Assessment of oral and dermal health risk exposures associated with contaminated water resources: an update in Ojoto area, southeast Nigeria

ABSTRACT In this paper, the oral and dermal health risks of potentially toxic elements in water samples collected from Ojoto area in southeast Nigeria were studied using HHRISK code and water quality index. The water samples were analysed for physicochemical parameters based on standard guidelines. Average concentration of the potentially toxic elements in the water was in the order: Pb2+ > Fe2+ > Zn2+ > Ni2+ > Cr3+. To assess the level of surface and groundwater pollution, water quality index was calculated. Results of the water quality index suggest that 11% of the water samples are in good condition; 25% have poor quality, 3% have very poor quality, and 53% have quality that is unfit for human consumption. The HHRISK code was used to quantify the health risks associated with the use of the water resources. Results revealed that most of the water samples expose their users to carcinogenic and non-carcinogenic health risks. Cumulative non-carcinogenic risk scores (for both children and adults) and the majority of cumulative carcinogenic risk values were found to be above regulatory limits. The adult population is exposed to lower non-carcinogenic and carcinogenic health risks, implying that children are more vulnerable. The water supplies are of substandard quality and could cause serious health issues when ingested than when used for bathing and washing purposes. Simple linear regression models showed positive agreement between the results of the WQI and HHRISK code. To safeguard the water resources, avoid additional water contamination, and reduce public health hazards associated with poor water quality, strategic mitigation strategies are recommended.

Population expansion, increased water scarcity, urbanisation, and climate change have all been identified as significant challenges for drinking water supply systems, according to studies.More than half of the world's population, particularly those in low-and middleincome nations, will be living in water-stressed areas by 2025 [13].As a result, determining the quantity of PTEs in various water sources is critical for accurate risk assessment of human health [14].PTEs are of great concern in drinking water, according to the Environmental Protection Agency (EPA) and the International Agency for Research on Cancer (IARC), owing to their carcinogenic and non-carcinogenic effects on human health.In more than 30 nations, arsenic, cadmium, and chromium in drinking water have been identified as a public health hazard.Drinking 1 litre of water per day with an arsenic (As) dose of 50 mg/L and a chromium (Cr) dose of 8.3-51 mg/L for a lifetime has been shown to induce lung, liver, bladder, and kidney cancers [15,24].It was also discovered that an arsenic dose of 0.0012 mg/kg/day administered through drinking water caused skin damage and respiratory issues.Chronic renal failure, anosmia, anaemia, cardiovascular disorders, hypertension, and osteoporosis are all linked to long-term cadmium exposure [25][26][27].Other side effects have been observed, including anaemia from Lead [16,23] gastrointestinal disorders from copper (Cu) [28,29], renal and liver damage from mercury, blood cholesterol [30,31], and heart disease from antimony (Sb) [32].
A multi-step approach that combines scientific evidence to estimate the risk(s) is required to quantify the probability and extent of deteriorative health effects resulting from human exposure to PTEs, and this evaluation has been dubbed Human Health Risk Evaluation (HHRE).Researchers have used the HHRE as a reliable technique for determining the risk associated with pollutant intake or absorption at various levels within exposed areas [17,[33][34][35][36][37][38][39][40].The HHRE has a substantial public health impact since it guides management decisions based on available data.
With the rapid advancement of technology, computer resources and intelligent solutions have been developed to detect pollution-prone zones and demarcate stable regions.Given that multiple variables are involved, the argument for using computer software packages for risk assessments is upon the possibility of operational errors [36].To model the primary exposure routes through which harmful chemicals reach humans, researchers have used computer-based software such as RISC, BIOPLUME, SADA, and BIOSCREEN [41][42][43][44].In general, these software packages have yielded useful findings for HHRE, but one of their major drawbacks is their inability to analyse hazardous chemical exposure at different concentrations and times.
Traditional water quality assessment in water resources involves comparing the levels of individual water quality parameters to their guideline or standard values based on assigned water usage or uses.This method of evaluation is straightforward and detailed, but it fails to provide a thorough and interpreted picture of water quality, which is particularly important for managers and decision-makers who need quick access to information regarding water bodies.Several water quality indices have been developed to convert water quality parameter values to an integrated indicator value in order to tackle this decision-making dilemma.By converting the amounts of water quality factors into a numerical score using mathematical methods, a water quality index (WQI) represents the general state of water bodies [18,[45][46][47][48][49][50][51].Water quality indexes are one of the most effective techniques for monitoring surface and ground water contamination, and they can also be used effectively in water quality improvement initiatives.This tool is also a mathematical strategy for converting a large amount of water characterisation data into a single value that measures overall water quality and is easily understandable by policymakers and concerned individuals [52][53][54].
The current study examines the drinking water quality and health risk assessment in Ojoto and its environs in southeastern Nigeria using WQI and HHRISK code, respectively.The HHRISK code presents a more advanced and comprehensive scope for health risk assessment than the conventional method utilised by Egbueri and Mgbenu [40] in this region.While the previous health risk assessment focused on only ingestion route [40], the present study considers both ingestion and dermal contact risks and also computed the aggregated/cumulative health risk of contaminated water resources in the area.Water scarcity has led to the exploitation of water resources for household, industrial and agricultural purposes in Nigeria's rural, suburb and urban areas.Human activities have increased as a result of agricultural and socioeconomic operations, and the situation has resulted in greater pollution of water sources.Residents of Ojoto and its surrounding areas in southeastern Nigeria seem to be exposed to several health problems due to contaminated water resources.Because of increased water demand in the region, the strain on water distribution systems has become untenable.As a result, residents seem to over-exploit the available water resources in this study area.The specific goals of the present research are to (1) identify the levels of PTEs pollution and assess the drinking quality of surface and groundwater supplies in this area based on WQI; (2) assess the health risks of PTEs in the water resources to adults and children based on oral and dermal exposure routes; and (3) investigate the correlation between the findings of WQI and HHRISK code using simple linear regression.This paper would provide researchers and decision-makers with the knowledge and information they would need to advance research, safeguard and manage the water quality.

