ABSTRACT
Concentrations of 222Rn and other toxic metals (Ni, Cu, Fe, Cd, Zn, Pb, Cr, and Mn) were measured by alpha spectrometry using Rad7 and atomic absorption spectrophotometry, respectively, in the water samples from the Ilokun dumpsite, Ado-Ekiti, Nigeria. The physicochemical parameters of the groundwater were also assayed to determine its suitability for drinking and irrigation purposes. While the physicochemical parameters met the World Health Organization (WHO)-safety standards, Cu, Fe, Cd, Pb, Cr, and Mn exceeded permissible limits. Hazard index (HI) values for adults (8.40) and children (39.23) indicated heightened susceptibility to non-carcinogenic health risks among both age group populations. The 222Rn concentrations present in the studied samples range from 5.4 to 23.1 Bq l−1 with an average of 13.9 Bq l−1. Approximately 60% of the samples have radon concentrations above the US Environmental Protection Agency (EPA)-maximum contaminant level of 11.1 Bq l−1. The evaluated radiation doses to the stomach and respiratory tract due to radon content in the water are well below the WHO-specified individual dose criterion of 0.1 mSv year−1. This study suggests a need for groundwater resource management strategies and measures to protect human health from radiological and toxicological risks associated with groundwater consumption around the Ilokun dumpsite.
HIGHLIGHTS
The study assessed the concentrations of 222Rn and toxic metals in water samples near a dumpsite.
The hazard index values for adults and children indicated heightened non-carcinogenic health risks.
Approximately 60% of the samples surpassed the USEPA-approved safety limit for 222Rn.
Despite elevated radon levels, the evaluated radiation doses to the stomach and respiratory tract were below the WHO dosage limit.
INTRODUCTION
Paucity of potable water has often necessitated the use of groundwater as an alternative drinking water source in many areas of the world. Within the vicinity of a dumpsite, groundwater may be prone to chemically toxic substances due to infiltration of hazardous materials, thereby increasing human health risk burden in addition to the already dissolved naturally occurring radionuclides. 222Rn is one of the naturally occurring radionuclides present in groundwater that presents significant health risks to humans. Although the exposure from 222Rn due to inhalation accounts for about half of the radiation dose to human beings received from natural radionuclides (UNSCEAR 2002), the radiation exposure from radon ingestion in water has also been considered important. Radon is a radioactive gas that occurs in the 238U decay series. It exists in three radioisotopes, namely, 219Rn, 220Rn, and 222Rn. Of the three radioisotopes, 222Rn is the most important due to its relatively long half-life (3.82 days). The cancer risk from radon ingestion in groundwater has been studied by many researchers around the world (Auvinen et al. 2005; Al-Alawy et al. 2018; Divya & Prakash 2019; Naskar et al. 2023).
Apart from the radiological health concerns posed by radon in groundwater, the groundwater reservoirs near dumpsites may also expose the local residents to potential risks of chemical toxicity. Groundwater contamination caused by leachate emanating from dumpsites has been a serious environmental concern all over the world (Aboyeji & Eigbokhan 2016; Parvin & Tareq 2021; Sanga et al. 2023). Dumpsites receive various forms of waste, encompassing industrial refuse, hazardous materials, and municipal solid waste (MSW). When these wastes decompose, they produce a liquid known as leachate, which comprises a blend of toxic metals, organic and inorganic compounds, pathogens, and other pollutants (El-Saadony et al. 2023). The makeup of leachates differs based on the nature of the waste, the landfill's age, hydrological conditions, landfill operation practices, and climatic conditions (Somani et al. 2019; Lindamulla et al. 2022). The leachate generated at dumpsites has the potential to infiltrate the soil and enter the groundwater system through natural fractures, sinkholes, or porous formations, resulting in aquifer contamination. Consequently, regions in close proximity to dumpsites are susceptible to groundwater contamination due to the potential for contamination from the nearby disposal site. If such contamination persists for long periods, it could pose significant health hazards to users of the local groundwater resource and to the surrounding natural ecosystem. If contaminated groundwater is used for drinking, cooking, or irrigation, it can lead to serious human health issues. Exposure to contaminants like heavy metals and organic compounds can cause various ailments, including neurological disorders, cancers, and reproductive problems. Groundwater contamination affects not only human populations but also ecosystems. Aquatic life can be harmed by toxic substances, leading to the disruption of natural habitats and reduction in biodiversity (Bassem 2020). Contaminated groundwater can also impact surface water bodies, such as lakes and rivers, through leachate discharge.
Illnesses stemming from the pollution of drinking water pose a significant challenge to human health (WHO 2017). While approximately 80% of global diseases are attributed to inadequate drinking water quality, this factor contributes to about 50% of child fatalities on a global scale (Lin et al. 2022). Against this background, the assessment of groundwater quality from radiological and chemical toxicity perspectives in the proximity of dumpsites becomes crucial to ascertain the water suitability for human consumption. The assessment will provide valuable insights for effective planning and sustainable administration of groundwater resources in the environs of a dumpsite. The Ilokun dumpsite, situated in Ado-Ekiti, is a prominent dumpsite among many others found across the country. Similar to other dumpsites in Nigeria, waste is deposited on excavated plots without considering the impact on the underlying environment (Aduojo et al. 2018). This practice contrasts with global best practices wherein dumpsites are designed with lined walls made of clayey materials or polyethylene geomembrane liners. These measures aim to minimize the upward and outward movement of pollutants produced by the disposed substances in dumpsites, thereby reducing the potential environmental impact.
