BEHAVIOR OF HEAVY-METALS IN SOILS .2. EXTRACTION OF MOBILE HEAVY-METALS WITH CACL2 AND NH4NO3

156 soil samples from arable fields, grassland and forest stands were analysed for the CaCl2- and NH4NO3-extractable contents of Cd, Zn, Mn, Cu and Pb. The average amounts of Cd, Zn, Cu and Pb extracted with CaCl2 are higher compared with NH4NO3 whereas the relation for Mn is vice versa. The proportion of the NH4NO3-extractable contents in percent of the CaCl2-extractable contents of Cd, Zn and Pb decrease with increasing pH, whereas the contents of Mn and Cu increase. Inspite of a differing extraction behaviour of the two salt solutions the CaCl2- and NH4NO3-extractable amounts of Cd, Mn, Zn und Pb are highly correlated and can be converted one into another. The mobile (CaCl2, NH4NO3) proportion of the corresponding total, EDTA and DTPA heavy metal contents is in close relation of the pH of the soils. Using CaCl2 solution the threshold pH values for an increasing mobility decrease in the order Cd > Mn > Zn > Cu > Pb, using NH4NO3 as extractant the order is Mn > Cd > Zn > Cu > Pb. In the case of CaCl2 as extractant soluble chloro-Cd-complexes will be formed so that the Cd mobility in soils will be overestimated in most cases.