MICROBIOLOGICAL INTERVENTIONS AT SOIL PLANT INTERFACE TO INDUCE LEAD MOBILITY AND ITS REMEDIATION

Abstract

Lead (Pb) is a toxic metal whose widespread use has caused extensive environmental contamination and health problems through food chain contamination in many parts of the world. Recently, phytoremediation has appeared as an effective and alternative solution to conventional physiochemical techniques for removal of Pb from contaminated soil. However, lack of understanding and information regarding Pb availability, speciation, uptake and translocation mechanisms, suitable plant species for hyperaccumulating Pb, microbial association that interfere phytoremediation process at plant soil interface are hindering its full-scale application. The aim of the current research was to develop an integrated plant-microbial association system for enhanced remediation of Pb contaminated soils using indigenous biological systems including plants and microorganisms. In the first step, extensive screening of ornamental plants locally grown in Pakistan was done for selection of Pb hyperaccumulator plant. Fortunately, two plants Pelargonium hortorum and Mesembryanthemum criniflorum were selected based on significantly higher Pb accumulation (>1000 mg Pb kg-1 in shoot dry biomass) and better translocation i.e., higher accumulation in shoot compared to root without significant (p<0.05) decrease in plant dry biomass (up to 1500 mg kg-1 soil Pb conc.). The selected plants were further investigated for root induced changes in rhizosphere during three-week culture in special cropping device fabricated locally. Results indicated significant ability of P. hortorum to acidify rhizosphere soil (ΔpH= -0.22 pH units) and increasing dissolved organic compounds (DOC) contents (1.4-1.7 –folds) that induced Pb mobility in soil (1-2 –folds) compared to M. criniflorum and control soil.