Change of the arsenic content in soils of the Linfen-Yuncheng basin, Shanxi, China

Study of the change in As content in surface and deep-level soils in the Linfen-Yuncheng basin shows that the contents of arsenic and related elements in topsoils are slightly higher than the background values of soils nationwide and that there is appreciable difference in content of As with different phase states: the soluble and exchangeable fractions have low to undetectable arsenic contents (1.5%); Fe/Mn oxyhydroxide-bound As is the second largest fraction (10%) in tested soils; the organic fraction (10%) makes up a significant portion; and the residual fraction (60%) accounts for the largest portion. Some statistics methods, such as the correlation analysis and regression analysis, were used to study the spatial variability of arsenic in soils in relation to their influence factors. Physico-chemical properties, such as pH of soils, magnetic susceptibility, total organic carbon (TOC) and content of the clay size fraction, affect As with different phase states to different degrees: the water soluble fraction of As has a close relationship with pH values; TOC shows a distinct positive correlation with humus-bound As; both the magnetic susceptibility and content of the clay size fraction have a distinct positive correlation with the As content in soils. Results of the study show that As has a very significant correlation with Fe, Mg, Cu, Zn, Mg, K and F, indicating that As in topsoils in the study area is mainly of natural origin. Further regression analysis indicates that the As content in soils increases with increasing contents of iron oxide, hydroxide and sulfide. The As content in soils increases with depth: there are more As in the intermediate layer and less As in the upper and lower layer, which is likely to be related to such factors as the pollution of arsenic, alkaline soil condition, absorbability of plants and use of phosphate fertilizer in the study area.