Transformation of Chemical Forms and Migration Characteristics of Cadmium and Selenium During Soil Formation on Black Rock Series

College of Environmental and Resource Sciences,Zhejiang University

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    Black rock series contains high amounts of cadmium and selenium. During weathering and soil formation on the rocks, the chemical form transformation and release of cadmium and selenium from the rocks can have an impact on the surrounding ecological environment. In this study, a black rock series distribution area of Hetang formation of the Lower Cambrian was selected in Northwest Zhejiang. By collecting horizonal soil samples from soil profiles along different parts of the terrain (hill upslope, hill middle slope, hill downslope, inter hill valley bottom and valley terrace), the quantity and chemical form transformation patterns of cadmium and selenium during the process of weathering soil formation and weathering material migration of the black rock series were discussed. The results showed that total cadmium and total selenium in the soils decreased from parent rock to soil. The loss of cadmium and selenium in the weathered matter of black rock series increased with the increase of transportation distance along the hilly slope, and the loss of cadmium and selenium in the process of evolution from slope deposit to diluvium was greater than that from residual to slope deposit. The cadmium and selenium lost from the weathered materials could affect the content of cadmium and selenium in the topsoil derived from the alluvial of the downstream river in the way of water diffusion, but the degree of influence decreased with the increase of distance. With the increase of the transportation distance of weathered materials and the evolution of soil, the transformation of carbonate bound cadmium and residual cadmium to water-soluble cadmium, exchangeable cadmium, organic matter bound cadmium and oxide bound cadmium occurred. The residual selenium was gradually activated and transformed into exchangeable selenium, organic matter bound selenium and oxide bound selenium. The results also showed that soil water-soluble cadmium, exchangeable cadmium (selenium) and organic matter bound cadmium (selenium) increased toward the surface. The organic enrichment of selenium and topsoil was more obvious than that of cadmium. The results indicates that the weathering of black rock series could not only directly affect the content of soil cadmium and selenium in its distribution area through residue, but also affect the content of soil cadmium and selenium in the surrounding area through water diffusion.

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  • Received:December 10,2023
  • Revised:February 22,2024
  • Adopted:February 28,2024
  • Online: April 29,2024
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