Occurrence of bisphenol A, nonylphenol, octylphenol and heavy metals in groundwater from selected communities in Ibadan, Nigeria

The last two decades have witnessed growing scientific concerns and public debate over the potential adverse effects that may result from exposure to certain groups of chemicals known as endocrine disruptors (EDs) or endocrine disruptive chemicals (EDCs). Endocrine disruptive compounds are exogenous agents that interfere with the synthesis, secretion, transport, metabolism, binding action, or elimination of natural blood-borne hormones that are present in the body and are responsible for homeostasis, reproduction and developmental processes (Sahay & Reddy 2012). However, a large number of these EDCs have been released into the environment in large quantities since the Second World War (Colborn et al. 1993). Bisphenol, nonylphenol (NP) and octylphenol (OP) are among some of the suspected EDCs. Bisphenol A (BPA) is a monomer synthesized from acetone and phenol and is used mainly as an intermediate in the production of epoxy, polycarbonate and polyester resins (Matsumoto et al. 2003). Polycarbonate plastics have many applications such as the production of some food and drink packaging like water and baby bottles, compact discs, impact-resistant safety equipment and medical devices including those used in hospital settings (Matsumoto et al. 2003). Moreover, baby bottles made of polycarbonate plastic are a potential risk to children (Cao & Corriveau 2008). BPA can also be found in certain thermal paper products such as some cash registers and automated teller machine (ATM) receipts (Babu et al. 2015). All these potential sources of BPA increase the chance of human exposure.

Nonylphenol is used as a precursor in the production of nonylphenol ethoxylate, an anionic surfactant used in the manufacture of antioxidants, detergents, lubricating oil additives, solubilizers, emulsifiers and modifiers in paints, pesticides, textiles and some personal care products (Soares et al. 2008). Similarly, octylphenol, a solid chemical at 20 °C and 101.3 KPa, is used in the production of phenolic resins and ethoxylates (Brooke et al. 2005). These resins are used to make tyres, printing inks and electrical insulation vanishes. Octylphenol ethoxylate is used mainly in emulsion polymerization, textile processing, water-based paints, pesticide formulation, veterinary medicine and other applications (Ying et al. 2002). Nonylphenol and octylphenol have attracted attention due to their prevalence in the environment and their potential role as EDs and xenoestrogen (Mergel 2011). Bisphenol A, NP and OP are of concern to public health because of the high potential for human exposure and their demonstrated animal toxicity. Previous studies on experimental animals and wildlife have linked exposure to BPA, NP, OP and other EDCs with reductions in male fertility, a decline in the numbers of males born and abnormalities in male and female reproductive systems (Bonefeld-Jorgensen et al. 2007; NIEHS 2010).

Heavy metals are a risk factor for human health. A range of heavy metals such as cadmium, lead, mercury, arsenic, manganese and zinc are known to cause varying negative health effects, including effects on the endocrine system (Iavicoli et al. 2009; Łuszczek-Trojnar et al. 2014; Li et al. 2021). Heavy metals widely detected in groundwater include lead, iron and manganese (USGS/Water Science School 2018; Li et al. 2021). Lead is a metal found in natural deposits and its route to the environment includes lead-based paints, mining and plumbing activities, gasoline and its use as a water additive. The health effects of human exposure to lead are well known. They include impairment in the synthesis of haemoglobin, delay in physical and mental development, deficits in attention span and learning disability in children, while for adults, it can cause an increase in blood pressure when they are exposed for a long time. Lead is also considered a human carcinogen (Jaishankar et al. 2014). Iron and manganese are naturally occurring components of the earth's crust and their occurrence in groundwater is usually due to natural geogenic processes. Iron is an essential element in human nutrition. It is a cofactor for many proteins and enzymes. Iron poisoning can result from exposure to excessive amount of iron and can lead to different negative health outcomes such as diarrhoea, gastrointestinal ulceration, hepatic necrosis and death. Excessive intake of iron also increases the risk of cancer (Jaishankar et al. 2014). Manganese is required for the functioning and activation of many cellular enzymes. It plays a crucial role in the metabolism of carbohydrates, cholesterol and amino acid. Some of the implications of elevated levels of manganese in drinking water include unpleasant taste, odour and staining colour of water, while elevated manganese in blood circulation causes neurotoxicity in humans.

