Heavy metals are the most common type of pollution and an important factor in environmental evaluation [13]. These metals come from water runoff, wastewater discharge from industrial, agricultural, and urban sources, and the chemical leaching of bedrock [14]. The ecosystem is constantly threatened by the presence of heavy metals in soils [15] especially in wetland areas like lakes. Concerns about the possible impacts on the environmental fate and transport of heavy metals have been raised by the startling rise in soil concentrations of these metals. This increase could be caused by waste discharge, pollution, or other human activities. Heavy metal pollution in soils, resulting from surface water runoff and groundwater leaching [16] negatively impacts the quality of water bodies that are undergoing treatment [17]. Because wetland areas serve as natural reservoirs for heavy metals by absorbing runoff from the surrounding catchment [18] the buildup of these pollutants over time may cause the quality of lake water to deteriorate [19]. Furthermore, metal pollutants have the ability to move into the water column and then land on the lakebed [20] where they may cause aquatic life to become secondary contaminants [21].

Elevated levels of heavy metals in wetland soils are likely to negatively impact many hydrophytic plant species, may seriously impair their normal root functions [22]. Because of their special function in the biogeochemical cycling of metals and their capacity to signal the beginning of metal pollution in other ecosystems [23] wetlands are of particular interest to researchers. Wetlands are attractive locations for scientific research because of these features [24]. Additionally, the buildup of heavy metals may pose a threat to wetland ecosystems, which are renowned for their high biological productivity and rich biodiversity [25]. In addition to having high atomic weights and densities, heavy metals are impervious to biodegradation and destruction [26].

Because of their tendency to accumulate, heavy metal concentrations typically rise easily [27]. Even though some metals like zinc and copper are thought to be less harmful, at high concentrations they can still be extremely dangerous. Long-term exposure to these metals can cause a number of acute and chronic illnesses, such as organ failure, stomach pain, disorientation, and lung cancer [28]. The various chemical components and their concentrations, which are mostly determined by the local geological environment, have an impact on the quality of the water [29]. The main causes of water pollution, which impacts both surface and groundwater sources, are industrial operations and municipal solid waste [30]. High concentrations of heavy metals make water unfit for human consumption in many places [31]. Hence many individuals might have adverse health complications if drinking water contains excessive amounts of heavy metals. Numerous factors, including the duration of exposure, the toxicity of the heavy metal, and individual susceptibility, affect how much damage is done to the body [32].

MATERIALS AND METHODS

Study vicinity

The lake is a typical lowland inland valley with a series of unique floodplain areas, important for nature conservation. The wetland is located within the heart of Owerri. Hence, all run off waters are channeled into the wetland which is a major concern of this study as this could introduce contaminants into the wetland as well as the groundwater sources. The floodplain areas are mainly seasonally inundated grassland and reedbed habitats. It is an upper river course and flows through some arable and relatively intensively managed farmland before entering the designated area. The main channel of Lake Nwaebere has been heavily modified and partly straightened for land drainage. There are some directly connected water bodies with the main river and several drainage channels within the floodplain. Table 1 shows the longitudinal and latitudinal location of where the samples were collected while (Figure 1) is the google map of Lake Nwaebere Figures 2a & 2b showed pictures of the lake while Figure 2c is the picture when the samples were being collected. Due to urbanization some parts of the lake were reclaimed and most street runoffs from different parts of the city were channeled into the lake. These streets runoffs constitute a major source pollution of Lake Nwaebere.

Collection of samples and analysis

Water samples were collected from five separate sites in the lake, using five distinctly marked sample containers (plastic bottles) for physical and chemical examination.

Soil samples were collected using a clean plastic trowel at five distinct locations within the wetland, utilizing five clearly labeled polyethylene bags for sample collection.

The heavy content of both the water and soil samples were determined using Varian AA240 Atomic Absorption Spectrophotometer was employed to analyze the heavy metals in the samples following the methodology established by the American Public Health Association (APHA) in 1995.

Data Analysis

Microsoft Excel 2010 was used to analyze the data for correlation, mean, and standard deviation. In order to assess the likelihood of water contamination and the consequences of contaminated wetland soil and water.

Contamination Factor

The ratio of each heavy metal to its background values is known as the contamination factor (CF) was determined using Eq. 1. The proper methodology will be used to carry out the calculation.

