Phytoremediation Potential and Essential Oil Quality of Peppermint Grown in Contaminated Soils as Affected by Sludge and Time

This study aimed to assess the effect of incubation time and sewage sludge on peppermint biomass, essential oil yield, and Zinc (Zn), lead (Pb), and Cadmium (Cd) concentrations in the plant tissues as well as assessing phytoremediation potential of peppermint grown in contaminated calcareous soils. A greenhouse experiment was conducted by growing peppermint (Mentha pipertia L.) in two contaminated soils treated with three levels of sewage sludge (0, 10, and 30 g kg-1) over two incubation times (30 and 120 days). Results revealed an increase in plant biomass and essential oil yield with an increase in incubation time and the sewage sludge amount. The concentrations of Zn, Pb, and Cd in plant tissues increased significantly in all treatments, except Cd concentration in plants growing on 10 g kg-1 of sewage sludge and incubated for 120 days. No traces of Zn, Pb, and Cd were found in essential oil of plants treated with 10 g kg-1 of sewage sludge. In other treatments, the concentrations of these metals in the essential oil were found within the limits recommended for medicinal plants. Unlike the bioaccumulation factor, the translocation factor of the studied metals decreased with an increase in the sewage sludge amount and incubation time. Although peppermint was not a sustainable plant to lower the pollution load, as the biomass production increased significantly and metals concentrations in essential oil remained within the recommended limits in all treatments, it can be concluded that peppermint can be used for cultivation in contaminated soils treated with sewage sludge.