Assessment of Heavy Metal Content in Soil and Vegetation of Mangrove Forest after Oil Spill in Bodo Community, Rivers State, Nigeria

Abstract

Mangrove forests are critical coastal ecosystems that provide essential environmental services. However, they are highly vulnerable to contamination from anthropogenic activities, such as oil spills. Hence, this study assessed the heavy metal content in soil and two dominant mangrove species—Rhizophora racemosa and Rhizophora harrisonii in the Bodo community, eleven years after a major crude oil spill. Four locations—A (Numuu Agbibel), B (Numuu Forge), C (Numuu Bia), and D (Numuu Alia) were purposefully selected. Soil and leaf samples were collected in triplicates during the rainy season and analyzed for copper (Cu), cadmium (Cd), chromium (Cr), lead (Pb), and nickel (Ni) using standard methods. Cd and Ni were not detected in the soil and leaves across the locations. The mean concentrations of heavy metals in soil ranged from 0.47–1.06mg/kg for Pb, 0.04–0.17mg/kg for Cr, and 4.81–10.22mg/kg for Cu. No significant variations were observed in the concentrations of Pb, Cr, and Cu across the locations. In leaf samples, Pb concentrations ranged from 0.28–2.45mg/kg, Cr from 0.07–0.39mg/kg, and Cu from 2.32–6.92mg/kg. The variations in the heavy metal concentrations were not significantly different across the sites (p>0.05), except for Cu at location A. The concentrations of Pb, Cr, and Cu in both the soil and leaves were below the permissible limits. This study provides baseline data for future evaluation of heavy metal concentration dynamics in soil and the evaluated mangrove species. The need to repeat the study during the dry season to ascertain seasonal trends is emphasized.