C_metal and C_background represent the contamination of heavy metal and background values will be obtained from the Nigerian standard for drinking water quality [33]. The degree of contamination is the total of all the CFs. The CF values were classified into four distinct categories: low contaminated: CF value < 1, moderately contaminated: CF value of 1 ≤ CF ≤ 3, highly contaminated: CF value of 3 ≤ CF ≤ 6, very contaminated: CF value > 6

Pollution Load Index (PLI)

The pollution load index was calculated using the contamination factors (Cf) according to Eq. 2. By taking the nth root of the product of the contamination factors for all metals, the PLI for the location can be determined by obtaining the n=root from the n=CFs that will be obtain for all

Where is C_f1× C_f2 × C_f3…. The individual contamination factor is represented by the variable C, while n denotes the quantity of heavy metals examined in the study. The description of PLI values is presented in Table 2.

Enrichment Factor (EF)

The enrichment factor (EF) serves as a commonly utilized metric for assessing the extent to which the concentration of an element in a sampling medium has been elevated due to anthropogenic influences, in comparison to its average natural abundance. This metric is particularly relevant in the context of mineral ore characterization. It is quantitatively defined as the minimum ratio by which the weight percentage of a mineral within an orebody exceeds its average prevalence in the Earth's crust. In the analysis of water and soil, the enrichment factor (EF) serves as an indicator of the extent to which the concentration of an element has risen as a result of human activities. The enrichment factor is employed to evaluate both the presence and the degree of anthropogenic contaminant accumulation in surface soil. The Enrichment factor is used to assess the presence and intensity of anthropogenic contaminant deposition on surface soil. It can also be used to assess contamination in various environmental media and is calculated by normalizing the concentration of a metal in the topsoil relative to the concentration of a reference element. The reference element should be stable in the soil, associated with finer particles, and not anthropogenically altered. Enrichment factor can be calculated

which is the ratio between the concentrations of the metal (M) and those of the normalizer (N)

QUALITY CONTROL

The reliability of the analytical results was upheld through adherence to established protocols and rigorous quality laboratory assurance measures. The analyses were performed, and the average values were derived from triplicate measurements. Deionized water was subjected to double distillation using the Eco-Still Mark, BSIC/ECO-4 (manufactured by Bhanu Scientific Instruments Company, India) prior to its application in soil digestion and the subsequent determination of metal content in soil samples. The reagents and chemicals utilized in the analysis were of high analytical grade and procured from Finlab Nigeria Limited, located in Owerri, Imo State, Nigeria, and were employed without any additional purification. All glassware and containers underwent thorough cleaning with detergent, followed by rinsing with deionized water and drying in an oven (DHG-9023A, B. Brans Scientific and Instrument Company, England).

The accuracy and precision of the determinations were preserved through the replication of sample analyses in conjunction with reference standards. The Atomic Absorption Spectrophotometer (AAS) exhibited instrumental detection limit (IDL) of 0.1 mg/kg, with minimum detection limits (MDL) of 0.0008 mg/kg for both Cadmium (Cd) and Chromium (Cr), and 0.015 mg/kg for Lead (Pb). The IDL for Gas.

RESULTS AND DISCUSSION

The result of heavy metal content (mg/L) of the lake Nwaebere (water) for both dry and rainy seasons is presented in Table III. The level of heavy metals (mg/kg) in the soil sample from Lake Nwaebere for both dry and rainy seasons is shown in Table IV. Zn levels were evaluated in both the lake water and wetland soils in the dry and rainy seasons. During the dry season, the mean Zn concentration in the lake was recorded at 0.829 mg/L, while in the rainy season; it decreased to 0.230 mg/L as presented in Table 3. It was observed that the mean Zn level in the Lake was below the WHO limit.  In the wetland soils, the concentrations were measured at 1.519 mg/kg during the dry season and 0.881 mg/kg in the rainy season as presented in Table 4. The average Zn concentrations in the wetland soils were all below the DPR target value. Though Zn is considered an important component found in different plant proteins, however, elevated level of Zn could be toxic to plants and animals. The observed wetland soil concentration of Zn recorded in the present study was below the value reported by Ubechu [3].