Past research endeavors (Olagunju et al. 2018; Olaseeni et al. 2018; Okunade et al. 2019; Omofunmi et al. 2020) carried out within the study locale have primarily concentrated on evaluating the impact of the waste dumpsite on both groundwater and soil quality. However, limited attention has been given to investigating the potential human health risks associated with the dumpsite. Also, there has been no assessment of the groundwater of the area from the radiological perspective. Hence, the objectives of this research are to conduct hydrogeochemical analysis of groundwater samples, assess the groundwater suitability for irrigation and domestic purposes, and determine the health risks associated with the ingestion of groundwater-borne radon and heavy metal in the vicinity of the Ilokun dumpsite in Ado-Ekiti, Nigeria.
MATERIALS AND METHODS
Location, geology, and hydrogeology of the study area
Location map of the study area showing the Ilokun dumpsite (Inset: Map of Nigeria) (Modified after Badmus et al. (2022)).
Location map of the study area showing the Ilokun dumpsite (Inset: Map of Nigeria) (Modified after Badmus et al. (2022)).
Geologic map of Ekiti State showing the area of study (digitized from Ogungbemi et al. (2022)).
Geologic map of Ekiti State showing the area of study (digitized from Ogungbemi et al. (2022)).
Data collection/quality assurance for hydrogeochemical analysis
A total of 10 samples (S1–S10) of water were collected spatially from residences within a radius of 500 m from the center of the Ilokun dumpsite during the dry season (December 2023). To comply with the World Health Organization (WHO) and the American Public Health Association (APHA et al. 2017) water sampling guidelines, a bailer was employed to collect the samples, which were carefully transferred into 1-L plastic bottles. The sampled wells vary in depth from 9 to 35 m. Sample locations were recorded with the aid of a highly sensitive handheld GPS device (GARMIN GPS 72H). Prior to the water sample collection, the water pipelines were adequately flushed for several minutes to ensure that representative groundwater samples were collected in accordance with the measurement of water for radon protocol (ANSI/AARST MW-RN 2020). Immediately after collection, the bottles were tightly sealed to prevent aeration and then transported to the laboratory in a cooler with ice for subsequent analysis. The collected samples were stored in a refrigerator at a temperature of 4 °C and subjected to analysis within 72 h from when they were collected. The laboratory employed analytical-grade reagents for the analysis, ensuring reliability and precision by employing blanks and duplicate samples. Every specimen underwent assessment for 18 parameters, encompassing total dissolved solids (TDS), temperature, electrical conductivity (EC), and potential of hydrogen (pH), which were measured on site utilizing a portable device (Jenway 430). The analysis of cations, anions, and heavy metals was carried out on the collected samples at the chemistry laboratory of Afe Babalola University. Flame photometer (FP 902 PG model) was used to analyze calcium, potassium, and sodium concentrations, while the UV spectrophotometer (Jenway PFP7 model) was employed to analyze sulfate concentrations. Bicarbonate and chloride levels were ascertained through the titration technique. Furthermore, an atomic absorption spectrophotometer (AAS) of the Buck Scientific 211 VGP model with a detection limit of 0.001 was utilized to analyze the presence of additional elements, such as nickel, copper, lead, iron, magnesium, manganese, zinc, and chromium.
Hydrochemical analysis
The groundwater dataset was statistically analyzed with the aid of IBM Statistical Package for Social Sciences (IBM SPSS) version 22.0. Subsequently, a comparison was made between the mean, range, and standard deviation of the parameters being investigated and the standards prescribed by the WHO (2011). To characterize the hydrochemical compositions of the groundwater samples, the water chemistry data were analyzed with the aid of a Geochemist Workbench version 17.0 software and the findings were visually depicted on Schoeller and Piper diagrams.

Evaluation of health risks resulting from heavy metals







Exposure parameters for average daily intake (Badmus et al. 2022)
Parameters . | Unit . | Children . | Adults . | References . |
---|---|---|---|---|
EF | ![]() | 365 | 365 | Ametepey et al. (2018) |
ED | years | 6 | 30 | Alidadi et al. (2019) |
AT | days | ![]() | ![]() | Haque et al. (2018) |
IR | ![]() | 2 | 2 | Ojo et al. (2020) |
BW | ![]() | 15 | 70 | Haque et al. (2018) |
Parameters . | Unit . | Children . | Adults . | References . |
---|---|---|---|---|
EF | ![]() | 365 | 365 | Ametepey et al. (2018) |
ED | years | 6 | 30 | Alidadi et al. (2019) |
AT | days | ![]() | ![]() | Haque et al. (2018) |
IR | ![]() | 2 | 2 | Ojo et al. (2020) |
BW | ![]() | 15 | 70 | Haque et al. (2018) |
EF, exposure frequency; ED, exposure duration; AT, average time; IR, ingestion rate; BW, body weight.

The reference dose indicates the highest permissible amount of a harmful substance that can be taken in over a lifetime without causing any expected negative health effects (USEPA 2022; Nativio et al. 2024). The values of the RfD considered for this study are outlined in Table 2.
RfD values considered for the study
Parameters . | RfD values . | References . |
---|---|---|
Fe | 0.70 | Yadav et al. (2018) |
Mn | 0.14 | Yadav et al. (2018) |
Zn | 0.30 | Yadav et al. (2018) |
Cu | 0.04 | Yadav et al. (2018) |
Ni | 0.02 | Liang et al. (2017) |
Cr | 0.11 | Liang et al. (2017) |
Pb | 0.004 | USEPA IRIS (2011) |
Parameters . | RfD values . | References . |
---|---|---|
Fe | 0.70 | Yadav et al. (2018) |
Mn | 0.14 | Yadav et al. (2018) |
Zn | 0.30 | Yadav et al. (2018) |
Cu | 0.04 | Yadav et al. (2018) |
Ni | 0.02 | Liang et al. (2017) |
Cr | 0.11 | Liang et al. (2017) |
Pb | 0.004 | USEPA IRIS (2011) |
RfD, reference dose.
