Introduction
Pollution such as Air, water, soil, marine, and odor resulting from unmanaged solid waste and singeing at various abattoir sites remains a pressing global concern due to its persistent, (bio)accumulative, and toxic nature. Ajah et al., (2022) reports that in developing countries, particularly across many States in sub-Saharan Africa, illegal dumpsites often lack proper containment systems, enabling leachates enriched with metals such as lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and nickel (Ni), major ions such as Ammonium (NH₄⁺), Phosphate (PO₄³⁻), Polycyclic aromatic hydrocarbons (PAHs), emerging pollutants such as, pharmaceuticals personal care products (PPCPs), endocrine-disrupting compounds (EDCs), and microplastics to infiltrate surrounding soil, meat, crops, surface water, and groundwater systems [1, 2, 3]. This contamination is compounded by regional hydrological patterns and seasonal rainfall variability, which intensify leachate mobilization and pollutant spread, especially during the raining season as reported by Isah et al., (2023) [3].
In Nigeria, the increasing urban population and improper waste management practices in various states and communities in both urban and rural area have exacerbated environmental exposure pathways. Communities of particular concern are those living in close proximity to these unregulated dumpsites and who rely on unregulated singed hides from (goats, cow and cattle) from local abattoir for meats, shallow crops, ground and surface water sources for drinking, domestic use, and subsistence farming. These populations face chronic exposure risks through the ingestion of contaminated water, meat and food crops irrigated with polluted sources or cultivated on or around impacted soil [4, 5].
Women, children, and economically disadvantaged individuals bear disproportionate burdens, not only due to physiological vulnerabilities but also because of their roles in water collection, food preparation, and agriculture. Shridhar et al., [6] reported that Heavy metals such as Pb and Cd are known to interfere with neurological development in children, while long-term ingestion of As and Cr has been linked to carcinogenic and endocrine disrupting effects [4]. Moreover, these contaminants pose significant threats to food safety, with several studies reporting elevated concentrations of metals in leafy vegetables and tubers cultivated near waste sites [5, 6].
Recent studies have underscored the need for site specific risk assessments that integrate both environmental distribution and human exposure metrics. Yet, few have employed comprehensive spatial mapping combined with statistical and laboratory analyses to examine the multi-pathway exposure from contaminated dumpsites in various communities in Enugu State, southeastern Nigeria. This study aims to fill that gap by evaluating the levels and spatial patterns of heavy metal contamination in groundwater, surface water, and leachate samples around selected abattoir and dumpsites in Enugu State. The study also highlights associated human health risks, particularly through agricultural and domestic exposure routes. The outcomes are intended to inform regulatory policy, environmental remediation, and sustainable urban waste management strategies while safeguarding water resources and public health.
Materials and Methods
Materials
All water and leachate samples were collected using standard clean sampling methods. High density polyethylene (HDPE) bottles (pre)rinsed with deionized water were used to avoid contamination. pH measurements were conducted on-site using a calibrated portable pH meter. Samples were preserved and transported in ice packed coolers to the laboratory for analysis. Sample digestion was performed using analytical-grade nitric and hydrochloric acids. Metal quantification was carried out using a Varian AA240 Atomic Absorption Spectrophotometer (AAS) calibrated with multi-element standards. A fume hood and water bath were employed during digestion to ensure safety and completeness of metal extraction. All reagents and instruments met ACS grade purity specifications. A detailed list of sampling equipment, reagents, analytical instruments and Statistical Tools and Software is provided in Supplementary S1.
Study area description
The study was conducted within the Enugu State area located in southeastern Nigeria (Latitude 6° 2′ 46′′ N to 6° 22′ 10′′ N, Longitude 7° 28′ 36′′ E to 7° 37′ 43′′ E), which includes several abattoir sites, dumpsites and water sources such as rivers, groundwater, and surface water bodies. The city is accessible via major highways, including the Enugu-Ebonyi Highway, Enugu-Port Harcourt Highway and Enugu-Onitsha Highway, and is characterized by a tropical climate with a raining (udu-mmiri) season from April to November and a dry (okochi) season from December to March. It is underlain by the Coniacian Agbani Formation and Campanian Enugu Shale. The sampling locations as shown in Figure 1a and the waste pollution flowchart Figure 1b, chosen for this study include both contaminated and non-contaminated sites, providing a comprehensive analysis of pollution from leachates and their effects on nearby water bodies.
