Abstract
The study evaluated contamination levels of some rivers in Nwangele, Southeastern, Nigeria using pollution and health risk indices as well as irrigation quality assessment. Samples were analyzed using standard methods. The result revealed pH values ranging from 4.59 ± 0.33 to 5.41 ± 0.31 in wet and dry seasons. Levels of Fe, Ni, Pb, and Zn at 5.30 ± 4.16, 0.94 ± 0.38, 0.61 ± 0.15, and 7.45 ± 6.45 mg/L, respectively, were observed. A high pollution load index (PLI) (1.46) was observed at Nwangele River, while a low PLI (0.81) was recorded at Obiaraedu River. There is a major health risk if the water samples are not suitable for drinking, as shown by the water quality index values (> 300). The Hazard quotient and the total non-carcinogenic health hazard index through the dermal adsorption and ingestion of the surface water were < 1. However, chronic daily intake value > 1 was observed for children in both seasons due to high levels of some heavy metals, suggesting that intake of these surface waters may threaten the health of the inhabitants. Carcinogenic risk values were above 10−6 and 10−4 due to Pb levels in the surface water. This might seriously endanger the local population, particularly the kids. Irrigation quality analysis revealed that the water sources were suitable except for the increased magnesium level. The results suggested the need for appropriate treatment of the surface water sources before usage to prevent unforeseen health challenges. This could arise due to the possibility of bioaccumulation of the metallic contaminants which might take place over time.
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Introduction
Surface water sources consist of streams, rivers, reservoirs, lakes, and wetlands (Ubechu et al., 2022). Among all the natural gifts of nature, water is seen as second in importance to air (Enyoh et al. 2018; Onyenechere et al., 2021). Therefore, protecting the water sources is important for the present and forthcoming generations. Water is unavoidably indispensable and needed for human daily activities and metabolic processes (Ibe et al., 2021; Timothy et al., 2011). Water is an important chemical substance that is considered essential for all forms of life (Ibe et al., 2020a). The need for water has grown dramatically, particularly in developing nations like Nigeria where getting access to a clean water supply has remained a major obstacle for humanity (Ibe et al., 2020b). The increase in population, industrialization, and anthropogenic inputs have greatly influenced the quality of most surface water sources, thereby limiting their use for domestic, industrial, and agricultural purposes (Onyenechere et al., 2022). Unfortunately, the elevated pollution load of most of these river water sources makes the self-purification potentials of the rivers useless, which often leads to eutrophication (Ibe et al., 2019a; Ubechu et al., 2022). As such, surface water must often be purified before being used for household purposes and other uses.
Several factors contribute to surface water contamination, such as unguided disposal of electronic and metallic waste as well as indiscriminate discharge of industrial effluents (Chile-Agada et al., 2023; Ibe & Ibeachu, 2020; Ibe et al., 2018, 2019a), atmospheric deposits and emissions (Enyoh et al., 2019; Ichu et al., 2021; Muze et al., 2020), as well as roof and road runoffs (Ibe & Ibe, 2016; Ichu et al., 2018). The presence of adjacent farmlands and abattoirs, whose effluent could seriously deteriorate the surface water's quality, and agricultural activities may also have an impact on the amount of contaminants in surface water sources (Nzenwa et al., 2018; Ubechu et al., 2022). An essential part of this research is figuring out the possible health dangers connected to consuming water from these surface sources. Water contaminated with organic compounds, viruses, and heavy metals can be extremely harmful to the surrounding population's health (Akakuru et al., 2023a, 2023b).
A healthy economy and a healthy quality of life depend on agriculture. Thus, the preservation of the environment and socioeconomic progress depend heavily on water supplies (Gad et al., 2023). Crops of superior quality can only be produced with standard irrigation water since the quality of the water has a direct impact on the crops and the soils in which they are cultivated (Adegbola et al., 2019; Agidi et al., 2022). Rivers are generated by water streams that are influenced by microbiological, anthropogenic, and other contaminants, they are important for sustainability in terms of both environmental and socioeconomic advancement as well as quality of life (Bhat et al., 2021).
In many regions of the world, irrigation is considered essential for agriculture, and the quality of the water utilized for this purpose is crucial. The study looked at a number of physicochemical characteristics to determine whether these surface water sources were suitable for irrigation. The total amount of dissolved salts and the ionic composition of irrigation water vary significantly depending on the source of the water. Thus, being aware of irrigation water quality guarantees the sustainability of farming methods and guards against possible crop damage from water-related problems (Agidi et al., 2022; Akakuru et al., 2022). The quality of water exhibits significant variations depending on the source. Many surface water sources are susceptible to recurring contamination as a result of growing urbanization and industry, making them unsuitable for a variety of uses. It is necessary to take into account both the precise types of contaminants present and their overall quantity when evaluating the suitability of water for any given function, including irrigation (Eruola et al., 2020; Ukoha-Onuoha et al., 2022). This evaluation is important in optimizing irrigation practices, enhancing crop yields, and supporting the agricultural productivity of the study area.
Like many other parts of Nigeria, Nwangele struggles with issues linked to pollution and water quality as a result of both natural and man-made factors. It is critical to comprehend the physicochemical characteristics, pollution levels, and health hazards associated with these waterways for the sake of local residents' welfare as well as environmental preservation. This study took into account the assessment of health hazards related to consuming water from these sources in addition to the previously listed considerations. Comprehending these hazards is essential for developing ways to reduce them and protect the community's health.
Though there are reported studies on the quality of some surface water sources in Imo state, however, these works were mainly in urban and semi-urban areas (Akubugwu & Duru, 2001; Amadi et al., 2010) and industrial areas (Ajima et al., 2015; Ibe et al., 2019a). The only documented surface water report on Nwangele River merely compared the analyzed parameters with World Health Organization (WHO) standards and Nigeria Standard for Drinking Water Quality Standards (NSDWQ) (Anudike et al., 2019). Therefore, there is an urgent need to substantiate the level of pollution of these rivers using contamination and pollution models as well as irrigation quality assessment. This is required since the people living in the research region utilize the rivers on a regular basis without being aware of the water quality or any health risks. The importance of this study lies in the fact that the two rivers are the main source of water used by the inhabitants of the study area for their domestic and recreational purposes. Because the area lacks pipe-borne water supply and drilling boreholes for groundwater supplies is expensive, the residents must use the surface water sources. The current investigation is important since an earlier report found that one of the surface water sources (Nwangele River) is contaminated (Anudike et al., 2019). Therefore, more research is required to ascertain the degree of contamination in these rivers. The present study therefore seeks to carry out physicochemical, pollution, health risk, and irrigation quality evaluation of some surface water sources (Obiaraedu and Nwangele Rivers) in Nwangele, Southeastern, Nigeria. The novelty and uniqueness of the present study lies in the fact that Obiaraedu River has never been studied and most of the parameters and models used in analysis of the results have never been used to study any of the rivers investigated.
