An analysis of modes of occurrence and biological availability of the heavy metal elements in soil of the central and southern plain in Hebei

Abstract：Based on the study of topsoil of the central and southern plain in Hebei，the authors analyzed the morphology of seven heavy metals in topsoil，evaluated the biological availability of the heavy metal elements，and studied the factors which might affect the biological availability of heavy metal elements by means of correlation analysis. The results show that the content of element-available Cd is 36.83% in topsoil, the highest among all metal elements that have greater potential ecological harmfulness. The content of element-available and carbonate Pb is respectively 13.37% and 12.38%, suggesting smaller harmfulness because of neutral and alkaline soil in the study area. The total values of Cu, Hg, Cr, As, Zn that maintain stable state account for more than 90%, implying smaller harmfulness. The activity coefficients and migration coefficients of heavy metal elements in topsoil in the study area are respectively arranged in order of Cd > Pb > Hg > Cu > Zn> As > Cr and Cd > Hg > As > Cu > Pb > Zn > Cr, with the average of the Cd achieving respectively 0.330 and 0.160, implying a strong biological activity, instability and migration capability. Other soil heavy metals show smaller activity coefficients (except Pb) and migration coefficients，indicating that their biological activities are weak and it is difficult for them to transfer from soil to plants. The relationships between biological effectiveness and influential factors of various heavy metals are not the same; nevertheless, the dominant factor is the total amount of soil heavy metal elements, followed by pH, TOC, CEC, clay content and other factors. There exist complicated relations between them.