Geology
The study area in Figure 2 lies within the sedimentary basin of southeastern Nigeria, characterized by varying geological formations. The area consists of both igneous and sedimentary rock types that influence the behavior of pollutants and the leachate percolation into the groundwater systems as shown in Figure 2.
Hydrology and climate
Climate
The climate of the region is characterized by two distinct seasons: a raining (udu-mmiri) season from April to October and a dry (okochi) season from November to March as shown in Figure 3. These climatic variations influence water availability and the percolation of leachates into the groundwater systems. The hydrology of the region is dominated by rivers and streams which receive substantial inputs from surface runoff.
Hydrogeology
The groundwater in the study area as shown in Figure 4 is primarily contained in aquifers within the sedimentary formations. Chinye-Ikejiunor et al., reported that this water is vulnerable to contamination from the leachates of nearby dumpsites [9]. The region is home to both shallow and deep aquifers, with varying degrees of contamination based on proximity to pollution sources.
Sampling
Water and leachate samples were collected from 15 different locations in the study area as shown in Figure 1 above. The samples were preserved and analyzed for various metal concentrations including Mn, Fe, Cd, As, Pb, Ni, and Cr. The sampling methods were consistent with those described by Standard Methods for the Examination of Water and Wastewater (APHA, 2012). Sampling was carried out exclusively during the wet (Udummiri) season (May–August 2024) to assess peak leachate percolation effects on surrounding water sources.
Sample preservation and transport
All sampling bottles were pre-washed with 10% nitric acid and rinsed with deionized water. During sampling, each bottle was rinsed with sample water thrice before final collection. Samples were acidified with 2 mL of concentrated hydrochloric acid (HCl) and transported in ice-packed coolers stored at 4°C to the laboratory. All samples were analyzed within 48 hours in accordance with APHA (2005) procedures.
Laboratory analysis
Laboratory analysis was conducted using Atomic Absorption Spectroscopy (AAS) (Buck Scientific 220 model, USA) for the quantification of heavy metals in water and leachate samples. The standard procedure for water quality testing in Afolabi et al., (2024) was followed, as outlined in the literature [2, 8]. Sample digestion was done using HNO3 : HClO4 (3 : 1) at 95°C until a clear solution was obtained. Calibration was performed using standard reference solutions. Each sample was analyzed in triplicates to ensure both precision and accuracy of the results. Metals analyzed included lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), manganese (Mn), nickel (Ni), and iron (Fe). The AAS method was employed due to its high sensitivity and the ability to detect metals at trace concentrations making it ideal for environmental water analysis. Table 1 shows the heavy metals tested, laboratory procedures and equipment used for metal analysis in the water and leachate samples. Triplicate analysis was performed to ensure the precision and reliability of the results in Table 2.
Pollution and risk assessment
Environmental pollution was evaluated using the Heavy Metal Pollution Index (HPI), Contamination Index (CI), and Heavy Metal Evaluation Index (HEI). For health risk assessment, the United States Environmental Protection Agency (USEPA) methodology was applied.
I. Non-carcinogenic risks were assessed using Chronic Daily Intake (CDI), Hazard Quotient (HQ), and Hazard Index (HI).
II. Carcinogenic risks were calculated using Slope Factor (SF) and Probability of Cancer Risk (PCR).
Statistical analyses
Data were statistically analyzed using SPSS version 22 for Windows. The results were subjected to descriptive statistics, including means, standard deviations, and correlations. Additionally, spatial analyses using contour plots shown in Figure 5 were performed to visualize the distribution of metal concentrations across the sampling locations.
Results and Discussion
Description of the dumpsite
All the studied locations are characterized by uncontrolled waste disposal activities, posing considerable threats to surrounding water bodies and human health. The Ugwu Onyeama and Akwata dumpsites receive large volumes of domestic and industrial waste, with significant leachate migration observed during the rainy season. At the Ugwuaji site, the proximity of shallow wells and drainage channels facilitates the direct discharge of contaminants into surrounding water bodies. A particularly concerning case is the New Artisan Butcher Market as shown in Table 1 below, where waste generated from burning tires during singeing, used in singeing animal skins is dumped into a river that supplies water for meat washing and crop irrigation. These practices markedly increase the likelihood of heavy metal accumulation in food and water sources, thereby elevating the risk of dietary exposure among the local population.