Groundwater is a major source of fresh water for different uses, especially in developing countries like Nigeria where households rely on private wells for drinking and other domestic water uses. Interestingly, many Nigerian rural communities depend on shallow groundwater sources for domestic water use (Onyekwere et al. 2019). The quality of groundwater is of serious concern in Nigeria due to rapid urbanization and industrialization, agricultural practices, climate variability, and less regard for requirements on the safe discharge of waste and wastewater from industrial and domestic sources. The evaluated contaminants in this study have been shown to reach groundwater through various routes. The BPA occurrence in groundwater was noted to be associated with irrigation with reclaimed water, soil amendment with biosolids and proximity to landfills (Careghini et al. 2015). Similarly, NP contamination of groundwater has been linked mainly to landfill leachate, water from agricultural land, or seepage of septic tanks and sewer systems (Luo et al. 2014). For heavy metals, the contamination route could be proximity to industrial areas that use a range of chemicals in the production of batteries, paints, pharmaceuticals, leather, and agrochemicals or through the agronomic practice of applying agrochemicals (fertilizer and pesticide) that are retained in the unsaturated zone and reach groundwater through irrigation return flow (Vetrimurugan et al. 2017).

As mentioned earlier, EDCs enter the environment through the use of products containing them, sewage and manufacturing waste streams (Warhurst 1995; Ying et al. 2002). However, human exposure to EDCs may occur through ingestion of contaminated food (e.g., fish), contaminated drinking water, and contact with some personal care products and detergents. In Nigeria, open dumping has been the major management option for solid waste disposal (Arukwe et al. 2012), especially in peri-urban and rural communities. Also, the most prevalent management option for wastewater management is through dumping in open places and unplanned drainages (Nabegu 2010; Idris-Nda et al. 2013). These waste management practices may likely aid EDCs in finding their way to pollute groundwater sources. In Nigeria, empirical data on the levels of BPA, NP and OP in environmental compartments were mainly obtained from urban areas. For instance, Ignatius et al. (2010) documented the levels of BPA in potable water sources within the metropolis of Enugu. Also, Oketola & Fagbemigun (2013) reported concentrations of BPA, NP and OP in the waters and sediments of rivers Ogun and Ibeche in Lagos State. Similarly, Inam et al. (2019) reported the occurrence of BPA, NP and OP in New Calabar River in Port Harcourt. Little is known about the levels of BPA, NP and OP in the environment of rural areas in Nigeria. Given the importance of the groundwater system in water supply in the rural areas of Nigeria, information on levels of pollutants is required. However, studies that have examined the level of EDs in the groundwater system in rural areas in Nigeria are scarce. Only one study by Onyekwere et al. (2019) documented the levels of BPA, NP and OP in the rural areas of Anambra (Mgbaukwu and Umudioka) and Delta (Agbarho, Ikweghwu and Orhokpokpor) States. This study, therefore, provides information on the levels of BPA, nonylphenol and octylphenol in groundwater in Ibadan North-West and Ido Local Government Area of Ibadan, Nigeria.

Ibadan North-West (IbNW) LGA is one of the five LGAs that are within the metropolis of Ibadan as depicted. It has an area of 26 km² and a population of 154,029 from the 2006 census. Occupations of the residents in the LGA include commercial activities such as trading, artisanal works, public service and private sector workers.

The study was cross-sectional in design which involved laboratory analysis of groundwater samples to assess levels of bisphenol A, nonylphenol and octylphenol. A 3-stage sampling technique was employed in the selection of LGAs, wards and the communities where samples were collected. The first stage involved the selection of Ido and IbNW LGAs through simple balloting from the list of six rural and five urban LGAs, respectively. Wards were selected by simple random sampling at the second stage of sampling. In Ido LGA, Akufo, Erinwusi-Koguo, Gbekuba and Ido wards were selected, while Nalende ward was selected from IbNW LGA. In the third stage, communities were selected by simple balloting from the wards. In Ido LGA, samples were collected from Akufo, Idi Amu, Alagbaa, Ido and Gbekuba communities, while samples were collected from Omitowoju settlement in Nalende ward of IbNW LGA.

Groundwater samples were collected into a 300 mL amber-coloured glass bottle for determination of BPA, NP and OP. The collected water samples were preserved at the sampling sites by the addition of 1 mL of 99.9% HPLC grade HCl (Standard Methods 2005). 1 mL HCl was added to all collected water samples meant for the analysis of BPA, NP and OP to prevent the degradation of analytes until determination. Plastic bottles of 2 litres capacity were used to collect water samples for determination of physicochemical parameters, while olytetrafluoroethylene (PTFE) bottles of 100 mL capacity were used to collect samples for heavy metal analysis. The samples for heavy metal analysis were fixed with concentrated nitric acid to prevent the metals from adsorbing to the walls of the containers. The water samples were collected according to the recommended standard methods described by the American Public Health Association (Standard Methods 2005). The water samples were collected from 30 different sites, 15 from each LGA, comprising 26 hand-dug wells, two springs and two boreholes (Figure 1). Samples were collected in triplicate from all sampling points. The sample bottles were tightly stoppered after each collection and transported under 4 °C to the laboratory for BPA, NP, OP and physicochemical (including heavy metal) analyses.

