1 Introduction

Potable water or drinking water is water that does not present any significant risk to health over a lifetime of consumption, including different sensitivities that may occur between life stages [1]. Though access to safe drinking water has been considered a basic human right by the World Health Organization, about one to two billion people in the world lack safe drinking water [2]. Access to portable water is a daily challenge for many people in Nigeria and other parts of Africa [3,4,5,6]. The United Nations Children’s Fund (UNICEF) has said that sixty nine million Nigerians do not have access to safe drinking water and forty percent of households do not have access to clean water sources [7]. In most cities in Nigeria, the major sources of water are protected wells and long narrow wells drilled to access groundwater referred to as boreholes.

Land areas called mechanic villages are mapped out by the government of some countries like Nigeria for auto repair activities to reduce traffic congestion within the townships. The activities by the artisans in these sites have greatly polluted the soil and groundwater within and around their environs [8]. Many environmentally unfriendly chemical species like petroleum hydrocarbons [9,10,11,12,13,14,15], polychlorinated biphenyls [16], polybrominated diphenyl ethers [17], polycyclic aromatic hydrocarbons [18,19,20], anions [21,22,23] and heavy metals [24,25,26,27,28,29] from automobile repair and maintenance activities have been found in the air, soil and portable water sources in these areas.

Few reports are available on the quality of groundwater within and around the numerous mechanic villages in Nigeria. In a study by Arinze et al. [30] on the quality of potable water within automobile junk markets in Obosi and Nnewi, Nigeria, levels of manganese, copper, iron and nickel were found to be above WHO recommended standards for drinking water. Duru et al. [31] studied the quality of borehole water within the evacuated section of a mechanic village located in Orji, Imo State, Nigeria. The pH, nitrites, nitrates and phosphates levels in the portable water samples fell short of World Health Organization (WHO) standards. Adekitan et al. [32] studied the quality of groundwater within five mechanic villages in Abeokuta, Nigeria. They reported high levels of lead in all the water samples analyzed.

With the high rate of rural to urban migration to cities in Nigeria which has put a lot of stress on accommodation, many of these mechanic villages have been reclaimed and relocated to areas off the city settlements. Construction of residential buildings have long commenced in these evacuated sections without any form of environmental impact assessment.

The Nekede mechanic village is one of such locations. There is no published report on the quality of borehole water in the reclaimed section of this mechanic village and its environs. This study therefore carried out a comprehensive physicochemical assessment of the quality of water from borehole sources in this area to determine its suitability for consumption and possible impact on human health.

2 Materials and Methods

2.1 Study Area

The Nekede mechanic village is situated in Owerri West Local Government Area of Imo State. It lies between the geographical coordinates 5°26′0″ North and 7°2′0″ East. It is located in the sandy Benin Formation with undulating land surface, and drained by Otamiri and Nworie Rivers. In September 2017, the Imo State Government relocated the mechanics, welders, auto electricians and panel beaters in this area after more than 35 years of occupation (Fig. 1).

Fig. 1
figure 1

A section of the mechanic village evacuated for the construction of residential buildings

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2.2 Borehole Water Sample Collection and Analysis

The borehole water samples were collected at five different points marked A–E (Fig. 2) within the reclaimed land area where human settlement has already began. The coordinates at the sampling points were referenced with Garmin GPSMAP 76, a handheld global positioning system (GPS) unit and are shown in Table 1.

Fig. 2
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Map of Nekede mechanic village and its environs showing sampling points

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Table 1 Coordinates at sampling points
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Three sets of water samples were collected monthly between August and October 2018. The colour, pH, electrical conductivity (EC) and total dissolved solids (TDS) of the borehole water samples were analyzed in situ. Samples for heavy metal and anion determination were collected with sterile plastic bottles and transported to the laboratory for analysis. Analytical grade chemicals and double distilled water were used for preparing the chemicals for the analysis. For heavy metal analysis, an atomic absorption spectrophotometer was used. The proper hollow cathode lamp for a given metal was chosen and allowed to warm-up for 15 min. A series of standards of the element under analysis was run to obtain a calibration curve. This was followed by sample aspiration and determination of the concentration of the element. Anions in the water samples were analyzed with a photometer using the appropriate reagents for each anion under study.

Triplicate determinations were carried out for each parameter. A control set was taken from the borehole water source at the female hostel of the Federal Polytechnic in Nekede town, situated at about 2.5 km from the study area.

2.3 Preliminary Soil Analysis

Soil samples from each sampling point were analyzed to identify the presence, types and abundance of the heavy metals in the study area. Samples were collected in triplicates at a depth of 30 cm from each of the sampling points using a soil auger. The samples from each point were thoroughly mixed together, then spread on a glass plate and dried in an oven at 105 °C for 2 h. After cooling, they were sieved to particle size of 30 mesh using American Society for Testing and Materials (ASTM) standard sieves. The sieved soil samples were then subjected to X-ray fluorescence analysis.