Materials and methods
Study area
Obiaraedu River and Nwangele River are all in Nwangele, Imo state, Southeastern Nigeria (Fig. 1). The headquarters of Nwangele is Amaigbo. Its area is approximately 63 km2 (24 sq mi). The population census of 2006 indicates that the area has a population of 128,472 (FRN, 2006), with a projected population of 145,128 as of 2010 (NBS, 2011), which must have tremendously increased after over a decade. The two rivers (Figs. 1 and 2) serve as the study area's primary water supply for its residents. According to a previous publication, it is thought that human activity along and around the riverbanks must have had a detrimental impact on the two rivers' quality. (Anudike et al., 2019). This situation must have increased significantly because of the low elevation of the area, as well as road runoffs, channeled into the rivers due to recent road construction works in the area. The study area's anthropogenic activities have exacerbated this situation, which raises the possibility that the ecology there will be further threatened. Agricultural activities within and around the river banks and runoff from the fish farms and abattoir could contribute to the levels of organic and inorganic contaminants in the rivers. This is in addition to indiscriminate dumping of wastes from nearby markets and the presence of car wash as well as washing of cloths within the proximity of the river banks (Fig. 2a), which could also negatively impact the quality of the rivers. No doubt, these activities must have generally increased the pollution load of the receiving rivers, which may pose a great risk to the unsuspecting inhabitants of the area whose major sources of water for domestic usage are from the two rivers investigated.
Map of Nwangele L.G.A. and the surrounding area with sampling points
Sampling areas of Obiaraedu (A), Nwangele river (B)
Climate and geology of the study area
The region is in the tropical rainforest zone, which has two distinctly different seasons, the dry season and the wet season. The wet season starts in April up to October, with peak incidence between June and September, whereas the dry season is witnessed in November and lasts till the end of March yearly. The warmest part of the dry season is between January and February, with daylight temperature of about 30 °C, while July and August signal periods of heavy rainfalls when the lowest ambient temperature of about 20 °C or less is observed. The estimated evapotranspiration rate is between 1450 and 1460 mm/year. Also, low relative humidity is observed within November to December, and January to March which is the driest period in the area, with about 95% relative humidity values in wet periods (Iwuchukwu et al., 2018).
Rainfall remains a significant factor that greatly influences environmental studies. The area has an annual mean rainfall of about 2500–4000 mm with over 89% of the rainfall witnessed between May and October. The regularity of rainfall events results in a large quantity of surface runoff due to the sloppy nature of the catchment area which leads to flooding-related problems in the location. The rainfall events which sometimes take place as intense heavy showers go together with enormous flooding. The flooding menace results in the leaching of topsoil, extensive sheet wash, groundwater infiltration, as well as extensive runoff into nearby rivers and streams, which could eventually elevate the level of contaminants in the rivers (Ibe et al., 2019a).
A comprehensive geology and physiography of the area under investigation has been reported (Onyeagocha, 1980). The area is underlain by Benin Formation, consisting largely of clays and sandstones. Also, there are insertions of clays and sand increasing in depth with the clay thickness, having well-sorted out sandstones and sands with grain-like sizes that range from coarse to grains of fine sediments. The variegated colored sands are loose and friable, and the sandstones are very much ferruginized. The elevated percentage of sand (70–100%), small intercalations of shale, and the nonexistence of distinctive brackish or marine microfauna make the Benin formation easily recognized. The thickness of the formation varies from 200 to 2000 m, with over 90% sand and sandstone found in the location having less significant shale enclosure. Absorptivity and spreading due to the presence of sand, which makes up over 90% of the sequence layer in the area as well as storage capacity is typically higher (Uma, 1989). The formation has excellent aquifer characteristics, with high transmissivity, permeability, and a mean yearly recharge of about 2 × 109–5 × 109 billion cubic meters per annum (Uma, 1989).
Sample collection
The Obiaraedu River and the Nwangele River were the two (2) rivers from which random water samples were taken. The upstream, middle stream, and downstream were sampled. The sample points were represented as Ob and Nw for Obiaraedu and Nwangele Rivers, respectively. The rivers' wet season ran from June to August 2019, during which time samples were taken. The rivers' dry season ran from November to December 2019, during which time samples were taken again in January 2020. Plastic bottles that had been cleaned were used to gather the samples. The samples were collected using cleaned plastic bottles. The plastic bottles used were appropriately cleaned, washed, and rinsed with deionized water. Samples for heavy metal content determination were acidified with 2 drops of 2 M HNO3 to ensure sample stability and maintain the oxidation state of the metallic elements in the sample as well as to reduce adherence onto the wall of sample containers and preserve it for further analysis.
Sample analysis
The parameters analyzed in the samples include the physical parameters; color (Col.), electrical conductivity (EC), pH, and total dissolved solids (TDS). Nitrate (NO3−), phosphate (PO42−), and sulfate (SO42−) concentrations were measured. The metallic elements; calcium (Ca), cadmium (Cd), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), potassium (K), sodium (Na), zinc (Zn) and lead (Pb), as well as the dissolved oxygen (DO) were also determine. The parameters; Col, EC, pH, TDS, and DO were analyzed as soon as the samples were obtained and taken to the laboratory. The electrical conductivity was measured using the Hanna HI8733 EC meter. pH was measured using the Jenway 3510 pH meter. The electrical conductivity (EC) and total dissolved solids (TDS) were measured with a Groline TDS/EC meter by Hanna Instruments. A Jenway 9071 digital oxygen analyzer was used to determine the surface water samples' dissolved oxygen (DO) concentration. Concentrations of anions and color were determined using Hanna multi-parameter bench photometer HI 83200. Nitrate levels were determined by cadmium reduction method within 48 h at 525 nm. Sulphate was determined by turbidimetric method at 466 nm and phosphate levels were by amino acid method at 525 nm. The metallic content of the river water samples was determined after digestion with HNO3 using an Agilent 240FS fast sequential flame absorption spectrophotometer. The concentration of Na and K were determined by flame atomic absorption spectrophotometer with Jenway clinical PFP7 Flame photometer (Onyenechere et al., 2022).
