**2.3 Digestion of water samples for metal analysis**

Water sample, 250 cm3 , was measured into an evaporating dish and concentrated HNO3 measuring 5.0 cm<sup>3</sup> was added. The mixture was digested for about 1 hour on a heating mantle in a fume cupboard at temperatures of 90–95°C, and the quantity was reduced to 25 cm<sup>3</sup> with a colour that is characteristics of a complete digestion. The clear digest was brought down and allowed to cool. It was filtered using Whatman filter paper no. 1 into a 50-cm<sup>3</sup> volumetric flask that had been washed with an acid and properly rinsed with deionised water. The filtrate was made up to the mark with deionised water and kept awaiting metal analysis with atomic absorption spectrophotometer (AAS) [21].

### **2.4 Metal analysis**

Heavy metals such as Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the digested water samples were determined using atomic absorption spectrophotometer (AAS) (ICE 3000AA0213410.VI.30 System).

*Occurrence and Impact of Heavy Metals on Groundwater Sources: A Case Study of Two… DOI: http://dx.doi.org/10.5772/intechopen.110444*

### **2.5 Statistical analysis**

Data obtained from the study were subjected to statistical tools such as mean, standard deviation, and correlation using SPSS.

### **2.6 Heavy metal pollution index (HMPI)**

Countries, institutions and organisations have always provided recommended standard limits for different heavy metals in water for the purpose of being able to ascertain the quality of water with respect to individual metal contents. However, this does not give any information on the pollution level of metals in water with regard to all the metals that are detectable [18]. Heavy metal pollution index (HMPI) is a technique that determines the quality of water by providing information on the influence of each detectable metal on the overall quality of water. The values for ranking are 0–1, and the importance of each quality considerations is inversely proportional to the standard permissible limits [18].

The stages involved in the calculation of unit weight of the *i*th parameter, the calculation of the quality rating for each parameter and the addition of these subindices in the overall index are as follows:

$$W\dot{\mathbf{u}} = \frac{k}{\text{Si}}\tag{1}$$

where *Wi* is the unit weight for the *i*th parameter, *Si* is the recommended standard limit for the *i*th parameter and *k* is the proportionality constant. The quality rating for individual parameter *Qi* can be evaluated as follows:

$$Qi = \frac{100 \times Mi}{Si} \tag{2}$$

where *Qi* is the sub-index of the *i*th parameter, *Mi* is the concentration of the *i*th heavy metal, *Si* is the recommended standard limit for the *i*th parameter and 100 is the critical pollution index value

$$\text{HMPI} = \frac{\sum (Qi \times Wi)}{\sum Wi} \tag{3}$$

where HMPI is the heavy metal pollution index, *Qi* is the sub-index of the *i*th parameter and *Wi* is the unit weight for the *i*th parameter [18].

### **2.7 Metal index (MI)**

Metal index when evaluated for drinking water gives information of the likely additive effects of all the detectable heavy metals in water on the health of humans and that greatly aid the determination of the overall quality of water. MI can be computed as follows:

$$\text{MI} = \frac{\text{Mi}}{\text{Si}} \tag{4}$$

where MI is the metal index, Mi is the observed metal level in water and Si is the highest recommended permissible limit. MI is a tool used to determine the quality and suitability of water that is meant for drinking. The classification of water quality using metal index are; <3.0 very pure, 0.3–1.0 pure, 1.0–2.0 slightly affected, 2.0–4.0 moderately affected, 4.0–6.0 strongly affected and >6.0 seriously affected [18].

## **3. Results and discussion**

**Table 1** shows the sample locations in the study area, **Tables 2** and **3** show the concentrations of heavy metals in samples of water from boreholes and hand-dug wells, respectively, in Keffi and **Tables 4** and **5** show the concentrations of heavy metals in samples of water from boreholes and hand-dug wells, respectively, in Karu.

The mean values of cadmium in water samples from boreholes and hand-dug wells in Keffi were 0.039 and 0.039 mg/L, respectively, while for Karu the mean cadmium values were 0.037 and 0.04 mg/L, respectively. All these values are higher than the range of 0.00–0.011 mg/L reported for cadmium in Azare groundwater system [22] but are lower than the mean value of 0.08 mg/L of cadmium in water reported for stream water in Bauchi metropolis [23]. But the values are higher than the value of 0.003 mg/L recommended as the acceptable permissible limits by the SON [19] for cadmium in water that can be used domestically and industrially. Cadmium in water may be due to the mineralisation of cassiterite and also as a result of the use of insecticides, fertilisers and pesticides for farming and could be leached into groundwater systems. It could also come from wastes and effluents generated domestically like used batteries and other waste materials and eventually find its way into the water systems. High intake of cadmium via water is associated with toxicity to the kidney [19].

