Organic matter. Soil Organic Matter is a key for sorbing
phase for metals. The dissolution of humic acid at higher
pH is responsible for dissolution of Cu and Pb from soil.
Organic matter is important for the retention of metals by
soil solids, thus decreasing mobility and bioavailability.
However because of the complexation of metals by soluble
OM, the addition of OM can result in release of metals
from solids to the soil solution.The increase in the solubility
of the Cu and Pb is related to the dissolution of the HA
component of the organic matter. This indicates that
solution phase speciation reactions with organic matter
dominate the partition of these metals at higher pH. Because
under high pH, the DOM increases as a result solubility of
HA.