Study of the chronology of environmental impact of vehicular and industrial emissions in some parts of greater Accra region using tree rings

Abstract

This study determined the heavy metals pollution chronologies from vehicular and industrial emissions in the atmosphere using tree-rings as bio-indicators. Haatso atomic road and Tema Industrial area in the Greater Accra Region over the years have been the major hot spots for vehicular and industrial pollution respectively. Swietenia mahagoni (Mahogany) tree which is over 50 years in age was chosen for this study because it produces annual growth rings which is vital for the reconstruction of past climates. Tree ring counting method was used to determine the ages of both trees, at the various locations; Haatso Atomic road (1957-2018) and Tema Industrial Area (1968 - 2018). Energy Dispersive X-ray Fluorescence (EDXRF) was utilized to determine the presence and concentration of the following heavy metals (Cu, Mn, Zn, Pb, Cd, Fe and Ni) in the tree rings sampled. Concentration of Cu, Mn, Zn, Pb, Cd, Fe and Ni at the two sampling sites ranged from (1.92—9.84mg/kg), (2.58 – 5.49 mg/kg), (5.37 – 15.78mg/kg), (0.12—0.60 mg/kg), (0.01—0.09 mg/kg) (11.21—90.13 mg/kg) and (0.10 – 0.99 mg/kg) respectively. Surprisingly an increasing trend in concentration was observed for (Cd, Fe and Mn) with levels higher than the WHO guideline for heavy metals in the plant. The concentration of Cu, Zn, Pb, and Ni at both sampling sites were below WHO maximum limit by a factor of 1.2. Statistical analysis performed on the data from both sites revealed a strong positive correlation (0.85) between growth rings width of tree sampled from Haatso-Atomic road and that of the Tema Industrial area. It was observed that wet seasons correlate with high growth rate of trees while low precipitation seasons correspond to low or no growth rate of trees.