The HI value serves as a screening tool to evaluate the significant health concerns due to heavy metal exposure through groundwater ingestion (Edokpayi et al. 2018; Yadav et al. 2018).
If the HI surpasses a value of one, it indicates the potential for non-carcinogenic health repercussion within the population exposed (Edokpayi et al. 2018).
Radon measurement
For the purpose of radon measurement, 10 samples of groundwater were also collected from the same sample sites described above for hydrochemical water sampling. The water samples were obtained in accordance with the sampling guidelines provided in the American Association of Radon Scientists and Technologists (AARST)/American National Standards Institute (ANSI) document (ANSI/AARST MW-RN 2020). A Durridge Rad7 radon monitor (Serial Number: 03093) was employed for the radon concentration measurement in the samples. The instrument was used because of its versatility. It is capable of determining radon concentration in water within 30 min. For the water samples collection, 10 250 mL sample vials supplied with the RadH2O accessory kits of the Rad7 instrument were used. The water samples were prevented from air contact during the collection process and thereafter transported to the laboratory for analysis. At the laboratory, the 250 mL sample vial was connected to the Rad7 instrument in the setup explicitly described by Ajiboye et al. (2018).



Calculation of ingestion and inhalation doses






RESULTS AND DISCUSSION
Physicochemical parameters and heavy metal concentrations
Table 3 presents an overview of the physicochemical parameters and heavy metal concentrations observed in the studied groundwater. It compares the descriptive statistics of these parameters with the recommended limits set by the WHO (2011). The groundwater pH varied between 6.76 and 7.69, with an average of . The observed mean pH indicates a slightly alkaline nature of the groundwater within the investigated region. The EC values varied between 114.85 and 338.61 μS/cm, with an average of
. The TDS varied between
with an average value of
. Bicarbonate, sulfate, chloride, magnesium, calcium, potassium, and sodium have a mean concentration of
,
,
,
,
,
, and
, respectively. All the measured physicochemical parameters of the groundwater were found to be within the acceptable limits set by the WHO for safe drinking water (Table 3).
Comparison of statistical summary of groundwater parameter with the World Health Organization standard
Sample . | pH . | TDS . | EC . | HCO3− . | SO42− . | Cl− . | Mg2+ . | Ca2+ . | K+ . | Na+ . | Fe . | Mn . | Zn . | Cu . | Pb . | Ni . | Cr . | Cd . |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
S-1 | 7.69 | 148.50 | 296.21 | 7.36 | 1.35 | 15.24 | 2.87 | 27.20 | 32.75 | 8.35 | 0.37 | 0.41 | 0.78 | 0.48 | 0.11 | 0.00 | 0.76 | 0.01 |
S-2 | 7.02 | 116.34 | 254.58 | 5.95 | 2.14 | 11.62 | 3.22 | 17.70 | 28.50 | 4.35 | 0.29 | 0.62 | 0.81 | 0.40 | 0.08 | 0.01 | 1.08 | 0.01 |
S-3 | 6.85 | 155.27 | 310.73 | 9.21 | 3.06 | 22.52 | 1.96 | 24.45 | 41.25 | 12.55 | 0.45 | 0.80 | 0.52 | 0.41 | 0.06 | 0.01 | 0.97 | 0.02 |
S-4 | 6.76 | 161.59 | 338.61 | 8.16 | 2.97 | 24.49 | 2.96 | 19.50 | 30.75 | 9.70 | 0.50 | 0.91 | 0.92 | 0.58 | 0.03 | 0.00 | 0.85 | 0.01 |
S-5 | 7.33 | 93.75 | 185.25 | 3.33 | 0.91 | 7.27 | 1.98 | 13.85 | 15.60 | 7.40 | 0.19 | 0.29 | 0.27 | 0.32 | 0.05 | 0.00 | 0.49 | 0.00 |
S-6 | 7.43 | 108.32 | 216.83 | 4.17 | 1.32 | 10.37 | 2.27 | 21.50 | 18.25 | 5.80 | 0.20 | 0.31 | 0.31 | 0.29 | 0.03 | 0.00 | 0.41 | 0.01 |
S-7 | 7.51 | 76.56 | 145.95 | 3.05 | 1.06 | 8.15 | 6.15 | 33.35 | 50.75 | 17.30 | 0.62 | 0.92 | 0.65 | 0.70 | 0.07 | 0.01 | 0.85 | 0.02 |
