Ecological restoration of heavy metal-contaminated soil using Na-bentonite and green compost coupled with the cultivation of the grass Festuca arundinacea

Chemophytostabilization is a valuable alternative to many traditional methods of reducing the concentration of heavy metals in soil affected by industrial activity. In this study two soil additives - Na-bentonite and green compost were used separately and as a mixture combined with Festuca arundinacea to reclaim soil highly contaminated with Cd, Zn and Pb. It was found that a decrease in heavy metal concentrations (57-87% for Cd, 48-91% for Zn and 30-82% for Pb) in the amended soils was connected with the application of soil additives rather than with plant vegetation. Both of the soil additives contributed to achieving a higher biomass of F. arundinacea (1.5- to 9.5-fold) than in the non-amended soil. The accumulation of Cd, Zn and Pb in the plant organs was generally higher in the roots than in the shoots. Both soil additives positively influenced the soil enzymes activity and microbial functional capacity. Moreover, they altered the structure of microbial communities in the chemophytostabilized soils. The calculated soil quality indices confirmed that the combined amendments with grass vegetation were most effective in the soil reclamation than other treatments. The obtained results clearly indicate that the chemophytostabilization creates new opportunities for using bentonite and green compost as well as tall fescue grass to limit the transfer of toxic metals from polluted soils to the trophic levels of ecosystems.