Location, topography and climate
Ojoto and its surrounds are located between the latitudes of 06°00′N and 6°05′N and the longitudes of 06°50′E and 07°00′E (Figure 1).The area is bounded on the north by Umuoji, on the west by the Iyiowa Forest, and on the east by the erosion-ravaged Agulu-Oko-Ekwulobia-Nanka Districts in Anambra State, Nigeria.Onitsha is around 15 kilometres southeast.The research region is situated on the top of the Awka-Orlu Ridge, which has mild dipping portions.The highest elevations are found in the eastern parts of the area (near Ichida), after which the Rivers Obibia and Odoh drastically decrease the terrain to gullies of various sizes and shapes.The research area has two different seasons: a wet/ rainy season (which runs about from April to November) and a dry season (which runs roughly from December to March).The area's annual rainfall ranges from 1500 to 2000 mm, with the driest month (during the dry season) frequently recording less than 30 mm.The southwest trade winds from the Atlantics and the northeastern wind flowing through the Sahara are blamed for the two seasons.The area receives consistent insolation throughout the year due to its geographic location.During the dry seasons, temperatures can reach up to 32°C [55].While there are rising socioeconomic activities, policymakers are not paying enough attention to the negative consequences of this growth and development (e.g.high waste creation per capita, waste disposal, and insufficient water resource operation and implementation).In such a context, available water systems (both surface and groundwaters) are subjected to contamination and loss of quality.

Geology and hydrogeology
The Eocene Nanka Sandstone and the Oligocene-Miocene Ogwashi Formation are the two major geologic formations that underpin the study region (Figure 1).The Nanka Formation regressive deposits [56] represent the final stages of the second phase (Campanian-Eocene) of compressive motions that were important in the folding of the Abakaliki Anticlinorium [57].The Ogwashi Formation was deposited around the end of the Eocene, and the depocentres were shifted downwards to produce the Niger Delta.The Nanka Formation is formed of continuous crumbly sand, claystones, shales, sandy shales, and fine-grained fossiliferous sandstone intervals with occasional thin bands of limestone.It covers about 80% of the region and spans the central and eastern portions [58,59].The Ogwashi Formation, which rests on top of the Nanka Sandstone, is made up of a mix of poorly graded sandstone, light-coloured mudrocks, and lignite seams [60].Okoro et al. [61,62] reported on the Nanka Formation's numerous aquifer parameters, including hydraulic conductivity, transmissivity, and pumping test estimations.For the Ogwashi Formation, two significant aquifer systems have been identified.The first is the alluvial terrace deposit, which is more common and shallow, while the second is formed of iron-rich water and found at vast depths [63].

Sampling and physicochemical analysis of water resources
In the study area water samples (n = 28) were collected from various sources, including streams (n = 3), hand-dug wells (n = 3), springs (n = 5), and boreholes (n = 17).The various locations are depicted in Figure 1.Flowing taps were used to gather samples for the boreholes.All samples were obtained in 1-litre plastic bottles that had been cleaned with fresh water and dilute HCl acid before being used [55].The samples were properly packaged and preserved before going to the lab for processing.pH, chloride (Cl − ), sulphate (SO 4 2-), bicarbonate (HCO 3 − ), nitrate (NO 3 − ), and PTEs (zinc (Zn 2+ ), iron (Fe 2+ ), nickel (Ni 2+ ), chromium (Cr 3+ ), and lead (Pb 2+ )) were all investigated and utilised in this study.To test the pH in situ, a portable pH metre was employed (Testr-2).During the analysis of the PTEs, the American Public Health Association [64] created standard analytical techniques that were scrupulously followed.The amounts of Cl and HCO 3 were determined using titrimetric techniques, whereas the concentrations of NO 3 and SO 4 were determined using spectrophotometry.The concentrations of the PTEs were determined using AAS (atomic absorption spectrophotometry; Bulk Scientific 210VGP) method.The parameters were analysed to see if the water resources in the research region were suitable for drinking and domestic usage.

