The Role of Humic Acid on Phytoremediation of Pb through a Pasture Collar Plant (Xeanthium vetelus)

One of the new approaches for increasing phytoremediation efficiency of heavy metals in contaminated soils is using soil chelating agents. In order to evaluate the effect of humic acid (HA) application on elevating the solubility of lead (Pb) in the soil and its uptake by the collar plant (Xeanthium vetelus), an experiment was carried out under greenhouse conditions. The factors included: 1) lead (Pb0, Pb250, Pb500 and Pb1000 mg kg-1 from Pb(NO3)2) and 2) humic acid (HA0, HA100 and HA200 mg kg-1. At the end of growing period selected soil biological parameters including basal respiration (BR), microbial biomass carbon (MBC), relative water content (RWC), proline amount and lead concentration in roots and shoots of plant, plant transfer factor (TF), Bio-concentration factor roots and shoots (BAF) were measured. Results showed that increasing the intensity of soil lead contamination decreased microbial respiration, microbial biomass carbon, relative water content of plant tissue, biological concentration factor of shoot, root bio-concentration factor and transfer factor plant, however increased proline, the concentration of lead in shoot and root at the collar plant. Furthermore, the application of humic acid reduced proline amount in treatments as follows: HA 0> HA 100> HA 200. Also, results suggested that humic acid showed a positive effect on bioavailable Pb, BR and MBC and bioavailable Pb in HA200 increased by 62.35 percent compared to HA0. Generally, despite of positive effect of HA on Pb uptake, collar plant couldnt be suitable for Pb phytoremediation as it accumulated Pb