Study On Uranium Bioavailability And Migration Model In Soil-Plant System

In this paper,the bio-availability and migration model of uranium were studied around soil-plant system,and the main factors influencing soil uranium occurrence mode wereanalyzed by orthogonal test;the absorption and bioaccumulation characteristics of the three hyperaccumulator i.e.sunflower,purple pakchoi and broad bean were studied;finally,the bioavailability of uranium in soil sunflower system was analyzed,and the migration model of uranium in soil plant system was preliminarily explored.The test results show that:(1)The effects of different exogenous uranium pollution treatments(0,25,50,100mg/kg),different disposal time(30,60,90,120d)and different proportion of nutrient soil(10%,20%,30%,40%)on the physical and chemical properties of soil and the occurrence mode and total amount of uranium:the proportion of nutrient soil had the greatest effect on the physical and chemical properties of soil.pH was negatively related to the proportion of nutrient soil,and the average value was 5.11 at 40%,while organic matter and total nitrogen were positively related to the proportion of nutrient soil,and the average values were 44.16 and 2.95g/kg at 40%.The total phosphorus and total potassium increased at first and then decreased with the increase of the proportion of nutrient soil.The concentration of exogenous uranium pollution had the greatest effect on the occurrence mode and total amount of uranium.The average values of different uranium occurrence modes reached the maximum at 100mg/kg,which were 0.038,12.54,16.97,9.58 and43.54mg/kg respectively.(2)With different exogenous uranium pollution treatments,the characteristics of uranium bioaccumulation of sunflower,purple pakchoi and broad bean were different in different growth times(30,60,90,120 d),among which sunflower showed better tolerance.The maximum biomass of sunflower was 8.63g at 120d in the control group.The concentration of uranium in the whole sunflower increased with the increase of the concentration of exogenous uranium,and increased with the increase of growth time.The maximum value was 300.79mg/kg at 100mg/kg,and the residual concentrations of uranium in the soil at 120d were 0.51,3.37,8.24 and 11.42mg/kg lower than those at 60d.Moreover,under the treatment of 100mg/kg exogenous uranium,the occurrence modes of uranium varied with the change of growth time:the exchangeable mode increased by 8%,the bound mode of iron manganese oxide decreased by 2%,the organic mode decreased by 3%,and the residual mode decreased by 2%;the growth time significantly increased the bioaccumulation factor of sunflower.Under the treatment of 100mg/kg,the bioaccumulation factors of 30,60,90 and 120d were 1.51,2.01,2.08 and 3.16,respectively.The maximum value of uranium extraction was 1122.41ug at 100mg/kg at 120d,and the highest absorption rate of sunflower was 2.73mg/kg�d~-11 at 120d.The overall migration factor did not change much,and maintained at 0.67-0.94.(3)In the soil sunflower system,the activity coefficient MF in the soil decreased first and then increased with the increase of the concentration of uranium pollution,and the MF at 120d increased by 0.05,0.07,0.05 and 0.05 respectively,bigger than those at 60d.The BCF values(bioaccumulation factor)of sunflower organs were different,which showed root>stem>leaf and flower.The BCF values were 0.54,0.20,0.17 and 0.12 at the concentration of 100mg/kg uranium at 120d respectively.The BCF values of stems and leaves were significantly correlated with the exchangeable mode of uranium(r=0.96**,0.89*),and negatively correlated with the bound mode of iron manganese oxide(r=-0.94*,-0.94*);the relationship between the concentration of uranium in the soil and the concentration of uranium in the sunflower can be fitted by linear model,that between the growth time of sunflower and the concentration of uranium in the soil can be fitted by linear model,that between the concentration of uranium in the soil and the concentration of uranium in the sunflower can be fitted by quadratic curve,and that between the concentration of uranium in the soil and the concentration of uranium in the sunflower can be fitted by Freundlich model.