The levels of Fe were evaluated in both the lake water and the wetland soils during the dry and rainy seasons. The recorded concentrations of Fe in the lake were 0.363 mg/L during the dry season and 0.328 mg/L in the rainy season. These values were higher than the WHO limit as indicated in Table 3. The observed elevated concentration of Fe in the lake could be associated with runoffs that were channeled into it. In the wetland soils, the concentrations were measured at 4.561 mg/kg for the dry season and 1.814 mg/kg for the rainy season (Table 4). Lower concentration of Fe was recorded in the soils compared to the DPR target value. The observed increased level of Fe recorded in the lake could be associated with the fact that this metal is among the abundant metals [25]. Fe is one of the essential elements. Combination of Fe and protein is known to be essential in the metabolism of living organisms. Iron is also important in Also, most enzymatic processes like synthesis of chlorophyll in plants require the presence of Fe However, it is worthy of note that overdose of Fe in humans at a level above 40 mg/kg could result to moderate intoxication of the gastro-intestinal system.

Pb is a metal that poses significant toxicity risks, negatively affecting the growth and respiratory functions of marine life. Consequently, it is imperative to remove Pb from aquatic ecosystems to protect both human health and the environment [34]. Exposure to it can cause severe damage to the central nervous system and critical organs such as the kidneys and liver. Furthermore, it adversely affects reproductive health and disrupts essential cellular and neurological processes. Elevated Pb levels are linked to a range of health problems, including anemia, insomnia, headaches, dizziness, irritability, muscle weakness, hallucinations, and kidney damage [35]. The levels of Pb were measured in the lake water and wetland soils during both the dry and rainy seasons. In the lake, the recorded concentration of the metal was 0.0192 mg/L in the dry season and 0.016 mg/L in the rainy season. In the wetland soil, the concentrations were 0.013 mg/L during the dry season and increased to 0.028 mg/L in the rainy season (Table 3). It is noteworthy that Pb concentrations in the lake water were higher during the dry season compared to the rainy season, whereas the soil samples exhibited increased Pb levels during the rainy season compared to the dry season. These results suggest that the lake water is significantly contaminated with Pb, with concentrations surpassing the standards established by the World Health Organization. In contrast, the Pb levels in the soil remained below the thresholds set by the Department of Petroleum Resources. High Pb levels in water sources have been associated with indiscriminate disposal of materials that contain lead such as paints, batteries, and pipes within water sources and landfill [36].

Ni significantly affects the quality of river water and the aquatic life it supports. It contributes to the global decline in environmental quality, leading to the contamination of soils, groundwater, sediments, surface water, and air with hazardous and toxic substances [37]. The concentrations of Ni in Lake Nwaebere and its wetland soil are detailed in Tables 3 & 4 & Figure 3 is the graphical representation of heavy metals content of water in lake Nwaebere for both seasons while Figure 4 is the heavy metals content of the soil sample from lake Nwaebere for both seasons. The average concentrations of Ni in the lake were recorded at 0.0175 mg/L during the dry season and 0.0178 mg/L during the rainy season. In the wetland soil, the concentrations were found to be 0.000 mg/kg in the dry season and 0.058 mg/kg in the rainy season. It was noted that Ni concentrations were higher in the rainy season compared to the dry season, with no Ni detected in the soil during the dry season. This indicates that the presence of Ni in the area may be linked to runoff. The findings reveal that both the lake and soil samples exhibited Ni contamination; however, the levels were lower than established standards in some samples but were found to be above standards especially in lake water samples. Some of the sources of Ni in the environment include super alloys, non-ferrous alloys, and stainless steel, from vehicle parts as well as the use of pigments paints containing nickel. In addition, Ni could leach into water bodies from discarded electrical materials and metal works [25]. Nickel plays significant part in the biological activities of plants and most micro- organisms [38]. However, it has been reported that high levels of Ni may be toxic, which could be carcinogenic to organisms. Elevated Ni levels in water could be carcinogenic and teratogenic to mammals [39].

Cd waste generated by various industries predominantly accumulates in wetlands. The primary sources of these waste streams include zinc production, welding, electroplating, the use of pesticide fertilizers, cadmium-nickel batteries, nuclear fission plants, phosphate ore processing, and bio-industrial manure. Cadmium has a strong affinity for organic matter, making it highly hazardous [40] as its accumulation in the food chain poses significant health risks. The concentrations of cadmium in the environment were assessed, revealing mean levels of 0.024 mg/L for dry season and 0.032 mg/L for raining season respectively in water from Lake Nwaebere (Tabl0e 3 and 0.025 mg/kg and 0.019 mg/kg for dry and raining season respectively im wetland soils (Table 4). The findings indicated that the cadmium concentration in Lake Nwaebere's water was significantly elevated compared to World Health Organization standards. Additionally, cadmium levels were found to be higher during the dry season and lower during the rainy season, suggesting a correlation with human activities. The lake is frequented by automobile operators and artisans who wash various vehicles in its vicinity, leading to the introduction of dirt and engine oils into the water body.

