| In recent years,with the development of industrial production,lead(Pb)has been widely used,and soil Pb pollution has become a serious environmental problem.After Pb enters the farmland soil,its toxicity and availability will change due to differences in soil environment and plant type,posing a potential threat to the safety of agrncultural products,which may finally threaten human health through the food chain.Therefore,it is important to explore the transformation mechanism and distribution characteristics of Pb in the soil and its bioavailability in soil-vegetable systems.This study is based on 21 typical farmland soils and selected green chili{Capsicum annuum L.)as the test plant.The changes of the availability and distribution characteristics in the soil were explored by means of total analysis,chemical extraction and ultrastructural analysis(TEM).Also,the transportation,enrichment and distribution characteristics of Pb in chilies were included.In addition,prediction models of soil Pb bioavailability were constructed based on the analysis above.The main results are as follows:(1)The availability changes and distribution characteristics of Pb were analyzed,in the rhizosphere and non-rhizosphere soil,respectively.In the treatment group of acid soil,the extraction rate of Pb by HNO3 was higher than that of EDTA,but there was no significant difference between the two in neutral and alkaline soils.It is investigated that rhizosphere activation of chili caused an increase in the extraction rate of EDTA-Pb and HNO3-Pb in alkaline soil.Clarify that soil pH and organic matter content are the two key factors affecting Pb activity in soil.(2)The absorption,transportation and accumulation characteristics of Pb in chili were analyzed.The addition of exogenous Pb(250-350 mg/kg)had no significant effect on the plant height,fresh weight and root weight among the chilies.The Pb content in various parts of chili from high to low was:root>stem>leaf>fruit;and the order of transport factors(TF)was stem>leaf>fhuit.The exceeding rate of Pb content in the chili fruits to the food safety standard(0.1 mg/kg,in fresh weight)in the control group is 0%,with the low treatment group(Pb 125-175 mg/kg)11%,and the high treatment group(Pb 250?350 mg/kg)22%.The ultrastructure of chili root and fruit was observed by transmission electron microscopy(TEM),which found that the addition of exogenous Pb had a certain toxic effect on the chili cells.It is further clarified that combined with the physical and chemical properties of the soil,the soil pH value is the main controlling factor affecting the accumulation of Pb in the edible part.(3)The prediction models for the bioavailability of chili Pb were constructed.Three sets of prediction models for Pb content in green chili fruits were constructed based on total soil Pb,EDTA-Pb and HNO3-Pb content,along wtih soil physical and chemical properties.The optimal factors were soil pH and CEC,and R2adj were greater than 0.7,respectively,which showed good effect of the fit.Furthermore,The measured values were used to verify the model,the fitting values are mostly distributed in the 95%prediction interval,and evenly distributed on both sides of the 1:1 line,showing good prediction results.In addition,the field samples were collected to furtherly verify the constructed prediction models,which showed high reliability.In this paper,based on the analysis of Pb content in soil and chili plants by pot experiment,the accumulation characteristics,migration and enrichment and main controlling factors of Pb in soil-chili system were explored.Based on the prediction equation,the soil Pb safety critical value can provide a theoretical basis for soil Pb risk assessment and soil standard formuilation in China,so as to ensure the safe production of vegetables. |
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