Heavy metal contents and chemical speciations in sewage-irrigated soils from the eastern suburb of Beijing, China

Author: Zhifan Chen ^{1, 2}, Ye Zhao ^1*, Qiang Li ¹, Jiejuan Qiao ¹, Qing Tian ³ and Xitao Liu ¹

Received 20 June 2009, accepted 10 October 2009.

Abstract

Accumulation of heavy metals in agricultural sewage-irrigated soils has originated increasing concern. This study analyzed the total concentrations and chemical speciations of heavy metals including Cd, Cr, Cu, Zn and Ni in sewage–irrigated soils in the eastern suburb of Beijing, China. Here Tessier sequential extraction was adopted to analyze the chemical fractionations, and their concentrations were determined by ICP-MS. The results showed that there was remarkable buildup of Cd, Cr, Zn and Cu in sewage-irrigated topsoils compared to reference topsoils. Besides, the total Cd and a part of Ni were beyond Chinese agricultural soil environmental quality criteria. In sewage-irrigated soils, Cd, Cr, Ni, Zn and Cu were dominated by residual fractions and few was present in exchangeable and carbonate fractions as a result of higher soil pH. The order of Cu, Zn and Ni in sewageirrigated topsoils in each fraction was residual > organic > Fe-Mn oxide > exchangeable > carbonate, for Cd in sewage-irrigated soils the order was residual > Fe-Mn oxide > organic > exchangeable > carbonate and for Cr in sewage-irrigated soils the order was residual > organic > Fe-Mn oxide > carbonate > exchangeable. However, for Cu and Ni in sewage-irrigated subsoils the order was organic > residual > Fe-Mn oxide > carbonate > exchangeable; for Zn the order was organic > residual > exchangeable > Fe-Mn oxide > carbonate, and for Cd the order was residual > exchangeable > organic > Fe-Mn oxide and carbonate. The mobility and bioavailability of the five metals declined in the following order: Zn, Cu, Ni, Cd and Cr. However, compared to other four metals, Cd was more mobile and bioavailable in the sewage-irrigated topsoils than in the reference topsoils. Higher Cd contents in sewage-irrigated soils may constitute potential risk on food security and human health.