Heavy metals are frequently mobilized and distributed in groundwater near landfills, making it crucial to monitor groundwater quality as residents consume this water. Also, rainfall and the environment in landfills and slag heaps have a major role in determining how much water and contaminants seep into subterranean water aquifers from the mass of numerous landfilled waste materials. Furthermore, dissolved components-including heavy metals-are released in varied amounts as a result of environmental degradation processes [11].

A variety of physical, chemical, and biological factors can impact the extent of pollution released from waste that is deposited in nature [12]. The chemical form of the element and its bonding mechanism with the matrix, the shape, form, and size of the material, the surrounding temperature of the material, the redox potential, and the length of the material-liquid contact are the main factors that determine the leaching process of heavy metals [13].

The pH of water is a vital indicator of its quality. "Logarithmic units" are used to express the acidity or basicity of the water; each number represents a variation of 10 times. The pH of the majority of water is regulated by the carbon dioxide, bicarbonate, and carbonate equilibrium system. As a result, a higher concentration of carbon dioxide will produce a lower pH, while a lower content will produce a higher pH. The quality of water can be negatively impacted by pH levels both high and low. While high pH water imparts an unpleasant taste and reduces the effectiveness of chlorine water disinfection, low pH water dissolves metals and other materials [14].

The pH of the water also affects the solubility and availability of chemical constituents such as carbon, nitrogen, and phosphorus as well as the subsequent mobility of chemical elements, which includes heavy metals [15]. The solubility of heavy metals determines their toxicity as pH level also influences the solubility of heavy metal compounds, particularly when they are in the form of oxides, hydroxides, carbonates, or mineral forms, with lower pH values typically translating into greater toxicity [16]. Very low pH values increase the solubility and mobility of heavy metals. It has a significant impact on the ease with which heavy metals contaminate the environment. A solid residue is also formed when cationic and anionic constituents adsorb and desorb on mineral or organic surfaces that have a pH-dependent charge, in addition to the precipitation or dissolution of minerals [17]. These mechanisms contribute to a general tendency of leaching which is pH-dependent, meaning that an increase in pH causes the release of anions and an increase in cations [18].

Apart from their distinct chemical speciation, anions and cations possess different leaching schemes. pH is a parameter that can be used to gauge the degree of toxicity in water pollution as well as the mobility of chemical elements in water [19]. pH is one of the most significant factors among the many that influence the migration and transformation of metals [20]. Extremely high pH levels usually increase the solubility of elements and compounds, making toxic chemicals more "mobile.". Instead of becoming assimilated into the sediment, metal cations such as lead, copper, and cadmium are released into the water when the concentration of hydrogen ions increases. As doses of heavy metals increase, so does their toxicity [21]. Changes in the system's pH will have an effect on the migration and distribution of heavy metals. Transition metals like Cu, Zn, Cr, Cd, and Ni migrate into water as the pH rises [22]. Additionally, anthropogenic activities can lead to heavy metal enrichment in water bodies, indicating geochemical variability and the impact of pH on metal toxicity [23].

ELECTRICAL CONDUCTIVITY

Water quality can be assessed using electrical conductivity, a physicochemical parameter that indicates the presence of ions for the transmission of electrical current. The WHO recommends that the electrical conductivity of drinking water not exceed 400 μS/cm [24]. The electrical conductivity of water tells us how many ions are dissolved in it, but not anything specific about the minerals themselves. Pure water has a low electrical conductivity, making it a poor conductor of electric current. Also, water has a higher electrical conductivity when its ion concentration is higher, the amount of solutes dissolved in it determines the water's conductivity level [25]. The conductivity of water is influenced by inorganic dissolved particles, which can be anions or cations such as phosphates, nitrates, sulfates, calcium, iron and potassium.

