The Geochemical Behavior And Plant Transport Of Heavy Metals In Soils With Different Particle Sizes Caused By Lead Pollution

Soil is the supporting system of the human ecosystem.With the acceleration of the industrialization process,the emission of pollutants is increasing and heavy metals are important components of them.These pollutants discharge into soil with atmospheric dry or wet deposition.Plant is the starting point of ecosystem producers and bioaccumulation and they absorb the release of heavy metals by ions or particles,and threaten the health of human beings entering the body through the food chain,causing health risks of ecological environment and population.The geochemical behavior and plant effect of heavy metals in different size soil particles are different.This is also the focus of heavy metal biogeochemistry research and attention.This study selected Shaanxi lead-polluted area soil as the research sample,obtained different soil particle size of micro aggregates(50-250?m,5-50?m,1-5?m,<1?m)component through wet extraction,and.characterized their physical and chemical properties and geochemical behavior of heavy metals.In addition,we selected the fine soil particles(<1?m)components exposed as plants migration hydroponic experiment to study heavy metals eco-geochemical behavior of different size fractions,which could provide theoretical and technical support of lead-polluted soil ecological environment health assessment and pollution control in arid and semi-arid regions.The results are as follows:(1)In lead-polluted soil,with the decrease of soil particle size,soil pH,specific surface area,organic matter and heavy metal content increased significantly,quartz,feldspar and other minerals decreased,calcite and chlorite and other secondary minerals increased,crystal decreased,amorphous substance increased,Pb mainly existed as single lead and mostly in small size soil which was related with battery production industry.(2)Meanwhile,the modified BCR sequential extraction results showed that the overall trend of each element migration was:Pb>Mn>Cu>Zn>Ni>Co>Cr,the various speciation of the element was increased with the decrease of particle size.Among them,more than 95%lead belonged to the top three speciations.With the decrease of soil particle size,the oxidized Pb content was significantly increased,indicating the lead activity in soil was very strong and easy to migrate into the environment,and the lead speciation in the environment and soil particle size were closely related.The particle fractions of the comprehensive potential ecological risk index arranged in order:1?m(401.42,strong risk)>1-5?m(357.84,strong risk)>bulk soil(327.49,strong risk)>50-250?m(262.17,strong risk)>5-50?m(183.61,strong risk).As the particle size decreased,the index of activity coefficient,contamination coefficient and potential ecological risk increases,from the perspective of potential ecological risk,soil potential ecological risks were extremely strong,especially in less than 1?m fraction,Pb and Cu had the larger mobility factor and potential ecological risk,and the relevant departments should pay enough attention.(3)In term of the soil fine particle solution under different concentrations of electrolyte experiment,it showed that the effective particle size first increased rapidly and then entered a platform slowly until time reached equilibrium.Compared the adsorption capacity of the soil fine particles under different temperature by adsorption thermodynamics simulation model(pH=6.5),the results showed that the adsorption of Pb2+,Cu2+ and Zn2+ belonged to the endothermic reaction and Sb3+ belonged to the exothermic reaction,Pb2+,Zn2+,Sb3+ tended to Freundlich isothermal adsorption model and Cu2+ tended to Langmuir adsorption isotherm.Cu2+,Zn2+ and Sb3+ were conducive for soil fine particles adsorbing Pb2+.In addition,the desorption rate could be obtained according to the degree of desorption of soil fine particles of four different metal ions,Sb3+ was easily from soil fine particles in desorption and desorption rate of up to 71.13%,Pb2+,Cu2+,Zn2+were not easy from the soil fine particles desorbed into the water environment and the highest rate of less than 10%.(4)During the cultivation of the different concentrations soil fine particles solution,the biomass of maize seedlings increased firstly and then decreased with exposure concentration increased,seedlings moisture content did not change significantly and showed no obvious increase in ecological toxicity.Various root morphology of maize seedlings first increased and then decreased with the exposure concentration increased,overall.Most important of all,the root morphological data of the highest concentration fine particles solution was less than the control group,which illustrated the fine particle had begun to produce stress effect on the growth of maize seedlings.Meanwhile,the leakage rate of potassium ion increased at the maize seedlings root with the increase of lead concentration,indicating that different treatment conditions could cause the damage of cell membrane integrity of maize seedling roots.The lead content increased gradually in the maize seedlings of being exposed 7d,the migration coefficient showed a decreasing trend,indicating that Pb was more likely to accumulate in maize seedlings roots than transfer the ground.In addition,in the maize seedlings experiment,Mn and Zn content in shoot were higher than that in root,indicating that they were easily absorbed by maize seedlings roots and transferred to ground.And in term of the Cu,Ni,Co and Cr,the maize seedlings shoot content was below the root,indicating that these elements were easy to accumulate and absorb in the root rather than transfer to shoot.