Thermodynamic and Microbial Constraints on Redox-Induced Mobilization of Redox-Sensitive Metal(loid)s in Shallow Aquifers of Enugu
DOI:
https://doi.org/10.58885/ijees.v2i1.17.eoKeywords:
Redox-sensitive metals, Groundwater contamination, Microbial metal reduction, Enugu aquifers, Arsenic mobilization, Thermodynamic modeling, Iron and manganese oxides, Environmental geochemistry.Abstract
This study investigates the thermodynamic and microbial factors controlling the redox-induced mobilization of redox-sensitive metal(loid)s—iron (Fe³⁺), manganese (Mn), and arsenic (As)—in shallow aquifers across Enugu metropolis, Nigeria. A total of 25 water and sediment samples were collected from hand-dug wells and streams across five geographical areas: Ologo, Trans-Ekulu, Amechi, Ajali River/9th Mile and Centenary geographical areas. Samples were collected using sterile bottles, stored under cool conditions, and analyzed in the laboratory using Atomic Absorption Spectrophotometry (AAS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), following standard EPA analytical methods. All analyses were performed in triplicate, and results were reported as mean concentrations in milligrams per liter (mg/L). Results reveal spatial variability in metal concentrations influenced by local hydrogeochemical conditions. In the Ologo area, iron ranged from 0.300 to 0.390 mg/L, manganese from 0.154 to 0.300 mg/L, and arsenic from 0.029 to 0.068 mg/L. Amechi samples showed iron levels between 0.250 and 0.355 mg/L, manganese concentrations remained stable (0.150–0.165 mg/L), and arsenic ranged narrowly from 0.043 to 0.049 mg/L. In the Ajali River/9th Mile region, iron and manganese were elevated (0.301–0.420 mg/L and 0.220–0.260 mg/L, respectively), with arsenic ranging from 0.028 to 0.035 mg/L. Centenary Water sites recorded lower iron concentrations (0.180–0.290 mg/L), moderate manganese (0.150–0.190 mg/L), and low arsenic (0.020–0.027 mg/L). Trans-Ekulu exhibited the highest iron variability (0.220–0.718 mg/L), consistent manganese (0.225–0.229 mg/L), and low arsenic levels (0.013–0.016 mg/L). These findings indicate heterogeneous redox conditions influencing metal mobilization, with certain areas exceeding recommended iron limits for drinking water. The data contribute to understanding metal distribution patterns in Enugu’s aquifers and underscore the need for continuous monitoring to safeguard public health.
References
Appelo, C. A. J., and Postma, D. (2005). Geochemistry, Groundwater and Pollution (2nd ed.). CRC Press.
Bethke, C. M., Sanford, R. A., Kirk, M. F., Jin, Q., and Flynn, T. M. (2011). The thermodynamic ladder in geomicrobiology. American Journal of Science, 311(3), 183–210. https://doi.org/10.2475/03.2011.01
Egboka, B. C. E., Nwankwor, G. I., Orajaka, I. P., and Ejiofor, A. O. (1989). Principles and problems of environmental pollution of groundwater resources with case examples from developing countries. Environmental Health Perspectives, 83, 39–68. https://doi.org/10.1289/ehp.898339
Eze, V. N., and Ugwoke, P. E. (2021). Assessment of heavy metals in groundwater sources in Enugu State, Nigeria. Environmental Monitoring and Assessment, 193(2), 87.
Ibeneme, S. I., Anike, L. O., and Ezema, P. O. (2020). Hydrogeochemical and health risk assessment of heavy metals in groundwater sources in parts of Enugu, Nigeria. Environmental Earth Sciences, 79(8), 1–14. https://doi.org/10.1007/s12665-020-08983-9
Ibeneme, S. I., Nwankwo, C. N., and Okeke, A. C. (2020). Heavy metal contamination of groundwater resources in a Nigerian urban settlement. Journal of Environmental Science and Health, Part A, 55(12), 1501–1510. https://doi.org/10.1080/10934529.2020.1768674
Ibeneme, S. I., Okoye, N. O., and Ogbonna, C. I. (2020). Assessment of heavy metal concentrations and water quality indices of hand-dug wells in Enugu urban, southeastern Nigeria. Journal of Environmental Science and Pollution Research, 26(5), 4934–4945. https://doi.org/10.1007/s11356-019-04171-7
International Agency for Research on Cancer (IARC). (2012). Arsenic, metals, fibres and dusts. IARC monographs on the evaluation of carcinogenic risks to humans (Vol. 100C). Lyon, France: IARC. https://publications.iarc.fr/120
Kawasaki, Y., Zhang, W., and Wong, M. H. (2011). Health risk assessment of heavy metals in well water and surface water in the Pearl River Delta, China. International Journal of Environmental Research and Public Health, 8(6), 2022–2037. https://doi.org/10.3390/ijerph8062022
Kawaski, Y., Zhang, Z. W., and Hasegawa, T. (2011). Health effects of manganese in drinking water: Neurotoxicity and reproductive impact. Toxicological Reviews, 30(1), 37–45. https://doi.org/10.1007/s00204-010-0565-2
Keen, C. L., Ensunsa, J. L., and Watson, M. H. (2000). Nutritional aspects of manganese from experimental studies. NeuroToxicology, 20(2–3), 213–223.
