Toxicology of Heavy Metals to Subsurface Lithofacies and Drillers during Drilling of Hydrocarbon Wells

Okoro, Emeka Emmanuel and Okolie, Amarachi G. and Sanni, Samuel Eshorame and Omeje, Maxwell (2020) Toxicology of Heavy Metals to Subsurface Lithofacies and Drillers during Drilling of Hydrocarbon Wells. Scientific Reports, 10 (6). p. 152.

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Abstract

This study investigates the toxicological efects of heavy metals on lithofacies of the subsurface in a drilled hydrocarbon well as well as, to the drilling crew and people in an environment. The pollution levels of selected heavy metals were considered alongside their ecological efects during dry and wet seasons. The health hazard potential of human exposures to the metals, were estimated in terms of intensity and time using the USEPA recommended model. The heavy metal concentration for each layer decreased across the lithofacies as follows; Layer 5> Layer 4> Layer 3> Layer 2> Layer 1. The average concentrations of the heavy metals present in the samples obtained from the formation zone, varied signifcantly and decreased in the order of Al> Zn> Ni> Pb>Cr>Cu>Cd> As> Hg. The highest concentration of Al, Cu, and Zn in this present study were within the maximum allowable limits whereas, those of As, Cd, Hg and Ni were all above their maximum allowable limits. Among the transition metals analysed, the maximum mean daily dose of Pb (9.18 × 10−6mg/kg/d) and Cr (1.42 × 10−6mg/kg/d) were confrmed susceptible to human carcinogens and environmental toxins. The estimated hazard quotient shows that the dermal pathway is the most likely route via which the drilling crew and people in the environment can get contaminated. The cancer risk values for the Pb (7.72 × 10−4), Cd (1.35 × 10−1), Ni (9.97 × 10−3), As (1.50 × 10−1) and Cr (3.16 × 10−3) are all above the acceptable values. The cancer risk contribution for each metal was in the order of As>Cd> Ni>Cr> Pb. Layer 5 had the maximum Geo-accumulation index for the heavy metals considered. This higher Geoaccumulation index noted at the depth in Layer 5 may be attributed to the efect of water basin with turbidity currents, deltas, and shallow marine sediment deposits with storm impacted conditions. Also, the pollution from lead (Pb) in the dry season was maximum with an Igeo value> 5 for all the lithofacies considered because of the low background concentration of the metal. During the wet season, the heavy metal pollution rate was moderate for Zn whereas, it was extremely polluted with respect to Pb. The ecological risk potential of Pb shows that the associated ecological risks range from 536 – 664 in the wet season (i.e. extremely strong) and 2810 – 3480 in dry season (extremely strong). The high level of Pb pollution found in the area at such shallow depth may be due to the sedimentary folds possibly caused by the full spectrum of metamorphic rocks and primary fow structures at shallow depths. This was used to identify the environmental sensitivities of the heavy metals during the dry and wet seasons.

Item Type:	Article
Subjects:	Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General) T Technology > TP Chemical technology
Divisions:	Faculty of Engineering, Science and Mathematics > School of Engineering Sciences
Depositing User:	Mrs Hannah Akinwumi
Date Deposited:	30 Apr 2020 14:52
Last Modified:	30 Apr 2020 14:52
URI:	http://eprints.covenantuniversity.edu.ng/id/eprint/13296

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