Quality control
In order to maintain quality control in the employed analytical methods and guarantee result correctness and precision throughout the analysis, standard procedures were adhered to. To guarantee the quality of analytical results, standard procedures were ensured with laboratory quality assurance properly adhered to with the samples analyzed in triplicates and results calculated as mean values. Reagents of superior analytical grade were obtained from Finlab Chemical Laboratories Nigeria Ltd. in Owerri for the analysis. Glassware and containers used for sampling and sample analysis were all washed with detergents and deionized water. The glassware was further soaked overnight in a solution of 10% HNO3 in 1% HCl solution, and later rinsed in deionized water and oven-dried with DHG 9023A (B. Brans Scientific and Instrument Company, England). Eco-Still Mark, BSIC/ECO-4 (Bhanu Scientific Instruments Company, India) was used to produce the double-distilled deionized water for sample analysis. Chemicals and reagents from HANNA Instruments were utilized to determine the anion concentration utilizing the Hanna HI8320. Agilent 240FS fast sequential flame absorption spectrophotometer used for metallic content analysis has a precision of about < 0.5% RSD and sensitivity greater than 0.9Abs. The instrument has a detection limit of 0.0001 ppm for elements in soil and water and a lower value at ppb levels for hydride-forming elements.
Data analysis
These data were evaluated for their mean and standard deviation using Microsoft Excel 2010. Correlation analysis was carried out to establish the source and relationship of the observed contaminants in the samples using IBM SPSS version 20.0. The acquired data were further subjected to pollution and contamination models to determine the degree of contamination. Also, the water quality index (WQI) and chronic daily intake (CDI) were determined as well as carcinogenic risk (CR) that could result from consumption of water from these sources. To determine if the water sources are suitable for irrigation, an assessment of irrigation quality and an investigation of the health concerns associated with using surface water sources are also necessary.
Contamination factor
To determine the degree of individual metal contamination in the water samples, the contamination factor was used. This was computed using Eq. 1.
where Cf is the contamination factor, Cmetal represents the concentration of heavy metal contained in the water sample, and Cstandard is the standard metal concentration. The WHO permissible limits for safe drinking water were taken as the standard metal centration for the water samples.
Pollution load index (PLI)
The pollution load index (PLI) was applied to establish the level of heavy metal pollution of the river waters investigated using Eq. 2.
where Cf1, Cf2, Cf3.….Cfn is the individual metal contamination factor, while n is an indication of the number of metals analyzed. PLI value > 1 indicates that the investigated sample is polluted and requires instantaneous intervention to ameliorate the cause of the pollution, while PLI value < 1 is an indication that the sample is not polluted and may pose no adverse effect.
Water quality index (WQI)
WQI is an arithmetic expression used to transmute a large number of adjustable data into one number which denotes the water quality level. The WQI was developed according to methods adopted by Duru et al. (2017) and Ibe et al. (2020a) according to Eqs. 3–6.
where Ww is equal to the comparative weight, wr indicates the weight of every single parameter and n is the number of parameters.
where qr is the quality ranking according to Eq. 4, cp is the level of the analyzed parameters (mg/L), and cs is the WHO drinking water quality standard. To work out the WQI, the SIr was established for each chemical parameter using Eq. 5, which is then used in determining the WQI according to Eq. 6.
SIr is the sub-index of the rth parameter, where n indicates the number of parameters. The benchmark values were acquired from World Health Organization (WHO) standard for drinking water (WHO 2007, 2008/2011). The WQI values were categorized according to earlier reports (Chatterjee & Raziuddin, 2002a, 2002b; Onyenechere et al., 2021).
Assessment of health risk
Health risks resulting from human exposure to metallic contaminants could be either by dermal, ingestion, inhalation, or absorption, which are the normal contact passageways for water. The investigated rivers are frequently used by the inhabitants of the area studied for most of their domestic and recreational activities. Therefore, it is important to estimate the health risks due to regular use of these surface water sources. The exposure dose due to the use of these river waters was accomplished using Eqs. 7 and 8 according to the USEPA risk estimation method (Eludoyin & Oyeku, 2010; Li & Zhang, 2010; Naveedulla et al., 2014; USEPA, 1989).
where Exping is the exposure dose via ingestion of the water (mg/kg/day); Expderm is the exposure dose via dermal absorption (mg/kg/day); Cwater indicates the average level of the measured metals in the water sample (mg/L); IR implies the rate of ingestion (2.2 L/day for adults; 1.8 L/day for children); EF is the frequency of exposure (365 days/year); ED is duration of exposure (70 years for adults; and 6 years for children); BW shows the mean body weight (adults = 70 kg; children = 15 kg for); AT is the averaging time (365 days/year × 70 years for an adult; 365 days/year × 6 years for a child); SA signifies the exposed skin area (18,000 cm2 for adults; 6600 cm2 for children); Kp represents the dermal permeability coefficient of the water, (cm/h), 0.001 for Cu, Mn, Fe and Cd, whereas 0.0006 for Zn; 0.0001 for Ni; and 0.004 for Pb (Ibe et al., 2019a; Li & Zhang, 2010); ET is the exposure time (0.58 h/day for adults; 1 h/day for children), and CF indicates the conversion factor (0.001 L/cm3) (USEPA, 2009). Potential non-carcinogenic risks of exposure to the heavy metals were established by evaluating the calculated exposure through ingestion and dermal absorption Eq. 9, as the hazard quotient (HQ). Summation of the toxicity potential due to the daily intake of the river water through the two pathways was established using Eq. 10 as the hazard index (HI).
where RfDing/derm is the oral reference dose through dermal and ingestion pathways (mg/kg/day). The values of RfDderm and RfDing were taken from earlier publications (Boateng et al., 2019; Igbal & Sham, 2013; Wu et al., 2009a, 2009b). Values of HQ and HI below one (< 1) were deemed safe and deemed to be significantly non-carcinogenic, whereas values more than one (> 1) could potentially provide significant health hazards (USEPA, 2016).
where HIing/derm is the hazard index through ingestion as well as dermal contact.
Chronic daily intake (CDI) of the surface water sources
The chronic daily intake as a result of using the surface water sources on a daily basis was calculated using Eq. 11.
where Cwater represents the concentration of metal in water in (mg/L), Exp is the exposure dose resulting from intake of the water samples, while BW indicates the whole body weight (Ibe et al., 2020a; Yonglong et al., 2015).
Carcinogenic risk (CR) of using the surface water
The carcinogenic risk or cancer risk (CRing) is an indication of the tendency of an individual to develop cancer in his lifetime which may result from his exposure to carcinogenic materials within a certain number of years (Wu et al., 2009a, 2009b). The cancer risk (CRing) of ingesting the water from the river water samples were calculated using Eq. 12
where SFing represents the cancer slope factor. The SFing value for Pb is given as 8.5 mg/kg/day (Ibe et al., 2020b; Naveedullah et al., 2014; USEPA, 1989, 2005).