Heavy metal concentration and spatial distribution
Table 2 above and Figure 6a presents the concentrations of selected heavy metals in leachate, surface water, and groundwater samples from 15 studied locations in Enugu State, Nigeria. The result reveals notable variations in the concentrations of manganese (Mn), iron (Fe), cadmium (Cd), arsenic (As), lead (Pb), nickel (Ni), and chromium (Cr). The highest concentrations of Pb and Cd were recorded in Leachate samples, ranging from 5.1 μg/L to 14.0 μg/L for Pb and 0.3 μg/L to 0.7 μg/L for Cd. These concentrations exceed the World Health Organization (WHO) and Nigerian Standards for Drinking Water Quality (NSDWQ) limits for both Pb (10 μg/L) and Cd (3 μg/L), suggesting significant contamination of the water sources from singeing processes at abattoir and various dumpsite leachates. The Fe and Mn concentrations were relatively high across all sample types, particularly in Leachates. For instance, Fe concentrations ranged from 4.0 μg/L to 14.4 μg/L, and Mn concentrations ranged from 9.8 μg/L to 14.2 μg/L. These elevated levels are indicative of organic matter decomposition at the dumpsites and the mobilization of metals under the influence of acidic leachates [8]. Nickel (Ni) and Chromium (Cr) concentrations were found to be lower in comparison, with values ranging from 0.1 μg/L to 4.3 μg/L for Ni and 0.8 μg/L to 2.5 μg/L for Cr. Although these metals did not exceed the WHO permissible limits, their presence in the water samples indicates potential long-term health risks, particularly in communities relying on shallow groundwater sources.
In addition to heavy metals, the pH values of water samples from different sources were also analyzed to assess the acidity or alkalinity of the water. Figure 6b presents a contour plot of the pH values across the sampling sites. This plot illustrates the spatial variability in pH, with acidic conditions prevalent near the dumpsites, particularly Dumpsite 1 and Dumpsite 3, where lower pH values indicate a more acidic environment due to leachate infiltration.
The seasonal variations in metal concentrations were further analyzed in relation to rainfall patterns and groundwater contamination. Figure 7a and 7b illustrate the annual rainfall and temperature variations in the study area, showing peak precipitation between May and October. This period corresponds with the wet season, during which surface runoff and leachate infiltration are more prominent, facilitating the transport of heavy metals into surrounding groundwater and surface water systems. Wet season samples showed significantly higher concentrations of cadmium (Cd), lead (Pb), and manganese (Mn), aligning with studies that emphasize the role of rainfall in the migration of pollutants [12]. The dry season exhibited lower concentrations, with more localized accumulation of metals in the leachate.
Hydrogeological impact
The hydrogeology of the Enugu State region is characterized by both shallow and deep aquifers that are vulnerable to contamination from dumpsite leachates. Figure 8 presents a hydrogeological cross-section, which illustrates groundwater flow patterns and the movement of leachate plumes from nearby dumpsites toward residential wells. The shallow aquifers in the study area are particularly susceptible to contamination due to the lack of protective clay layers, which makes it easier for leachates to migrate into the groundwater systems [1]. This finding supports earlier studies that noted the high vulnerability of shallow aquifers in urban settings.
Source identification via multivariate statistics
Principal Component Analysis (PCA)
Principal Component Analysis (PCA) was employed to identify the sources of heavy metal contamination in the study area. The first two principal components (PC1 and PC2) accounted for over 78% of the total variance, with PC1 associated with Fe, Mn, and Ni, and PC2 linked to Cr and Cd. The PCA biplot in Figure 9 indicated that Fe, Mn, and Ni originated from a common source, likely due to organic matter decomposition and industrial effluents. Conversely, Cr and Cd were found to have a distinct source, likely industrial discharges and wastewater from manufacturing processes. The Pearson correlation matrix also revealed significant positive correlations between Pb, Cd, and Ni, suggesting a shared pollution source, likely from leachate infiltration and improper waste disposal [2].
Single-Factor Analysis of Variance (ANOVA)
A single-factor ANOVA was conducted to determine if there were significant differences in the concentrations of metals across the different sample types (Leachate, Groundwater, and Surface Water). The results indicated that Pb and Cd concentrations differed significantly between the sample types (p < 0.05). Specifically, Leachate samples exhibited the highest concentrations of Pb (ranging from 5.1 μg/L to 14.0 μg/L) and Cd (ranging from 0.3 μg/L to 0.7 μg/L), exceeding the WHO and Nigerian Drinking Water Quality Standards. This finding suggests that dumpsite leachates are a significant source of contamination for nearby water bodies as shown in Figure 10 below.
