Higher solubility of heavy metals in soil solution at
alkaline pH was attributed to enhanced formation of organic
matter metal complexes after ionization of weak acid groups.
Extensive evidence exist that in this pH range most
dissolved heavy metals are present as metal soluble organic
ligand complexes. The degree of stabilization achieved by
compost appears to be very important in determining
potential mobility of heavy metals. Carillo et al., (2000)
reported that, Cd can move readily in sandy loam soils, but
OM in the surface layer will act as a sink for Cd and will
reduce the rate of movement. Distruction of heavy metals
between soil and solute is the key for evaluating the
environment impact of the metals. For Cu, in particular OM
both solid and dissolved can affect its mobility substantially.
(Temming hoff et al., 1997) The concentration of DOM is
partly controlled by Ca by sorption. Ca can act as a bridge
between negatively charged DOM and negatively charged
soil particles both clay mineral and oxides.The heterogenity
of sorption sites is larges for natural solid OM than for
dissolved purified HA.