Heavy Metal Concentration and Risk Assesment of Oil Spill Contaminated Soil from Ogoni in Rivers State, Nigeria

This study investigated the level of Cu, Zn, Fe, Pb, V, Ni and Cd in sediment samples of an oil-spillimpacted site in Ogoni land, Okenta Alode, Eleme local government area, Rivers state, Nigeria. Soil sediments were collected from six different stations, with two from each station at surface (0 – 15 cm) and in-depth (15 – 30 cm) levels. One of the stations involves a bioremediated site, which was used as the control for the study, while the other station involves oil-spill-impacted sites. Bioremediated soil, obtained at about 200 meter away from the contaminated site was also collected making a total of twelve (12) samples, with the coordinates of the locations recorded with GPS device. Sample preparation and analysis were carried out using American Society of Testing Material (ASTM) D5708 (classic wet chemistry method) using the appropriate NIST standards. The filtrate which was containing the heavy metals in solution was then analyzed using the Shimadzu-1 model of Flame Atomic Absorption Spectrophotometer (APHA3111). The hierarchy of the concentrations of metals in the sediments appeared in the trend thus; Fe > Cu > Zn > Cd > Ni > V > Pb and metals concentration in the selected stations descended in the order of P1/S/O1 > P3/D/O2 > P2/S/O1 > P3/D/O2 > P4/S/O1 > P5/D/O1 > P5/S/O1 > P1/D/O1 > P4/D/O1 > P2/D/O1 > P1/D/CO1 > P1/S/CO1. The concentration of metals in the sediments were within the permissible limits and similarly have their ADI, THQ and HI lower than their respective reference dose (RfD) and less than 1, while the LCR of Cd were within the permissible range for carcinogens. Iron and Cd resulted to very high ecological risk and pollution. Also, Fe and Cd are implicated in resulting to high ecological risk and pollution. It is thus recommended that the rate of anthropogenic activities that tend to elevate heavy metals contamination and intoxication in this study location be reduced to curb the risk of heavy metals bioaccumulation and possible health effects in humans.