| The radionuclide strontium-90 has the characteristics of strong radioactivity,long half-life and high toxicity.It can endanger human health after entering the human body through the migration of the food chain.Plant rhizosphere is the necessary way for radionuclides to migrate from soil to plant.Rhizosphere effect will affect the occurrence of radionuclides.This paper analyzed the morphological changes of strontium in the root system by simulating the root exudate solution.At the same time,an artificial organicinorganic composite colloid was prepared to study the mechanism of soil colloid adsorption of strontium and its influencing factors as well.According to the level of carbon concentration in the soil and the classification of root exudates,four different root exudate solutions were configured.During the 90-day culture period,the content of water-soluble strontium decreased from 3.00 mg·kg-1 to about 0.65 mg·kg-1.The content of organically bound strontium increased significantly to about 2.90-3.12 mg·kg-1.Exchangeable strontium,as the most active form of occurrence in the soil,fluctuates significantly in the early stage of cultivation,and the content shows a significant downward trend after 30 days.The initial content of carbonatebound strontium increased by about 3.5 mg·kg-1.The iron-manganese-bound strontium occupied a small proportion in all forms,and there was a certain fluctuation during the culture.Residual strontium asthe most stable form.The content was stable between 100 mg·kg-1 and 109 mg·kg-1.Root exudates affects the morphological transformation of strontium,which in turn affects the bioavailability of strontium.It was found that the diversity of root exudates was more likely to cause the conversion of the stable form of strontium to the active state comparing with the carbon concentration.The bioavailability(RAC)of all groups was above the medium risk,and the activation effect of the HC+HD group was the most siginificant one.At last,the RAC gradually droped below 30%and the risk was downgraded to a mediumlevel.In order to further study the adsorption performance of colloids on strontium and the influence of environmental factors,field soil colloids and artificial organic-inorganic composite colloids were prepared to.The adsorption capacity of artificial composites for strontium reached 6.86 mg·g-1,which was 6.70 mg·g-1 for thearable soil colloids.Kinetic fitting found that the adsorption process for both colloids was more in line with the second-order kinetic model,indicating the chemical adsorption.pH had no obvious influence on the adsorption,but the ionic strength and the concentration of organic matter had obvious influence on the adsorption.The organic carbon in field colloids included polysaccharide C-O bonds,-COOH,-OH and other organic carbon functional groups,and the adsorption rate of strontium to the soil colloid was reduced by about 9.25%after removing the organic matter.The root exudates had a lot of organic acids,a certain amount of carbohydrates,amino acids and other organic substances.Based on the experimental results,we inferred that the presence of root exudates in the rhizospHere would affect the adsorption and migration of strontium by soil colloids. |
