Radionuclide contents in soil, sediments and food samples, and incidences of cancer in oil producing localities in Imo State south-east Nigeria

Abstract

The communities in Ohaji-Egbema and Oguta Local Government Areas (LGAs) are surrounded by about 83 oil wells. Investigations indicated that crude wastes were not properly managed, and there were reported high number of cancer cases in the LGAs. Therefore, assessment of radionuclide contents in environmental and food samples, and incidences of cancer in the LGAs was carried out to determine any possible relationship between natural radionuclides in soil and sediment samples, and farm products, establish any possible relationship between reported cancer incidences and actual environment of the inhabitants, and develop models that could predict committed effective dose equivalents in yam, cassava and fish samples from radioactivity in soil and sediment samples. Soil, yam and cassava samples were collected from farmlands while sediment and fish samples were collected from rivers in the communities. The collected samples were prepared and taken to the laboratory for measurement. A well-calibrated lead-shielded 76 mm × 76 mm NaI (Tl) detector was deployed for the radiological investigation. It had a modest resolution of about 8% at 662 keV. Activity concentration of 214Bi (determined from its 1.760 MeV gamma-ray peak) was chosen to provide an estimate of 226Ra (238U) in the samples, while that of daughter radionuclide 208Tl (determined from its 2.614 MeV gamma-ray peak) was chosen as an indicator of 232Th. Potassium-40 was determined by measuring the 1.460 MeV gamma rays emitted during its decay. Results indicate that mean activity concentrations obtained from Ohaji-Egbema and Oguta are higher than those obtained from the control LGAs for 226Ra and 232Th which may be attributable to the geological variations of the study areas. The absorbed dose rates from Ohaji-Egbema and Oguta are slightly higher than world average value of 51 nGyh−1 while the committed effective dose equivalents from the study areas are less than world average value of 1.1 mSvy−1. The percentage contributions of natural radiation exposures to incidence of cancer in the study areas are less than 7% which implies that cancer incidences in the study areas may not be due to natural radioactivity levels. Hence, natural radioactivity levels may have been elevated in the communities of the oil producing localities but the concentrations are not yet frightening. In future environmental radioactivity studies, the developed models could be very useful.