2.4 Instrumentation

The percentage content of heavy metals in the soil samples was determined using a compact multi-element bench top Energy Dispersive X-ray Fluorescent Analyzer (EDXRF) EDX3600B by Skyray Instrument [precision: 0.0% deviation; detection limit: 0.0001% (1 ppm) − 99.99%]. The concentration of heavy metals in the water samples was determined using Agilent 240 AA Atomic Absorption Spectrophotometer (accuracy level: 99.776%; precision: 97.568%). The colour and concentration of anions in the water samples was determined using multiparameter bench photometer HI 82300 by HANNA Instruments.

2.5 Data Analysis

Contamination factor (Cf), Pollution Load Index (PLI) and Water Quality Index (WQI) models were used to assess the contamination and pollution status of the water samples in this area.

The Cf was used to ascertain the level of soil contamination by a single element or ion [33]. It assessed the presence and intensity of a given contaminant in groundwater and was determined using Eq. (1):

$${\text{C}}_{\text{f}} = \frac{{{\text{C}}_{\text{m}} }}{{{\text{C}}_{\text{b}} }},$$
(1)

where Cm is the concentration of a particular parameter in the water and Cb is the reference concentration of that parameter. The WHO standards for drinking water were taken as the reference concentrations.

The PLI gives a summative indication of the overall level of toxicity at a particular sampling point. It was determined mathematically using Eq. (2):

$${\text{PLI}} = ({\text{C}}_{{{\text{f}}1}} \times {\text{C}}_{{{\text{f}}2}} \times {\text{C}}_{{{\text{f}}3}} \times \cdots \times {\text{C}}_{\text{fn}} )^{{\frac{1}{\text{n}}}} ,$$
(2)

where n is the number of parameters considered in the study and Cfn is the contamination factor for each individual parameter.

The WQI was calculated to ascertain the overall suitability of the borehole water in this area for human consumption. Three steps were followed in computing the WQI. In the first step, each parameter was assigned a weight (wi) according to its relative importance in the overall quality of the borehole water for drinking purposes. Weights ranging from 1–5 were assigned to the parameters, with the highest weights assigned to parameters with adverse health effects.

In the second step, the relative weight (Wi) was computed using Eq. (3):

$$W_{i} = \frac{{w_{i} }}{{\mathop \sum \nolimits_{i = 1}^{n} w_{i} }},$$
(3)

where Wi is the relative weight, wi is the weight of each parameter and n is the number of parameters.

In the third step, a quality rating scale (qi) for each parameter was calculated from Eq. (4) by dividing the concentration of a given parameter in the water sample by its reference standard (WHO) and then multiplying the result by 100:

$$q_{i} = \frac{{C_{i} }}{{S_{i} }} \times 100,$$
(4)

where Ci is the concentration of each parameter in each water sample in mg/L, and Si is the reference standard (WHO).

To compute the WQI, the SI was determined for each chemical parameter from Eq. (5), which was then used to calculate the WQI using Eq. (6):

$$SI_{i} = W_{i} \times q_{i} ,$$
(5)
$${\text{WQI}} = \sum SI_{i} ,$$
(6)

where SIi is the sub index of the ith parameter.

3 Results and Discussion

The energy dispersive X-ray spectra of soil from the different sampling points in the study area are shown in Fig. 3.

Fig. 3
figure 3

X-ray fluorescence spectra of soil samples collected at 30 cm depth from sampling points A, B, C, D and E

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The percentage contents of the detected toxic metallic elements from the above plots are given in Table 2.

Table 2 Percentage composition of toxic metals in the soil at the different sampling points
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Their mean composition increased in the order Cd < As < V < Cr < Mn < Pb < Cu < Ni < Co < Mo < Zn < Ti < Fe. The concentration of these heavy metals and those of the other water quality parameters in the water samples from the sampling points are summarized in Table 3. Molybdenum, titanium, vanadium, sulphate and nitrite were not detected in all the water samples. The mean values of the detected parameters were compared with WHO standards for drinking water [34] and are shown in Table 4.

Table 3 Values of water quality parameters in the triplicate studies
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Table 4 Mean concentration of analyzed parameters compared with WHO standards
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The control data for the analyzed quality parameters indicated that their elevated levels at the study area were due to the anthropogenic activities that took place at the time before the area was reclaimed. These activities include discharge of waste automobile oils on the bare ground, metal welding, scrap metal collection and storage in open spaces, spraying of automobile parts etc. Heavy metals and other pollutants from these activities leach into the soil and over time are washed into the groundwater (Fig. 4).