MATERIALS AND METHODS

Geographical Depiction of Study Vicinity

Owerri Municipal, located in Imo State, Nigeria, is a Local Government Area with its headquarters situated in the city of Owerri. According to the 2006 census, it spans an area of 58km² and has a population of 127,213. Owerri city is strategically positioned at the meeting point of roads leading from Port Harcourt, Onitsha, Aba, Orlu, Okigwe, and Umuahia. Owerri experiences a tropical wet and dry climate, characterized by rain throughout most months of the year with a short dry season. The city is affected by the Harmattan during the early part of the dry season, although it is less severe compared to other Nigerian cities. The wet season in Owerri is characterized by warm, oppressive, and overcast conditions, while the dry season is hot, muggy, and mostly cloudy. Throughout the year, temperatures typically range from 67°F to 87°F and rarely drop below 60°F or exceed 90°F. The geographical map of the study location is presented in Figure 1.

SAMPLES COLLECTION AND ANALYSIS

Six random locations were selected to collect water samples from boreholes for this investigation with the help of a Global Positioning System (GARMIN etrex 20 model). Before filling each container, they were thoroughly washed with the water from the borehole. 1ml of nitric acid was added to each liter of the plastic container used to evaluate the heavy metals, the control samples were taken 500 meters from the sample locations and analyzed at Springboard Research Laboratory, Awka, Anambra State Nigeria.

ASSESSMENT OF PHYSICOCHEMICAL PROPERTIES OF THE WATER SAMPLES

The American Public Health Association (APHA) proposed methods for testing were used for the water samples collected. Both the pH and electrical conductivity(µs/cm) of the samples were immediately measured with a pH meter and conductivity meter. Salinity, turbidity and TDS levels were assessed with the use of APHA methods. Field calibrations took place at the sample location. Prior to assessing the pH of the water samples, the pH probe was calibrated using buffer solutions with pH values of 7 and 10 [26,27].

LABORATORY ANALYSIS

Methods of Heavy Metal Analysis of Water Samples

Heavy metal analysis was carried out using FS240AA Atomic Absorption Spectrophotometer following the American Public Health Association method. The samples underwent digestion with concentrated nitric acid prior to analysis using AAS. To prepare the water sample, it was thoroughly shaken, and 100mL of each sample was transferred into a 250mL Pyrex beaker. 10ml of concentrated nitric acid was then added. The solution was gently heated and evaporated on a hot plate until the volume was reduced to about 20mL. Subsequently, 5mL of concentrated nitric acid was added, followed by the addition of 5mL of hydrogen peroxide. A watch glass was quickly placed over the beaker. The mixture was heated steadily until a clear solution formed and white vapors appeared. It was allowed to cool to room temperature before adding distilled water. The solution was then filtered through Whatman paper No. 42. The filtrates were transferred into a 100ml volumetric flask, made up to the mark with distilled water, and mixed well. The resulting solution was then transferred into a polypropylene bottle for AAS analysis. Each batch of samples was prepared using the same method as the reagent blanks. AAS Buck Scientific Model was utilized for analyzing all the solutions for heavy metals. Additionally, an analysis of a mixture of metal standards (Pb, Fe, Mn, Cd, Cr, and Ni) prepared from their stock solutions was conducted to ensure analytical data quality assurance. The specimen was drawn into the flame of oxidizing air and acetylene. Observing the sensitivity for 1% absorption was possible when the liquid sample was aspirated. The instrument was set up and the operational conditions were established based on the manufacturers' specifications. The standard reference material (SRM 2783) filter from the National Institute of Standards and Technology (NIST) was analyzed for elemental concentrations using the same protocol as the samples. The analyses were validated by comparing the results with the certified values, which were found to be within the ±5% range. The precision and accuracy of the analytical instrument were evaluated through triplicate standard analysis. The analysis of each heavy metal was performed in triplicate, and the mean values were recorded [28,29].

QUALITY ASSURANCE

In order to acquire calibration curves, the apparatus was first calibrated using atomic absorption standards for each heavy metal that was buck-certified. Stock solutions of 1000 mg/L for different metals were used to prepare calibration standards. To eliminate equipment drift, reagent blanks were run at intervals of every ten sample analyses. Accuracy, precision, and reproducibility were assessed by analyzing all samples in triplicates. The solutions were prepared and utilized on the days the analyses were carried out.

