RUHUNA JOURNAL OF SCIENCE Vol 13 (1): 41-51, June 2022 eISSN: 2536-8400 Faculty of Science http://doi.org/10.4038/rjs.v13i1.114 University of Ruhuna Faculty of Science, University of Ruhuna Sri Lanka 41 Characterization and risk evaluation of water samples collected from boreholes situated around a dumpsite in Obalende, Lagos, Nigeria Tajudeen O. Yahaya*1, Yunusa Abdulganiyu2, Titilola F. Salisu3, Abdulmalik Abdulazeez1, Abdulrazaq Izuafa1, Sofiat A. Sanni1, Abdulmumini I. Ahmadu2 1Department of Biological Sciences, Federal University Birnin Kebbi, PMB 1157, Kebbi State, Nigeria 2Department of Geology, Federal University Birnin Kebbi, Nigeria 3Department of Zoology and Environmental Biology, Olabisi Onabanjo University Ago-Iwoye, Ogun State, Nigeria *Correspondence: yahaya.tajudeen@fubk.edu.ng, ORCID: https://orcid.org/0000-0002-5252-6536 Received: 08th September 2021, Revised: 03rd March 2022, Accepted: 17th June 2022 Abstract: Dumpsites are used worldwide for waste disposal because they are cost- effective and have the capacity to contain enormous amounts of waste. However, concerns are rife about the impact of dumpsites on the quality of nearby groundwater. The present study assessed the quality of borehole water near a dumpsite in Obalende, Lagos, Nigeria. Heavy metal, physico-chemical, and microbiological tests were performed on the samples of the water using standard techniques, and the results were compared to the WHO permissible limits. The average daily oral ingestion (ADOI), average daily dermal ingestion (ADDI), and hazard quotient (HQ) of the heavy metals were also estimated. The heavy metal analysis revealed non-permissible levels of zinc, iron, lead, and manganese, while nickel, cadmium, and silicon were within the permissible limits. Physico-chemical analysis showed that turbidity, total suspended solids, total dissolved solids, nitrate, and phosphate were within the permissible limits, but not the pH, electrical conductivity, chloride ion, sulphate and dissolved oxygen. The microbiological examination indicated that the water had high levels of bacteria and coliform counts. The HQ of Zn, Fe, and Pb, mainly through dermal exposure was above the recommended limits (>1). Overall, the results suggest that the water may predispose consumers in the area to Zn, Fe, Pb, and Mn toxicities as well as microbial infections. Consequently, consumers are advised to treat the water before consuming it. Keywords: Average daily ingestion, bacteria, dumpsite, Lead, Nitrate 1 Introduction Increasing population expansion and industrialization in Lagos, Nigeria is synonymous with high waste generation (Akande 2018). These wastes include domestic, https://rjs.ruh.ac.lk/index.php/rjs/index http://doi.org/10.4038/rjs.v13i1.114 https://creativecommons.org/licenses/by-nc/4.0/ mailto:yahaya.tajudeen@fubk.edu.ng https://orcid.org/0000-0002-5252-6536 T. O. Yahaya et al. Characterization of borehole water near a dumpsite in Nigeria Ruhuna Journal of Science Vol 13 (1): 41-51, June 2022 42 agricultural, and industrial wastes and may be classified as liquid, solid, or gaseous (Adebayo and Obiekezie 2018). Most of the wastes are disposed of in open dumpsites across the state by private sectors, local governments, and the Lagos State Waste Management Authority. Some wastes are also disposed of indiscriminately within the metropolis and water bodies. The dumpsites are poorly managed and concerns are rife about the possible impact of these dumpsites on the quality of nearby groundwater (Aboyeji and Eigbokan 2016, Oyedele and Oyedele 2017). The major environmental contaminants in dumpsites are toxic elements and microorganisms. Organic wastes in dumpsites produce microorganisms that degrade them, such as Bacillus, Escherichia coli, Klebsiella, Proteus, Pseudomonas, Staphylococcus and Streptococcus spp., Aspergillus, Fusarium, Mucor, Penicillium, and Saccharomyces spp. (Williams and Hakam 2016, Hamid et al. 2019). The decaying wastes produce weak acidic chemicals, which combine with liquids in the waste to form leachate and landfill gas (Hamid et al. 2019). Additionally, inorganic