Water quality index
Water quality index (WQI) was used to assess the surface and groundwater quality in the research area for consumption.This index, established by Brown et al. [65] after Horton [66], gives a thorough summary of the state of surface and groundwater quality for residential use.However, WQI has some limitations.For example, WQI may not provide sufficient information regarding the true state of the water quality.In addition, the index may not meet the needs of many users of water quality data.Finally, there may be bias in the calculation, as the assignment of weights to parameters depends on user's discretion [67].Nevertheless, it seems that WQI has more benefits than drawbacks.It is a simple and valuable tool for conveying water quality information to the public and decision makers [68,69].In Eq. 1, the computation of WQI was done in two steps: where W i denotes the parameter's relative weight, and Q i denotes the parameter's quality index.
Step 1: Each parameter tested in the water samples was given a relative weight (W i ) based on their respective value in total water quality.The unit weights of each of the 10 parameters studied (pH, Cl − , SO 4 2-, HCO 3 − , NO 3 − , Fe 2+ , Zn 2+ , Ni 2+ , Cr 3+ , and Pb 2+ ) were calculated using the following formula (Eq.2): with S i being the water quality parameter's acceptable standard value and k being the proportionality constant determined using the formula (Eq. 3) below: Step 2: Using Eq. ( 4), we determined the quality index for each parameter: where Va is the measured value of parameter i, Vi denotes the ideal value of parameter i (0 for all parameters, except pH which is 7.0), and Vs represents the WHO-recommended standard for parameter i.When the quality rating is zero, there are no contaminants present.Whereas a quality rating of 0 < Qi < 100 indicates that the contaminants are beyond the acceptable limits [69].
Based on the absolute value of the index found by computations, the calculated WQI values are divided into five categories: 'excellent', 'good', 'poor', 'very poor', and 'unfit for drinking'.

Human health risk assessment
Human health risk assessment is an important technique for contaminated area management because it identifies risks associated with chemical pollutants exposures and aids in risk management and contaminated area remediation [70][71][72].The HHRISK code, as proposed and developed by Neris et al. [36], was employed in this work.The HHRISK code enables quick and precise risk evaluation.The production of a spatio-temporal matrix for the analysis of aggregated risk for different exposure pathways and the cumulative for exposure to numerous chemicals, as well as the estimation of uncertainties associated with risk calculations, is a major novelty of this method.It's based on a tweaked set of equations from the US Environmental Protection Agency [73].
The water intake route, whose daily intake dose was determined by Eq. ( 5), and the dermal contact route, whose daily absorption dose was calculated by Eq. ( 6), were examined in this work as two routes of human contamination by different chemical species (Fe 2+ , Zn 2+ , Ni 2+ , Cr 3+ , and Pb 2+ ) [36,[73][74][75].The risk assessment was carried out for both adults and children in the context of a domestic situation.The concentrations of PTEs in water resources in the study area were examined, and the spatiotemporal risk assessment was carried out periodically (∆t), with chemical species concentrations in the study area alternated.As a means of allowing for analysis at multiple time periods in order to improve risk reduction and management in diverse locations [36].
where: D ing-wat represents the daily intake dose (mg kg −1 d −1 ), C water is the chemical concentration in water (mg L −1 ), IR w represents the ingestion rate of water (L d −1 ), EF is the exposure frequency (d y −1 ), ∆t is the time variation (y), D der-wat is the daily absorption dose (mg kg −1 d −1 ), CF is the volumetric conversion factor (L cm −3 ), SA w is the skin surface area available for contact with water (cm 2 ), PC is the dermal permeability (cm h −1 ), ET w is the water exposure time (h d −1 ), BW is the body weight (kg) and AT is the averaging time (d) [33,36,76].
Chemical species can have both non-carcinogenic and carcinogenic effects on humans, and the evaluation of the two types of effects on human health is done differently.Noncarcinogenic risks emerge when exposure dosages exceed specified thresholds, which vary based on the chemical species and method of exposure.The carcinogenic risks assessment calculates the likelihood of a resident developing life-threatening cancer as a result of persistent exposure to carcinogenic species [77].For each chemical species and exposure route, the non-carcinogenic hazard quotient (HQ) and probable carcinogenic risk (CR) were determined.Equation 7was used to get the non-carcinogenic risk quotients.Equation 8, on the other hand, estimated the probabilistic carcinogenic risk.
where D is the exposure level (or intake) for a chemical species during a given time period, RfD is the reference dose for that chemical species, and SF is the slope factor, which turns predicted daily doses averaged over a lifetime straight into the chance of an individual acquiring cancer.
Because the risk assessment included several exposure routes (n), the aggregated hazard index (HI agg ), which is the sum of the computed HQ for each exposure route, was determined, as indicated in Eq. 9. Calculating the aggregated potential carcinogenic risk (CR agg ) using Eq. 10 can be done in the same way for carcinogenic risk [36].
The cumulative hazard index (HI cum ) and the cumulative potential carcinogenic risk (CR cum ) were computed using Equations.11 and 12 to produce the cumulative hazard index (HI cum ) and the cumulative potential carcinogenic risk (CR cum ) for the final risk assessment.Equation 13 was used to compute the estimated parameters' standard uncertainties [36].
where x i is the ith exposure parameter in each scenario, s(x i ) is the ith parameter's standard uncertainty, and (@ F/@ x i ) is the i th variable's partial derivate, also known as sensitivity coefficients (c(x i )).
According to the United States Environmental Protection Agency [75], values of HI < 0.1 indicate no risks, 1 > HI ≥ 0.1 indicate minimal risks, 4 > HI ≥ 1 indicate moderate risks, and HI ≥ 4 indicate substantial risks to human health.There are considerable carcinogenic hazards and are considered unacceptable when the CR value surpasses 1.10 −4 (1 in 10,000 persons has a chance of getting cancer).Residents are at a low risk when the CR is between 1.10 −4 and 1.10 −6 , and there is no risk when the CR is less than 1.10 −6 [33,36,76,78].

