Study Of Biotic Ligand Model Based On Lead In Rice Planting System

With the development of industrialization,the soil pollution in China’s agricultural land is becoming more and more serious,and the content of heavy metals in the soil continues to increase,which poses a risk to food security and human health that cannot be ignored.As one of the more rapidly developing toxicity mechanism models in recent years,the Biotic Ligand Model（BLM）has been successfully applied to predict the water quality criteria in aquatic environment,and also has good prediction effect on the bio-availability of heavy metals in soil solution,which can be used as a medium to link soil and crops.Therefore,in this study,a BLM model of lead for rice based on the assumption of Biotic Ligand Model and simulated soil solution environment through hydroponic experiments,and the established BLM model was used to predict the soil solution lead threshold for rice system,and a method for deriving soil thresholds combining the MSM-BLM-crop system was further proposed.The main results of the study are as follows.（1）The main toxic species of Pb and the competing cations that can be used to attenuate its toxicity were identified.When the p H is 4.0～6.5,Pb²⁺was the main toxic species,accounting for more than 90%of the solution.Increasing the activity of H⁺,Ca²⁺,and Mg²⁺was able to reduce the EC50(Pb²⁺)by2.79,2.57,and 7.56 times,respectively,while increasing the activity of Na⁺and K⁺did not have a significant effect on the toxicity of Pb²⁺to rice root elongation.（2）A Pb-rice-BLM model was established.The values of model parameters were clarified,and the binding constants of the three competing cations to rice root ligand sites were Log K_{Mg BL}=4.03,Log K_HBL=2.06,and Log K_{Ca BL}=1.58.The binding constants of Pb to rice root surface ligand sites were fitted,Log K_{Pb BL}=3.26,and when Pb produced 50%inhibition of rice root elongation,the proportion of ligand sites occupied by Pb²⁺was 64%when Pb produced 50%inhibition of rice root elongation,and thus the EC₅₀ prediction equation for Pb toxicity to rice was obtained.（3）A method for predicting soil Pb thresholds in combination with MSM-BLM-crop system was proposed.The soil solution Pb concentration thresholds for the food security production rice system should be in the range of 1.67×10^-3 to 5.68×10^-3 mg/L.The coupled MSM-BLM-crop system model predicted the heavy metal Pb thresholds of 64.1～138,228～475,and 647.5～1362 mg/kg for the rice soil sample sites in Changsha,Hunan,Tongling,Anhui,and Shenyang,Liaoning,respectively.