wastes such as electronics and food containers contain toxic elements, particularly heavy metals, including Lead (Pb), Mercury (Hg), Arsenic (As), Cadmium (Cd), and Nickel (Ni) (Popoola et al. 2019). Over time, the leachate, along with toxic elements and microorganisms, leaches into the soil and groundwater, compromising drinking water quality (Vodyanitskii 2016). Heavy metals generate free radicals in animals and plants and cause oxidative damage (Rehman et al. 2018). Microorganisms enter the cells and disrupt the immune function or elicit toxins (Alberts et al. 2002). Groundwater is the commonest source of drinking water in most parts of Lagos (African Groundwater Atlas 2019). This is due to insufficient or inefficient pipe-borne water, comparable to what is obtainable in other regions of Nigeria and developing nations (Yahaya et al. 2020a). Furthermore, when properly managed, groundwater is economical, safe, consistent in quality and quantity, and ample for humans (Umar et al. 2017). Thus, it becomes imperative to keep regular monitoring of the quality of groundwater around dumpsites to prevent health hazards. Literature searches show that there is a dearth of information on the quality of groundwater around a dumpsite in Obalende, Lagos, Nigeria. Obalende is highly cosmopolitan and one of the most populated areas in the city. This study, therefore, characterized the quality and evaluated the levels and risk of heavy metals in water collected from boreholes situated around a dumpsite in Obalende, Lagos, Nigeria. 2 Material and Methods 2.1 Description of the study area This study was carried out in Obalende, Lagos, Nigeria (Figure 1). Lagos is the capital of Lagos State, at latitudes of 6°37ʹN and 6°70ʹN and longitudes of 2°70ʹE and 4°35ʹE. Lagos covers an area of approximately 3,577 km2, of which land constitutes 2,798 km2 T. O. Yahaya et al. Characterization of borehole water near a dumpsite in Nigeria Ruhuna Journal of Science Vol 13 (1): 41-51, June 2022 43 and water covers 779 km2 (Wang et al. 2018). Lagos is bordered by the Republic of Benin on the west; Ogun State on the east and north; and the Atlantic Ocean on the south. The state is characterized by tropical vegetation, many water bodies, and high rainfall (Yahaya et al. 2019a). Obalende is among the most densely populated areas in Lagos, but, unfortunately, there are no government-approved dumpsites in the area. So, residents dump all sorts of waste indiscriminately, mainly along the McGregor canal, under the bridge, in Obalende. This has resulted in heaps of filthy and stinking waste in the area, necessitating an assessment of the effects of these wastes on the nearby drinking water sources. Fig 1: Water sampling locations in the Obalende area, Lagos, Nigeria 2.2 Sample collection Water samples were collected randomly from ten boreholes situated within dwelling places at about 100 m from the dumpsite in February 2021. The samples were collected in polyethylene terephthalate plastic bottles that had been prewashed with a detergent solution, sterilized with 10% nitric acid for 24 h, and then rinsed with distilled water (Yahaya et al. 2020a). The samples were covered tightly and refrigerated at -10 °C in the laboratory. T. O. Yahaya et al. Characterization of borehole water near a dumpsite in Nigeria Ruhuna Journal of Science Vol 13 (1): 41-51, June 2022 44 2.3 Physicochemical and heavy metal analysis The physicochemical properties of the water were characterized based on the guidelines for measuring water quality as described by APHA (2012). Time-sensitive properties, such as pH, temperature, and electrical conductivity, were measured on-site with a digital pH meter, a mercury-in-glass thermometer, and a conductivity meter, respectively. Other properties such as total suspended solids (TSS), total dissolved solids (TDS), turbidity, dissolved oxygen (DO), chloride, sulphate, nitrate, and phosphate were measured in the laboratory as described by Yahaya et al. (2020b). Heavy metal analysis was carried out as described by Yahaya et al. (2019b). One milliliter of each sample was transferred