Groundwater samples were extracted via liquid–liquid extraction. 200 mL of the water sample was first filtered through glass fibre filters (Whatman GF/F, 1 μm effective pore size) to remove suspended particles. One hundred (100) μL each of 1 mg/L BPA-d16 was added to the filtrate as internal standards. Extraction was carried out first with 50 mL dichloromethane and then with 25 mL hexane. Extracts were combined and dried over anhydrous sodium sulphate. For all extraction procedures, methanol was added to enhance the isolation of analytes, particularly bisphenol A. Clean-up of the extracts was achieved with a glass syringe (20 mL) loaded with silica gel, glass wool and anhydrous sodium sulphate, and then eluted with 5 mL of a mixture of dichloromethane and hexane (2:1). The syringe was first conditioned by soaking in hexane before and after packing. The purified extracts were then re-constituted in 2 mL hexane.

To enhance the detection of analytes by GC, due to the low volatility of the analytes, the purified extracts were derivatized by reacting with acetic anhydride (Goodson et al. 2002; Mayer et al. 2007; Zhao et al. 2009). One hundred (100) μL of the purified extract was transferred into a glass tube, followed by the addition of 2 mL of 1 M NaHCO₃, and 1 mL of 1 M NaOH solutions. The tube was mixed for a few seconds to dissolve the extract. Two (2) mL n-hexane and 10 mL acetic anhydride were then added. The tube, tightly capped and manually shaken violently for 1 min, was then left at room temperature for 30 min. The supernatant of n-hexane was transferred carefully into a glass centrifuge tube using a micropipette. The n-hexane mixture was then allowed to dry on standing. The dried extract was re-dissolved in 100 μL of n-hexane and transferred into a 2 mL amber glass vial.

The derivatized extract was analysed for BPA, OP and NP by using a gas chromatograph-mass spectrometer (GC-MS). Separation of BPA, OP and NP was achieved by injecting about 1 μL of each extract into the GC in a splitless mode through a capillary column (3.0 m length, 0.2 mm internal diameter, 0.2 μm film thickness). Helium gas was used as the carrier gas, an eluent to extract the analytes from the column. As the carrier gas sweeps the analyte molecules through the column, motion is inhibited by the adsorption of the analyte molecules either onto the column walls or onto packing materials in the column. The rate at which the molecules progress along the column depends on the strength of adsorption, which, in turn, depends on the type of molecule and the stationary phase materials. Since each type of molecule has a different rate of progression, various components of the analyte mixture were separated as they progress along the column and they reached the end of the column at different retention times. The operational conditions of the GC-MS are summarized in the Supplementary material.

Collected water samples were analysed for pH (using the Jenway pH meter) and conductivity using the Jenway 470 conductivity meter. Total dissolved solids (TDS) were determined using the Jenway 470 TDS meter; total alkalinity by titration with a standard acid (HCl, using methyl orange indicator); and chloride by titration against AgNO₃ using the K₂CrO₄ indicator. A colorimeter (Jenway 6510, England) at 410 nm was used to determine NO₃-N.

For the determination of heavy metals, 50 mL of water samples were digested with 5 mL of HNO₃ in a 250 mL beaker. The digest was cooled, filtered and transferred to a 25 mL standard flask. Thereafter, the filtrate was made up to the 25 mL mark with distilled water and kept in clean vials before composition analysis. The concentrations of Pb, Fe and Mn in the extract were determined with an atomic absorption spectrophotometer (Buck Scientific 210 VGP). For standard calibration, standard solutions of Pb (0.0, 1.0, 2.0, 3.0 and 4.0 mg/L), Mn (0.0, 2.0, 4.0, 8.0 and 10.0 mg/L) and Fe (0.0, 2.0, 4.0, 8.0 and 10.0 mg/L) were prepared and the absorbance of these standard solutions was measured. A calibration curve was generated from the values obtained and concentrations of the metals were determined from the calibration curve.

All reagents used for the analysis were of analytical grade and high purity. Bisphenol A d16 was used as an internal standard to monitor method performance and to estimate the percentage recovery of each analyte. Multiple extractions were performed for each sample to maximize analyte recovery. Sample blanks were prepared and analysed for the same analyte to monitor interference and circumvent cross contamination. Replicate determinations were used to check the precision of the analytical method. After every five (5) samples, the calibration curve was reset with standard solutions with the highest concentration of each element to ensure that the test with the atomic absorption spectrophotometer was in control.

