Impact of Radioactivity and Heavy Metal Concentrations from subsurface formation cuttings on the Environment
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An assessment of Naturally occurring Radioactive Materials (NORM) and heavy metals (Al, Cr,
As, Hg, Ni, Cd, Pb, Cu and Zn) from drill cuttings of six different layers in the subsurface of an
oil well in the Niger-Delta was carried out. The assessment was carried out to estimate the
radionuclides and heavy metals in the drill cuttings and as well determine, the radiological risks
posed by the radionuclides and heavy metals to operators and nearby-inhabitants. The radionuclide
activities and heavy metal concentrations of the samples were analyzed. The health hazard
potential of human exposures to the metals, were estimated in terms of intensity and time using
the USEPA recommended model. The average concentrations of the heavy metals present in the
samples obtained from the formation zone, varied significantly and decreased in the order of Al >
Zn > Ni > Pb > Cr > Cu > Cd > As > Hg. The mean activity concentration for the different
radionuclides are 238U, 232TH and 40K were 3.9, 17.5 and 221.2 Bqkg-1 respectively. Comparing
the results from this study with those of a previous study, shows that for sandstone formations, the
uranium (238U) concentration was greater in the current study than what was obtained in the
previous study while the 232TH and 40K concentrations were lesser in the former than the latter. A
similar observation was made for a shale formation whereas, for a sandstone shale formation, the
estimated 238U, 232TH and 40K concentrations are less than those of the previous study. The
radionuclide activities decreased in the order of Layer 2 > Layer 1 > Layer 4 > Layer 5 > Layer 3
> Layer 6 whereas, for the heavy metal concentration obeyed this trend: Layer 5 > Layer 4 > Layer
3 > Layer 2 > Layer 1 > Layer 6. The risk assessment for the Annual Effective Dose Rate was greater than the allowable limit; while the exposure factor for heavy metal was within the allowable
limit.
Keywords
T Technology (General), TP Chemical technology