DETERMINATION OF RADIONUCLIDE AND HEAVY METALS IN WATER, SEDIMENTS AND FISH SAMPLES FROM ONDO AND DELTA STATES NIGERIA

Abstract

The exploration and exploitation of oil take place in the rivers within Ondo and Delta States of Nigeria and these rivers serve as the major source of fishes and water consumed by the populace in these states. The widespread and dangerous consequence of the oil and gas industry; a major user of radioactive sources and the largest producer of radioactive wastes is pollution which is associated with virtually all stages of oil and gas production. This has led to the study of the concentration levels of heavy metals and activity concentrations of radionuclides in water, sediments and fish samples in twenty-one oil-producing communities and four control sites within Ondo and Delta state of Nigeria. The Atomic Absorption Spectroscopy (AAS) and the High Purity Germanium (HPGe) detector based gamma spectroscopy were used for all measurements. Results from this work indicates heavy metal concentration levels exist in the order of Pb > Cr > Ni >Cd in all sampling locations in Ondo and Delta state. Some heavy metals (Cadmiun in Gbaramatu and Lead in nearly all sampling location) occurred above the natural occurring values which indicates pollution of the sampling points in the studied area. The high concentrations of Lead which portends danger to the inhabitants of this area can also be attributed to the leaded fuel used in speedboats by the local fishermen. The heavy metals determined in this study are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens according to the U.S. Environmental Protection Agency, and the International Agency for Research on Cancer The distributions of the radionuclide activity concentration in the two states under consideration show that activity values across the state (oil producing and non-oil producing communities) are high for all samples as the values are close to the worldwide average concentrations. vii There is no significant difference between the activities in most oil producing communities when compared with activities of the control sites. Analysis of the fish samples showed higher concentration of 40K in Nile Tilapia compared with concentrations in the African catfish in both states. This may be attributed to tilapia scaly nature as fish scales have tendencies to absorb and accumulate 40K. All estimated values of effective dose in fish are below the annual dose limit of 0.4mGyyr-1 and estimated bioaccumulation factors as a model to predict water-to-fish and sediment-to-fish transfer indicate high rate of transfer of radionuclide from water and sediment to fish. Committed effective dose (CED) values which show the effects of exposure to the whole body of the individuals that consume these fishes, indicate highest exposure of 7.82 μ Sv at Awoye in Tilapia samples collected from Ondo State. Total bodily exposure values to 40K, 232Th and 238U in Catfish and Tilapia are all below the dose limit of 0.05 Sievert. The values of the radiological assessment indices obtained for all water, sediment and fish samples were observed to be lower than limits internationally reported and fall within the permissible maximum values, hence the radiation hazard at study areas are negligible.