to a pre-washed 100-ml beaker containing an analytical grade of 25 ml of aqua regia mixture (70% HNO3 and HCl in a ratio of 3:1, respectively) and 5 ml of 30% H2O2. The mixture was digested in a digestion vessel at 80 °C until a homogenous solution was obtained. Afterwards, the solution was cooled, filtered through a Whatman No. 42 filter paper into a 50-ml volumetric flask, and diluted to the mark with deionized water. The filtrate was subjected to atomic absorption spectroscopy using a UNICAM spectrophotometer (model 969) to determine the concentrations of zinc (Zn), iron (Fe), sodium (Na), manganese (Mn), lead (Pb), cadmium (Cd), nickel (Ni), and silicon (Si). 2.4 Microbial analysis The total bacterial counts were estimated using the membrane filtration technique as described by Brock (1984). To this end, 100 ml of each water sample was filtered through a sterile cellulose filter (0.2 µm pore size), and the filter was inoculated into a nutrient agar plate and incubated at 35 °C for 24 h. The total number of bacterial colonies formed on the plate was estimated using a colony counter. The membrane filtration technique was also used to estimate the coliform count. However, the two-step enrichment method was used for microbial growth. The filters containing the bacteria were inoculated into an absorbent pad saturated with lauryl tryptose broth and incubated at 35 °C for 2 h. The filters were thereafter transferred to an absorbent pad saturated with M-Endo media and incubated at 35 °C for 22 h. The sheen colonies were observed and estimated by a colony counter. 2.5 Risk assessment The risks of heavy metals in the water samples were estimated using equations 1, 2, and 3 (USEPA, 2003 and 2004). ADOI = Cx × Ir × Ef × Ed Bwt⁄ × At ⋯ ⋯ ⋯ ⋯ [1] T. O. Yahaya et al. Characterization of borehole water near a dumpsite in Nigeria Ruhuna Journal of Science Vol 13 (1): 41-51, June 2022 45 In equation 1 above, ADOI represents the average daily oral ingestion of a heavy metal per kilogram of body weight, Cx is the concentration of heavy metals in water, Ir stands for the ingestion rate per unit time, Ef indicates the exposure frequency, Ed is the exposure duration (average life expectancy of a resident Nigerian), Bwt means body weight, and At is the average time (Ed x Ef). The standard values for these parameters were adopted from Yahaya et al. (2020a). ADD1 = Cx × Sa × Pc × Et × Ed × Et Bwt⁄ × 𝐴𝑡 ⋯ ⋯ ⋯ ⋯ [2] In equation 2 above, ADDI is the average daily dermal ingestion of heavy metals, Cx represents the concentration of heavy metals in water, Sa denotes the total skin surface area, Pc indicates the chemical-specific dermal permeability constant (cm/h), Et is the exposure time (h/day), Ef stands for the exposure frequency (days/years), Ed reveals the exposure duration (years), Bwt is the body weight, and At is the average time (Ed x Ef). The standard values for these parameters were adopted from Yahaya et al. (2020a). 𝐻𝑄= Exposure RFD ⋯ ⋯ ⋯ ⋯ [3] In equation 3 above, HQ represents the hazard quotient via oral or dermal ingestion (no units) and RFD stands for oral/dermal reference dose (mg/L/day). Oral/dermal reference doses for the selected heavy metals were adopted from Yahaya et al. (2020a). 2.6 Data Analysis The levels of heavy metals and microorganisms in the water samples were presented as mean ± standard deviation (SD) using Excel software. The ADOI, ADDI, and HQ of the heavy metals were also calculated using Excel. 3 Results & Discussion 3.1 Physico-chemical properties of the water samples Table 1 shows the physico-chemical properties of the water samples. The pH, electrical conductivity, TDS, chloride ion, sulphate, and DO levels were all within the World Health Organization's (WHO) allowable drinking water limits. However, the turbidity, TSS, nitrate, and phosphate were above the permissible limits. This finding suggests that waste from the dumpsite contaminated the water, making it unsafe to drink. The high TSS showed that the water contained high inorganic and organic materials, resulting in high turbidity. High turbidity is associated with endemic