The levels of Mn in Lake Nwaebere and its associated wetland soil were assessed and analyzed. The average concentration of Mn in Lake Nwaebere was found to be 0.388 mg/L for dry season, while in the wetland soil, it was 0.511 mg/kg. Conversely, the lake water exhibited a lower mean concentration of 0.059 mg/L for water in raining season, and the wetland soil showed 0.113 mg/kg in raining season. The findings indicated that Lake Nwaebere is indeed contaminated with Mn; however, the concentrations are below the established safety standards. Notably, Mn levels were elevated during the rainy season in the lake water, whereas higher concentrations were observed in the soil samples during the dry season. Mn is one of the more prevalent elements in the Earth's crust and is extensively found in soils, sediments, rocks, and water. Potential sources of Mn include metal alloys, batteries, and materials used in glass and ceramics [41]. The indiscriminate disposal of waste along the lake's banks may lead to the leaching of harmful heavy metals into the water, further exacerbating the contamination of the lake [42].

It was noted that Zn concentrations were elevated in both water and soil samples as shown in Figures 3 & 4 during the dry season in comparison to the rainy season. The results suggested that both the lake water and soil were contaminated with Zn, although the levels remain below the limits established by the World Health Organization for water and the Department of Pollution Regulation for soil.

It is noteworthy that Fe levels were higher in the dry season compared to the rainy season in both water and soil samples. The results suggested that both the lake water and soil showed contamination with Fe, though the concentrations were below the limits established by the World Health Organization for water and the Department of Pollution Regulation for soil. However, elevated Fe levels in the surrounding soil may lead to increased Fe concentrations in the lake water due to surface runoff [43]. Prolonged exposure to high Fe levels can result in anemia [44]. In aquatic environments, Fe is generally found in the ferrous or bivalent form (Fe²⁺) [45].

The environmental presence of Zn is largely linked to human activities. Key anthropogenic sources of Zn include industrial operations and the use of liquid manure, compost, and agrochemicals such as fertilizers and pesticides in farming [46]. Furthermore, Zn may also stem from the mechanical wear of vehicles, as it is a component in the manufacture of brass alloys and can be found in brake linings, oil leak sumps, and cylinder heads. Fe is vital for the survival of both plant and animal life, despite its relative scarcity. The concentration of Fe in water can fluctuate significantly due to geological influences and other chemical components present in the waterway [47]. Fe is an essential nutrient for human health, with a recommended daily intake ranging from approximately 10 to 50 mg/day in drinking water. It plays a crucial role in the transport of oxygen in the blood of all vertebrates and certain invertebrates [48-50].

Variation of metal ion concentration

In the context of analysis of variance (ANOVA), the p-value, also known as the probability value 0.24997, serves as a statistical indicator that reflects the probability of observing the given data under the assumption that the null hypothesis holds true as presented in Table 5. This implies that not all the heavy metals are dependent on each other, in other words a higher value of a particular heavy metal will not translate to a proportional higher value in other heavy metals. This is also buttressed as the F-critical value (which is equally used to determine the statistical significance of the experimental data) of 2.5837 is higher that the F (of F-statistical) value.

Regression analysis and plot for the various sample locations for Heavy metals content of the lake Nwaebere (water) for both seasons

The normal distribution plot for Nwaebere lake shows linearity in samples C and E when compared with samples A, B and D, as shown in Figures 5a-5e with outliers in A, B and D. The histogram of all the sample location followed a normal distribution pattern, although with Ni not detected in Samples B, C, D and E.  Also, Pb was not detected in Sample D and E as reflected in the histograms. These regression analyses infer that there is less interdependence amongst the heavy metal and the introduction into this location is by anthropogenic means.

Regression analysis and plot for the various sample locations for Heavy metals content in soil at Lake Nwaebere for both seasons

The normal distribution plot for soil around the vicinity Nwaebere lake shows a greater linearity when compared to water in Nwaebere lake with samples D and E exhibiting very good slope, when compared with samples A, B and C, as shown in Figures 6a-6e with outliers. The histogram of most sample location followed a normal distribution pattern except for sample D, and as with Nwaebere lake, Ni was not detected in Samples A, B, C, D and E, as well as Pb which not detected in Sample B, D and E as reflected in the histograms. As with the water samples from the lake, the results of this regression analysis of the soil samples suggested that there is a lower degree of interdependence among the heavy metals detected in this area which could be predominantly attributed to human activities. These human activities are not unconnected with the influence of urbanization in the wetland like reclamation for developmental purposes.

