity thresholds of Zn in the acid red soil fall in the range of 37～51 mg·kg-1 and 127～312 mg·kg-1, respectively, as determined by different maize growth indexes, the sensitivity of the test endpoints follows order of：leaf area>straw dry weight >plant height>grain dry weight; however, the 10%（EC10） and half inhibition（EC50） concentration of toxicity thresholds of Zn in the paddy soil were 213～332 mg·kg-1 and 682～922 mg·kg-1, respectively, as determined by different rice growth indexes, the sequence of the sensitive of the test endpoints follows the order of：SPAD values>straw dry weight>plant height>grain dry weight. The field validation result showed the coincidences between the toxicity thresholds of Zn obtained in lab and field conditions varies in different tested soils, the closer EC10 and EC50 were observed in the paddy soil than those in the red soil. The predictive models of Zn toxicity thresholds established based on the lab test data can predict well the toxicity values of Zn to rice in paddy soil in field condition, e.g. the determined toxicity thresholds of Zn in the paddy soil in field condition fall in the two folds of the prediction interval, however, in terms of acid red soil, the predictive model underestimated the ecological risk of Zn in the soil. |