gastrointestinal illness (Mann et al. 2007). High levels of phosphate can cause digestive problems (Kumar and Puri 2012). Abnormal concentrations of nitrate can cause blue-eye T. O. Yahaya et al. Characterization of borehole water near a dumpsite in Nigeria Ruhuna Journal of Science Vol 13 (1): 41-51, June 2022 46 syndrome in children and pregnant women (Sawyerr et al. 2017). Sources of nitrate and phosphate in the water include agrochemicals, human and animal wastes, sewage leaks, detergents in industrial effluents, and run-off from fertilized farmlands (Adesuyi et al. 2015). The results of the current study are consistent with those of Odukoya and Abimbola (2010) and Osinbajo et al. (2016), who reported abnormal levels of some water quality parameters in groundwater surrounding dumpsites in Lagos. However, the result contradicts Majolagbe et al. (2011) and Kayode et al. (2018), who found no abnormal levels of nitrate and phosphate in groundwater around some dumpsites in Lagos. Table 1: Mean physico-chemical properties of the water samples obtained from boreholes around a dumpsite in Obalende, Lagos, Nigeria. Parameters Mean Concentrations Unit a Recommended values for drinking water pH 6.46±1.163 Unit 5.5-9.0 Turbidity 58.0±0.100 NTU ≤ 5 Electrical conductivity 176.6±0.208 µS/cm ≤ 1500 Total dissolved solid 657.0±3.46 mg/l ≤ 500 Total suspended solid 359.0±1.00 mg/l ≤ 100 Chloride 85.2±0.153 mg/l ≤ 250 Nitrate 103.1±0.058 mg/l ≤ 50 Phosphate 509.0±1.00 mg/l ≤ 0.1 Sulphate 25.46±0.031 mg/l ≤ 750 Dissolved oxygen 5.68±0.025 mg/l ≥1.0 a WHO, 2017 3.2 Levels of heavy metals in the water samples The levels of Zn, Fe, Na, Mn, Pb, Cd, Ni, and Si in the water samples are shown in Table 2. Zn, Fe, Mn, and Pb were detected above the permissible limits, but Na, Cd, Ni, and Si were within the permissible limits. These results again prove that the water might have been compromised and so not suitable for drinking. Hemochromatosis and tissue damage may result from an excess of Fe (Arko et al. 2019). High levels of Pb may cause high blood pressure, vitamin D and calcium metabolism imbalances, neurological disorders, and multi-organ damage (Popoola et al. 2019). Excess Zn may cause a range of symptoms, including nausea, diarrhea, and headaches (Helen and Othman 2014). Mn toxicity is associated with multi-organ damage and dopaminergic dysfunction (O'Neal and Zheng 2015). The results obtained under the current study are in line with those of Aboyeji and Eigbokhan (2016) and Oyeku and Eludoyin (2010), who detected abnormal concentrations of heavy metals in groundwater around Olososu dumpsite in Lagos, Nigeria. However, Longe and Balogun (2010) found no significant impact of a dumpsite on groundwater in Lagos with regards to heavy metal concentrations. T. O. Yahaya et al. Characterization of borehole water near a dumpsite in Nigeria Ruhuna Journal of Science Vol 13 (1): 41-51, June 2022 47 The risk assessment of the heavy metals further shows that daily intake of water may pose some risks. In particular, the ADDI of Zn was beyond the recommended limit (Table 2). Thus, residents are prone to toxic effects of Zn on the skin, such as skin lesions, decreased wound healing, and acrodermatitis (Plum et al. 2010). In addition, the HQ of oral ingestion of Fe and dermal ingestion of Zn, Fe, and Pb were greater than 1. This suggests that residents that live within the average life expectancy of Nigerians (55 years) are strongly at risk of Fe, Zn, and Pb toxicity. The risk becomes more significant with increasing age. Table 2: Levels, estimated average daily ingestion and Hazard quotient of heavy metals in water samples obtained from boreholes around a dumpsite in Obalende, Lagos, Nigeria. Heavy metals Levels (mg/l) a b Recommended values for drinking water Exposure Hazard quotient Oral (mg/day) Dermal (mg/day) c RDI Oral Dermal Zn 6.056±0.0017 5.0 0.186 9.079 8 0.002 30.263 Fe 30.45±0.0020 0.3 0.937 7.607 10 1.329 10.867 Na 1.46±0.0020 30-60 0.92 - 30-60 - - Mn 0.08±0.0018 0.05 0.0006 0.005 1.8 0.043 - Pb 0.097±0.0010 0.01 0.003 0.097 0.21 0.002 27.714 Cd BDL 0.003 - - 0.06 - - Ni