Irrigation quality analysis
Sodium absorption ratio (SAR)
SAR explains the degree to which irrigation water affects the cation exchange capacity in the soil. Increased sodium levels could affect soil permeability (Joshi et al., 2009). SAR is expressed according to Eq. 13.
Magnesium absorption ratio (MAR)
The level of magnesium in natural water is considered a determinant in its use for irrigation, as it could influence crop yield. MAR was established according to Eq. 14 (Nagaraju et al., 2006).
Kelly’s ratio (KR)
KR was also determined according to Eq. 15 to further establish the quality of the surface water sources for irrigation purposes.
The cation concentrations in mg/L were converted to concentration in meq/L using Eqs. 16 and 17
Results and discussion
The results of the analyzed surface water samples and the World Health Organization (WHO, World Health Organization, 2006) and Nigeria Standard for Drinking Water Quality (NSDWQ, 2007) are presented in Table 1.
Physicochemical characteristics
The mean pH values (Table 1) varied from 5.01 ± 0.07 to 5.11 ± 0.08 in the wet season for Ob and Nw, and 4.59 ± 0.33–5.41 ± 0.33 in the dry season for Ob and Nw, respectively. These observed pH values are low and considered acidic pH levels which are not in conformity with the standard pH (6.50–8.50) stipulated by WHO and NSDWQ guidelines for safe drinking water. The low pH observed in the seasons for the two rivers might be due to the dump sites which are very close to the Rivers where generated wastes from the nearby daily markets are dumped. Variation in pH levels of surface water bodies could be due to effluent discharge, runoff from nearby farmlands as well as decay of organic matter (Ibe et al., 2019a). The use of water for different purposes depends on the pH level of the water. Drinking water with a low pH can be detrimental since it can lead to acidosis, which can result in peptic ulcers (Akubugwu & Duru, 2001). The observed pH is in line with an earlier report study of the Nwangele River (Anudike et al., 2019). The pH level of water greatly determines the solubility of chemical components in it, and the presence of most nutrients needed for biological reactions in water (Rubiat et al., 2017).
DO is the oxygen existing in dissolved form in water bodies. Runoff from farmlands with high nitrogen and phosphate content has a major impact on its reduction. It may arise from the death and decay of marine life forms leading to the discharge of nitrogen compounds into water bodies consequently causing a decrease in dissolved oxygen levels. The DO levels ranged from 4.54 mg/L at Ob to 10.88 mg/L at Nw in the wet season, while in the dry season also, it was observed that the DO values ranged from 2.21 mg/L at Ob to 6.51 mg/L at Nw. The WHO and NSDWQ maximum allowed level of 500 mg/L was not exceeded by the higher mean DO values measured in the wet and dry seasons (Table 1). The presence of dissolved oxygen makes it possible for water to sustain aquatic life and enhances the activities of microorganisms in water bodies. Additionally, the capacity of the water to hold dissolved oxygen diminishes as the temperature rises due to the inverse connection between dissolved oxygen and temperature (Akakuru et al., 2022).
The electrical conductivity (EC) values obtained in this study (Table 1) ranged from 204.17 μs/cm at NW in the wet season to 324.14 μs/cm at Ob in the wet season too. However, these values are within the WHO and NSDWQ standards. Wet season EC values were higher than dry season values, presumably as a result of higher ionic concentrations from runoffs brought on by the local flooding threat. The electrical conductivity levels in water are determined by the amount of dissolved materials in it (Corwin & Yemoto, 2017). The quality and subsequent acceptability of water for different uses could be affected by the level of charged particles contained in it (Muze et al., 2020).
TDS is an indication of materials transported in suspension and solid forms. According to Rubiat et al. (2017), TDS is a sign of organic matter and dissolved inorganic salts in solution, both of which can degrade water quality. The TDS values ranged from 101.03 mg/L in the dry season at Nw to 194.40 mg/L in the wet season at Ob. TDS levels for the investigated rivers were all in line with the standard stipulated by WHO and NSDWQ for domestic water.
All of the sampling locations' water samples had colors that were below the allowable limit, which ranged from 8.00 ± 0.00 PCU during the wet period to 14.67 ± 1.54 PCU during the dry period. To a great extent, the color of the water is a determinant factor for its aesthetic value. The taste and physical appearance determines the acceptability of water for domestic usage and other purposes (Ibe et al., 2020b). Elevated color values are indications of low water quality due to materials dissolved in it.
Concentration of anions
The mean nitrate levels (Table 1) were all found to be below the WHO standard for safe drinking water in the two seasons and ranged from 1.20 ± 0.50 mg/L at Nw to 20.55 ± 1.62 mg/L at Ob in the two seasons as well. Nitrate values recorded in the present study are within the WHO and NSDWQ standards. Elevated nitrate levels have been reported in a related study of some water resources in Imo State (Ejiogu et al., 2017). Also, Vincent et al. (2012) reported similar findings in a related study of some surface waters in the Accra Metropolitan Area. Contamination of surface and groundwater by nitrate could occur through atmospheric depositions, the use of organic and inorganic fertilizers in farmlands, and the release of sewage and organic waste into the environment (Ibe et al., 2020c; Ihenetu et al., 2022; Opara et al., 2022). Additionally, the discharge of effluent due to industrial activities could increase the nitrate levels in surface and groundwater sources (Acharya & Ballav, 2011; Lee et al., 2011; Singh et al., 2006). Elevated nitrate levels may impede the oxygen transport process within the human red blood cells. Consumption of water containing elevated nitrate concentrations could cause breathing difficulties in children resulting from the reduced circulation of oxygen, as well as a blue baby syndrome, which could be referred to as methemoglobinemia (Ibe et al., 2020b; Majumdar, 2003).
Low sulphate values (Table 1) ranged from 7.41 mg/L at Nw to 13. 30 mg/L at Ob were obtained in both seasons, which were all within WHO and NSDWQ standards for domestic water. Similar findings were observed in sulphate values obtained from the study of the Imo River (Akpbundu et al., 2016). Similarly, the findings from Eyankware et al. (2022) revealed sulphate levels lower than WHO and USEPA set limits. Higher sulphate values were reported at the Iyishi River in Imo State due to effluent discharge (Ibe et al., 2019b). Elevated concentration of sulphate in surface and groundwater sources is responsible for the fluctuation of sulphur levels in most wetlands (Geurts et al., 2009). Naturally, sulphates are found in water sources; however, the concentration could be elevated due to anthropogenic inputs. The dissolution of sulphate-containing rocks and other minerals in the soil could enrich surface and groundwater sources with sulphate concentrations (Bashir et al., 2012). Though there is no proof of severe health risks in animals and humans due to excessive intake of water containing high sulphate levels, infants are more sensitive to sulphate contamination. The abrupt change from consumption of water with decreased sulphate level to that of elevated sulphate concentration may cause laxative problems for some people (Abdulrafiu, 2011).