Pollution index analysis

The evaluation of the degree of contamination in Lake Nwaebere and its adjacent wetland soil was conducted using various models, including the contamination factor, pollution load index and enrichment factor. The Contamination Factor (CF) serves as a measure of contamination relative to the average crustal composition of specific metals or to established background values. The degree of contamination in soil samples analyzed during dry and raining season revealed low contamination level across all sample locations as presented in Table 6, however for water samples the degree of contamination varied significantly with respect to the heavy metals analyzed, with Ni having high degree of contamination across both seasons, Pb and Cd very contaminated during dry and raining seasons. Though Zn exhibited moderate contamination in soil during dry season, the contamination level for Zn and Mn are low during raining season, all shown in Table 7.

The impact of pollution load index revealed that for raining season all locations are in perfect state, however for dry season sample locations A, B and E are in a declined state as presented in Table 8 implying that heavy metals present in contaminated soil can infiltrate the food chain and accumulate within the human body. This accumulation may result in various health problems, such as neurological disorders, hormonal imbalances, and cancer.

Enrichment Factor of the metals

Additionally, the Enrichment Factor (EF) was utilized as indicators to determine the extent and intensity of anthropogenic contaminants in surface soil which showed varying enrichment factors with respect to the heavy metals detected as presented in Table 9, while the pollution load index (PLI) serves as a tool for assessing the extent of heavy metal contamination in soil and sediments which revealed that the locations were perfect during the raining season while location A, B and E showed decline of site quality as presented in Table 9.

CONCLUSION

Lakes and their associated wetland soils serve as essential resources for humanity, as their chemical and physical properties significantly influence agricultural productivity and the quality of agricultural outputs, which are critical components of the Earth's life cycle. The concentration of heavy metals in these lakes and wetland soils can pose potential toxicity risks to both plants and their consumers. In water for dry season Ni, Zn and Mn are below the WHO limit while Fe, Pb and Cd are above the WHO limit, whereas in soil all the heavy metals detected are below the DPR limit. For the analysis of variance (ANOVA), the F critical value is below the F statistic value while the probability value is above 0.05 an indication that the heavy metals are independent of each other, an implication that the occurrence of these metals are due to anthropogenic activities as corroborated by the residual plot of the regression analysis. The degree of contamination for soil is low for all heavy metals detected across all sample location but exhibit varying degree of contamination in the water samples analyzed, while pollution load indices for soil is perfect in raining season but samples A, B and E exhibited decline in site quality in dry season. For enrichment factor, apart from Ni with no enrichment in dry season, all other heavy metals detected in this study showed varying degree of enrichment factor in both dry and raining season. So, the introduction of these metals into the food chain can presents a geochemical hazard due to their toxic effects on human health, particularly through bioaccumulation processes. Heavy metals may originate from the natural weathering of rocks or may be introduced through pollution resulting from human activities. An analysis of Lake Nwaebere and its wetland soils, utilized by the residents of Owerri municipality for washing, planting, and irrigation, revealed contamination with carcinogenic heavy metals.

ACKNOWLEDGEMENTS

The authors are grateful for the technical assistance offered by Ashabelem Martins Chidozie for his support during sample collection, research and data analysis

AUTHOR CONTRIBUTIONS

FCI: Conceptualized and was involved in the design of methodology, review, editing and supervision. BOK: Experimentation, formal analysis, investigation, and writing part of the original manuscript. FOC: Statistical treatment, writing part of the original manuscript, plagiarism check as well as its review, editing, and submission. BOU Contributed to reviewing and editing the manuscript. ASA: Contributed to reviewing and editing the manuscript. All authors read and approved the final manuscript.

FUNDING

No funding

DECLARATIONS

Availability of data and materials: Data and materials are made available upon request to the corresponding author.

Ethical approval and consent to participate: Not applicable.

Consent for publication: Not applicable.

Competing interests: The authors declare that they have no competing interests.

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  Table 1
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  Table 2
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  Table 3
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  Table 4
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  Table 5
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  Table 6
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  Table 7
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  Table 8
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  Table 9