Vulnerability assessment of soil cadmium with adsorption–desorption coupling model

Abstract

The transfer rate and extent of cadmium (Cd) to groundwater and plants were controlled by soil adsorption and desorption processes, which directly affect agro-environment safety. Cd mobility shift is critical for the correct assessment of pollution vulnerability in different soil types. But the existing experimental methods and traditional quantitative prediction models are time-consuming and have a small scope of adaptation. In this paper, a coupling model of soil Cd adsorption and desorption was developed based on quantitative retention factors to explore the sensitivity of soil environmental factors for Cd pollution and quantify the spatial distribution pattern of Cd pollution vulnerability in highly heterogeneous soils in China. Results showed that: (1) The type of background electrolyte affected Cd adsorption and desorption capacity in soil solution. The performances of the single background electrolyte models (NaNO3, CaCl2, NaCl, KNO3) are better than the mixed background electrolyte model. (2) The contribution values of adsorption and desorption models were compared by sensitivity analysis. (3) Vulnerable areas of soil Cd pollution with higher risk than expected were selected by using the adsorption–desorption coupling model in China, including Tibet Autonomous Region, Xinjiang Uygur Autonomous Region, northwestern Sichuan Province, southeastern Qinghai Province, Guangdong Province, Guangxi Province, and Yunnan Province. Our adsorption–desorption coupling model can be used as an assessment tool expressing the soil Cd pollution vulnerability based on the available state of Cd, which is expected to provide the quantitative scientific basis for the formulation of Cd quality standard systems and soil remediation measures for regional soil environment protection.