General water quality description
The hydrogeochemical parameters of surface and groundwater quality are shown in Table 1.Recognising water quality is important since it is the defining attribute that determines whether it is suitable for drinking, agriculture, or industry [79].Table 1 summarises the results of numerous parameters studied of water samples from the study area, including average, standard deviation, and mean.The Nigeria Industrial Standard (NIS) [21] and World Health Organization (WHO) [13] have established drinking water quality criteria.For water quality assessment, the behaviour of physicochemical parameters such as pH, Cl, SO 4 , HCO 3 , and NO 3 , and PTEs (Zn 2+ , Fe 2+ , Ni 2+ , Cr 3+ , and Pb 2+ ) has been investigated.

pH
The pH is a measurement of the equilibrium between hydrogen ions (H + ) and hydroxyl ions (OH − ) in water, and it determines whether a solution is acidic or alkaline [80].In many forms of geochemical solubility calculations, the pH of groundwater is crucial [81].The permitted pH range for drinking water is 6.5-8.5 [13,21].Most of the water samples in the study area have pH values ranging from 4.0 to 6.4 (Table 1), indicating that the surface and groundwater in the area is mildly acidic.This could be due to anthropogenic activities such as sewage disposal and fertiliser use in the study area's densely populated coastline sector, followed by natural phenomena such as brackish water intrusion into sandy aquifers, which starts the weathering process of underlain geology.Acidic water has been linked to mucous membrane cell destruction, as well as eye and skin discomfort [4,82].Acidic water also adds significantly to metal corrosion and affects disinfection efficiency, which has an indirect impact on human health [83].

Chloride ion (Cl − )
One of the most common inorganic anions found in natural water is chlorides.Weathering, leaching of sedimentary rocks and soils, agricultural operations, and home sewage can all cause chloride to accumulate in surface and groundwater.A high chloride concentration is thought to be a sign of pollution caused by high organic waste from animals or an industrial region [84].Chloride concentrations above a certain level are damaging to people's hearts and kidneys, as well as indigestion, taste, palatability, and corrosion.Chloride levels ranged from 2.0 to 62 mg/L in this study, with an average of 13.643 mg/L.According to NIS [21] and WHO [13], the maximum allowed limit of chloride in drinking water is 200-300 mg/L, and all samples fall within this range.Chloride measurements can be used to detect the entrance of different-composition waters, as well as to track and measure the rates and volumes of water mass migration.Increased Cl − concentration, on the other hand, causes heart and kidney damage, as well as indigestion, taste, and palatability problems [85].The amount of sulphate in the water ranged from 7.0 to 130 mg/L.Sulphate concentrations averaged 40.643 mg/L, indicating that all samples were within the acceptable range.
If the sulphate concentration exceeds the extreme permitted limit of 250 mg/L by WHO [13] and NIS [21] for drinking water, it might react with human organs, causing vermifuge effects on the human system [86].Sulphates are produced by bacteria such as chlorothiobacteria and rhodothiobacteria oxidising their ores and H 2 S. Their ions are found naturally in water and have been linked to few or no health problems.High sulphate concentrations are found in contaminated water sources.Sulphate build-up in water, on the other hand, can cause an increase in pH, resulting in acidosis [87].Excess sulphate in water has yet to be linked to any other health concerns or adverse effects.

