Geochemical Cycling of Metals in Plant – Soil System in Selected States of the Central Niger Delta Region of Nigeria

Abstract

T Heavy metal pollution is a global concern due to their toxic effects of some of them. The geochemical cycling of heavy metals within the soil- plant system is unavoidably necessary. It enables the distribution of these metals within the eco-system. However, where the metals predominantly reside, and the type of metal is of primary importance. The geochemical cycling of nine heavy metals were investigated in this study using fundamental parameters of metal concentration, uptake ratio and relative soil enrichment factors. Soil and plant samples were collected from locations within the vicinity of oil facilities in Delta, Bayelsa and Akwa Ibom states in Nigeria. The control samples were taken around the areas where there was no visible oil activity. The samples were appropriately pre-treated before the determination of their metal content using Agilient Microwave Plasma Atomic Emission Spectroscopy (MPAES) instrument, model 4200. Iron had the highest concentration in both the soils and plants (74.72mg/Kg and 11.98mg/Kg) respectively while arsenic and mercury had the lowest concentrations in the soils and plants (0.012mg/Kg and 0.034mg/Kg) respectively. The concentration of mercury was below detection level (<0.002mg/Kg) in the soils. The concentrations were within the permissible levels except chromium. The concentration of the metals varied in the following order in the soils; topsoil, 0-15cm: Fe> Ni>Cr>Pb>Sr>V> Cd> As. In the bottom soil, 15-30cm, the same order was observed though the metal concentrations were lower. The order of variation in the plant was different from that of the soil, Fe> Cr> Sr> V> Ni> Cd > Pb > As > Hg. The range of the mean values of uptake ratios was 0.296 – 43.177 indicating that most of the metals were more in the plant than in the soil. The range of the mean values of the relative soil enrichment factor was 1.107 -1.283, indicating that there was no metal pollution as the values were less than 2. Although there was no evident heavy metal pollution, prompt and adequate monitoring is necessary.