Agglomerative Hierarchical Cluster Analysis (AHCA)
Agglomerative Hierarchical Cluster Analysis (AHCA) was performed to group sampling sites based on similar contamination profiles. The cluster analysis revealed that sites near the dumpsites, such as Dumpsite 1 and Dumpsite 3, clustered together, suggesting a common source of heavy metal pollution. This aligns with the PCA results, confirming the impact of leachate infiltration and waste decomposition on water contamination.
Pearson Correlation Analysis
Pearson correlation analysis was applied to assess the strength of the relationship between different heavy metals. The results in Figure 11 showed significant positive correlations between Pb, Cd, and Ni (r > 0.8, p < 0.01), suggesting that these metals likely originate from the same source. This correlation supports the hypothesis of leachate infiltration from the dumpsites as a major contributor to contamination. Additionally, Fe and Mn also showed a significant positive correlation, indicating their co-occurrence and shared source, possibly linked to organic matter decomposition at the dumpsites.
Environmental and Health Risk Assessment
The exposure assessment was conducted using the concentrations of heavy metals in the Leachate, Groundwater, and Surface Water samples collected from 15 sampling locations. These values were used to assess the potential exposure pathways for adults and children living near the dumpsites. The main exposure pathways considered in this study were: a). Ingestion of contaminated water (via drinking and food preparation), b). Dermal contact (from bathing or washing with contaminated water), c). Inhalation of aerosols in areas with leachate runoff. For each pathway, exposure doses were calculated based on the concentrations of heavy metals in the tested water samples and the contact frequency. The USEPA (United States Environmental Protection Agency) guidelines for assessing non-carcinogenic and carcinogenic risks were applied. As shown in Figure 12, the Hazard Quotients (HQ) and Hazard Indices (HI) for lead (Pb) and cadmium (Cd) exceeded the acceptable limit of 1.0, indicating significant health risks, especially for children living near Dumpsite 1 and Dumpsite 3. The dermal exposure and ingestion pathways for children showed the highest HQ values for Pb and Cd, confirming that young children are particularly vulnerable to the non-carcinogenic effects of these metals. The carcinogenic risk for lead (Pb) and chromium (Cr) also exceeded the acceptable threshold of 1.0 × 10⁻⁴ at several locations, suggesting potential long-term health effects from exposure to these metals. This environmental exposure assessment highlights the need for targeted public health interventions, such as groundwater treatment, regular water quality monitoring, and public education on the dangers of using contaminated water sources.
Comparison with previous studies
The contamination levels observed in this study are consistent with findings from other parts of sub-Saharan Africa, where dumpsite leachates have been shown to significantly impact groundwater quality. Afolabi et al. (2025) reported similar contamination in Nigeria, while Edet, et al., (2022) documented comparable heavy metal pollution levels in surface waters near dumpsites in Cross River State, southern Nigeria. These studies support the findings of the current research and highlight the widespread nature of heavy metal contamination from poorly managed waste disposal sites in Africa [13, 2].
Long-term health effects of heavy metal exposure in areas with similar contamination profiles
The long-term health effects of heavy metal exposure, particularly from lead (Pb), cadmium (Cd), and chromium (Cr), can have significant consequences on both the environment and public health. In areas where contamination profiles are similar to those observed in this study, where Leachate and Groundwater are found to have elevated concentrations of these metals, several chronic health conditions may arise.
Lead (Pb) exposure
Chronic exposure to Pb is a well-documented risk factor for numerous health conditions, particularly for children. Pb can accumulate in the human body over time, leading to neurological impairments, including cognitive deficits, behavioral changes, and reduced IQ in children [5]. Pb exposure is also associated with kidney damage, high blood pressure, and anemia in adults. In communities near dumpsites, where Pb concentrations exceed the safe threshold (1.0 × 10⁻⁴), residents, particularly children who are more vulnerable, face the long-term risk of developing these health issues. Long-term exposure to Pb from contaminated water sources increases the likelihood of cumulative health damage over the course of an individual’s life, including developmental delays and reduced academic performance [4].
