Evaluation of ecological risk due to suspended particulate matter-bound heavy metals deposited on selected plants in an urban area

Abstract

Heavy metal concentrations bound to suspended particulate matter (SPM) originating from industrial processes, vehicular emissions, road dust, and solid waste incineration pose serious ecological risks. Their persistent deposition on vegetation disrupts the ecological balance and endangers environmental health through long-term accumulation in sensitive ecosystems. This study investigated the ecological risks posed by SPM-bound heavy metals (Ag, Cd, Bi, Pb, Ga, Co, Mn, Cu, Mo, Ni, V, Zn, and Cr) deposited on the leaves of selected plant species across Delhi, India, during pre- and post-monsoon. The assessment involved calculating the enrichment factor (EF), contamination factor (C_f), contamination degree (C_deg), potential ecological risk factor (E_r), and potential ecological risk index (PER). Two-way ANOVA, Pearson's correlation, and Hierarchical Cluster Analysis (HCA) were employed for statistical analyses. The highest EF values were recorded for Co (11.23), Pb (3.26), and Ni (7.17) at the traffic-prone site in Bougainvillea glabra. Maximum C_f values were observed for Cd (3.58) and Zn (11.17). The highest E_r values were noted for Cd (158.34; Ficus religiosa L), Ni (5.89; F. religiosa), Pb (23.25; Ficus benjamina L), Cu (10.89; F. benjamina), and Zn (13.78; B. glabra). F. religiosa exhibited the highest PER of 199.39, while B. glabra showed the lowest of 110.17. Two-way ANOVA revealed significant differences (p < 0.05) in SPM-bound heavy metal concentrations. Cr exhibited positive correlations (0.358 ≤ r ≤ 0.817) with Ni, Pb, and Cu. Findings highlighted critical ecological risk from SPM-bound heavy metals in urban areas, necessitating suitable mitigation efforts.