The Transport Characteristics And Risk Prediction Of Phosphorus And Arsenic In Different Site Soils

In recent years,due to human agricultural and industrial activities,the problem of heavy metal pollution in soil has become increasingly serious.Among them,heavy metal arsenic（As）has the characteristics of high mobility and high toxicity.Therefore,the migration and accumulation behavior of As in the soil environment has attracted widespread public attention.Due to the impact of heavy metal As on crop growth and safety risks to human health,there are technical difficulties in the extraction and determination of As in actual production control processes,which hinders research on the migration behavior of As in soil.Phosphorus（P）and As are different elements of the same main group,which have the advantages of low toxicity,simple determination methods,and low cost.Previous studies have shown that the two have the same properties in many aspects.However,there is currently a lack of strong evidence on whether the migration and accumulation behavior of the two in soil is similar.This study selected three soils from different sites（paddy soil,cinnamon soil,and red soil）,and used the same group elements P and As as the research objects to explore the adsorption of P and As by three soils,clarifying the adsorption behavior of P and As in different types of soil;At the same time,through the indoor soil column migration test of P and As,the migration and accumulation laws of P and As in different soil type under different physical and chemical factors and the similarity of the migration and accumulation behavior of the same group elements P and As in soil were revealed,which provided a basis for the method of tracing the migration behavior of As in soil by the same group element P,and provided a technical method for rapid estimation of the specific distribution of soil As pollution and environmental risk.The main conclusions are as follows:（1）Through SEM images,it can be concluded that the surface of brown soil is the roughest,followed by paddy soil and red soil;Through XRD spectra,it can be found that cinnamon soil has a crystallization peak of CaCO₃,while cinnamon soil and red soil also have crystallization peaks of FeCl₃ and AlCl₃ compared to paddy soil.The isothermal adsorption process of P and As on three types of soil is best fitted with the Freundlich model,and their adsorption process for P and As is multi molecular layer adsorption;The maximum adsorption capacities of rice soil,brown soil,and red soil for P were 0.1846 mg g^-1,0.2263 mg g^-1,and0.1723 mg g^-1,respectively;The maximum adsorption capacities for As（V）are 0.1489 mg g^-1,0.2012 mg g^-1,and 0.1212 mg g^-1,respectively.The results of the kinetic adsorption experiment showed that the fitting effect of the pseudo second-order kinetic model was the best.The adsorption process of P and As in the three types of soil was mainly chemical adsorption,with cinnamon soil taking the longest time to reach adsorption equilibrium,followed by paddy soil and red soil.（2）The movement of P and As in the three site soils will be affected by pH and ionic strength.Under acidic conditions,the migration ability of P in soil is weakest.With the increase of pH,the recovery rate of P in paddy soil,brown soil,and red soil all increase to varying degrees,indicating that the migration ability of P increases with the increase of pH in all three soils;According to the experimental results,the migration ability of As in soil also increases with the increase of pH,indicating that alkaline environments are more conducive to As migration in soil.P.The recovery rate of As in the three soils decreased with the increase of ionic strength,indicating that high ionic strength would inhibit the migration of P and As in the soil,and the inhibition ability was paddy soil>cinnamon soil>red soil.By comparing the migration behavior of P and As in three types of soil,it can be found that there is similarity in the migration behavior of P and As under different factors.When physical and chemical factors change,the fitting results of the migration behavior between P and As show high similarity.Among them,using nonlinear fitting can better describe the similarity in the migration behavior of P and As in the three types of soil sites.（3）The change of pH and ionic strength will affect the accumulation behavior of P and As in soil.When pH=4,the accumulation ability of P in soil is strongest,and as pH increases,the accumulation amount of P gradually decreases;In addition,according to the experimental results,it can be found that P has the strongest accumulation ability in brown soil,followed by red soil and paddy soil,and the accumulation ability of P and As decreases with the increase of pH in all three soils,indicating that P and As are more likely to accumulate in the soil under acidic conditions.The cumulative ability of P in all three soils under different conditions is greater than that of As.By analyzing the retention curves of P in three soils,it was found that the total accumulation of P increased with the increase of ionic strength,indicating that high ionic strength promoted the accumulation of P in soil.The accumulation behavior of P and As in three types of soil has good similarity.Under different physical and chemical factors,correlation heat map analysis was conducted on the accumulation amount of P and As in different depths of soil.It was found that the relevant parameter（R²）reached above 0.7 under different conditions,indicating a good positive correlation between the accumulation behavior of P and As in soil media.Moreover,with the change of environmental factors,P The cumulative behavior of As also maintains good similarity.