DATA ANALYSIS

Ms-Excel, Minitab, and Statkigdom were utilized for the data analysis in this research study.

RESULTS AND DISCUSSION

A graphical representation of the physicochemical parameter analyzed in the study is shown in Figure 1 showing that the sample possessed the highest EC and TDS and the lowest pH and salinity, showing the inverse relationship between these parameters.

pH

Table 1 & Figure 2 provided a descriptive statistic of the physicochemical parameters and heavy metals for the groundwater samples that were analyzed. The pH value of groundwater samples indicated their acidic nature (pH ranged from 2.89 to 5.56), As per WHO's recommended maximum permissible limit of pH from 6.5 to 8.5. pH value of different water samples is outside the desirable and suitable range indicating that the water in the vicinity is acidic [30]. In acidic water, iron, manganese, copper, lead, and zinc are frequently found [31]. High lead content in drinking water is the main issue with acidic pH [32]. Adults who use it run the risk of developing health issues like high blood pressure, cancer, stroke, kidney disease, and memory loss [33,34].

ELECTRICAL CONDUCTIVITY

The electrical conductivity of analyzed samples stood in the range of 27 to 338 μs/cm. The least value of 27μs/cm and the highest value of 338μs/cm were obtained. The value of electrical conductivity fell below the WHO desirable limit as presented in Table 1 & Figure 2. A sign that pollution is entering the water source or groundwater could be an unusually high electrical conductivity [35]. Although a measurement of electrical conductivity cannot identify the specific pollutant, it can assist in determining whether a problem exists that could also affect invertebrates. Water with high conductivity can leave minerals on plumbing fixtures and have a bad taste and smell [36].

TURBIDITY

This is a measure of the transparency of water, indicating the amount of light absorbed or scattered by suspended particles such as clay, sludge, and microorganisms, affecting the clarity of the water ranged between 5.78 to 9.17 ppm which is far above the WHO standard of 5.00ppm. Higher turbidity levels are habitually connected to higher centralizations of pathogenic microorganisms, including specific microscopic organisms, infections, and parasites [37]. These microorganisms can deliver side effects like issues, loose bowels, cerebral pains, and queasiness. Decreasing the amount of light that reaches the water, hinders the ability of submerged aquatic plants to photosynthesize and lowers their biomass and growth rates. Lowering fish disease resistance. Obstructing vision makes it harder for predators to find prey. The more prominent the turbidity level in drinking water, the more noteworthy the opportunity for gastrointestinal diseases in people [38]. Although turbidity by itself may not always pose a direct risk to public health, it can be a useful indicator of hazardous events occurring throughout the water supply system, and it may also signal the presence of pathogenic microorganisms [39].

TOTAL DISSOLVED SOLIDS (TDS) AND SALINITY

This is the measurement of all inorganic and organic substances that are present in the water. These substances include minerals, salts, metals, and other impurities that can dissolve in water. TDS is measured in parts per million(ppm) or milligrams per liter (mg/L) ranging between 22.9 to 172.5ppm less than the WHO permissible limit of 300ppm  while the salinity which measures the dissolved salt content of the groundwater, which is a strong contributor to conductivity and helps determine many aspects of the chemistry of natural waters and the biological processes within the behavior of groundwater measure 0.0001 in samples A, B, C and D and ND in samples E and F. A taste that is either salty, bitter, or brackish is caused by elevated TDS in drinking water, but it does not pose a health risk [40]. Two minerals that are oftentimes found in TDS, calcium and magnesium, can likewise prompt staining, scale advancement, and hard water. It can make problems like kidney stones, diabetes, and gastrointestinal issues like diarrhea and stomach pain worse. In addition to these harmful effects on one's health, high TDS levels can make water taste or smell bad, leading to less water consumption and an increased risk of becoming dehydrated. Also increased salinity in water can lead to a decrease in biodiversity [41]. A species' fitness for survival in a given environment is reduced by salinities that fall outside of its tolerance range or at its boundaries because they change, inhibit, or prohibit a species' behavior [42]. They can also limit germination and reproduction [43].