Bicarbonate (HCO 3 − )
The existence of organic materials in the aquifer that is oxidised to produce carbon dioxide, which promotes mineral dissolution, is one probable source of bicarbonate [88].Half of the bicarbonate ions would come from the fossil carbon in the calcite and dolomite in the aquifer.Water resources are enriched in calcium, magnesium, and bicarbonate ions as a result of weathering.The weathering of silicate minerals can produce bicarbonate ions [89].Bicarbonate levels ranged from 0 to 5 mg/L, with an average of 1.382 mg/L.It was discovered to be lower than the WHO [13] and NIS [21] guideline limit of 250 mg/L.

Nitrate ion (NO 3 − )
In rural areas, nitrate is one of the most common surface and groundwater pollutants.Fertilisers, septic systems, and manure storage or spreading operations are the main sources of nitrate in surface and groundwater.The nitrate ion is not maintained in soil because nitrate compounds are soluble.As a result, nitrate is the nitrogen species most vulnerable to leaching.Excessive nitrate levels in drinking water are especially dangerous for newborns, whose underdeveloped digestive systems allow nitrate to be converted to nitrite, resulting in methemoglobinemia [90].Levels of nitrate in the range of 100-200 mg/L start to impair the health of the general population, although the effect on any particular person is dependent on a variety of circumstances.They are not, however, regarded indicative of the presence of more hazardous household or agricultural contaminants like germs or pesticides [91].All NO 3 − concentrations measured in surface and groundwater samples were found to be below the standard limit (10-15 mg/L) established by NIS [21] and WHO [13], ranging from 0 to 18.481 mg/L, with an average of 1.962 mg/L.

Iron (Fe 2+ )
Iron, like manganese, is found in rocks, soil, and minerals in the form of ores (magnetite, taconite, and haematite), accounting for around 5% of the Earth's crust [92].In its pure state, ferric hydroxide is a dark-grey substance that can be found in both surface and groundwater.In this study region, iron concentrations ranged from 0.0 to 3.6 mg/L on average, with a low of 0.0 and a maximum of 3.6 mg/L.(Table 1).Fe 2+ pollution in many of the water samples exceeds the WHO [13] and NIS [21] standard level (0.3 mg/L).The observed Fe concentrations over the allowed range might be attributed to (1) weathering of iron minerals and rocks (mineralogical and piezometry features) in the soil at the investigated sites, and (2) leaching of iron natural deposits into surface and groundwater bodies.In humans, however, anaemia has been documented as a result of an iron deficiency.Haemosiderosis (liver damage), diabetic mellitus, arteriosclerosis, and a variety of other neurological illnesses are all caused by drinking water with high Fe 2+ levels [93,94].

Zinc (Zn 2+ )
Zinc is found in rocks and soils in low amounts, mostly as sulphide ores and to a lesser extent as carbonates.The majority of zinc enters water through artificial paths, such as byproducts of steel manufacture or coal-fired power plants, waste-fired power plants, and fertiliser that may leak into surface and groundwater.Zinc is a necessary PTE that serves as a catalyst for enzymatic action in the human body [95].This PTE is present in very small amounts in drinking water, which may reduce the risk of deficiency in the diet.Its accumulation in the human body, on the other hand, has negative consequences such as stomach cramps, nausea, vomiting, a drop in good cholesterol, and the acceleration of anaemia [96].Zinc values ranged from 0.00 to 0.54 mg/L in the study area (Table 1).The zinc concentration in all of the samples tested was below the WHO [13] and NIS [21] permitted standard levels of 3-4 mg/L.It's possible that zinc in its natural mineral form (sphalerite) did not leach into subsurface water bodies in all of the samples studied [97].Medical specialists, on the other hand, have identified electrolyte imbalance, vomiting, acute renal failures, and abdominal discomfort as signs of human zinc overexposure.

Nickel (Ni 2+ )
Ni concentrations ranged from 0.00 to 0.34 mg/L in this study area.The concentration of Ni in most of the water samples was found to be below NIS [21] and WHO [13] standard limit of 0.02-0.07mg/L.The dissolution of nickel-bearing rocks is the principal source of nickel in surface and groundwater.Leaching from metals in contact, such as water supply pipes and fittings, is the source of nickel in drinking water.Ni is commonly found in the divalent state.However, it can also be found in the oxidation states of +1, +3, or +4 [98].
Nickel enters the intestines of animals through feeds and water, and is excreted as dung, which is flushed down the drain and eventually infiltrates surface and groundwater.
Between the study and control wells, there were substantial disparities in nickel values.
It is a necessary PTE, but it is poisonous in big quantities, making it detrimental to human health.It has also been discovered as a possible human cancer carcinogen [99].

