Assessment of occurrence and origin of toxic metals in groundwater sources for domestic use in Enugu, Nigeria : pilot study results

MacAllister, D.J. ORCID: https://orcid.org/0000-0001-8893-9634; Aladejana, J.A.; Lapworth, D.J. ORCID: https://orcid.org/0000-0001-7838-7960; Chenery, S.; Eduvie, M.; Iorkumbur, E.; Kadiri, D.; Onwuka, S.; Smedley, P.; Tijani, M.. 2022 Assessment of occurrence and origin of toxic metals in groundwater sources for domestic use in Enugu, Nigeria : pilot study results. Nottingham, UK, British Geological Survey, 48pp. (OR/22/061) (Unpublished)

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Abstract/Summary

In April of 2021, during routine water quality testing on five handpump borehole sources installed by WaterAid in Ugwuaji, Engugu, Nigeria, lead and cadmium were discovered to be above permissible limits in three of the handpump sources. As a result, WaterAid Nigeria commissioned the British Geological Survey and University of Ibadan to conduct further investigation of the occurrence, concentration and origin of lead in handpump boreholes in the Engugu region. This report describes the findings of a pilot study which focused on identifying the origin and quantifying the concentrations of dissolved and total lead (Pb) and cadmium (Cd) present in boreholes equipped with handpumps. Concentrations of Pb and Cd in handpump boreholes were also compared to concentrations of these elements in other water source types, including shallow hand-dug wells, surface water and boreholes with submersible pumps installed. A total of 32 water samples were collected, including seven shallow hand-dug wells and six surface water samples. Five water samples were also collected from one shallow hand dug well and four handpump boreholes outside Ugwuaji. In addition, a small number handpump component samples were collected (i.e. PV pipe and metal scrapings). Six samples of soil from well cuttings and rocks along the river channels were also collected for Pb isotope analysis to identify potential sources of Pb within groundwater. The samples were sent to three different laboratories (National water resources institute (NWRI) International Institute of Tropical Agriculture (IITA) and British Geological Survey (BGS)) for analysis of major ions and trace metals (focusing on Pb and Cd). The results of the elemental analysis found no consistency in concentrations of either Pb or Cd between laboratories. While some level of variation between results from different laboratories is to be expected, the differences in Pb and Cd concentrations between the laboratories are significant, non-systematic and beyond what might reasonably be expected, raising concerns about the accuracy of results reported from the local labs. Possible sources of uncertainty could be the purity of the acid used, the standards used, and other QA procedures used by the Nigerian labs. The results from the BGS laboratories indicate that concentrations of Pb and Cd are below WHO guideline values and Nigerian permissible limits in most samples. A single unfiltered sample (i.e. total concentration which includes dissolved and particulate Pb) from the BGS analyses had Pb concentration (10.5 μg/L) exceeding the WHO and Nigerian guideline values for drinking water of 10 μg/L. Median Pb and Cd samples were highest in samples taken early in the morning before the days pumping had begun (5.01 μg/L and 0.036 μg/L respectively) suggesting the handpump materials as a possible source of both elements. There was no systematic increase in heavy metal concentrations for Pb and Cd in unfiltered samples compared to filtered samples, suggesting that for most samples analysed these contaminants are in solution. However, further work on paired dissolved and total samples would help quantify the proportion of dissolved and particulate concentrations and indicate the risk of drinking unfiltered water from the handpump boreholes. No samples analysed by BGS had Cd concentrations exceeding the WHO or Nigerian guideline values for drinking water for Cd of 3 μg/L and 5 mg/l respectively. Analysis also showed samples from four sites exceeding the guideline value/national standard for fluoride (1.5 μg/L) in drinking water (range 2.39-2.49 μg/L). The lead isotope data suggest that the lead found in the water samples analysed (i.e. samples with > 1 μg/l) does not come from the local soil/sediment/cuttings. It appears to be a mixture of lead found in the PVC pipes, scrapings from other handpump components and industrial or lead based petrol (likely in the form of air particulates). Further analysis would be required to definitively identify the source of the lead found in the water samples but the initial analysis suggests that the handpump components are a likely candidate. However, it is important to re-emphasize that lead concentrations in the waters analysed were not found at levels that exceed WHO guideline or Nigerian standards, although some studies suggest that there is no safe concentration for lead in potable water supplies. Recommendations for further work to understand the discrepancies between laboratory results and the origin of lead are as follows: 1. More detailed inter-laboratory comparison. Certified water quality standards and solutions with known element concentrations should be prepared at BGS and analysed independently by all three laboratories. No standard solutions were sent to the Nigerian laboratories in the preliminary study. 2. Further collection and analysis of water quality samples from a larger sample of handpump and other sources to better establish a baseline for total and dissolved Pb and Cd concentrations. 3. More extensive and detailed Pb isotope sampling and analysis including collection of a range of end members from the local area (i.e. air particulate samples).

Item Type:	Publication - Report
Funders/Sponsors:	British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed but not externally peer-reviewed.
Additional Keywords:	Groundwater, GroundwaterBGS, IGRD
Date made live:	03 Apr 2023 08:42 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/534303

Item Type:

Publication - Report

Funders/Sponsors:

British Geological Survey

Additional Information. Not used in RCUK Gateway to Research.:

This item has been internally reviewed but not externally peer-reviewed.

Additional Keywords:

Groundwater, GroundwaterBGS, IGRD

Date made live:

03 Apr 2023 08:42 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/534303