Soluble metal pool as affected by soil addition with organic inputs.

The potential impact of diverse inputs of organic matter (hay, maize straw, and peat) on the mobility and bioavailability of Cd, Cu, Pb, and Zn was examined at laboratory scale for three soils with contrasting properties and for two moisture regimes: field capacity and saturated conditions. Soil solution was characterized for total soluble metals, dissolved soil organic carbon, and ultraviolet absorbance at 254 nm. Speciation analyses were performed with WHAM VI. For field capacity conditions, metal mobility increased (Pb>Cu>Zn>Cd) for all soils and treatments compared with controls and was significantly correlated (p<0.05) with dissolved organic matter (r=0.540). Solubilization of organic matter was mostly driven by Al mobilization (r=0.580, p<0.05) and variations in solution pH. The bioavailable pool of metals, estimated as free ion activities, decreased with the increasing occurrence of metal-organic matter complexes, which was accompanied by an increase in solution of highly aromatic organic matter. Soil saturation generally decreased metal mobility and the ratio of metal-organo matter complexes in solution. Consistently, such effects were accompanied by a decrease in the solubilization of organic matter and lower mobilization of Al, Fe, and Mn.