S-8 | 7.15 | 88.91 | 171.58 | 2.14 | 2.65 | 7.49 | 5.67 | 26.80 | 38.50 | 10.60 | 0.53 | 1.08 | 0.65 | 0.81 | 0.09 | 0.01 | 1.17 | 0.02 |
S-9 | 7.60 | 56.12 | 114.85 | 6.84 | 0.58 | 9.59 | 2.32 | 10.45 | 8.20 | 3.65 | 0.22 | 0.32 | 0.21 | 0.25 | 0.02 | 0.00 | 0.29 | 0.01 |
S-10 | 7.60 | 62.56 | 128.26 | 5.19 | 0.72 | 10.07 | 3.07 | 19.55 | 13.50 | 5.05 | 0.31 | 0.42 | 0.19 | 0.17 | 0.01 | 0.00 | 0.42 | 0.01 |
S | 6.50–9.50 | 1,500 | 1,200 | – | 500 | 250 | 20 | – | – | 200 | 0.30 | 0.50 | 5.00 | 0.50 | 0.01 | 0.02 | 0.05 | 0.005 |
Min. | 6.76 | 56.12 | 114.85 | 2.14 | 0.58 | 7.26 | 1.96 | 10.45 | 8.20 | 3.65 | 0.19 | 0.29 | 0.19 | 0.17 | 0.01 | 0.00 | 0.29 | 0.00 |
Max. | 7.69 | 161.59 | 338.61 | 9.21 | 3.06 | 24.49 | 6.15 | 33.35 | 50.75 | 17.30 | 0.62 | 1.08 | 0.92 | 0.81 | 0.11 | 0.01 | 1.17 | 0.02 |
Mean | 7.29 | 106.79 | 216.28 | 5.54 | 1.68 | 12.68 | 3.25 | 21.44 | 27.81 | 8.49 | 0.37 | 0.61 | 0.53 | 0.44 | 0.05 | 0.00 | 0.73 | 0.01 |
SD | 0.31 | 36.21 | 75.95 | 2.24 | 0.90 | 5.85 | 1.40 | 6.42 | 12.98 | 4.01 | 0.14 | 0.28 | 0.26 | 0.19 | 0.03 | 0.00 | 0.29 | 0.00 |
SES | – | – | – | – | – | – | – | – | – | – | 6 | 5 | – | 3 | 9 | – | 10 | 8 |
Sample . | pH . | TDS . | EC . | HCO3− . | SO42− . | Cl− . | Mg2+ . | Ca2+ . | K+ . | Na+ . | Fe . | Mn . | Zn . | Cu . | Pb . | Ni . | Cr . | Cd . |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
S-1 | 7.69 | 148.50 | 296.21 | 7.36 | 1.35 | 15.24 | 2.87 | 27.20 | 32.75 | 8.35 | 0.37 | 0.41 | 0.78 | 0.48 | 0.11 | 0.00 | 0.76 | 0.01 |
S-2 | 7.02 | 116.34 | 254.58 | 5.95 | 2.14 | 11.62 | 3.22 | 17.70 | 28.50 | 4.35 | 0.29 | 0.62 | 0.81 | 0.40 | 0.08 | 0.01 | 1.08 | 0.01 |
S-3 | 6.85 | 155.27 | 310.73 | 9.21 | 3.06 | 22.52 | 1.96 | 24.45 | 41.25 | 12.55 | 0.45 | 0.80 | 0.52 | 0.41 | 0.06 | 0.01 | 0.97 | 0.02 |
S-4 | 6.76 | 161.59 | 338.61 | 8.16 | 2.97 | 24.49 | 2.96 | 19.50 | 30.75 | 9.70 | 0.50 | 0.91 | 0.92 | 0.58 | 0.03 | 0.00 | 0.85 | 0.01 |
S-5 | 7.33 | 93.75 | 185.25 | 3.33 | 0.91 | 7.27 | 1.98 | 13.85 | 15.60 | 7.40 | 0.19 | 0.29 | 0.27 | 0.32 | 0.05 | 0.00 | 0.49 | 0.00 |
S-6 | 7.43 | 108.32 | 216.83 | 4.17 | 1.32 | 10.37 | 2.27 | 21.50 | 18.25 | 5.80 | 0.20 | 0.31 | 0.31 | 0.29 | 0.03 | 0.00 | 0.41 | 0.01 |
S-7 | 7.51 | 76.56 | 145.95 | 3.05 | 1.06 | 8.15 | 6.15 | 33.35 | 50.75 | 17.30 | 0.62 | 0.92 | 0.65 | 0.70 | 0.07 | 0.01 | 0.85 | 0.02 |
S-8 | 7.15 | 88.91 | 171.58 | 2.14 | 2.65 | 7.49 | 5.67 | 26.80 | 38.50 | 10.60 | 0.53 | 1.08 | 0.65 | 0.81 | 0.09 | 0.01 | 1.17 | 0.02 |
S-9 | 7.60 | 56.12 | 114.85 | 6.84 | 0.58 | 9.59 | 2.32 | 10.45 | 8.20 | 3.65 | 0.22 | 0.32 | 0.21 | 0.25 | 0.02 | 0.00 | 0.29 | 0.01 |
S-10 | 7.60 | 62.56 | 128.26 | 5.19 | 0.72 | 10.07 | 3.07 | 19.55 | 13.50 | 5.05 | 0.31 | 0.42 | 0.19 | 0.17 | 0.01 | 0.00 | 0.42 | 0.01 |
S | 6.50–9.50 | 1,500 | 1,200 | – | 500 | 250 | 20 | – | – | 200 | 0.30 | 0.50 | 5.00 | 0.50 | 0.01 | 0.02 | 0.05 | 0.005 |
Min. | 6.76 | 56.12 | 114.85 | 2.14 | 0.58 | 7.26 | 1.96 | 10.45 | 8.20 | 3.65 | 0.19 | 0.29 | 0.19 | 0.17 | 0.01 | 0.00 | 0.29 | 0.00 |
Max. | 7.69 | 161.59 | 338.61 | 9.21 | 3.06 | 24.49 | 6.15 | 33.35 | 50.75 | 17.30 | 0.62 | 1.08 | 0.92 | 0.81 | 0.11 | 0.01 | 1.17 | 0.02 |
Mean | 7.29 | 106.79 | 216.28 | 5.54 | 1.68 | 12.68 | 3.25 | 21.44 | 27.81 | 8.49 | 0.37 | 0.61 | 0.53 | 0.44 | 0.05 | 0.00 | 0.73 | 0.01 |
SD | 0.31 | 36.21 | 75.95 | 2.24 | 0.90 | 5.85 | 1.40 | 6.42 | 12.98 | 4.01 | 0.14 | 0.28 | 0.26 | 0.19 | 0.03 | 0.00 | 0.29 | 0.00 |
SES | – | – | – | – | – | – | – | – | – | – | 6 | 5 | – | 3 | 9 | – | 10 | 8 |
All concentrations in mg/L except EC (μS/cm) and pH (no unit). S, standard prescribed by WHO guidelines; SD, standard deviation; SES, sample(s) exceeding standard.
