The Role of Vascular Plants in the Phytoremediation of Fly Ash Deposits

Abstract

Fly ash is generated by coal combustion in thermal power plants during the production of electricity worldwide. Fly ash contains Si, Al, Fe, Ca, Mg, Na, K, As, B, Cu, Zn, Mn, Cd, Co, Cr, Ni, Pb, Mo, and Se as well as persistent organic pollutants (POP)s. Fly ash is disposed to artificial fly ash dumps in the form of thin slurry. Metal(loid)s from fly ash deposits leach in the surrounding environment and can cause environmental risks for soil, air, and water. To overcome this environmental problem, phytoremediation represents an urgent need for providing the recovery of degraded areas and improving human well-being. In this regard, the main phytoremediation techniques which use the plants to reduce the mobility and availability of toxic pollutants in fly ash are phytostabilization, rhizodegradation, phytoextraction, phytodegradation and phytovolatilization. Efficient biological recultivation and phytoremediation of fly ash deposits is achieved by seeding of grasses - legume mixtures and planting trees and shrubs. These species act as pioneering plants at the initial stage of revegetation at the degraded sites, they start the recovery process, improve physico-chemical properties of fly ash, provide erosion control, enhance moisture conservation and retain nutritive substances which are later used by spontaneous colonizers. Herbaceous plant species that are capable to grow on fly ash deposits should be perennial, fast growing, have an extensive root system, have the ability of vegetative propagation, fix nitrogen, and should be capable to tolerate adverse physico-chemical properties of fly ash, high temperature and drought. Resistance of plants to high concentrations of pollutants can be achieved by avoidance and / or tolerance. Finally, physiological response of plants to stress could be used to monitor the success of the ecorestoration project providing significant information about the capability of plants to grow and survive on fly ash deposits. Keywords: fly ash, vascular plants, metal(loid)s, organic compounds, phytostabilization, rhizodegradation, phytodegradation, excluders, accumulators, adaptation