RADAR CHART

The multivariate observation of the physicochemical parameters analyzed in the water samples is displayed in Figure 2. Every heptagonal shape represents an individual observation of the parameters analyzed. This strong relationship between EC and TDS is buttressed in the colored portion of the radar chart presented in Figures 2 & Figure 3 & Table 2.

The covariance matrix of a multivariate random variable is a measure of dependence between the components of the variable as represented in Table 3. In this case, pH showed a stronger negative inverse variation with TDS than Electrical conductivity, implying that the higher the numerical value of the pH, the lower the conductivity, an indication that the higher the acidity of the water the higher the electrical conductivity, as well as a strong positive variation with turbidity. Electrical conductivity and TDS however shared an extremely strong positive variation.

HEAVY METALS

The concentrations of the heavy metal analyzed in this study are presented in Table 3 & Figure 4 as well as their corresponding pH.

The Heavy metal toxicity load (HMTL) of the groundwater based on the relative toxicity level of heavy metals in the different samples is presented in Table 4.

Iron (Fe)

Iron is an essential component for healthy body function and general Health. The range of iron concentrations in this study is 0.012 to 0.135 ppm. In none of the sample locations was the iron content higher than recommended by the World Health Organization (WHO). Iron is a necessary component of human nutrition [44]. Although there isn't currently a set standard for the amount of iron in drinking water [45], exceeding the allowable limit may alter the taste and make the water less appealing [46]. This is because the amount of iron in drinking water doesn't have a major impact on health [47].

Lead (Pb)

Studies on groundwater indicate that lead is a very dangerous element. When this element is used excessively, health issues and environmental contamination result. The lead concentrations in the samples analyzed ranged from 0.001 to 0.021 ppm, exceeding the WHO recommendation of 0.001 ppm. The main contributors to lead pollution in groundwater are soldering, gasoline, cosmetics, paints that contain lead, burning fossil fuels, and industrial soil pollution [48]. Renal damage, effects on the nervous system, and mental impairment may occur when this element is present in water sources in higher than permitted amounts [49].

Manganese (Mn)

Manganese is typically found in the environment, but because of agricultural practices, it can end up in water supplies. Human health depends on manganese; deficiencies can cause skeletal malformations and issues with reproduction. Conversely, excessive intake of this element can lead to neurological and mental disorders [50]. The results of Mn in this study which range from 0.002 to 0.256 and are displayed in Table 4 & Figure 4, demonstrate that all water sources have lower manganese concentrations than those advised by the World Health Organization (WHO). It is believed that there is no manganese metal risk to humans or other living things in the groundwater that is the subject of this study [51].

Chromium

One of the three relatively stable valence states of chromium (III, Cr (VI)) is the metallic state of chromium, Cr [52]. Further valence states are possible, though they are not very stable. Under typical ambient circumstances (pH 6-9), Cr (III) is comparatively insoluble in water, producing only hydroxides and oxyhydroxides in addition to a solid solution with iron [53]. However, Cr (VI) is very soluble and mobile in the environment. However, the range of Cr found in the water samples that were analyzed is from 0 to 0.016 ppm higher than the WHO limit of 0.1 ppm.

Cadmium (Cd)

The World Health Organization has set a standard limit of 0.003 ppm for this metal. Consequently, all of the samples have cadmium concentrations that are higher than the WHO-recommended threshold. Research on the metal cadmium in drinking water reveals that, even at low concentrations, it poses a risk to humans and other living organisms. In particular, cadmium-containing compounds can be very harmful to people. Eating plants is one of the main ways that humans get cadmium because it is easily absorbed by plants. Cadmium overload can result in abnormalities related to the skeleton, liver, and kidneys, among other organ systems [54].

