Study On Cd,Hg Migration And Transformation In Soil-Plant System

With the rapid development of China’s economy and society,the problem of soil heavy metal pollution is becoming more and more serious,Cd and Hg are the main pollutants.In this paper,through the pot-cultivation and imitate-culturing tests,the migration and transformation mechanism of Cd and Hg in soil-plant system are explored,and the following results are obtained:1,Indian mustard,chinese cabbage and Shanghai Brassica chinensis was selected and the simulated solution was Cd Cl2 and the concentration gradient was 0,5,10,20,50 mg/L to the Cd migration and transformation mechanism in the soil-plant system.The main enrichment place of Cd in 3 kinds of plants is the root.With the increase of Cd concentration in simulated solution,the content of Cd in the abovementium and the Indian mustard transfer coefficient increase.And the enrichment coefficient of Cd is greater than 1.Under the high concentration simulated solution enviroment,Indian mustard transfer coefficient is greater than 1 and shows a high tolerance to Cd,so it could be regarded as a super-enriched plant.However,other two do not have the ability of continuous high enrichment to Cd,and the tolerance of them is poor.2,Indian mustard and chinese cabbage was selected and the simulated solution was Hg Cl2 and the concentration gradient was 0,5,10,20,50 mg/L to explore the Hg migration conversion mechanism in the soil-plant system.The main enrichment place of Hg is the root of plants.With the concentration increase in simulated solution,the Hg enrichment coefficient of the two plants decrease,and both were less than 0.5,so they cannot be classified into Hg super-enrichment plants.Both plants showed poor tolerance to Hg.When the hg exceeded 5 mg/L in the solution,the plants showed symptoms of poisoning.3,Indian mustard and Chinese cabbage was selected to explore the soil-plant system methylmercury and ethyl mercury migration conversion mechanism.The enrichment coefficient of methyl mercury in plant is more than 1,which is much larger than ethyl mercury.methyl mercury and ethyl mercury in Indian mustard follow the relationship that pr>ps>pl.pr,ps and pl represent the content in the root,stem and leaf C.For the Chinese cabbage the content in root is highest,and that in stem and leaf content are equivalent.With the increase of the concentration of simulated solution,the transfer coefficient of Indian mustard and Chinese cabbage show a downward trend,and the upward transport efficiency of methylmercury and ethyl mercury was inhibited.4.Methylmercury and ethyl mercury were not detected in soil samples treated by Hg Cl2 solution,and methylmercury could only be detected in plant samples treated by Hg Cl2 solution.Methylmercury is mainly concentrated in plant roots,and methylation of mercury occurs mainly at plant roots.With the increase of Hg Cl2 concentration,the content of methylmercury in plants increased,and the transfer of methylmercury in plants was not inhibited by Hg2+.