The mean values of chromium in water samples from boreholes and hand-dug wells in Keffi were 0.05 and 0.055 mg/L, respectively, while for Karu the mean cadmium values were 0.051 and 0.058 mg/L, respectively. All these values are within the range of 0.00–0.29 mg/L for chromium in boreholes and hand-dug well in both dry and wet seasons reported for selected rivers in Nasarawa State [24]. These


**Table 1.**

*Sampling locations in Keffi and Karu, Nasarawa State, Nigeria indicating sample numbers.*

*Occurrence and Impact of Heavy Metals on Groundwater Sources: A Case Study of Two… DOI: http://dx.doi.org/10.5772/intechopen.110444*


### **Table 2.**

*Mean values of heavy metal contents in borehole water samples in Keffi LGA.*


### **Table 3.**

*Mean values of heavy metal contents in hand-dug well water samples in Keffi LGA.*


### **Table 4.**

*Mean value of heavy metal contents in borehole water samples in Karu LGA.*


### **Table 5.**

*Mean value of heavy metal contents in hand-dug well water samples in Karu LGA.*

values are lower than majority of the mean values for water samples from three different streams that had not detected, 0.93, 1.58 and 0.65, 0.49, 1.12 mg/L for dry and wet seasons, respectively, reported for groundwater sources in Okene Local Government Area, Kogi State [25]. Apart from the mean value of chromium in water from boreholes in Keffi, all the other values are slightly higher than the value of 0.05 mg/L recommended as the acceptable permissible limits by the SON [19] for chromium in water that can be used domestically and industrially. Chromium comes from wastes and effluents generated domestically. The deficiency of chromium causes impaired insulin function, hence increased insulin secretion and the risk of diabetes mellitus. High intake of chromium that is more than the recommended standards causes cancer [19].

Copper was not detected in water samples from both boreholes and hand-dug wells in Keffi but was, however, detected in boreholes and hand-dug wells in Karu and had mean concentrations of 0.59 and 0.62 mg/L, respectively. These values are higher than the mean value of 0.51 mg/L for copper in water reported for water sources in Bauchi metropolis [23] as well as the mean value of 0.1669 0.1414 for copper in the groundwater systems of Azare [22]. The mean values from this study are lower than the value of 1.00 mg/L recommended as the permissible tolerable limits, and a concentration higher than this limit is always associated with gastrointestinal disorder [19].

The mean values of iron in water samples from boreholes and hand-dug wells in Keffi were 0.114 and 0.115 mg/L, respectively, while for Karu the mean iron values were 0.116 and 0.099 mg/L, respectively. The mean values from this study are lower than the value of 0.30 mg/L recommended as the permissible tolerable limits [19]. Iron is one of the components of haemoglobin responsible for the transport of oxygen in the body. It also aids in the oxidation of carbohydrates, proteins and fats as well as helping to prevent anaemia [26]. The concentration of iron, which is more than the acceptable limits, supports iron-dependent bacteria to cause deterioration in water quality [27]. Iron sources are domestically generated wastes, runoffs and probably the geological formations of the location under investigation. The level of iron can be reduced or removed completely from water through aeration [28].

The mean values of manganese in water samples from boreholes and hand-dug wells in Keffi were 0.054 and 0.058 mg/L, respectively, while for Karu the mean iron values

### *Occurrence and Impact of Heavy Metals on Groundwater Sources: A Case Study of Two… DOI: http://dx.doi.org/10.5772/intechopen.110444*

were 0.055 and 0.060 mg/L, respectively. These values are lower than the mean values recorded for boreholes and hand-dug wells in dry and wet seasons, which were 0.42 mg/L for boreholes and 0.34 mg/L for hand-dug wells in dry season and 0.36 mg/L fore boreholes and 0.44 mg/L for hand-dug wells in wet season [25]. The values are also lower than 0.34 mg/L for manganese in water reported for water sources in Bauchi metropolis [23]. The mean values from this study are lower than the value of 0.20 mg/L recommended as the permissible tolerable limits [19]. Manganese is found in the environment due to the activities and from domestic wastes. High level of manganese in water above the recommended tolerable limits causes neurological disorder [19].