BDL 0.02 - - 0.500 - - Si BDL NA - - - - - a Values were expressed as mean ± SD, BDL: below detection levels, NA: not available, b WHO: World Health Organization, 2017; c RDI: Recommended daily intake (Yahaya et al. 2020a) The possible sources of Fe in the water include steel and iron scraps, and sewage (Garba and Abubakar 2018). Zn might have been introduced through metal processing, anti-oxidants, detergent/dispersant, vehicle brakes, and tire wear (Jeong 2022). Pb could have been introduced by oil spillage from mechanical workshops, welding, panel beatings, Pb-bearing glass, pottery glazes, batteries, old lead-based paints, lead pipes, and sewage sludge (Tongesay et al. 2018). Possible sources of Mn in the water include iron and steel scrap, traffic emissions, glass, dry batteries, and chemicals (Garba and Abubakar 2018). 3.3 Levels of microorganisms in the water samples Table 3 reveals the levels of bacteria, coliform, and fungi in the water samples. The total bacteria and coliform were detected at levels above the WHO permissible limits, while fungi were not detected. These results further suggest that the water may not be suitable for drinking. Waterborne bacteria may cause diseases such as cholera, diarrhoea, typhoid fever, and dysentery (Philip et al. 2017). Excess iron concentration T. O. Yahaya et al. Characterization of borehole water near a dumpsite in Nigeria Ruhuna Journal of Science Vol 13 (1): 41-51, June 2022 48 might have increased the turbidity of the water and promoted bacterial growth (Sawyerr et al. 2017). Table 3: Levels of microorganisms (mean ± SD) in the water samples obtained from boreholes around a dumpsite in Obalende, Lagos, Nigeria. Microorganism Mean Level (CFU/ml) Permissible Limit (WHO 2008) Total bacterial 1011 ± 50.14 ≤100 CFU/ml Total coliform 400 ± 20.00 0 CFU/ml Total fungi/yeast ND 0 CFU/ml ND: not detected; CFU/ml: coliform forming unit per milliliter, WHO: World Health Organization. High levels of other nutrients in the water, such as nitrate and phosphate, might have also induced bacterial growth (Singh 2013). The detection of coliforms in the water samples indicated that the water was contaminated by organic matter, particularly faecal matter (Adelekan and Ogunde 2012). Certain strains of coliforms such as Escherichia coli 0157:H7 can cause urinary tract infections, bacteremia, meningitis, diarrhea, and acute renal failure (Gruber et al. 2014, Sawyerr et al. 2017). The result of the present study is consistent with those of Adeyemi et al. (2007) and Odukoya et al. (2013), who detected high microbial populations in groundwater obtained near dumpsites in Lagos, Nigeria. 5 Conclusions The results have demonstrated that the borehole water is turbid and contains non- permissible levels of TSS, nitrate, phosphate, Fe, Zn, Mn, Pb, and microbial populations (bacteria and coliforms). The HQ of Zn, Fe, and Pb, mainly through dermal exposure, was above the threshold of 1. This indicates that daily ingestion of the water may predispose consumers to health risks, particularly those related to Zn, Fe, and Pb toxicities. From the findings of this study, we recommend that borehole water in the locations be treated before consumption, and boreholes should not be located within 100 m of the diameter of the dumpsite. Residents should be informed about the dangers of drinking contaminated water. The government should devise a strategy to prevent people from dumping wastes in or along the canal. Similar studies like the current study should be carried out periodically in the locations. Acknowledgements Two anonymous reviewers are acknowledged for comments on the initial manuscript. T. O. Yahaya et al. Characterization of borehole water near a dumpsite in Nigeria Ruhuna Journal of Science Vol 13 (1): 41-51, June 2022 49 References Aboyeji OS, Eigbokhan SF. 2016. Evaluations of groundwater contamination by leachates around Olusosun open dumpsite in Lagos metropolis, southwest Nigeria. Journal of environmental management 183: 333–341. https://doi.org/10.1016/j.jenvman.2016.09.002. 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