Among the various heavy metals studied, 60% of the analyzed samples exceeded the iron concentration limit of 0.30 mg/L set by the WHO. While iron is a vital mineral needed for various bodily functions, excessive intake of iron through water can pose health risks. Heightened concentrations of iron in drinking water have been linked to a higher probability of experiencing gastrointestinal issues, iron overload (hemochromatosis), and teeth discoloration, among other potential concerns. This study supports previous findings on iron concentrations in Nigerian groundwater, as reported by the United Nations International Children's Emergency Fund (UNICEF 2018).
Manganese concentrations varied between 0.29 and 1.08 mg/L. Approximately half of the collected samples have manganese concentrations that exceed the maximum threshold of 0.5 mg/L prescribed by the WHO. Groundwater manganese primarily originates from the natural breakdown of manganese-bearing minerals through the weathering process, while human-activities derived industrial waste, sewage, and dumpsite leachate contribute to anthropogenic manganese presence. Prolonged exposure to excessive manganese levels in adults can lead to neurological impairments characterized by hallucination, symptoms akin to Parkinson's disease, and emotional instability (Badmus et al. 2022). Furthermore, elevated manganese concentrations in children have the potential to hinder learning and adversely affect their intelligence quotients.
Copper is a vital element that plays a crucial role in maintaining human health, but it is required only in small amounts in the human diet. Excessive copper intake can lead to significant toxicological concerns, including symptoms such as nausea, diarrhea, vomiting, and stomach cramps. Approximately 70% of the assayed samples exhibited copper concentrations that aligned with the recommended limit of 0.50 mg/L set by the WHO, while the remaining 30% exceeded this limit.
The analysis of lead contents in the samples under investigation revealed that 90% of the samples surpassed the lead concentration threshold of 0.01 mg/L set by the WHO. The United States Environmental Protection Agency (USEPA 2014) reported that lead is a highly hazardous heavy metal known to cause severe health issues such as high blood pressure and renal problems in adults, and slows physical and mental development in children even in small concentrations.
Chromium is a naturally occurring element, and its presence in groundwater can be influenced by geological factors, as well as human actions. In the area under investigation, chromium concentrations surpassed the WHO's acceptable threshold of 0.05 mg/L in all the samples examined. These levels varied between 0.28 and 1.17 mg/L, with an average value of . As reported by WHO (2004), elevated levels of chromium in the human body can lead to corrosion of the intestinal tract. According to Myers et al. (2023), the detrimental impacts of chromium toxicity on humans encompasses a broad spectrum of adverse outcomes, including stomach cancer, disruption of calcium metabolism, intestinal cancer, and renal disorder.
The levels of zinc and nickel observed within the study area conform to the permissible limits established by the WHO. By contrast, cadmium concentrations in the groundwater samples ranged from 0.00 to 0.02 mg/L, exceeding the WHO recommended limit of 0.005 mg/L in 80% of the samples. Consequently, the studied samples meet the safety thresholds for zinc and nickel. However, Samples S-7 and S-8, taken from wells located farther from the dumpsite, show higher levels of chromium, lead, cadmium, manganese, iron, and copper. These concentrations surpass the WHO recommended limits and exceed those found in most samples closer to the dumpsite.
Although the dumpsite may contribute to the anthropogenic presence of heavy metals in groundwater, a plausible explanation for the elevated concentrations observed in the present study suggest a significant influence of geogenic processes such as weathering of metal-bearing minerals, hydrothermal alteration, metasomatic processes, and deep weathering profiles. These factors can collectively or individually contribute to the mobilization and concentration of these metals in groundwater. Olagunju et al. (2018) previously documented comparable results in an earlier study conducted within the same study area.
Hydrochemical facies


Piper diagram showing hydrochemical facies of the groundwater samples around the Ilokun dumpsite.
Piper diagram showing hydrochemical facies of the groundwater samples around the Ilokun dumpsite.
Schoeller diagram


Schoeller diagram showing concentrations of the major ions in the studied samples.
Schoeller diagram showing concentrations of the major ions in the studied samples.
Also, chloride concentrations exhibited higher levels compared with other anions. The most likely sources of elevated chloride in the study area are fluid inclusions within crystalline rocks, remnants of ancient marine influence, hydrothermal alteration, or deep crustal brines. These sources reflect the complex geological history and processes that have affected the geology of the study area (Basement Complex) over time.
The relative abundance of major ions followed the sequence: for cations and
for anions. These findings categorically highlight the prevalence of inorganic salts within the groundwater samples. The Schoeller diagram provides a clear visualization of these trends, shedding light on the dominant chemical constituents in the investigated wells around the dumpsite.
Irrigation water quality assessment
Assessing water quality for irrigation purposes is crucial to safeguard crop health, soil fertility, environmental integrity, and human well-being. By understanding the composition of irrigation water, farmers can adopt appropriate water management strategies, choose suitable crops, and employ irrigation practices that contribute to sustainable agricultural practices and overall ecosystem health. The irrigation indices considered in this study as outlined in Table 4 provide a comprehensive framework for assessing the irrigation viability. The groundwater samples' dissolved salt content is evaluated through EC and categorized according to the salinity hazard classes outlined in Table 4. The results indicate a consistently high water quality level, ranging from good to excellent, for irrigation purposes. Specifically, 60% of the samples are classified as excellent water, while the remaining 40% are categorized as good water. This assessment underscores the appropriateness of the analyzed groundwater samples for effective irrigation practices.
