Adsorption and permeability of heavy metals (Fe, Cu, Pb, Zn, Cr, and Cd) onto the adaxial cuticle of Ficus elastica leaf

Abstract

Air pollution represents a serious worldwide problem as atmospheric deposition of pollutants widely affects human and wildlife health. Heavy metals are significant pollutants with high toxicity, persistence, and bioaccumulation. In an environment polluted by industry and transportation, deposits of heavy metals on the leaves and their subsequent uptake by the plant occur. The leaf cuticle is the most important barrier between plant tissue and the atmosphere. To understand the processes of adsorption of heavy metals and their diffusion into the leaf, adaxial cuticles of Ficus elastica were enzymatically isolated and used in batch adsorption experiments and permeability measurements using diffusion chambers. A demonstration experiment with a whole leaf was also carried out, which pointed to the real uptake of metals by the leaf. Cuticles were subjected to characterization by methods of elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. In the adsorption experiment, significant differences in the maximum adsorption capacity (Cd>Pb>Cr>Fe>Cu>Zn), and mechanism of adsorption (Langmuir model for Fe and Cr, Freundlich model for Zn, Cu, Pb, and Cd) were found. The permeability of intact adaxial cuticle for studied heavy metals did not differ significantly. The extent of foliar uptake differed between metals, with the relatively highest uptake of Fe and Zn. The transport of metals in the leaf was also observed. It seems that adsorption to the leaf surface more than the permeability of the cuticle is a limiting factor for foliar uptake of heavy metals from atmospheric deposits.