Three factors affect plant and soil metal concentrations:
(1) the quantity factor, which represents the total amount of metals bio-available;
(2) the intensity factor, which represents the activity of metals in the soil solution;
and (3) the reaction kinetics, which represents the rate of metals transferred from the solid to the liquid phase and to the plant roots.
The effect of the organic matter on improved metal mobility in soil may be attributed to its influence on factors 1 and 3, in the sense that the high presence of DOM in soil treated with OFMSW acted as ligands for metals, enhancing the metals’ availability for plants and their solubility in soil.
This assumption was confirmed by the fact that the DOC content in the OFMSW-amended soil was much higher than control at the start of the trials.
observed an increase in metal content bound to DOM when a DOM concentration increased in leachated-polluted groundwater.
reported that an increase in the concentration of DOM increases metal extractability from the soil through elevated metal uptake by plants.
The mechanism by which plants uptake heavy metals bound to DOM is not yet well understood.
Nevertheless, some authors observed that DOM or low molecular-weight organic acids, which comprise DOM, can be taken up by plant roots along with the metals that they have bound.