Distribution of As and As_(V) adsorption potential onto topsoil in the Datong Basin, northern China

State Key Laboratory of Biogeology and Environmental Geology & School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China

^* Corresponding author: zeyongchi@cug.edu.cn

Abstract

Datong Basin is a typical groundwater irrigation area in northern China contaminated by As. In order to reveal the distribution of As and the adsorption behavior of As_(V) onto topsoil in the Datong Basin, a total of 40 topsoil core samples were collected from a 2 m core. Samples were used for chemical composition analysis and an isothermal adsorption experiment. Results show that the collected samples are not contaminated. The adsorption capacity (S_tot value) of topsoil for As_(V) at the study site ranged from 257 to 1027 nmol/g with an average of 505.2 ± 200.2 nmol/g. Vertically, both S_tot value and topsoil components exhibit a vertical zoning with a positive correlation between the S_tot value and K₂O, CaO, MgO, Al₂O₃, Fe₂O₃ contents while Na₂O and SiO₂ are inversely correlated. Fe₂O₃ content shows a strong positive correlation with As content while Al₂O₃ does not. Moreover, the correlation between S_tot value and Al₂O₃ is much better than Fe₂O₃. These results indicate that Fe minerals are the main reservoirs of As in the natural topsoil at the study site. Furthermore, both Fe minerals and clay minerals can adsorb As_(V), but clay minerals have a greater storage potential. This result indicate that a combined effect of Fe minerals and clay minerals for As_(V) accumulation onto topsoil should be considered during geochemical modeling and further agricultural management.