BEHAVIOR OF HEAVY-METALS IN SOILS .1. HEA VY-METAL MOBILITY

158 soil samples with widely varying composition were analysed for the ir total, EDTA, DTPA and CaCl2 extractable contents of Cd, Zn, Mn, Cu and Pb. By means of single and multiple regressions the relations betw een the different heavy metal fractions and the pH, organic carbon and clay content were considered. The correlations between the total, EDT A and DTPA extractable contents are very close, whereas the CaCl2 extr actable contents are not or only weakly correlated with these fraction s. According to these statistical results the former fractions are con sidered to be the total quantity (total content) and the reactive quan tity (EDTA and DTPA extractable contents) of the heavy metals, whereas the CaCl2 extractable fraction represents the mobile fraction of the heavy metals in soils. The multiple regressions show that the mobile c ontent of heavy metals is closely correlated with each of the quantity fractions and with soil pH. In the same way the proportion of the mob ile fraction (in %) of the total, EDTA and DTPA extractable heavy meta l content of the soil samples is closely related to the soil pH. Hereb y the proportion of the mobile content of the various elements increas es in the pH range 6,5 - 3 below element-specific threshold pH values (in brackets) in the order Cd (6,5) > Mn (5,7) > Zn (5.3) > Cu (4,5) > Pb (3,5). In the pH range 6,5 - 7,5 mainly Cu and to a lesser degree also Pb show an increasing mobility due to the influence of soluble or ganic substances.