**1. Introduction**

One of the most important substances in the life of living organisms is water [1]. It is of very great value because of the roles it play in living organism: aid digestion, flushing of wastes from the body, transportation of nutrients, regulation of body temperature and maintenance of other bodily functions [2]. The establishment of stable human settlements, rural, semi-urban and urban areas, is dependent largely on the readily available portable water sources [3]. Over the decades, there has been an increased demand for water that is of good quality, and this could be attributed to ever increasing human population, urbanisation and industrialisation [3].

In developing countries, these increased demands for water lead to the use of any available water sources to meet the daily water need of inhabitants. The known

sources of water are either surface water (rivers, dams, lakes, pond and a few others) or groundwater (boreholes, hand-dug wells and spring) [4]. The surface water sources are readily accessible, because to have access to the groundwater sources, energy in some forms would have to be expended and in some cases requires funds needed for digging. However, there are many settlements where the surface water sources are not available as well as the pipe-borne supply; therefore, the inhabitants are left with no option but to resort to groundwater sources for their daily water need. Groundwater forms a vital domestic and agricultural water sources in rural and urban communities of most developing countries, Nigeria inclusive [5]. Groundwater storage is better with the sedimentary aquifer compared to crystalline basement. Boreholes fail at a high rate in the basement and in areas with basement complex; handdug well is always the main source of water [6].

The source of groundwater is the water cycle, and the water is always stored in the aquifer beneath the earth surface. Water that falls as precipitation (rain or snow) flows along the surface of the ground, and it infiltrates into the ground of the surface and is stored in the spaces of soil pores and the fractures of rock formations as groundwater. Due to this reason, groundwater is always believed to be comparatively cleaner than surface water systems that receive contaminants directly [6].

In the recent past, the contamination of groundwater sources has become an issue of very serious environmental concern [7]. There is a vast range of contaminants that affect groundwater sources, and heavy metals are of a particular interest since they have potentials for toxicity even at low concentrations. Although some are essential mineral elements and very important to life (Fe, Cu, Zn and a host of others), at elevated levels, they could become deleterious with associated health risks [8]. Heavy metals are chemical elements, metals or metalloid with a specific gravity five times that of water and have potentials for toxicity. The major source of heavy metals in potable water is the contamination of groundwater and surface water sources [9]. Many heavy metals are natural constituents of the environment. However, elevated levels of these heavy metals in the environment could be attributed to the anthropogenic activities of man. Groundwater contamination could come from industrial sewage, proliferation of dumpsites for domestic wastes without due consideration to government rules, mining, agricultural run-off and a few other factors [9].

It is of utmost importance to assess the metal contents in water from either surface or groundwater sources. This is because even though the trace element could be very essential to animals and humans for biochemical activities, when present at levels higher than recommended limits, it could lead to some morphological disorders in humans, such as mutagenic effect, reduced growth, increased mortality and a host of others [10, 11]. The use of dumpsites as farmland is a common practice in urban and sub-urban centres in Nigeria because decayed and composted wastes enhance soil fertility [12]. These wastes often contain heavy metals in various forms and at different contamination levels. Some heavy metals like As, Cd, Hg and Pb, which are particularly hazardous to plants, animals and humans [13], could find their ways into these water bodies through leaching as well as runoff waters. Also, from farmlands that had agrochemicals and fertilisers applied on them, these agro-based products contain metals like Cu, Mg, Mn, Pb or Zn, which could eventually be found in groundwater through run-off and infiltration [14].

Heavy metals are given serious concern because they are not biodegradable, largely immobile in soil and tend to concentrate and persist for a long time in the environment [15]. Due to the non-biodegradable nature of heavy metals at elevated levels, they could easily undergo bioaccumulation. There is a bioaccumulation of chemical

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

specie in a biological system when there is an increase in the concentration of specie in the biological system compared to its concentration naturally in the environment [16]. One of the easiest means by which metals get to living organism is through water and, if present at elevated levels, is associated with serious health risks. For instance, some are carcinogenic and could cause neurological disorder, liver and kidney dysfunctions and a lot of other serious health challenges; hence, there is the need to assess the metal contents of groundwater sources [17].

Several research works have been done within and outside the shores of Nigeria to assess the metal contents of groundwater sources. These include the evaluation of heavy metals in groundwater, South of Najaf, Iraq [4], the evaluation of heavy metals in groundwater around Keshere and its environs, upper Benue Trough, North-eastern Nigeria [18], the determination of heavy metals in borehole and hand-dug well in selected areas of Mubi, Adamawa state, Nigeria [9] and a host of others.

The government is solely responsible for the provision of potable water in Nasarawa State just like in almost all states in Nigeria, and in most cases, it is characterised by low productivity and few areas covered, and there is always inefficiency and ineffectiveness in the delivery. Most citizenry that do not benefit from the provisions by the government, therefore, depend on the available sources, groundwater (wells and boreholes) whose quality cannot be certified satisfactorily. And, as such, cases of water-associated health problems abound due to drinking and other domestic usage of water from these sources. This study is geared towards investigating the heavy metal contents in water from these sources in accordance with the requirements of the Standards Organisation of Nigeria (SON) [19] to ascertain the suitability of water from boreholes and hand-dug well in Keffi, Karu and their environs for domestic purpose.

### **2. Materials and methods**

### **2.1 Study area**

Keffi and Karu Local Government Areas (LGAs) are part of the 13 local government areas in Nasarawa State, Nigeria. The location of Nasarawa State on the World Map is latitude 8° 00<sup>0</sup> to 8° 30<sup>0</sup> N and longitude 8° 30<sup>0</sup> to 9° 00<sup>0</sup> E. The temperature of the study area could be described to be generally very warm with high humidity (**Figure 1**). There are two seasons in the area: dry season (October to March) and the rainy season (April to September). A high percentage of the population from the communities in these areas depends largely on groundwater sources (boreholes and hand-dug wells) for their daily water need. Then, others that reside in the headquarters of the local government areas rely on boreholes and deep hand-dug wells sank by individuals and the government for their daily water supply. Pipe-borne water supply is available in some places with epileptic operations. The communities used for this study are AgwanLambu/High Court, DadinKowa/Angwan Kwara, Yelwa and City centre all in Keffi and Uke, Auta-Balefi, Masaka, Ado/New Nyanya/Karu and Mararaba all in Karu Local Government Area.

### **2.2 Sample collection, treatment and preservation**

Samples were taken from boreholes and hand-dug wells in both Keffi and Karu Local Government Areas. Samples of water were collected two times in a day for a period of two weeks. Variation in the day and time samples were collected was

**Figure 1.** *Map of Nasarawa State showing Keffi, Karu (study Areas) and other LGAs.*

observed in order to take care of changes that might occur at irregular intervals at the point of collection. Samples of water from borehole were collected from the taps bringing water from the borehole, and those of the hand-dug wells were collected with the use of a fetcher. All the samples collected were stored in clean 1500-cm<sup>3</sup> white plastic containers that had been properly washed by soaking overnight in 0.1 mol/dm<sup>3</sup> nitric acid solution and washed with soap solution. They were then rinsed with deionised water and concentrated nitric acid before being filled with deionised water to the locations designated for sampling. The containers were then emptied and rinsed with the samples to be collected severally before the sample collection proper. The sample containers were covered (air tight), properly labelled and immediately transported to the laboratory awaiting digestion and metal analysis [20].