The detection limits (DLs) of the analyte were determined by the lowest possible dilutions of the analyte. The DLs (mg/L) of the GC-MS used for analysis were 0.00137 for BPA, 0.00037 for NP and 0.00075 for OP. The DLs (mg/L) of the atomic absorption spectrophotometer used for the analysis of heavy metals were 0.030 for Mn, 0.050 for Fe and 0.080 for Pb, while its quantification limits were 0.091 for Mn, 0.152 for Fe and 0.242 for Pb.

Data were analysed using Statistical Package for Social Sciences (SPSS, Windows Version 18, Chicago, IL). The mean and the corresponding standard deviation were used to summarize the characteristics of the water samples, while the results were compared with the Standards Organization of Nigeria (SON) for drinking water and the World Health Organization (WHO) Guidelines for drinking water quality. A non-parametric Kruskal–Wallis test was used at a 5% level of significance to determine if there were significant differences in the median values of water quality parameters across the sampling area.

The physicochemical characteristics of the groundwater sources are presented in Table 1. The pH values of the groundwater samples from both the wells and boreholes in IbNW and Ido Local Government Areas were within the permissible limits of 6.5–8.5 specified by the World Health Organisation (WHO) and Standards Organisation of Nigeria (SON). These, thus, indicate that groundwater samples from both the wells and boreholes in the two LGAs satisfied the pH requirement for potable water sources as specified by WHO and SON (SON 2007; WHO 2011). However, the pH values observed for the spring water sources in Ido Local Government Area were slightly acidic and below the recommended limit (WHO 2011). This could be due to the fact that the spring is an unprotected source of water and is open to pollution from various sources such as run-off water from farmlands. The implication of utilizing water from the spring water sources for domestic purposes such as drinking is that it could lead to corrosion of pipes in houses (Ojekunle et al. 2020) and contribute to negative effects on the gastrointestinal tract, which has the potential to result in diarrhoea (Obiefuna & Sheriff 2011).

Other parameters such as total solids, TDS, alkalinity, chloride and nitrate were within the permissible limits by WHO for both IbNW and Ido water sources (WHO 2011). However, the conductivity of well water samples in the IbNW Local Government [1233.0 (624.0) μS/cm] Area exceeded the limit recommended by WHO and SON. This is similar to the findings of some previous studies that reported high concentrations of electrical conductivity (Ganiyu et al. 2018; Ojekunle et al. 2020). The high concentrations of EC have been attributed to the lithologic constituent of the sampling area as well as the anthropogenic activities predominant in the area (Ojekunle et al. 2020). The conductivity of borehole water samples in IbNW LGA, well and spring water samples from Ido LGA were within the recommended limits.

Lead was not detected in any of the water sources from both IbNW and Ido LGAs. A large proportion of well water samples from Ido LGA and 38.5% in IbNW had iron concentrations that exceeded the SON and WHO recommended limits. Furthermore, the entire sampled borehole in IbNW LGA and the springs in Ido LGA showed iron concentrations that exceeded the permissible limits. Manganese concentrations were within the recommended limit by WHO and SON.

A Mann–Whitney test was performed to evaluate whether the physicochemical parameters of well water in IbNW LGA differed from those of well water in Ido LGA. The results are presented in Table 1. The results indicated that well water in IbNW LGA had significantly higher pH than well water in Ido LGA (U = 23.000, p = 0.002). Similarly, the conductivity of well water from IbNW LGA was higher than that of Ido LGA (U = 29.000, p = 0.004). Also, the concentration of TDS in well water was significantly higher in IbNW LGA compared to the value obtained in Ido LGA. Significantly higher concentrations of alkalinity (U = 26.500, p = 0.003), chloride (U = 32.000, p = 0.007) and manganese (U = 38.000, p = 0.015) were recorded in well water from IbNW LGA compared to the values obtained in Ido LGA. The results also indicated that there were no differences between values of total solids (U = 65.000, p = 0.300), nitrate (U = 69.000, p = 0.426) and concentration of iron (U = 57.000, p = 0.158) in well water from IbNW LGA and well water from Ido LGA.