Nickel

Nickel is just one of many widely distributed environmental trace metals. It exists in various forms in the air, water, and soil. While nickel is a vital component for plants in limited quantities, unreasonable focuses can be dangerous. Additionally, it is harmful to human health. Nickel is generally found in regular waters as the particle Ni (H2O)6 ²⁺ at pH scopes of 5 to 9. Nickel in drinking water is primarily caused by metals leaching from pipes, which come into contact with the water. Additionally, nickel has the potential to dissolve in nickel-containing rocks and enter particular groundwater sources. Despite this, the samples used in the study lacked nickel. Metal mining, smelting, burning fossil fuels, applying fertilizer and organic manures, disposing of household, industrial, and municipal waste, and vehicle emissions are examples of human-caused activities that release nickel into the environment [55].

EIGENVALUES

The eigenvalues mirror the change of the significant parts, while the first difference is shown along the inclining of the covariance grid. The original three dimensions account for 60% of the variance, while the three primary components explain 98.9995% of the variation Table 5 & Figure 5.

From the dendrogram in Table 6 & Figure 6, the pH chunk simplicifolous indicates that it is completely different from the other parameters, it is rightly so as the unit and characteristic measurement of pH is different from heavy metals. Also, the reverse numerical relationship between acidity and heavy metal as the decrease in pH values signifies an increase in the acidic characteristics of water. In this trend, the relationship could be interpreted to be the higher the acidity of water the closer the relationship to these heavy metals. The connection between the chunks of Fe and Pb is the closest link to the bottom of the dendrogram, an implication that they have the closest link. Mn and Cr belong to different clades which proves their level of differences; hence Mn is closest to Fe and Pb, followed closely by Cr.

So, the plots in Figures 7-10 showed the relationship as explained in the dendrogram, the closer angles between Fe and Pb showed their close link and their positive correlation, while that of Mn and Cr showed that they are not likely correlated. The large angular difference between the pH values and the heavy metals showed a negative correlation with respect to their numerical values which implies that the lower the numerical values the negative their correlation, hence the higher the acidity the more closely related they tend to be.

Understanding the following helps in the interpretation of the loading plot and biplot:

• Positive correlation exists between the two variables that two vectors represent when they are near one another and create a small angle.
• There is little chance of a correlation between them if they meet at a 90° angle.
• They have a negative correlation when they diverge and create a huge angle, almost 180°.

A graphical tool that illustrates the variation in PCA that is explained by each component is the scree plot. Plotting the eigenvalues versus the component number indicates how much each component contributes to the overall variance. The scree plot in Figures 11 & 12 displays how much variation each principal component captures from the data. If the first two or three PCs are sufficient to describe the essence of the data, the scree plot is a steep curve that bends quickly and flattens out as observed in these figures.

CONCLUSION

The pH of the medium has a significant impact on the properties and behavior of metals. The toxicity of heavy metals is increased by low pH because it enhances their solubility as many components become less soluble at higher pH values, the composition of the solution is significantly altered as low pH causes metal solubility to be high and increases the toxicity of metals.  As a result, heavy metals become more soluble and accessible in low pH water, making them generally more toxic.

Correlation analysis indicates a significant negative relationship between the analyzed physicochemical parameters in groundwater in this study which are pH, TDS, and EC, indicating that the more the groundwater's acidic content, the higher the TDS and EC. The correlation analysis technique has been shown to be a very useful tool for monitoring physicochemical parameters in groundwater and their relationship, there is however a strong positive correlation between the pH and turbidity, suggesting that the more acidic the groundwater is, the less turbid the water is.

The influence of pH on heavy metal is seen in the correlation matrix and dendrogram. pH showed a negative correlation with all the detected heavy metals in this study, with a stronger negative relationship with Fe, a less strong negative relationship with Cr and a moderately negative relationship with Mn and lead, which implies that the more acidic the groundwater is the higher the Fe content, followed closely by Cr, Mn and Pb.

DISCLOSURE STATEMENT

The authors declare no conflict of interest with respect to the publication of this manuscript.

CREDIT AUTHOR STATEMENT

CFO: Investigation, Writing-Original Draft Preparation, Statistical Treatment. IFC: Conceptualization, Supervision, Methodology. ASA: Reviewing and Editing. BOI: Resources, Methodology, Reviewing and Editing. NBC:  Plagiarism check, Reviewing and Editing.

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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