Nickel was not detected in water samples from both boreholes and hand-dug wells in Keffi but was, however, detected in boreholes and hand-dug wells in Karu and had mean concentrations of 0.018 and 0.019 mg/L, respectively. These mean values are slightly lower than mean value of 0.02 mg/L for nickel in water reported for water sources in the metropolis of Bauchi, Nigeria [23]. The mean values from this study are lower than the value of 0.020 mg/L recommended as the permissible tolerable limits, and a level higher than this is associated with possible carcinogenic effects [19]. Nickel comes from activities that originate from mechanic workshops, dumpsites and fertiliser-rich sewage sludge [23].

The mean values of lead in water samples from boreholes and hand-dug wells in Keffi were 0.009 and 0.012 mg/L, respectively, while for Karu the mean iron values were 0.011 and 0.015 mg/L, respectively. All these values are lower than the mean concentration of lead, 0.1100 0.1097 mg/L, in groundwater systems of Azare [22] as well as the mean concentration of 0.048 mg/L for lead in water sources [23]. The concentrations of lead from this study are all higher than the recommended tolerable limits of 0.01 mg/L except for lead level in boreholes in Keffi, and anything above this limit can cause cancer, interfere with vitamin D metabolism, affect mental development in infants and is toxic to the central and peripheral nervous system. Sources of lead in the environment are mechanic, battery charger workshops as well as car wash spots and wastes generated domestically.

The mean concentrations of zinc in water samples from boreholes and hand-dug wells in Keffi were 0.105 and 0.121 mg/L, respectively, while for Karu the mean iron values were 0.107 and 0.125 mg/L, respectively. These mean concentrations are within the same range with the mean concentrations for zinc in boreholes from three different locations, which are 0.10, 0.11 and 0.12 mg/L reported for groundwater sources in Benin City, Edo State and Agbor, Delta State, all in Nigeria [20]. The mean values from this current work are lower than the recommended permissible limits of 3.00 mg/L [19].

**Tables 6** and **7** shows the results of statistical analysis for test of significance between heavy metal contents of borehole water samples and hand-dug well water samples from Keffi Local Government Area and Karu Local Government Area, respectively. From the results shown, there were no significant differences between all the heavy metal contents in borehole and hand-dug well in both Keffi and Karu. The p-values for all heavy metal contents did not conform to p < 0.05, with the implication that for all the parameters, there were no significant differences between the borehole water samples and the hand-dug well water samples from Keffi Local Government Area and Karu Local Government Area. This could be attributed to the fact that in each location or study area, the geologic formation of the soil is the same for places where boreholes or hand-dug well had been drilled.

**Table 8** shows the mean HMPI and MI of water from Keffi and Karu Local Government Areas. HMPI was used in the characterisation of water from boreholes


**Table 6.**

*Heavy metals in borehole and well water samples in Keffi LGA (p < 0.05).*

and hand-dug wells from Keffi and Karu Local Government Areas. The characterisation gave values that were compared with the critical values to assess the extent of heavy metal pollution [18]. The mean HMPI values calculated were 77.33 and 92.08 for borehole water and hand-dug well water, respectively, in Keffi and 105.27 and 127.41 for borehole water and hand-dug well water, respectively, in Karu. The values from Keffi are lower than the critical value of 100, while those of Karu are slightly higher. Higher values are indication of pollution of water from the Karu. The discrepancy could be attributed to the fact that some parameters, such as Cu and Ni, were not detected in water samples from Keffi but were detected in the ones from Karu. The HMPI for both water sources is high, and it signifies that the source of the contaminants could be infiltration of runoffs from dumpsites of domestic wastes.

MI values for borehole and hand-dug well waters were 0.564 and 0.606, respectively, in Keffi, and for Karu the values were 0.634 and 0.723, respectively. These values, however, suggest that the water sources from the study area are pure and not affected with heavy metal pollution when compared to the water quality classification scheme adopted [18].


**Table 7.** *Heavy metals in borehole and well water samples in Karu LGA (p < 0.05).* *Occurrence and Impact of Heavy Metals on Groundwater Sources: A Case Study of Two… DOI: http://dx.doi.org/10.5772/intechopen.110444*


### **Table 8.**

*HMPI and MI of water samples from Keffi and Karu LGAs.*