The source of Fe and Mn in groundwater could be through natural geogenic processes and anthropogenic input (Vetrimurugan et al. 2017). Iron (Fe) and manganese (Mn) occur naturally in soils, rocks and minerals and are found in the aquifer when groundwater comes in contact with these solid materials. The reducing conditions, residence time and well depth have been reported to be the key factors leading to the dissolution and migration of Fe and Mn to groundwater (Zhang et al. 2020). Some of these factors could have been responsible for the occurrence of Fe and Mn in groundwater in the study locations. For instance, the groundwater sources at the study locations are generally deep wells, which probably explains the occurrence of Fe and Mn in well water for some locations. Anthropogenic input could be from industrial effluent, sewage, indiscriminate dumping of organic waste and landfill leachate. Iron (Fe) and manganese (Mn) in groundwater from the study locations could be attributed to some of these factors. The decomposition of organic matter depletes the oxygen in water and aids dissolution and migration of Fe to groundwater (Zhang et al. 2020). Most of the wards in Ido LGA, where a higher risk of iron in groundwater was observed, are rural areas. They lack reliable sanitation services; sanitary refuse disposal methods and open defecation are common features of these areas. These practices probably explain the observed trend of Fe in groundwater in Ido LGA.

This study assessed the levels of bisphenol A, nonylphenol and octylphenol in groundwater samples from Ibadan North-West and Ido Local Government Area, Ibadan, Nigeria. Laboratory analysis of the groundwater samples for BPA, NP and OP detected 0.00279 mg/L of NP in spring water sampled at Idi Amu community in Ido LGA. BPA and OP were not detected in any of the 30 groundwater samples (Table 2). Unlike previous studies that have detected BPA, NP and OP in various samples of groundwater, surface water and sediment (Li et al. 2010; Karalius et al. 2014; Staniszewska et al. 2015; Lv et al. 2016; Inam et al. 2019; Onyekwere et al. 2019), this study did not detect BPA and NP in any samples analysed. This could be attributed to the nonexistence of BPA and OP containing materials, which perhaps might contaminate the groundwater sources sampled despite the reported indiscriminate and improper disposal of waste (Arukwe et al. 2012).

The present study found an NP concentration of 0.00279 mg/L in the spring groundwater. The observed concentration of the NP was below 0.015 mg/L proposed for nonylphenol by the Danish Environmental Protection Agency (Wenzel et al. 2003). Comparable concentrations of NP have been detected in surface water and groundwater in Nigeria. Inam et al. (2019) reported concentrations of NP that ranged from 0.00020 to 0.00215 mg/L in New Calabar River in Port Harcourt, Nigeria. A previous study by Oketola & Fagbemigun (2013) also reported a concentration of NP that ranged between 0.0439 and 0.0794 mg/L in surface water in Lagos, Nigeria. Onyekwere et al. (2019) detected concentrations of NP that ranged from 0.0001 to 0.0903 mg/L and 0.0037 to 0.0570 mg/L in shallow groundwater samples from rural settlements in Delta State and Anambra State, Nigeria, respectively. The recorded concentration of NP in this study is within the global range of concentrations (3 × 10⁻⁷–0.0373 mg/L) when compared with the data from different countries previously reviewed (Careghini et al. 2015; Inam et al. 2019). Nevertheless, the spring water source was unprotected and open to contamination from agricultural and storm water run-off from nearby farmland as observed during sample collection. These findings suggest that residents who drink water from all the water samples collected were not at risk of adverse health effects that may occur from exposure to BPA and OP. However, consumers of the spring water at Idi Amu may be at risk of being exposed to nonylphenol, but at a level with no adverse health implications.

Bisphenol A, nonylphenol and octylphenol have been assessed in groundwater samples. Only NP was detected at levels below the maximum allowable concentration in drinking water from a spring at Idi Amu community. Bisphenol A and octylphenol were not detected in all the samples in both IbNW and Ido Local Government Area. The pH value observed for the spring water sources in Ido Local Government Area was acidic and below the recommended limit. The electrical conductivity of well water samples in IbNW Local Government Area exceeded the limit recommended by WHO and SON. Lead was not detected in any water sources from both IbNW and Ido LGAs. In this study, manganese concentrations were found in 76.9% of wells in IbNW and 69.2% in Ido LGA. Concentrations of electrical conductivity and chloride of the well water in IbNW LGA were significantly higher compared to that of Ido LGA. Also, the concentration of manganese of the well water in IbNW LGA was higher than the manganese concentration obtained in Ido LGA. Consumers of water from all the well water samples in IbNW and Ido LGA as well as boreholes in IbNW were not at risk of adverse health effects that may occur from exposure to BPA and OP. However, consumers of spring water at Idi Amu may be at risk of being exposed to nonylphenol, but at a level with no adverse health implications. Nevertheless, there is a need to protect the spring source of water from either human or natural sources of contamination. Public awareness should be created on the protection of groundwater sources from contamination as they are the source of water for most domestic purposes.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.