Phosphorus is considered an important and basic nutrient needed for the proper growth and development of aquatic organisms. Phosphate at a reasonable amount is appropriate for the growth of phytoplankton (Ugwu et al., 2016). Phosphorus is considered a restraining nutrient in most water sources. Thus, in order to prevent eutrophication and preserve the quality of water sources, it is necessary to monitor the phosphate concentration in surface water sources like rivers (Holman et al., 2008). The mean phosphate levels (Table 1) in both rainy and dry seasons range from 27.45 ± 7.99 to 81.33 ± 0.81 mg/L and 17.87 ± 0.40 to 80.76 ± 1.68 mg/L, respectively. Samples from Nw and Ob were considerably contaminated by phosphate. The farms near the rivers may have runoffs containing fertilizers containing phosphorus or phosphates, which must have been applied for agricultural purposes, contributing to the elevated phosphate levels. (Elinge et al., 2011; Singh et al., 2012). In addition, the high phosphate level may also result from the decay of organic matter within the Rivers and the fragmentation of rock, which subsequently accumulate or sediment in the River (Singh et al., 2012). Phosphates are needed by plants and animals for development, however, elevated concentration in the human body above the maximum limit could pose health risks, which may damage the kidneys, and cause osteoporosis (Calvo & Uribarri, 2013). Critical phosphate toxicity can aggravate hypocalcemia and related symptoms. Phosphate toxicity can result in the accumulation of crystals of calcium phosphate in different tissues and cardiovascular calcification (Singh et al., 2012). Elevated phosphate and nitrate levels in surface water sources contribute to excessive algal formation (Singh et al., 2012).
Concentration of metallic elements
The results of metal concentrations obtained in the area studied are presented in Table 1 as well as in Fig. 3. The result indicates that for Ca2+, Mg2+, and Na+, the mean values; 3.62 ± 0.10 mg/L, 4.67 ± 0.94 mg/L, and 4.99 ± 0.10 mg/L were recorded at Ob in dry season, while 5.23 ± 0.21 mg/L, 5.22 ± 0.21 mg/L and 8.20 ± 0.27 mg/L were recorded at Nw in wet season, respectively. It further noted that for the cations; Ca2+, Mg2+, and Na+, the mean concentrations were, respectively, 3.87 ± 0.15, 3.94 ± 0.56 and 3.94 ± 0.56 at Ob and 4.92 ± 0.27, 4.22 ± 0.17 and 6.68 ± 0.57 at Nw in dry season. These nutrients are needed by living organisms like human beings for the proper functioning of the body. The concentration of Na+ in all the samples was less than the limit value of 200 mg/L stipulated by NSDWQ. Elevated sodium levels in water have no known health effect on the human body (NSDQ, 2007). Calcium is a vital element needed for the development of strong bones and teeth; it also assists in the metabolism of muscles (Turan et al., 2003). The presence of calcium and iron are needed in the body for energy metabolism, functioning of the central nervous system, and hemoglobin formation (Ibe et al., 2019b; Ishida et al., 2000). About 800 mg of calcium is required daily by an adult for proper functioning (Alaimo et al., 1994).
The average heavy metal levels in the samples in wet/dry seasons
The bar chart in Fig. 3 represents the mean heavy metal distribution in the samples in the two seasons. Cadmium was not detected in any of the samples in both seasons. According to Fig. 3, the values recorded for iron (Fe) in the wet season were higher than WHO and NSDWQ standards of 0.3 mg/L. In the dry season, the mean values of Fe at Ob and Nw were 1.12 ± 0.12 mg/L and 10.21 ± 0.10 mg/L, respectively. A mean value of 2.69 ± 0.27 mg/L was observed for Ob, while a more elevated mean value of 7.17 ± 0.20 mg/L was recorded for Nw, both in the wet season. Fe occurs in most surface and groundwater sources through natural processes like the weathering of hard mineral aggregates that contain iron. The concentration of Fe released into water sources through natural occurrences could be influenced by anthropogenic activities, which may increase the level of Fe in these water sources. The observed elevated level of Fe in the samples especially in the wet period may be attributed to runoff into the Rivers. In addition, iron is believed to be one of the elements considered to be abundant in the Earth’s crust. A high level of Fe could influence the aesthetic value of water sources, which could stain clothes when the water is used for laundry. Ingestion of excessive Fe may damage the liver and other major organs and cells in the human body (Asare-Donkor et al., 2016).
Copper is a vital nutrient, but a water contaminant at elevated levels (Amadi et al., 2016). The Cu levels obtained in the present study were all below the WHO standards. Mean values of 0.01 ± 0.01 and 0.19 ± 0.48 mg/L were recorded for Nw and Ob, respectively, in the dry season, while 0.05 ± 0.03 and 0.02 ± 0.01 mg/L were, respectively, observed for Nw and Ob in the wet season. The low level of copper in the present study is in line with the result observed in Nwangele River (Anudike et al., 2019) and River Nworie (Duru and Nwanekwu, 2012). Similar findings were also seen in a study carried out on Nworie River, Imo State (Amadi et al., 2010). Excessive intake of Cu-contaminated water may result in oliguria and acute renal failure, and could likely cause haematuria, bleeding, as well as hepatocellular toxicity, (Agarwal et al., 1990; Ashish et al., 2013; Hefnawy & Elkhaiat, 2015).
The nickel level in the wet season for Ob (0.61 ± 0.05 mg/L), Nw (0.81 ± 0.11 mg/L), and in the dry season for Ob (1.50 ± 0.19 mg/L), and Nw (0.81 ± 0.11 mg/L) were all higher than the standards values recommended by WHO and NSDWQ. Increased Ni values in water sources could be associated with its use in paints and pigments in addition to indiscriminately discarded batteries and runoff from metal works (Duru et al., 2021; IARC, 1990). Nickel plays a major role in some biological processes of microorganisms and plants (Asare-Donkor et al., 2016). Though, nickel is needed in the human body for certain processes, elevated concentration could be toxic and may cause cancer (Kumar et al., 2016).
