Remediation of Mine Tailings and Fly Ash Dumpsites: Role of Poaceae Family Members and Aromatic Grasses

Abstract

Phytoremediation is an established technique for amelioration of soil contaminated with complex mixtures of heavy metals of anthropogenic origin. Coal fly ash and mine tailings include a conglomerate of heavy metals such as Cr, Pb, Hg, As, Ni, Cd, Cu, Mn, and Fe depending on the source of coal/ore and cause large-scale ecotoxicity. Unreclaimed mine tailing sites and coal fly ash dumpsites are a worldwide problem, presenting a source of contamination for nearby communities. The disposal sites are subject to erosion and are major causes of air pollution. Phytoremediation using plants for in situ stabilization and immobilization of these heavy metal-contaminated sites has gained momentum in the past few decades due to its cost-effectiveness and environmental sustainability. In this regard, the use of grasses is of prime importance due to their rapid growth, large biomass, resistance to phytotoxicity, and genotoxicity by heavy metals as compared to herbs, shrubs, and trees. Phytostabilization by the compact root system of grasses retards the formation, mobility, and bioavailability of hazardous leachates by high uptake and accumulation of the complex mixtures of heavy metals within them. Such grasses prevent natural succession by weeds and other plants leading to safe grazing by animals. Among the members of Poaceae, aromatic grasses are economically important plants due to their essential oil production. They rank higher than edible grasses, which are susceptible to heavy metal contamination in their edible parts. Various biochemical and molecular mechanisms govern the ADME (absorption, distribution, metabolism, excretion) of heavy metal contaminants in grasses growing in mine tailings and fly ash dumpsites. Metal-binding phytochelatins, metallothioneins, and antioxidant enzymes have key functions in these mechanisms. This chapter encompasses the role of members of Poaceae and aromatic grasses in phytoremediation of mine soil and coal fly ash with emphasis on their biochemical and molecular mechanisms.