Study On Immobilization And Remediation Of Cadmium And Arsenic Combined Pollution Soil By Different Soil Amendments And Their Mix

Cadmium (Cd) and arsenic (As) are typical toxic elements. The combined pollution of them often happens in paddy fields, threatening the quality of agricultural products, human health and ecosystem. Rice is the main crop in southern China. Relatively speaking, soil pollution in southern China is more seriously than other areas by cadmium and arsenic. The two toxic chemicals tend to accumulate in rice plants, rice has become a major route of human intake of cadmium arsenic. In order to explore the effects of different soil amendments, select paddy soil as research subject and silkworm excrement biochar, calcium silicate and ferrous sulfate as the research materials, conduct a laboratory experiment, and assess the effect of the repair, so as to provide a solution to solve the content of cadmium and arsenic exceeded in rice.The main research results are as follows:1)Laboratory experiment:The pH level of the soil was significantly decreased with the application of 1%(mass percent)ferrous sulfate alone and 0.5% ferrous sulfate plus 0.5%biochar. In contrast, the single application of 1% calcium silicate,1% biochar,0.5% calcium silicate plus 0.5% biochar and the combination of the three materials(every material accounts for 0.33% by mass percent) could significantly increase the pH level of the soil. All treatments increased the soil organic carbon content by 5.52-26.95%, except for ferrous sulfate. While the soil CEC content significantly increased by 43.07% and 20.62% with the application of calcium silicate plus biochar and ferrous sulfate plus biochar. The soil CEC content significantly decreased by 16.06% and 14.59% with the application of calcium silicate plus ferrous sulfate as well as the combination of three materials. The available content of As in soil significantly reduced by 48.06% and 33.75% respectively,with the application of ferrous sulfate and ferrous sulfate plus biochar. The addition of calcium silicate, biochar, ferrous sulfate plus biochar significantly reduced the available Cd content in soil, decreased by 19.56%,14.29% and 33.32% respectively. The correlative analysis showed that the available As content was significantly and positively correlated with the soil pH level. The available content of Cd and the content of CEC in soil showed a significant negative correlation. Considering all soil remediation effects of various processing, the treatment of ferrous sulfate plus biochar showed the best result, which made the available As content in soil decreased by 33.75% and the available Cd content decreased by 33.32%.2)Rice pot experiments:The results showed that the treatment of 0.5% (mass percent) ferrous sulfate plus 0.5% biochar and the treatment of 0.25% ferrous sulfate plus 0.75% biochar promote tillering, their tillers both increased significantly than the contrast. The results show that adding ferrous sulfate in soil, can obviously promote the growth of rice tillers and improve rice production.The treatment of 0.5% ferrous sulfate plus 0.5% biochar significantly decreased soil pH level by 0.69 units while the effects of other treatments are not significant. All treatments significantly increased soil organic carbon content by 7.43-18.43%. Among all the treatments, the result of 0.17% ferrous sulfate plus 0.83% biochar is the most significant one, increasing the soil organic carbon content by 18.43%. The whole effects of the three treatments containing ferrous sulfate increased soil organic carbon content are better than the three treatments containing calcium silicate. All treatments significantly reduced the available content of As in soil, except for 0.25% ferrous sulfate plus 0.75% biochar treatment. The treatments of 0.25% ferrous sulfate plus 0.75% biochar,0.17% ferrous sulfate plus 0.83% biochar,0.5% calcium silicate plus 0.5% biochar, 0.25% calcium silicate plus 0.75% biochar,0.17% calcium silicate plus 0.83% biochar all reduced the available content of Cd in soil.The treatment of 0.25% ferrous sulfate plus 0.75% biochar made the minimum contents of Cd in brown rice,0.17% ferrous sulfate plus 0.83% biochar made a second low. The treatment of 0.5% ferrous sulfate plus 0.5% biochar made the minimum contents of As in brown rice,0.25% ferrous sulfate plus 0.75% biochar made a second low. In summary,0.25% ferrous sulfate plus 0.75% biochar was the best treatment to decrease the Cd, As content in brown rice.The correlative analysis showed that the available content of As and Cd in soil was significantly negatively correlated with the CEC content. And the available content of Cd in soil was negatively correlated with the SOC content of soil.In summary,0.25% ferrous sulfate plus 0.75% biochar was the best treatment to remedy combined pollution soil of cadmium and arsenic. The treatment can reduce the available content of As and Cd by increasing the SOC contents. The treatment can promote tillering and reduce rice plant accumulating Cd, As in brown rice by changing the bioconcentration factors and translocation factors of Cd and As in rice.3)A11 the results showed that, the treatment of 0.25% ferrous sulfate plus 0.75% biochar can prevent soil pH from decreasing, increase the SOC content, thereby reducing the available content of As and Cd in soil and reduce the content of Cd, As in rice.