Phytoremediation potential of the perennial crops giant reed and switchgrass to soils contaminated with heavy metals

Among the various impacts caused by man to the environment, soil contamination deserves attention. This gives rise to a number of environmental problems such as desertification, contamination of water resources and contamination of food crops, which can lead to serious health problems for humans directly or indirectly. To avoid these situations, it is necessary to decontaminate the soils, which can occur through various techniques (physical, chemical and biological methods). The use of plants for the decontamination of soils (phytoremediation), and specifically the use of energy crops, is an interesting alternative. Along with the decontamination action, the biomass produced may provide an additional income, when used for bioenergy or biomaterials, and the process contributes to the bioeconomy by reducing the dependence on fossil fuels. Therefore, the aim of this work was to study the effects of different heavy metals (Zn, Cr, Pb, Cd, Ni, Cu) on giant reed (Arundo donax L.) and switchgrass (Panicum virgatum L.) growth, productivity and biomass quality. The soils were artificially contaminated and the concentrations chosen were based on the limits established by the Decree Law 276 of 2009 (Portuguese regulation that establishes the regime for the use of sewage sludge in agricultural soils)-Zn: 450 mg/kg; Cr: 300 mg/kg; Pb: 450 mg/kg; Cd: 4 mg/kg; Ni: 110 mg/kg and Cu: 200 mg/kg. Results indicate that both switchgrass and giant reed are crops tolerant to Zn and Pb contamination. In contrast, for both crops, in Cr contaminated soils, a significant decrease in productivity was noted. Switchgrass was unable to grown in the Cr contaminated soils. Cadmium, nickel and copper also affected the yields of both crops, but not so significantly as chromium. In this establishment year, giant reed was three times more productive than switchgrass, and therefore showed to be more promising in heavy metals contaminated soils. Biomass is being characterized to evaluate the phytoremediation ability of both crops to the heavy metals studied