The present study was conducted to investigate the chemical fractions of
heavy metals in six different soil experiment locations which received sewage sludge
for long time. The total contents of In, Cu, Ni and Cd, as average of all soils were
251,83.5, 29.6 and 2.11 ug/g, respectively. The distribution of various fractions for all
metals (as % from total content) followed the order: Exchangeable; 2.5 for In, 1.6 for
Cu, 2.2 for Ni and 2.8% for Cd < Carbonate; 10 for In, 11 for Cu, 9.7 for Ni and 11.4%
for Cd < Oxides; 14 for In, 14 for Cu, 11 for Ni and 11 % for Cd < Organically
complexes; 21 for In, 39 for Cu, 25 for Ni and 24% for Cd. The soluble,
exchangeable, organically and oxide forms of In, Cu, Ni and Cd represented a
negative relationships with soil pH. However, the Carbonate form showed a positive
relationship with soil pH and CaC03 contents. The soluble form of metals represented
a small percentage of total contents (0.37 for Zn., 0.15 for Cu, 0.46 for Ni and 0.25%
for Cd). A highly significant correlation (R² = 0.98, 0.98, 0.96, 0.92, p < 0.01, for In,
Cu, Ni, and Cd, respectively) was obtained between soluble and exchangeable forms.