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

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 (Stot 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 Stot value and topsoil components exhibit a vertical zoning with a positive correlation between the Stot 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 Stot 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.