High mean levels of Pb; 0.68 ± 0.020 mg/L and 0.78 ± 0.35 mg/L were observed in the wet season for Ob and Nw, respectively. A similar elevated mean Pb levels were also recorded in the dry season for Ob (0.51 ± 0.15 mg/L) and Nw (0.45 ± 0.28). The observed high Pb levels were far higher than the WHO and NSDQW standards for drinking water. Increased levels of Pb in surface water sources may be from improperly disposed lead acid batteries (WHO, 2018). Another source of high Pb concentrations in water sources could be through indiscriminately disposed of Pb-containing materials such as paints, metal pipes, and lead batteries (Boateng et al., 2019). Consumption of water with Pb values above 0.01 mg/L may result in neurological problems in unborn babies and younger children (WHO, 2003). Drinking water containing high levels of lead has been linked to neurological disorders and brain damage (Bulut & Baysal, 2006).
A lower mean zinc level (0.59 ± 0.02 mg/L) below WHO and NSDWQ standards was recorded in the wet season for Ob. However, elevated mean Zn value was obtained in the wet (14.57 ± 0.51 mg/L) and dry (10.98 ± 0.81) seasons for Nw, and dry season (3.65 ± 0.15 mg/L) for Ob, which was very high above the WHO and NSDWQ permissible values. Zinc is an important trace metal that is present in nearly all food types and potable water sources as salts or in the form of organic complexes. The main source of zinc is normally through diet (WHO, 2003). Zinc is present in flora and fauna as an important component of various proteins. Because zinc possesses antioxidant qualities, it has been shown to preserve human muscles and skin from rapidly aging. (Wu et al., 2009a, 2009b). However, the concentration of Zn in water above threshold levels may be toxic. Zinc can be found in the surroundings as a result of anthropogenic activities through industrial uses, its presence in composted materials, liquid manure, as well as agricultural chemicals like animal feeds, pesticides, and fertilizers (Nitasha & Sanjiv, 2015). Another important source of Zn in the surroundings could be linked to the erosion of metallic roofing sheets like Al, Zn, galvanized roofing sheets, and atmospheric depositions (Chang et al., 2004; Enyoh et al., 2019; Gromaire-Mertz et al., 1999; Ibe & Ibe, 2016; Njoku et al., 2016; Opara et al., 2022). High intake of Zn may result in stomach cramps, vomiting, fever, nausea, and diarrhea, and may cause a deficiency of copper (Duru et al., 2017; Elinder, 1986).
Correlation analysis
Correlation analysis has been used in environmental studies to forecast similarity in the source of pollution (Asare-Donkor et al., 2016; Naveedullah et al., 2014). The result of correlation analysis for some of the investigated surface water parameters at a significant level of 0.05 is shown in Table 2. The result indicated positive correlations among the analyzed parameters. It was observed that Na has a positive correlation with PO42−, Ca, Fe, Zn, Mg, and Pb with correlation coefficients of 0.427, 0.752, 0.991, 0.839, 0.559, and 0.608, respectively. A moderate positive correlation was recorded for Mn/NO3− (0.417), Mn/Mg (0.484), Mn/Cu (0.483), and Mn/Pb (0.789), while Zn had a strong positive relationship with Ca, Fe, and Pb with a correlation coefficient of 0.901, 0.768, and 0.513, respectively. It was further observed that Fe correlated positively with Ca, Mg, and Pb with correlation coefficients of 0.701, 0.654, and 0.632, respectively, as Ni also correlated positively with NO3− (0.662). The observed positive correlations suggested that the analyzed parameters were influenced by similar factors.
Also, the correlation matrix revealed several negative correlations among the parameters in the dataset. Notably, there is a strong negative correlation between NO3− and PO42− (− 0.664), indicating that as one increases, the other tends to decrease. A similar strong negative correlation exists between PO42− and SO32− (− 0.628). Cu and Zn (− 0.477) exhibited a moderate negative correlation, suggesting an antagonistic relationship between these two metals. Furthermore, Ni and Mn (− 0.777) showed a very strong negative correlation, indicating an inverse relationship between these elements. These correlations offer valuable insights into the interplay and dynamics of these chemical components in the area investigated. A similar correlation matrix was observed in both seasons which suggested that related anthropogenic inputs were responsible for the observed river quality.
Contamination factor
The contamination factor was determined according to Eq. 1. The observed contamination factor values were ranked as Cf < 1 for low contamination, 1 ≤ Cf < 3 implies moderate contamination, 3 ≤ Cf < 6 indicates high contamination, while 6 ≤ Cf is an indication of very high contamination according to earlier reports (Ibe et al., 2019a, 2020a; Onyenechere et al., 2022). The samples were, therefore, considered to have a contamination factor ranging from low contamination to very high contamination due to elevated Fe, Ni, Pb, and Zn levels in the samples.
Pollution load index (PLI)
Pollution load index was established using Eq. 2. The PLI results as presented in Table 3 suggested that Ob showed a low PLI (< 1) in the dry season (0.83), while in the wet period PLI (> 1) value of 1.37 was recorded for Ob. High PLI > 1 was observed in both seasons for NW; 2.60 in the dry season and 2.99 in the wet season. A factor that contributed to the observed PLI in the samples was due to elevated lead, iron, nickel, and zinc concentrations in the analyzed samples. High intake of Fe-polluted water may damage the liver and other important cells in the human heart, could lead to liver failure, and could eventually cause death (Asare-Donkor et al., 2016). Elevated lead concentrations have the potential to harm the kidneys and brain, as well as disrupt the neurological system in humans (Bulut & Baysal, 2006; Utang et al., 2013).
Water quality index (WQI)
WQI was determined using Eqs. (3–6). The result of the WQI analysis is presented in Table 4. Results indicated that the WQI of the sampled rivers in wet and dry seasons were all above the accepted level for good drinking water quality. The calculated WQI values for the studied rivers in the wet season were 1458.05 for Ob and 2649.09 for Nw. Similarly, elevated WQI values were observed in the dry season with a value of 1160.33 for Ob and 2414.60 for Nw. The elevated WQI results suggested that the investigated surface water sources were severely polluted which implies the unsuitability of the river water samples for drinking and other domestic uses. Anthropogenic activities around and within the Rivers might have contributed to their contamination. The water quality index has been applied in the determination of the quality of surface and groundwater sources to ascertain their usage for various purposes (Bordalo et al., 2006; Duru et al., 2017; Ibe et al., 2019a. The observed unsuitability of the sampled surface water sources for drinking as suggested by WQI analysis is attributable to the high concentration of some of the analyzed parameters (Fe, Ni, Pb, Zn, and PO42−) above the WHO and NSDWQ permissible limit for drinking water. Therefore, the analyzed surface water sources may pose serious health risks to the inhabitants of the study area. Hence, there is a need to subject these surface water sources to rigorous treatment and purification processes if they are intended to be used for domestic activities.