Fig. 4
figure 4

Nekede mechanic village showing a auto waste disposal point, b Auto engine servicing pit, c abandoned automobiles, d auto scrap metal dump

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The conductivity, total dissolved solids, alkalinity, manganese, zinc, chromium, copper, arsenic, iron, chloride and nitrate were all below the permissible limit set by the WHO. The colour of the water at sampling point C was 20 Platinum Cobalt Units (PCU) which is above 15 PCU stipulated by the WHO. Colour is not a toxic characteristic of portable water but a secondary parameter that affects its appearance and palatability.

The pH of portable water measures its degree of acidity or alkalinity and is an aesthetic quality of water. However, too high or too low pH can be a sign of chemical or heavy metal pollution. The pH of all the samples investigated were acidic ranging between 5.12 and 5.58 as against the 6.50–8.50 stipulated by the WHO. Exposure to extreme pH values can result to irritation to the eyes, skin and mucous membranes [35].

Lead is a cumulative toxicant that affects multiple body systems. It is distributed in the bones, brain, liver and kidney where it accumulates over time [36]. Lawal et al. [37] reported lead levels ranging from 0.01 to 1.05 mg/L in water samples from boreholes close to auto mechanic workshops in Obio/Akpor local government area in Rivers State, Nigeria. In this study, lead levels were found to range between 0.22 and 0.42 mg/L. These values were much higher than the value 0.01 mg/L stipulated by WHO. Young children are very vulnerable to the toxic effects of lead and can suffer adverse health effects, which impair brain and nervous system development. It causes long-term harm like high blood pressure and kidney damage in adults. It can also result to miscarriages, stillbirths, premature births or low birth weights in pregnant women. More than three quarters of global lead consumption is form the manufacture of lead-acid batteries for motor vehicles [38].

The possible sources of nickel in groundwater around mechanic villages includes dumping of stainless steel, non-ferrous alloys and super alloys from automobile parts around the workshop area, use of nickel containing automobile pigments and paints, indiscriminate discard of automobile electronic parts and welding activities by panel beaters [39]. The nickel levels in the borehole water samples in the studied area ranged between 1.03 and 1.12 mg/L which is higher than the guideline set by the WHO. High nickel intakes in humans can lead to nausea, vomiting, diarrhea, giddiness, lassitude, headache, and shortness of breath [40].

Cadmium compounds are used in batteries, electronic components and often times electroplated onto steel as an anticorrosive material [41]. Cadmium levels in borehole water ranging between 0.01 and 1.20 mg/L have been reported by [37]. At the Nekede mechanic village study site, cadmium concentration ranged between 0.01 and 0.03 mg/L. These values were higher than the 0.003 mg/L limit set by the WHO. Exposure to high cadmium levels can result to kidney dysfunction and osteoporosis in humans [42].

Discharge of chemicals containing phosphate species into the soil and subsequent leaching into ground water can cause damage to the environment and deteriorate water quality [23]. The Phosphate levels in the borehole water samples ranged between 0.14 and 0.34 mg/L which is higher than the 0.03 mg/L set by the WHO. High phosphate intake has been reported to be the cause of cardiovascular diseases, damage to blood vessels and induced aging processes [43].

3.1 Pollution Modeling

The data in Table 4 were analyzed using contamination and pollution models so as to give a lucid picture of the portability of the borehole water samples. The Cf values as specified by [44] are given in four levels and are shown in Table 5.

Table 5 Contamination factor ranking
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The values of the Cf were used to determine the PLI (Eq. 2). PLI value greater than 1 is polluted, less than 1 indicates no pollution, whereas values equal to 1 indicates contaminant loads close to the reference concentration [45]. The Cf and PLI of parameters with severe health impacts are shown in Table 6.

Table 6 Cf and PLI of heavy metals and anions in the borehole water samples
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All the borehole water samples were highly contaminated by lead and nickel. Samples from points A, B and E were highly contaminated by cadmium and phosphate ions. Water samples from point D were also highly contaminated by phosphate ions. Water contaminant load in samples from point E had value above 1.00 showing that borehole water around this point was polluted. Water samples from point B had pollution load close to WHO reference concentrations.

The WQI of portable water can be classified into five types [46] and are shown in Table 7.

Table 7 Water Quality Index values and classes
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The calculated WQI of the water samples from the sampling points in this study using the mean concentrations of the identified contaminants with health impact are given in Table 8.

Table 8 Water Quality Index values of borehole water from the sampling points
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The data from this model showed that borehole water from all the points sampled were unsuitable for drinking.

4 Conclusion

The findings from this study showed that all the borehole water samples in this area were acidic and had very high lead and nickel levels. Cadmium contamination in the borehole water at sampling points A, B and E was very high. Phosphate contamination level in all the borehole water samples from all the sampling points apart from sampling point C was very high. Water Quality Index model showed that all the borehole water samples studied were unsuitable for drinking. Dwellers in this area whose only means of portable water are these boreholes stand the risk of developing serious health problems like kidney damage, impaired brain development in children, osteoporosis and cardiovascular diseases.