Deposition and uptake of metals in urban canopy: Atmospheric arsenic sequestration

Abstract

The present study deals with quantifying the effectiveness of tree species in capturing atmospheric particulates and accumulating toxic elements like arsenic. This was achieved by analyzing the exposed leaves of six tree species (Ficus bengalensis, Ficus religiosa, Polyalthia longifolia, Anthocephalus cadamba, Putranjiva roxburghii, Alstonia scholaris) and foliar dusts deposited on those leaf surfaces for elemental content in Kolkata Metropolis, India. Morphology of leaf surface and chemical composition of foliar dust were examined using ESEM-EDAX. Amount of foliar dust is generally higher on adaxial surface in which agglomerates of atmospheric particulates cause clogging of stomata. Elemental composition in foliar dusts and canopy leaves were separately analyzed by EDXRF technique. Among the trace elements, heavy metals were found in considerable amount in the order Al>Zn>Pb>Cu>As>Cd>Co. Factor analysis suggests that co-associated, metallic elements are emitted as vehicle-derived pollutants as well as diffuse industrial emissions. Particulate arsenic is likely associated with combustion-derived materials and smelting operations. Significantly correlated arsenic between foliar dusts and plant leaves suggest atmospheric contamination to the urban ecosystem. P. roxburghii, A. cadamba and P. longifolia exhibited higher content of toxic metals including arsenic indicating their higher uptake capacity. The effectiveness of tree species in accumulating atmospheric particulates, particularly sequestration of atmospheric metals is the main outcome of this study.