Lovley, D. R., Holmes, D. E., and Nevin, K. P. (2004). Dissimilatory Fe(III) and Mn(IV) reduction. Advances in Microbial Physiology, 49, 219–286. https://doi.org/10.1016/S0065-2911(04)49005-5
Lovley, D. R., Phillips, E. J. P., Gorby, Y. A., and Landa, E. R. (2004). Microbial reduction of uranium. Nature, 350(6317), 413–416. https://doi.org/10.1038/350413a0
McArthur, J. M., Ravenscroft, P., Safiullah, S., and Thirlwall, M. F. (2001). Arsenic in groundwater: Testing pollution mechanisms for sedimentary aquifers in Bangladesh. Water Resources Research, 37(1), 109–117.
McMahon, P. B., and Chapelle, F. H. (2008). Redox processes and water quality of selected principal aquifer systems. Ground Water, 46(2), 259–271. https://doi.org/10.1111/j.1745-6584.2007.00385.x
Nealson, K. H., and Saffarini, D. (1994). Iron and manganese in anaerobic respiration: environmental significance, physiology, and regulation. Annual Review of Microbiology, 48(1), 311–343. https://doi.org/10.1146/annurev.mi.48.100194.001523
Nealson, K. H., and Scott, J. (2002). Ecophysiology of the genus Shewanella. In Dworkin, M. (Ed.), The Prokaryotes: An Evolving Electronic Resource for the Microbiological Community. Springer.
Nwankwoala, H. O., and Amadi, A. N. (2013). Hydrochemical facies and ionic ratios of groundwater in Port Harcourt, Southern Nigeria. Applied Water Science, 3(3), 641–651.
Oremland, R. S., and Stolz, J. F. (2005). Arsenic, microbes and contaminated aquifers. Trends in Microbiology, 13(2), 45–49. https://doi.org/10.1016/j.tim.2004.12.002
Ozoko, D. C., and Ezeugwu, I. O. (2025). Geomicrobiology of Aquifers in Enugu. European Journal of Applied Sciences, 13(2), 184–207.
https://doi.org/10.14738/aivp.132.18517
Ravenscroft, P., Brammer, H., and Richards, K. S. (2009). Arsenic Pollution: A Global Synthesis. Wiley-Blackwell.
Smedley, P. L., and Kinniburgh, D. G. (2002). A review of the source, behaviour and distribution of arsenic in natural waters. Applied Geochemistry, 17(5), 517–568.
Smith, A. H., Lingas, E. O., and Rahman, M. (2000). Contamination of drinking-water by arsenic in Bangladesh: A public health emergency. Bulletin of the World Health Organization, 78(9), 1093–1103.
Smith, A. H., Lopipero, P. A., Bates, M. N., and Steinmaus, C. M. (2000). Public health: Arsenic epidemiology and drinking water standards. Science, 296(5576), 2145–2146. https://doi.org/10.1126/science.1072896
Stumm, W., and Morgan, J. J. (1996). Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters (3rd ed.). Wiley-Interscience.
World Health Organization (WHO). (2017). Guidelines for Drinking-water Quality (4th ed., incorporating the 1st addendum). WHO Press.
World Health Organization (WHO). (2017). Guidelines for Drinking-Water Quality (4th ed.).
World Health Organization (WHO). (2017). Guidelines for drinking-water quality (4th ed.). Geneva: WHO Press.
Downloads
Published
How to Cite
Issue
Section
License
Copyright (c) 2017 Authors
This work is licensed under a Creative Commons Attribution 4.0 International License.
