Size fractionated phytomonitoring of airborne particulate matter (PM) and speciation of PM bound toxic metals pollution through Calotropis procera in an urban environment

Abstract

Phytomonitoring of airborne toxic metals (e.g., Pb, Cd, Cu, and Ni) at urban roadsides was conducted by studying accumulation patterns in the leaves of Calotropis procera through foliar dust, leaf samples, road dust, and soil samples. These samples were collected at four roadside sites over three consecutive months (March through May 2017). The results show that the leaves of C. procera can accumulate selected airborne toxic metals. The uptake pattern of ambient particulate matter (PM) on leaf surfaces was also examined by scanning electron microscopy (SEM), coupled with energy dispersive spectroscopy. Particle density analysis based on SEM images quantified and distinguished PM accumulation in a range of different sizes (0.2-100 mu m) on both sides of the leaves. PM throughout the leaf (e.g., in stomata, trichomes, and epidermal appendages) was found to contain 12 airborne metals, including Pb, Cd, Cu, Ni, and Zn. The overall results support the use of C. procera as a phytomonitoring tool to assess interactions between plants and metals.