Water quality indices for irrigation purposes
Indices . | Range . | Groundwater class . | % samples (n = 10) . |
---|---|---|---|
EC (Wilcox 1955) | <250 | Excellent | 60 |
250–750 | Good | 40 | |
750–2,250 | Doubtful | – | |
>2,250 | Unsuitable | – | |
TH as ![]() | 0–75 | Soft | 70 |
75–150 | Moderately hard | 30 | |
150–300 | Hard | – | |
>300 | Very hard | – | |
%Na (Wilcox 1955) | <20 | Excellent | 90 |
20–40 | Good | 10 | |
40–60 | Permissible | – | |
60–80 | Doubtful | – | |
>80 | Unsuitable | – | |
SAR (Richards 1954) | <10 | Excellent | 100 |
10–18 | Good | – | |
18–26 | Doubtful | – | |
>26 | Unsuitable | – |
Indices . | Range . | Groundwater class . | % samples (n = 10) . |
---|---|---|---|
EC (Wilcox 1955) | <250 | Excellent | 60 |
250–750 | Good | 40 | |
750–2,250 | Doubtful | – | |
>2,250 | Unsuitable | – | |
TH as ![]() | 0–75 | Soft | 70 |
75–150 | Moderately hard | 30 | |
150–300 | Hard | – | |
>300 | Very hard | – | |
%Na (Wilcox 1955) | <20 | Excellent | 90 |
20–40 | Good | 10 | |
40–60 | Permissible | – | |
60–80 | Doubtful | – | |
>80 | Unsuitable | – | |
SAR (Richards 1954) | <10 | Excellent | 100 |
10–18 | Good | – | |
18–26 | Doubtful | – | |
>26 | Unsuitable | – |
In the context of overall water hardness, the groundwater samples collected within the study area exhibited a spectrum of hardness ranging from . According to the criteria in Table 4, these samples falls within the category of soft to moderately hard water, confirming their appropriateness for irrigation purposes.
The categorization of groundwater based on its sodium content holds significant importance for irrigation due to sodium's potential reactivity with soil, which can impede soil permeability and adversely impact crop growth. The analysis of the groundwater samples reveals %Na values spanning 15.04 to 17.77%, all of which fall within the good to excellent water classification (Table 4). This assures the suitability and safety of the groundwater for use in irrigation.
The assessment of soil sodicity through the SAR offers insight into water-extracted soil properties. Prolonged irrigation with high-SAR groundwater can displace soil magnesium and calcium due to sodium's presence in the water. This displacement disrupts soil aggregate stability, ultimately leading to soil tilth deterioration. The SAR values for this study ranged from 0.24 to 0.72 meq/L indicating a low sodium hazard. These results underscore the excellent suitability of the studied samples for irrigation, according to the SAR guidelines presented in Table 4.
Assessment of health risks associated with heavy metals exposure in adults and children
For this study, we utilized the USEPA models established in 2001 for conducting health risk assessments related to heavy metals. The toxicity evaluations of heavy metals via daily intake consider factors such as water consumption rate, mean metal concentrations, age, and weight. Tables 5 and 6 present the estimated average daily intake (ADI) and the corresponding HQ values for Cd, Cr, Ni, Pb, Cu, Zn, Mn, and Fe, for both adults and children, respectively. These values have been compiled for the purpose of non-carcinogenic health risks assessment.
Average daily intake, reference dose, hazard quotient, and hazard index for adults
Metals . | Mean concentration ![]() | ADI ![]() | RfD ![]() | HQ . | HI . |
---|---|---|---|---|---|
Cd | 0.01 | ![]() | 0.0005 | ![]() | 8.40 |
Cr | 0.73 | ![]() | 0.003 | ![]() | |
Ni | 0.00 | ![]() | 0.02 | ![]() | |
Pb | 0.05 | ![]() | 0.004 | ![]() | |
Cu | 0.44 | ![]() | 0.04 | ![]() | |
Zn | 0.53 | ![]() | 0.30 | ![]() | |
Mn | 0.61 | ![]() | 0.14 | ![]() | |
Fe | 0.37 | ![]() | 0.70 | ![]() |
Metals . | Mean concentration ![]() | ADI ![]() | RfD ![]() | HQ . | HI . |
---|---|---|---|---|---|
Cd | 0.01 | ![]() | 0.0005 | ![]() | 8.40 |
Cr | 0.73 | ![]() | 0.003 | ![]() | |
Ni | 0.00 | ![]() | 0.02 | ![]() | |
Pb | 0.05 | ![]() | 0.004 | ![]() | |
Cu | 0.44 | ![]() | 0.04 | ![]() | |
Zn | 0.53 | ![]() | 0.30 | ![]() | |
Mn | 0.61 | ![]() | 0.14 | ![]() | |
Fe | 0.37 | ![]() | 0.70 | ![]() |
Average daily intake, reference dose, hazard quotient, and hazard index for children
Metals . | Mean concentration ![]() | ADI ![]() | RfD ![]() | HQ . | HI . |
---|---|---|---|---|---|
Cd | 0.01 | ![]() | 0.0005 | ![]() | 39.12 |
Cr | 0.73 | ![]() | 0.003 | ![]() | |
Ni | 0.00 | ![]() | 0.02 | ![]() | |
Pb | 0.05 | ![]() | 0.004 | ![]() | |
Cu | 0.44 | ![]() | 0.04 | ![]() | |
Zn | 0.53 | ![]() | 0.30 | ![]() | |
Mn | 0.61 | ![]() | 0.14 | ![]() | |
Fe | 0.37 | ![]() | 0.70 | ![]() |
Metals . | Mean concentration ![]() | ADI ![]() | RfD ![]() | HQ . | HI . |
---|---|---|---|---|---|
Cd | 0.01 | ![]() | 0.0005 | ![]() | 39.12 |
Cr | 0.73 | ![]() | 0.003 | ![]() | |
Ni | 0.00 | ![]() | 0.02 | ![]() | |
Pb | 0.05 | ![]() | 0.004 | ![]() | |
Cu | 0.44 | ![]() | 0.04 | ![]() | |
Zn | 0.53 | ![]() | 0.30 | ![]() | |
Mn | 0.61 | ![]() | 0.14 | ![]() | |
Fe | 0.37 | ![]() | 0.70 | ![]() |
The results reveal that, in the adult population, the HQ values for most heavy metals were consistently below unity, suggesting relatively low risk. However, chromium (Cr) exhibited an elevated HQ value of 6.97. With regard to the children, HQ values of 2.66, 32.43, 1.67, and 1.47 were obtained for Cd, Cr, Pb, and Cu, respectively. The HQ values follow the order of for both age groups. This signifies that Cr presents the most significant non-carcinogenic risk for both the adult and children populations in the study area. This can be attributed to its high environmental mobility as reported by Zhitkovich (2011).
