Occurrence and Distribution of Arsenic, Antimony and Selenium in Shallow Groundwater Systems of Ibadan Metropolis, Southwestern Nigerian.

Effiong Ukorebi Etim

doi:10.5696/2156-9614-7-13.32

Abstract

Background.Arsenic, antimony and selenium contamination of groundwater is of great concern due to the potential detrimental effects to human health.Objectives.This study investigates the occurrence and distribution of arsenic, antimony and selenium in the shallow groundwater system of Ibadan metropolis, southwestern Nigeria.Methods.A total of 210 groundwater samples were collected from 35 shallow wells (3.15–7.86 m) within the residential, commercial, industrial and agricultural areas of the metropolis during the dry and wet seasons. The average daily dose intake (ADD), hazard quotient (HQ) and hazard index (HI) of arsenic, antimony and selenium exposure in groundwater were calculated from these four studied areas for children and adults.Results.Average concentrations of arsenic, antimony and selenium in groundwater ranged between 2.17±3.49 to 33.8±37.2 μg/L, 13.5±15.0 to 33.2±36.8 μg/L and 7.33±6.22 to 46.3±22.4 μg/L, respectively. A corresponding analysis relay plot showed the order of occurrence of these trace metals in groundwater to be antimony>selenium>arsenic. The principal component analysis biplot showed that arsenic, antimony and selenium were fairly distributed in all of the study areas, suggesting the influence of geogenic factors. A total of 74.3% of sampling locations had antimony levels slightly above the World Health Organization (WHO) safe limit of 20 μg/L. Statistical t testing (0.05 confidence limit) showed a significant difference in seasonal levels of groundwater antimony concentration, with the dry season recording significantly higher levels with 100% of samples exceeding WHO safe limits. The chemical of highest potential human health concern is antimony, with a non-carcinogenic HQ risk factor >2 for both age groups. The overall non-carcinogenic HI was highest in the commercial area, 4.1989 for adults and 5.2487 for children.Conclusions.Antimony in groundwater within the Ibadan metropolis raises health concerns and a concerted effort is needed to identify its sources to avoid the risk of antimony toxicity.

Highlights

IntroductionArsenic and antimony are ubiquitous metalloids widely distributed in the earth’s crust and most commonly found in natural groundwater aquifers.[1,2,3] Concentrations in groundwater are often associated with geological formations such as igneous and sedimentary rocks, and ores of different metals.[4,5,6] They are introduced naturally into groundwater through weathering processes of geogenic mineral rocks, leaching of wet deposition and microbial activities.[7,8] Contamination can be caused by anthropogenic activities such as mining, groundwater abstraction, industrial effluent sources and pesticide application in agricultural fields.[9,10] More often, it is natural processes that play a dominant role in arsenic mobility in groundwater, while antimony pollution originates mainly from mining and industrial emissions.[5,10,11,12] Arsenic and antimony are mostly found in inorganic forms in groundwater as trivalent arsenic [As (III)] or pentavalent arsenic [As (V)], trivalent antimony [Sb (III) or pentavalent antimony [Sb (IV)]
The present study revealed slightly elevated groundwater concentrations of antimony within the Ibadan metropolis
A total of 74.3% of sampled groundwater wells contained antimony concentrations above the World Health Organization (WHO) safe drinking water limit of 20 μg/L

Summary

Introduction

Arsenic and antimony are ubiquitous metalloids widely distributed in the earth’s crust and most commonly found in natural groundwater aquifers.[1,2,3] Concentrations in groundwater are often associated with geological formations such as igneous and sedimentary rocks, and ores of different metals.[4,5,6] They are introduced naturally into groundwater through weathering processes of geogenic mineral rocks, leaching of wet deposition and microbial activities.[7,8] Contamination can be caused by anthropogenic activities such as mining, groundwater abstraction, industrial effluent sources and pesticide application in agricultural fields.[9,10] More often, it is natural processes that play a dominant role in arsenic mobility in groundwater, while antimony pollution originates mainly from mining and industrial emissions.[5,10,11,12] Arsenic and antimony are mostly found in inorganic forms in groundwater as trivalent arsenic [As (III)] or pentavalent arsenic [As (V)], trivalent antimony [Sb (III) or pentavalent antimony [Sb (IV)]. Antimony and selenium contamination of groundwater is of great concern due to the potential detrimental effects to human health. This study investigates the occurrence and distribution of arsenic, antimony and selenium in the shallow groundwater system of Ibadan metropolis, southwestern Nigeria. A total of 210 groundwater samples were collected from 35 shallow wells (3.15-7.86 m) within the residential, commercial, industrial and agricultural areas of the metropolis during the dry and wet seasons. The average daily dose intake (ADD), hazard quotient (HQ) and hazard index (HI) of arsenic, antimony and selenium exposure in groundwater were calculated from these four studied areas for children and adults. The principal component analysis biplot showed that arsenic, antimony and selenium were fairly distributed in all of the study areas, suggesting the influence of geogenic factors. Keywords. groundwater, risk assessment, arsenic, antimony, selenium J Health Pollution 13: 32-41 (2017)

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Conclusion