Chromium (Cr 3+ )
Chromium is found in rocks, soil, plants, animals, and volcanic emissions as a naturally occurring element.It is found in drinking water in two main forms: trivalent (chromium 3) and hexavalent (chromium 6).In the majority of the samples, the Cr 3+ concentration was found to be below the permissible range of 0.05 mg/L.(Table 1).Despite the fact that Cr 3+ concentrations were below the WHO [13] and NIS [21] permitted limit (0.003 mg/L), epidemiological studies have shown that long-term exposure to Cr 3+ can result in (1) kidney damage, (2) lung cancer, (3) high blood pressure, and (4) bone abnormalities (osteoporosis and osteomalacia).The presence of chromium in the samples analysed might be linked to waste discharge from a local industry in the study area, as well as galvanised steel pipe corrosion used to transport water from the ground level to the surface level [100].

Lead (Pb 2+ )
Lead is the most dangerous of all the PTEs since it is poisonous and damaging even at extremely low amounts [101].It can build up in body tissue, posing a health risk to humans.It builds up in bones, blood vessels, and other internal organs over time.It can gain entry to the human body via consuming food, water, and air [102].Aside from being a carcinogen, lead has an effect on the central nervous system of those who are exposed to it, which can result in delayed mental and physical growth in children, as well as a reduction in attention span and learning ability [103].The concentration of Pb 2+ in the water samples ranged from 0.00 to 3.087 mg/L, with an average of 0.530 mg/L (Table 1), indicating that the concentration is below the WHO [13] and NIS [21] standard limit of 0.01 mg/L.Pb 2+ pollution was discovered in roughly half of all water samples.This could be due to (1) leaching of organic lead ores in the soil into surface and groundwater [104], (2) greater volume of leaded gasoline exhausts from motor vehicles in the residential area, and (3) reaction of water with removed coated-lead from pipe's surface due to tumultuous water movement from ground to surface level.

Pollution and water quality assessment based on WQI model
The water quality index (WQI) was used to assess surface and groundwater quality for drinking purposes.The weights of the input parameters are shown in Table S9 (supplementary material) whereas the WQI values of the water samples are presented in Table 2.This index was chosen since it is calculated using water's physicochemical properties.It is divided into five categories (Table S10, supplementary material): class (I) WQI < 50 denotes excellent water, class (II) 50 < WQI < 100 denotes high quality water, and classes (III) 100 < WQI < 200 and (IV) 200 < WQI < 300 denotes bad and very poor-quality water, respectively.Water with a WQI of class (V) > 300 is not suitable for human consumption [37,65,66,68,69].The predicted WQI values for surface and groundwater varied from 65.79 to 17975.22,with an average of 3216.04 (Table 3).Table S10 (supplementary material) shows that 3 (11%), 7 (25%), 3 (11%), and 15 (53%) of 28 surface and groundwater samples were classified as good, poor, very poor, and not suitable for drinking, respectively.The high level of pollution in most of the water samples could be credited to illegal wastewater discharge into the water resources.Other factors, such as anthropogenic activities, roadway construction and farming operations have a negative impact on the surface and groundwater quality of these sampling sites.
Water quality monitoring is needed on a frequent and detailed basis in and around Ojoto and its environs, which is currently done by the local regulatory authority.It is critical to determine changes or trends in water quality over time and space, to obtain the information needed to design specific pollution prevention strategies, and to assess whether objectives such as pollution control flow or the provision of successful pollution control actions are being met.

