Comparative Evaluation of Tree Species for Phytoremediation of Heavy Metal-Contaminated Soil: Effects of Humic and Salicylic Acid Application

Abstract

In order to assess the efficacy of phytoremediation in restoring degraded soils, specifically those contaminated with oil residues, a research pot trial was conducted. The main objective of the study was to compare the phytoremediation performance of various tree species, namely Eucalyptus camaldulensis, Albizia lebbeck, Ficus carica, and Morus nigra which represented the main factor. Additionally, the investigation aimed to evaluate the impact of different rates of humic acid HA (0, 5, 10 g L -1 ) as a sub-main factor, as well as varying rates of salicylic acid SA (0, 250, 500 mg L -1 ) as a sub-sub-main factor, on the phytoremediation capabilities of these trees. The specific focus was on their ability to remove heavy metals i.e., Zn, Pb, Cd, Ni from oil residues-contaminated soil. The results showed that Albizia lebbeck transplants exhibited the lowest soil Zn concentration (15.62 mg Zn.kg -1 soil) and a removal rate of 78.98%. Similarly, Albizia lebbeck transplants exhibited the lowest levels of soil available Pb, Cd and Ni concentrations compared to the other tree species studied, with higher removal rates. Furthermore, the foliar applications of both humic and salicylic acids resulted in a reduction of Zn, Cd, Pb, and Ni residues. The uptake of these heavy metals by the roots increased with higher concentrations of HA and SA. Specifically, the lowest values were recorded when the trees were treated with a combined application of HA at a rate of 10 g L -1 and SA at a rate of 500 mg L -1 .