The Toxicity Thresholds (ECx) Of Pb And Its Predicted Models Based On Various Endpoint Determination

Nowadays the soil pollution by heavy metals in China has received more attention because of the harmful influence on food and body-healthy, the present environmental quality standard for soils which based on mental salts experiments lost sight of the difference between laboratory and real conditions. So it is important to go for research on the behavior and toxicity of metals in different soils of china in order to build a accelerated evaluation management system to guarantee the agricultural products quality and human health. This paper collected 10 site soils with a wide range of properties, barley root elongation, SIN, earthworm avoidance were used as endpoints with leached and unleached dispose. Does-response data were fitted to a log-logistic curve to obtain the threshold value, and established models based on soil properties and the ecological toxicity values. Results as follows:1. The results of barley root elongation indicated that the determined toxicity threshold(ECx, x=10,50) of Pb varied significantly between the soils, the 50% and the 10% inhibiting concentration of Pb to barley in soils ranged from 300mg/kg~3130mg/kg and 121mg/kg~633mg/kg, respectively, with maximum ratio of 10.4 and 5.1 folds among the tested soils. The result showed that the Pb toxicity threshold(ECx, x=10,50) increased significantly(P<0.05) in soils after leaching treatment, which indicating that the Pb toxicity decreased sharply after simulate rain leaching. The determined leaching factors(defined as the ratio of toxicity threshold ECx in leached soils to that of non-leached soils) based on the EC50 and EC10 ranged from 0.96~1.96 and 1.03~1.81, respectively, the obvious effect was observed for the Pb toxicity decreasing for the soils with pH<6.81 generally. The predicted models for Pb toxicity threshold in soils based on the main soil properties(pH, OC and CEC)can well predicted the Pb toxicity in soils with various soil properties.2. The results of SIN shows that: among the tested soils, EC10 and EC50 values which have been leached increased 0.7-2.0 and 0.8.0-2.6 folds to unleached EC50 and EC10 with the range from 40mg/kg~251mg/kg and 163mg/kg~912mg/kg,the Pb toxicity threshold increased significantlyin soils after leaching treatment. The predicted models for Pb toxicity threshold in soils based on the main soil properties(pH, CEC) can well predicted the Pb toxicity in soils with various soil properties(r2>0.95), and the pH is the best predicter in the model(r2>0.60).3. The avoidance of earthworm appeared at low concentration and the EC50 and EC10 ranged from 267mg/kg~867mg/kg and 50mg/kg~289mg/kg.The ratio of EC50 and EC10 between maximum and the minimum of different soil property can reach 3.24 times and 3.24 times respectively. The prediction model of Pb based on the different main controlling factors of the in the soil is obtained by multiple stepwise regression analysis of data, the pH is the best predicter in the model(r2>0.80). and the pH、CEC could contrl the 90% variability of the model(P<0.01). Earthworms appear avoidance in alower toxicity value than the acute toxicity, the difference appears significantly(P<0.05) between the avoidance values and SIN and barley root elongation values shows that: avoidance and SIN have a more quick-response at a lower concentration than phytotoxicity.4. The paper used 9 species toxicity data which were collected from CNKI. The SSD curves of Pb are well fitted with BurrⅢ which ranged from 44.79-189.10mg/kg, the HC5 of acid soil is lower than calcareous soil、alkaline soil, the biggest ratio can reach 4.3.We’ve come to the conclusion from SSD curves that: SIN and the avoidance of earthworm>vegetable plant>graminaceous crop, the SIN and the avoidance of earthworm are the most sensitive toxicity index than others. Finally we established functions that: log(EC10)=0.178pH+0.149log(CEC)+0.777(r2=0.97), pH and CEC were the best predictors in models which based on different soils.