Non-carcinogenic and carcinogenic risks due to ingestion
The HRQ values were computed individually for adult and children while performing a normal human health risk assessment as prescribed by the US EPA, taking into account the addition of the ingestion and dermal route hazard quotient for the PTEs investigated in this study.For both adult and child populations, Table 3 shows the HHRISK results for ingestion and dermal routes.Tables S1 and S2 (supplementary material, ingesting route) and Tables S3 and S4 (supplementary material, dermal route) present the comprehensive data of the health risk assessment for all PTEs.When HRQs exceed 1, there is a risk of a non-carcinogenic detrimental health consequence, necessitating quick investigation [17,19,105].In this study, the order of influence of the PTEs appears to be Pb 2+ > Fe 2+ > Zn 2+ > Ni 2+ > Cr 3+ for both children and adults, based on the ingestion route for HRQ analysis.In all water samples, the HRQ values for the PTEs (excluding Pb 2+ , Fe 2+ , and Zn 2+ ) were significantly lower than the US EPA [75] limits, as shown in Tables S1 and S2, supplemental material.As a result, it may be deduced that drinking untreated surface and groundwater poses a danger of Pb 2+ , Fe 2+ , and Zn 2+ poisoning.
According to scientific reports [19,20,36,37,75,105], HI >1 indicates that the noncarcinogenic health risk of absorbing a certain element is over the acceptable limit, whereas HI < 1 indicates that it is under the acceptability limit.The HI results suggest that 28% of the samples (S02, S03, S05, S14, S19, S26, S27, and S28) and 25% of the samples (S02, S03, S05, S19, S26, S27, and S28) predispose their users to significant noncarcinogenic, chronic risks in both children and adults respectively.The elevated HI of the samples is due to their high Pb 2+ , HQ levels.These samples classified as 'high risk' are the same ones classified as 'unfit for drinking' by the WQI.
The CR (for adults and children) at all water samples was evaluated for carcinogenic risk assessment owing to ingestion of water resources.The CR evaluation calculated an individual's lifetime risk of developing cancer as a result of drinking water contaminated with carcinogens [17].Pb 2+ appear to be the most responsible for carcinogenic risks among the PTEs studied (Tables S1 and S2, supplementary material).From Table 3b, it can Table 3. HHRISK results for ingestion and dermal routes for both adult and child populations.be observed that water samples; S01, S02, S03, S05, S06, S07, S08, S11, S13, S14, S18, S19, S23, S25, S26, S27, and S28 have unacceptable carcinogenic risks for both children and adults following exposure (CR > 1E-6) with S19 having the highest CR (1.63E-2 ± 9.78E-3), indicating that 1 in every 100,000 adults has a high risk of developing cancer [34,73).These results show that people of Ojoto and its environs who rely on surface and groundwater for drinking suffer significant carcinogenic risks, even after only a few minutes of contact to contaminated water.Adults and children who ingest water from S01, S02, S03, S05, S06, S07, S08, S11, S13, S14, S18, S19, S23, S25, S26, S27, and S28 locations are at the most risk, while those who make use of water from S04, S09, S10, S12, S15, S16, S17, S20, S21, S22, and S24 zones are the least affected (although the risks remain high).The excessive Pb 2+ concentrations in the water supplies are the source of these hazards (Tables S1 and S2, supplementary material).

Non-carcinogenic and carcinogenic risks due to dermal contact
PTEs such as Pb 2+ , Fe 2+ , and Ni 2+ were found to pose larger risks than others (Zn 2+ and Cr 3 + ) through the dermal contact route for both children and adults, based on their HRQ scores (Tables S3 and S4, supplementary material).It is worthy to note that the HI, which indicates a sample's chronic risk, can be classed as negligible (HI < 0.1), low risk (HI ≥ 0.1 < 1), medium risk (HI ≥ 0.1 < 4), and high risk (HI ≥ 4) [17,34,37,40,75,105]. Based on the aforementioned classifications, the overall HI scores per sample (Table 3a, S3 and S4, supplemental material) demonstrated that the waters represent negligible to low chronic risks.In comparison, 82% of the total samples pose negligible risk to children, while 18% pose a low chronic risk.Due to dermal contact with the examined PTEs in the waters, 85% of the samples pose negligible chronic risk, while 15% pose a low risk to the adult population as shown in Table 3a.Moreover, based on the predicted probability of cancer risk scores (Table 3b, S3 and S4), the majority of carcinogens represent considerable carcinogenic hazards when they come into contact with the skin.Among the PTEs evaluated, Pb 2+ appears to be the most responsible for carcinogenic risks (Table 3b and S5, supplementary material).Water samples S02, S03, S05, S13, S18, S19, S23, S26, S27, and S28 exhibit unacceptable carcinogenic risks for both children and adults after exposure (CR > 1E-6), with S13 and S18 having the highest CR (12.64E-05 ± 2.01E-05).Adults and children who are exposed to water through the dermal route from S02, S03, S05, S13, S18, S19, S23, S26, S27, and S28 locations are at the greatest risk.These risks are caused by high levels of Pb 2+ in drinking water supplies (Tables S3 and S4, supplementary material).

Aggregated HHRISK coefficients
Tables S5, S6, S7 and S8 provide the results of the aggregated (non-carcinogenic and carcinogenic) health risk assessment of surface and groundwater resources for both children and adults.HRQ tot scores were generated separately for both the children and adult populations in this study.The HRQ tot for the two exposure pathways (ingestion and dermal) were then added for each demographic group to provide the aggregated health risk of the PTEs studied.According to the results, all chemical species (PTEs) pose considerable aggregated non-carcinogenic and carcinogenic health concerns to both children and adults (Tables S5-S8), as their average scores for the research region surpassed the permissible thresholds of 1 and 1 ≤ 1E-6, respectively.Furthermore, the findings revealed that this risk affects roughly 60% of the water samples.
The order of influence of the PTEs on children (based on their HRQ tot average scores) is projected to be Pb 2+ > Ni 2+ > Cr 3+ in the aggregated non-carcinogenic health risk assessment (Table S5).Despite this, the overall carcinogenic health risk for children followed the Pb 2+ > Fe 2+ > Zn 2+ > Ni 2+ > Cr 3+ trend (Table S6).
The risk trend for aggregated non-carcinogenic health risk in the adult population was Pb 2+ > Fe 2+ > Zn 2+ > Ni 2+ > Cr 3+ (Table S7), while the risk trend for aggregated carcinogenic risk (adult) was Pb 2+ > Ni 2+ > Cr 3+ (Table S8).These patterns in the adult population were found to be identical to those observed in the children's population.Pb 2 + , Fe 2+ , and Zn 2+ were recognised as the most relevant PTEs influencing the surface and groundwater quality of the research area based on the results, since they had the highest HRQ tot and CR tot scores (Table S5-S8).