Considering the elevated vulnerability of children to pollutants, heavy metal HQ values above one should not be disregarded (Sudsandee et al. 2017; Kolawole et al. 2023). In this particular scenario, Cd, Cr, Pb, and Cu emerge as the primary factors driving non-carcinogenic health risks. To provide an overall assessment, the HI measures the collective non-carcinogenic risk associated with exposure to all considered heavy metals. The computed HI values (8.40 for adults and 39.12 for children) exceed the unity threshold, indicating a notable heavy metal pollution presence in the designated research area. As a consequence, the ingestion based exposure to these metals is likely to have substantial non-carcinogenic health implications for both adults and children residing in the study area. This emphasizes the need for robust interventions to mitigate heavy metal pollution and safeguard the well-being of the population, especially the children (Olujimi et al. 2015; Edokpayi et al. 2018).
Although dumpsites are sources of contamination of groundwater through effluents that seep into the groundwater system including heavy metals, among the studied samples, S-8 showed the highest concentrations of three out of the four heavy metals (chromium, cadmium, and copper, excluding lead), contributing significantly to the elevated HI values observed in the area. Notably, S-8 location is relatively farther from the center of the dumpsite suggesting that the dumpsite itself may not be the primary source of the increased heavy metal levels in the surrounding groundwater.
Radon concentration distribution in the groundwater
The distribution of 222Rn concentrations in groundwater around the dumpsite is detailed in Table 7. The table revealed a range from 5.4 to 23.1 Bq L−1, showcasing the variability in 222Rn concentrations. The average concentration across all measurements is determined to be of 13.9 Bq L−1. Six of the water samples representing 60% of the water samples exhibit radon concentrations surpassing the recommended safety threshold of 11.1 Bq L−1, as set forth by USEPA (1991). However, all the values are less than the WHO guidance level, which specifies that controls be implemented for all public water sources with radon concentrations above 100 Bq L−1 (WHO 2006).
Radon concentration in groundwater of the site
Sample ID . | Average radon conc. (Bq L−1) . | Std dev. (Bq L−1) . | RDSt (Infant), μSv year−1 . | RDSt (Children), μSv year−1 . | RDSt (Adult), μSv year−1 . | RDRT, μSv year−1 . |
---|---|---|---|---|---|---|
S-1 | 11.6 | 3.0 | 6.1 | 14.3 | 20.4 | 29.3 |
S-2 | 22.7 | 4.1 | 11.9 | 27.8 | 39.7 | 57.1 |
S-3 | 13.5 | 3.2 | 7.1 | 16.5 | 23.6 | 33.9 |
S-4 | 23.1 | 3.9 | 12.1 | 28.3 | 40.4 | 58.2 |
S-5 | 9.1 | 2.4 | 4.8 | 11.2 | 16.0 | 23.1 |
S-6 | 16.1 | 3.2 | 8.5 | 19.8 | 28.3 | 40.7 |
S-7 | 16.7 | 3.2 | 8.7 | 20.4 | 29.1 | 42.0 |
S-8 | 10.9 | 2.6 | 5.7 | 13.3 | 19.1 | 27.5 |
S-9 | 5.4 | 2.0 | 2.9 | 6.7 | 9.5 | 13.7 |
S-10 | 10.1 | 2.7 | 5.3 | 12.3 | 17.6 | 25.4 |
Sample ID . | Average radon conc. (Bq L−1) . | Std dev. (Bq L−1) . | RDSt (Infant), μSv year−1 . | RDSt (Children), μSv year−1 . | RDSt (Adult), μSv year−1 . | RDRT, μSv year−1 . |
---|---|---|---|---|---|---|
S-1 | 11.6 | 3.0 | 6.1 | 14.3 | 20.4 | 29.3 |
S-2 | 22.7 | 4.1 | 11.9 | 27.8 | 39.7 | 57.1 |
S-3 | 13.5 | 3.2 | 7.1 | 16.5 | 23.6 | 33.9 |
S-4 | 23.1 | 3.9 | 12.1 | 28.3 | 40.4 | 58.2 |
S-5 | 9.1 | 2.4 | 4.8 | 11.2 | 16.0 | 23.1 |
S-6 | 16.1 | 3.2 | 8.5 | 19.8 | 28.3 | 40.7 |
S-7 | 16.7 | 3.2 | 8.7 | 20.4 | 29.1 | 42.0 |
S-8 | 10.9 | 2.6 | 5.7 | 13.3 | 19.1 | 27.5 |
S-9 | 5.4 | 2.0 | 2.9 | 6.7 | 9.5 | 13.7 |
S-10 | 10.1 | 2.7 | 5.3 | 12.3 | 17.6 | 25.4 |
Assessment of equivalent radiation doses to the stomach and respiratory tract
The range of radon concentrations found in this study aligns with findings in similar geological contexts, as reported by Ajiboye et al. (2018). Similar concentration ranges were also documented by Adagunodo et al. (2023) in their groundwater radon study in Ibadan, Nigeria. These findings suggest that the radon concentrations observed in this study are likely due to background levels in the study area.