Assessment of health risk
Assessment of health risk was according to Eqs. 7–10. The result of the estimated dermal and ingestion exposure dose (mg/kg/day), due to the use of the investigated surface water sources is presented in Table 5. The health risk posed by the metallic elements in the investigated surface water sources on children and adults was determined to establish the potential risk to the inhabitants of the area. Table 5 indicates that the exposure dose due to the use of the surface water sources was < 1 for adults and children.
Results of the estimated HI and HQ of the investigated rivers are shown in Table 6. HI and HQ were calculated for the studied surface water sources in wet and dry periods for the examined metallic contaminants. The observed values of HQ and HI were all less than one (< 1) as shown in Table 6 for adults and children. The HQing and HQderm decreased according to the order lead > zinc > copper > iron > nickel > manganese and lead > iron > nickel > copper > zinc > manganese > cadmium, respectively, for both children and adults in the wet season. In the dry season, the HQing and HQderm values decreased according to the order nickel > lead > manganese > copper > zinc > iron and lead > zinc > nickel > copper > manganese > iron, respectively, for both children and adults. Estimated HQ and HI values > 1 could be a source of risk, especially for children (Sudsandee et al., 2017), probably because, children are more disposed to health risk by contaminants (Sudsandee et al., 2017).
Chronic daily intake (CDI) of the surface water sources
The result of the CDI analysis according to Eq. 11 is presented in Table 7. The CDI values for the heavy metals ranged from 9.30E−4 to 1.13E−1 and 3.10E−4 to 4.51E −1, respectively, for adults in dry and wet seasons. Also, the CDI values for children ranged from 4.80E−3 to 1.74 and 6.00E−3 to 1.31, respectively, for wet and dry seasons. It was observed that higher CDI values were recorded in the dry season for both children and adults. Elevated CDI value > 1 was recorded for children in both wet and dry seasons due to higher Zn concentration suggesting that intake of the surface water may threaten the health of the inhabitants of the investigated area.
The CDI indices of the metals for both ages were found to be in the order of Fe > Zn > Ni > Pb > Cu > Mg in the wet season; and Zn > Ni > Fe > Pb > Cu > Mn > Cd in the dry season. The presence of these heavy metals in the investigated surface water sources could pose health challenges to both adults and children. This may be possible if proper measures are not taken to circumvent the accumulation of these heavy metals in the inhabitants of the study area. This calls for an enlightenment campaign to advise the inhabitants of the area on the need to purify or treat the water before being used for domestic purposes. The result of the present study is in line with the submission of related works (Akakuru et al., 2023a, 2023b).
Carcinogenic risk (CR) of using the surface water
The result of carcinogenic risk analysis of Pb according to Eq. 12 is shown in Table 8. The carcinogenic risk of Pb for Ob and Nw was calculated for both ages in the wet and dry periods. The CR values of other metallic elements in Table 1 could not be established due to the absence of their carcinogenic slope factor in the literature. The maximum estimated CRing values are shown in Table 8. Carcinogenic risk levels between 10−6 and 10−4 could constitute a serious risk to an individual. Therefore, the findings of the current investigation indicated that Pb levels in the surface water sources could provide carcinogenic risks to children and adults.
Increased Pb levels in water could be from lead-acid batteries discarded in the area (WHO 2018), and disposed materials containing Pb such as paints (Boateng et al., 2019). Unborn babies and young children are at higher risk of neurological damage when water with levels of Pb > 0.01 mg/L is consumed (WHO, 2003). High Pb concentrations may cause brain damage and nervous system disorders (Bulut & Baysal, 2006; Ibe et al., 2020a).
Irrigation quality of the investigated water sources
The major source of irrigation water in the area under investigation is surface water sources owing to the high cost of drilling boreholes. With increased pressure on industries and agriculture, as well as an increase in living standards, water quality is becoming increasingly important. Ample water is essential for healthy plant development and growth, but irrigation water quality must also be well within allowable bounds to avoid adversely affecting plant growth. Irrigation water, whether drawn from streams or pumped from groundwater sources, may contain significant amounts of contaminants in solution, which may affect crop yield and degrade soil fertility (Obiefuna & Orazulike, 2011). Concentrations of dissolved solids, electrical conductivity, sodium absorption ratio (SAR), and magnesium absorption ratio to a large extent determine the quality of irrigation water. The result of irrigation quality analysis is presented in Tables 1 and 9
Total dissolved solids (TDS)
TDS is among the parameters that determine irrigation water quality. The salts may be due to weathering or dissolution of soil and rock materials. Therefore, these dissolved salts are distributed wherever the water is used, be it for irrigation or other purposes. The salts remain in the soil after water is used by plants and lost due to evaporation. There could be a salinity hazard when these excess salts are accumulated in the plant root zone. This could affect crop yield especially when the concentration is high to the extent that extraction of sufficient water by the plant root is inhibited due to elevated salt solution in the soil, which may cause water stress for the crops for some time (Joshi et al., 2009). The plant's growth rate slows if water uptake is significantly reduced. TDS values less than 450 mg/L are considered good, while TDS above 2000 mg/L are considered unsuitable for irrigation (Joshi et al., 2009). TDS levels recorded in the present study ranged from 96.59 mg/L in the dry season to 192.20 mg/L in the wet season (Table 3).
Electrical conductivity (EC)
One of the most important water quality recommendations for crop yield is electrical conductivity (EC), often known as water salinity (Ahmed et al., 2002). The major effect of elevated EC levels in water on the productivity of crops is the plant's inability to compete for water with ions in soil solution. Even if the soil appears wet, elevated EC levels reduce water availability to plants; hence, the water available to plants for growth and production is greatly reduced as the EC levels increase. Water is considered good for irrigation if EC value is < 250 μS/cm and unsuitable when values are above 750 μS/cm. The EC values recorded in the present study ranged from 145.31 ± 5.75 in the dry season to 320.54 ± 3.42 in the wet season as indicated in Table 3. These observed EC values, although lower than the WHO recommended level of 800μS/cm. This indicates the water's capacity to carry dissolved ions, which can impact soil and crop health. Monitoring and managing EC levels are essential for selecting suitable irrigation water sources and ensuring optimal crop growth and soil conditions (Adegbola et al., 2019; Akakuru et al., 2022).
Sodium absorption ratio (SAR)
SAR is regarded as a commonly used index for evaluating the sodium risk associated with irrigation water. It was utilized to determine the likelihood that Na+ may primarily accumulate in the soil, at the expense of Ca2+ and Mg2+, as a result of the regular use of water with elevated sodium levels (Gad et al., 2023). SAR is expressed according to Eq. 13. Sodium absorption ratio which is also known as sodium hazard is classified as low S1 (SAR < 10), medium S2 (SAR 10–18); high, S3 (SAR 18–26); and very high, S4 (SAR > 26). The result of irrigation water quality analysis as shown in Table 9 revealed SAR values ranging from 0.459 to 0.720 indicating low sodium hazard for the sampled rivers. When SAR falls within this range (SAR < 10), it is generally considered favorable for irrigation purposes, as it indicates a balanced composition of sodium ions relative to calcium and magnesium ions in the water (Eruola et al., 2020; Mohamed et al., 2023).