Cumulative HHRISK coefficients
The results of the cumulative health risk assessment for all of the examined water samples are presented in Table 3c.In general, the HRQ cum scores (for children) obtained in all surface and groundwater samples surpassed the specified acceptable limit, and the majority of the CR cum values likewise did.The cumulative non-carcinogenic health risk posed to the children population is estimated to be very high, with HRQ cum values ranging from 0.0143 to 44.8910 and an average of 6.7046.Conversely, the cumulative carcinogenic health risk of the examined water samples suggested a significant risk for children, with CR cum scores ranging from 0.00E+00 to 1.64E-02, with an average value of 2.25E-03 (Table 3c).
The HRQ cum scores in all samples exceeded their allowed limit, as did the majority of the CR cum values, according to the adult population's cumulative health risk assessment.The HRQ cum scores for all samples ranged from 0.0086 to 27.0125, with an average of 4.6661 (Table 3c), while the CR cum values for all samples ranged from 0.00E+00 to 9.84E-03, with 1.35E-03 as the average score (Table 3c).It's worth noting that these results appear to be similar to those recorded for the children's population, however the adult scores are often lower.As a result, children in the present study area are more susceptible to both non-carcinogenic and carcinogenic health risks.

Comparison between WQI and HHRISK code
Simple linear regression models (Figure 2) produced in this study showed the levels of agreement between the HHRISK code and the WIQ.With the p-values < 0.05, it was found that strong agreements (R 2 = 0.9993) exist between the non-carcinogenic health risks obtained by the HHRISK code and the WQI (Figure 2a and b).However, it was also realised that the carcinogenic risk findings of the HHRISK code weakly followed the same trend as the WQI (Figure 2c and d).Nevertheless, a closer observation through the findings of the WQI (Table 3) and those of the HHRISK (Table 3) revealed that the samples were classified to have poor and unsuitable drinking water quality are the same as those with higher health risks.

Conclusions
This paper examined the quality of surface and groundwater for domestic purposes via oral and dermal routes, as well as the human health risks associated with contaminated drinking water in the study region, utilising water quality index and HHRISK code.After considering the numerous findings of this study, the following conclusions were drawn: • The WQI model was used to analyse the surface and groundwater quality in the study region with values ranging from 65.79 to 17975.22 and an average value of 3216.04.The result shows that 3 (11%), 7 (25%), 3 (11%), and 15 (53%) of 28 surface and groundwater samples were graded as good, poor, very poor, and not fit for drinking.• Pb 2+ , Fe 2+ , Zn 2+ , Cr 3+ , and Ni 2+ concentrations were consistently higher than those recommended in all of the mentioned guidelines, rendering the water unfit for human consumption.• The degree of health risk effect of the PTEs for children and adult populations is predicted as follows in terms of aggregated non-carcinogenic HHRISK (HRQ tot ): Pb 2+ comes first, followed by Fe 2+ , Zn 2+ , Ni 2+ , and finally Cr 3+ .• For both children and adults, the aggregated carcinogenic risk (CR tot ) followed the Pb 2+ > Ni 2+ > Cr 3+ trend.• The carcinogenic and non-carcinogenic risk from drinking water intake based on ingestion exposure was higher than the US EPA risk safety level, indicating that residents in this study area may face greater health risks and that urgent attention should be paid to this area.• Generally, the adult population's scores were lower than the children's, meaning that children are more likely to be exposed to carcinogenic and non-carcinogenic substances through ingestion and dermal contact, and that inhabitants in Ojoto and its environs are more exposed to Pb. • More efforts, such as suitable purification systems and metal discharge management, are needed to minimise the potentially toxic elements level in drinking water in Ojoto and its environs.Furthermore, to safeguard the local population and prevent human health concerns, proper wastewater treatment facility utilisation must be adopted.

Disclosure statement
No potential conflict of interest was reported by the author(s).

Figure 1 .
Figure 1.Map of the study area showing the sample locations and geology.
a) Non-carcinogenic risks for adult and child b) Carcinogenic risks for adult and child c) Cumulative/aggregate risks for adult and child

Figure 2 .
Figure 2. Simple linear regression models showing the agreements between WQI and cumulative health risks.

Table 1 .
Register of the PTEs analysed in the water resources.

Table 2 .
WQI values of the water samples.