Correlation of groundwater radon and heavy metal concentrations
The Pearson's correlation coefficient defines the relationship between pairs of measured parameters. The Pearson's correlation coefficient matrix between radon and heavy metals is presented in Table 8. All tested pairs correlated positively. Radon and zinc conspicuously exhibit high correlation (). However, the correlation of radon with other heavy metals ranges from negligible to moderate correlation (typically 0–0.7).
Correlation of radon with heavy metal contents of groundwater
. | Fe . | Mn . | Zn . | Cu . | Pb . | Ni . | Cr . | Cd . | Rn . |
---|---|---|---|---|---|---|---|---|---|
Fe | 1 | ||||||||
Mn | 0.915 | 1 | |||||||
Zn | 0.625 | 0.648 | 1 | ||||||
Cu | 0.848 | 0.865 | 0.699 | 1 | |||||
Pb | 0.396 | 0.361 | 0.632 | 0.625 | 1 | ||||
Ni | 0.596 | 0.715 | 0.403 | 0.587 | 0.526 | 1 | |||
Cr | 0.692 | 0.828 | 0.797 | 0.770 | 0.709 | 0.806 | 1 | ||
Cd | 0.784 | 0.765 | 0.318 | 0.619 | 0.322 | 0.748 | 0.595 | 1 | |
Rn | 0.338 | 0.435 | 0.731 | 0.317 | 0.139 | 0.300 | 0.524 | 0.123 | 1 |
. | Fe . | Mn . | Zn . | Cu . | Pb . | Ni . | Cr . | Cd . | Rn . |
---|---|---|---|---|---|---|---|---|---|
Fe | 1 | ||||||||
Mn | 0.915 | 1 | |||||||
Zn | 0.625 | 0.648 | 1 | ||||||
Cu | 0.848 | 0.865 | 0.699 | 1 | |||||
Pb | 0.396 | 0.361 | 0.632 | 0.625 | 1 | ||||
Ni | 0.596 | 0.715 | 0.403 | 0.587 | 0.526 | 1 | |||
Cr | 0.692 | 0.828 | 0.797 | 0.770 | 0.709 | 0.806 | 1 | ||
Cd | 0.784 | 0.765 | 0.318 | 0.619 | 0.322 | 0.748 | 0.595 | 1 | |
Rn | 0.338 | 0.435 | 0.731 | 0.317 | 0.139 | 0.300 | 0.524 | 0.123 | 1 |
Between the heavy metals, iron and manganese clearly exhibit a very high correlation . Chromium shows a strong correlation (typically 0.7–0.9) with all the other heavy metals analyzed, suggesting they may share a common source or similar environmental pathways. In a previous study by Ajiboye et al. (2022) conducted in Southwest Nigerian cities, chromium concentrations in groundwater ranged from 0 to 195 ppb. However, in the current study, chromium levels are notably higher, ranging from 0.29 to 1.08 ppm (290–1,080 ppb). This significant increase, combined with the high correlation values, suggests that the elevated chromium levels may be due to environmental oxidation of chromium-bearing minerals, such as chromite, leading to the formation of hexavalent chromium. The high solubility and mobility of hexavalent chromium may explain its widespread presence and strong correlation with other heavy metals in the environment. Generally, all other pairs of heavy metals exhibit low to moderate positive correlation.
CONCLUSION
The present research focused on the comprehensive hydrogeochemical analysis of groundwater, with specific emphasis on assessing potential health risks associated with radon and heavy metal ingestion in the proximity of the Ilokun dumpsite. All major ionic concentrations fell within the prescribed limits set by the WHO. The hydrochemical composition demonstrated a predominance of alkaline earths over alkalies, while strong acids surpass weak acids, suggesting calcium-chloride water type as the predominant water type in the study area. The irrigation indices suggest that the studied groundwater is suitable for irrigation purposes. Chromium, cadmium, lead, and copper were found to be present at concentrations exceeding the acceptable limits in the analyzed samples pointing to potential contamination arising largely from geogenic contributions. The HI values of 8.40 and 39.12 were estimated for adults and children, respectively, indicating potential health risks of non-carcinogenic effects primarily driven by chromium, cadmium, lead, and copper. Radon and zinc exhibited high correlation in the groundwater samples. These findings suggest that the heavy metal and radon concentrations observed in the investigated samples are likely due to background levels in the area. The insights from this study may help in the development of strategies for managing and protecting groundwater resources in the study area from radon and heavy metal contamination.
FUNDING
The authors declare that no funds, grants, or other support were received during the preparation of this article.
AUTHORS’ CONTRIBUTIONS
G.O.B., O.S.O., and Y.A. conceptualized and designed the study. G.O.B., O.S.O., and A.P.J. acquired the data. G.O.B., O.S.O., Y.A., and O.A.A. managed the literature searches. All authors analyzed and interpreted the data. All authors drafted and revised the article. All authors read and approved the final version of the article.
DATA AVAILABILITY STATEMENT
All relevant data are included in the article or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.