Maintaining a low SAR is essential for preventing soil degradation and ensuring the long-term sustainability of agricultural practices (Akakuru et al., 2022). It is important to note that while the SAR values were within the acceptable range in this assessment, ongoing monitoring and periodic analysis are recommended to track any potential changes in water quality that could affect irrigation practices and agricultural productivity (Agidi et al., 2022). The result of this study is in line with an earlier submission by a related work which showed that 87% and 12.5% of groundwater sources studied were excellent (Agidi et al., 2022).
Magnesium absorption ratio (MAR)
MAR was established according to Eq. 14. MAR values above 50 are perhaps harmful and unsuitable for irrigation (Obiefuna & Orazulike, 2011). In most water sources, calcium and magnesium are in equilibrium, so as the soils become more alkaline, increased magnesium levels in water will reduce crop yields. MAR analysis revealed values ranging from 58.45 to 67.91 (Table 9), suggesting that the samples could be harmful for irrigation in terms of magnesium level. Ca2+ and Mg2+ are frequently in charge of preserving the equilibrium of the water, but salinity raises the concentration of magnesium in the water, which has an adverse effect on agricultural yield (Singaraja et al., 2014). A higher concentration of magnesium in the soil reduces the availability of potassium, which has a highly toxic effect on plants, resulting in damage to the plant and a notable development of color on the leave surfaces (Kundu & Nag, 2018). Water resource managers and agricultural practitioners need to be aware of these elevated MAR values and take the necessary precautions to lessen any potential harmful effects. These steps could be taken to use different water sources or apply soil management techniques to counteract the impacts of high magnesium levels and preserve crop yields and soil fertility (Eruola et al., 2020). To guarantee the sustainable use of irrigation water and maximize agricultural results, routine MAR value monitoring is also advised.
Kelly’s ratio (KR)
KR was determined according to Eq. 15. Kelly’s ratio < 1 is considered suitable for irrigation purposes. The KR values observed in the present study are within 0.193–0.259 (Table 9), indicating the suitability of the water sources for irrigation. Kelly's ratios of unity or less than one indicate high-quality irrigation water, whereas values above one indicate unsuitability for agricultural use because of alkali dangers (Al-Sabah, 2014). The KR values recorded in the present study differ from values reported by a related study in Rivers State Nigeria (Ukoha-Onuoha et al., 2022). However, Adegbola et al. (2019) reported that the KR values of the samples they studied were 100% good in the rainy and dry seasons. They noted that because there are no alkali risks in the water, the area provides good-quality water for irrigation.
The irrigation quality findings at the study areas, Ob and NW, showed modest differences in water quality indicators in the wet and dry seasons. Ob showed greater quantities of Ca2+, Mg2+, and Na+ than Nw did in both seasons. A high Ca2+ level was reported by a related study (Mohamed et al., 2023). Furthermore, for both observation points, the SAR values were higher during the wet season, suggesting a possible increase in sodium content during this time. The magnesium adsorption ratio (MAR) and potassium ratio (KR) data show stable levels of both parameters and are comparatively consistent between the wet and dry seasons. The results of this study indicate that seasonal variations exist in the parameters of water quality, which could have consequences for crop health and irrigation practices in the examined area. The current study's outcome agrees with the conclusions of studies conducted by Akakuru et al. (2022), Agidi et al. (2022), and Adegbola et al. (2019).
Conclusion
The study investigated some surface water sources in Nwangele, Southeastern Nigeria which include Obiaraedu River (Ob) and Nwangele Rive (Nw). The study was carried out in wet and dry periods using various quality assessment models to evaluate the surface water sources. The result revealed low pH values which were considered acidic pH levels and were not in conformity with the standard pH (6.50–8.50) according to WHO and NSDWQ guidelines for safe drinking water. High EC values were recorded in the study; however, these values were within the WHO and NSDWQ accepted limits. Elevated concentration of Fe was recorded in both seasons above WHO and NSDWQ limits. Ni levels in both periods were all above the WHO and NSDWQ guidelines. High Pb levels were also recorded in both dry and wet seasons, which were very high compared to the WHO and NSDWQ stipulated guidelines. Similarly, high zinc concentrations were observed in both seasons for Nw, and dry season for Ob. The high quantities of these metallic pollutants that have been discovered could be attributed to the careless disposal of debris and runoff from surrounding farmlands and roads. The present study has shown that the investigated surface water sources were contaminated by some heavy metals. The relatively high concentrations of some heavy metals render the investigated surface water sources unsuitable for domestic purposes without purification. The observed high contamination factor and pollution load index of the samples is an environmental concern. Given the extremely high water quality index readings (> 300), which indicate that the water samples are unfit for human consumption, there may be a health concern. The Hazard quotients and the total non-carcinogenic health hazard indices through the dermal adsorption and ingestion of the surface water were less than one. However, CDI value > 1 was observed for children in both wet and dry seasons due to higher Zn concentration suggesting that intake of the surface water may threaten the health of the inhabitants of the study area. Carcinogenic risk values were above 10−6 and 10−4 as a result of high Pb levels in the samples. This could pose a possible risk to the inhabitants of the area. Therefore, the results of this study revealed that Pb levels in the surface water sources could pose carcinogenic risks to both adults and children.
Irrigation water quality analysis indicated that the surface water sources could be used for irrigation purposes except for the slightly elevated magnesium level. Hence, the water source may be used for intensified agricultural practice in the dry season. A thorough picture of the water quality is provided by combining physical and chemical properties, WQI, and irrigation techniques to evaluate whether surface water is suitable for irrigation. This approach promotes sustainable development. It is suggested that in a circumstance of uncertain water quality, treatment, and purification are recommended to reduce the risk of water-related health challenges. It is also recommended that Government Agencies and Community leaders step up efforts to enlighten the inhabitants of the area on the quality of these surface water sources and the need to purify them before usage.
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Ibe, F.C., Ihenetu, S.C., Njoku, V.O. et al. Physicochemical, pollution, health risk, and irrigation quality evaluation of some surface water sources in Nwangele, Southeastern, Nigeria. Int J Energ Water Res (2023). https://doi.org/10.1007/s42108-023-00273-w
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DOI: https://doi.org/10.1007/s42108-023-00273-w