Cadmium (Cd) exposure
Cadmium is another heavy metal that poses serious long-term health risks, even at low concentrations. Chronic Cd exposure is linked to kidney dysfunction, particularly proximal tubule damage, which impairs the kidney's ability to filter waste from the blood [13]. The IARC (International Agency for Research on Cancer) has classified Cd as a Group 1 carcinogen, meaning it is carcinogenic to humans. Long-term exposure to Cd in contaminated water sources, especially in the vicinity of dumpsites, can result in increased lung cancer rates, as inhalation and dermal contact with Cd from polluted water may lead to higher lung tissue accumulation. This could increase the risk of cancer in long-term residents who frequently interact with contaminated water or nearby soil.
Chromium (Cr) exposure
Chromium, particularly hexavalent chromium (Cr(VI)), is highly toxic and has been classified as a Group 1 carcinogen by IARC. Long-term exposure to Cr(VI) can lead to lung cancer, nasal cancer, and gastrointestinal cancers, especially in individuals who are exposed through inhalation of contaminated air or ingestion of polluted water. The long-term consumption of water with high levels of Cr(VI), as observed in some sampling sites, can cause chromium toxicity, leading to organ damage, particularly in the kidneys and liver, and can exacerbate respiratory conditions [3]. Moreover, Cr exposure can induce allergic dermatitis and ulcerations upon direct contact with skin.
Cumulative health risks in areas with similar contamination profiles
The results suggest that areas with similar contamination profiles, where heavy metals are present in groundwater and surface water sources, will likely experience a cumulative problem of chronic health conditions. In areas like Dumpsite 1 and Dumpsite 3, where Pb and Cd exceed permissible limits, residents particularly children are at risk of developing neurological and renal diseases, cancer, and respiratory illnesses. These health risks are further compounded in regions where groundwater serves as the primary source of drinking water and where leachate infiltration is significant. As pH levels in contaminated waters become more acidic, the solubility of heavy metals increases, enhancing their potential for bioaccumulation and toxicity [10].
Conclusions
This study assessed the concentration and health risk implications of heavy metals in dumpsite effluents across selected locations in Enugu State, Southeastern Nigeria. The findings revealed significant contamination of water sources near municipal dumpsites, particularly with lead (Pb) and cadmium (Cd). Elevated concentrations of these metals in Leachate, Groundwater, and Surface Water exceeded World Health Organization (WHO) and Nigerian Drinking Water Quality Standards, posing serious non-carcinogenic risks to local populations, especially children. Through Principal Component Analysis (PCA), Single-Factor Analysis of Variance (ANOVA), and Agglomerative Hierarchical Cluster Analysis (AHCA), it was identified that Pb, Cd, and Ni shared a common pollution source, likely attributed to leachate infiltration from the dumpsites. The Pearson correlation analysis further supported this finding, showing significant relationships between Pb, Cd, and Ni, suggesting that these metals are co-transported via leachate. The health risk assessment, based on the Hazard Quotient (HQ) and Hazard Index (HI) models, indicated significant non-carcinogenic risks for Pb and Cd, particularly for children living near Dumpsite 1 and Dumpsite 3, where concentrations of these metals exceeded safe exposure limits for dermal contact and ingestion The carcinogenic risk values for Pb and Cr at Dumpsite 1, Dumpsite 3, and Akwata Dumpsite exceeded the acceptable threshold of 1.0 × 10⁻⁴, indicating potential long-term health risks from exposure to these metals. These sites, where Pb and Cr concentrations were significantly higher than the acceptable limits, are of particular concern for both the immediate and long-term health of nearby populations. These findings highlight the urgent need for: a). Improved waste management policies to prevent further contamination of water sources. b). Regular groundwater quality monitoring to ensure safe drinking water for affected communities. c). Public health interventions, particularly for vulnerable groups such as children, to reduce the health risks associated with heavy metal exposure. This study provides valuable baseline data for environmental risk governance in sub-Saharan Africa and demonstrates the utility of chemometric tools in identifying pollution sources and informing policy responses. One notable limitation of this study is that all environmental sampling was conducted exclusively during the wet season, a period typically characterized by elevated surface runoff and enhanced leachate migration into surrounding water bodies. Consequently, the heavy metal concentrations and associated risk metrics presented may reflect peak contamination conditions, potentially overestimating year-round exposure levels. To address this, future research should adopt a longitudinal, multi-seasonal monitoring framework that includes both dry and rainy seasons. Such an approach would provide a more nuanced understanding of temporal fluctuations in heavy metal mobility, bioavailability, and risk exposure, ultimately supporting more effective environmental and public health management strategies.
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