Plant Bark and Leaves as Bio-Indicators of Heavy Metals in Environmental Pollution Monitoring

Abstract

Environmental pollution from diesel generator emissions contributes to the accumulation of heavy metals in surrounding vegetation, especially in urbanizing areas. This study assessed the bio-indicator potentials of tree bark and leaves from Terminalia catappa near diesel generator plants at Mountain Top University. The work focused on toxic metals (As, U, Ag, Pb, Cd, Se), heavy metals (Ba, Ti, V, Cu, Sn), and essential metals (Fe, K, Mg, Zn, Ca, Na, Mn). Atomic Absorption Spectroscopy (AAS) revealed elevated levels of toxic metals such as Pb, Cd, and As, particularly in bark tissues. Notably, Pb reached 6.03 mg/kg in TL1 (tree leaves at location one) and over 6 mg/kg in TB1 (tree bark from location one), Cd ranged between 1.5 and 2.2 mg/kg, Ba (75.01 mg/kg in TB1) and (68.0 mg/kg in TB2), while Ti showed (90.1 mg/kg in TL3), (82.0 mg/kg in TL1) exceeding common phytotoxic thresholds. Barium recorded the highest heavy metal concentration in TB1, followed by Ti in TL3. SEM images confirmed the presence of particulate deposition more embedded in bark than on leaves—corroborating their role in pollution capture. The data highlight bark as a robust long-term indicator of environmental contamination, while leaves serve as responsive short-term sensors.