Environ Earth Sci DOI 10.1007/s12665-014-3656-0

ORIGINAL ARTICLE

Hydrogeochemical assessment of groundwater in Iwo, Ikonifin and Ife-Odan, Osun and Oyo states, Southwest Nigeria A. M. Gbadebo • H. Ayedun • A. I. Moses

Received: 13 June 2013 / Accepted: 20 August 2014 Ó Springer-Verlag Berlin Heidelberg 2014

Abstract Hydrogeochemical assessment of groundwater in some communities (Iwo, Ikonifin and Ife-odan) of Southwest Nigeria was carried out. The physicochemical parameters determined include pH, temperature, redox potential (Eh), electrical conductivity and depth of wells. The concentration of heavy metals was determined using Bulk Scientific model of atomic absorption spectrophotometer. Flame photometer was used to determine Na and K, while titration method was used to determine Mg and Ca. The obtained results indicate that the majority of the sampled wells were deep ([16 m) and the values of redox potentials (EH) recorded were mainly positive with the exception of a few. Most parameters were within the WHOrecommended limits in drinking water. DO was significantly higher at Ife-Odan with values of 4.96 ± 0.34 mgL-1, while wells from Ikonifin were significantly deeper than others. The PO43- and SO42-concentrations were significantly high, both in Ife-Odan and Iwo, which was attributed to possible runoff from diffuse sources (wastes). The piper diagram showed that the dominant cations were Na? and K?, while the dominant anions were CO32- and HCO32-, suggesting that the major ions are from water–rock A. M. Gbadebo Department of Environmental Management and Toxicology, Federal University of Agriculture, P.M.B. 2240, Abeokuta, Nigeria H. Ayedun (&) Department of Chemical Sciences, Ondo State University of Science and Technology, P.M.B 353, Okitipupa, Ondo State, Nigeria e-mail: [email protected]; [email protected] A. I. Moses Department of Earth Science, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria

interactions. The concentration of lead (Pb) was found to be higher than the recommended WHO limit of 0.05 mgL-1 in drinking water from most (80 %) of the samples. Significantly (P \ 0.05) high Pb concentration values were recorded from Ife-Odan (0.53 ± 0.04 mgL-1) and Ikonifin (0.6 ± 0.06 mgL-1). The cadmium (Cd) concentration was found to be slightly higher than 0.003 mgL-1, theWHOrecommended limit for all locations. Keywords Groundwater quality
Dug wells
Run-off
Piper diagram

Introduction Consumption of poor-quality water has been identified as one of the major causes of health problems in developing countries. The basic physiological requirement for drinking water as stipulated by the World Health Organization (WHO 2011) is about 2 l of water per head per day. It has been observed that a daily supply of 150–200 l cannot be met by the majority of developing countries such as Nigeria (Ademoroti 1996). Indeed, the WHO has estimated that approximately 80 % of all illnesses in the world are attributed to bad water supply and poor sanitation. This percentage includes about 10–20 million children who die each year of diseases associated with diarrhea (Morrison 1983). Developing countries carry a heavy burden of waterrelated diseases, because most residents use unhygienic water as their main source of drinking water and for other related uses. This has resulted in a large number of cases of water-borne diseases such as guinea worms, schistosomiasis, onchocerciasis, typhoid fever, dysentery, gastroenteritis, and other parasitic infections (Ademoroti 1996). However, access to safe drinking water and sanitation is

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critical in terms of health, especially for children. For instance, unsafe drinking water contributes to numerous health problems in developing countries, such as 1 billion or more incidence of diarrhea that occur annually (Mark et al. 2002). Groundwater is generally believed to be relatively protected, because it is held within the pore spaces of fractures and weathered regoliths depending on the geologic setting, which makes it widely and generally free from sediments and biological impurities. Therefore, shallow groundwater is the principal source of water to rural communities in many parts of Nigeria, especially areas underlain by basement rocks (Boboye 2008). In the rural settlements, groundwater resources are more preferred because of the ease and relatively cheap method of exploitation compared to surface water (Akujieze et al. 2003). This might be due to the fact that surface water is most of the time found to be colored with high turbidity and hence requires purification. Although groundwater is regarded as being protected from contamination, increasing population and anthropogenic activities have warranted its hydrogeochemical assessment and the need for quality sustenance and management (McDonald and Kay 1988; Freeze and Cherry 1984). Over the past decades, there has been increased research on the exploration and exploitation more than the quality assessment of groundwater in the basement complex of Nigeria, especially in the southwestern part of the country where the basement is mainly composed of igneous and metamorphic rocks (Grant 1969; Oyawoye 1972; Rahaman 1976). Various workers have evaluated the geochemical significance of the groundwater from the basement complex and in most cases it has been established that they are suitable for drinking following the WHO standard (Assez 1972; Mandel and Shiftan 1991; Offodile 1983). However, there are cases where groundwater generally varies significantly from the recommended standard for drinking water. This variation in well water chemistry has been related to the underlying bedrock types (Ako et al. 1990). The overall hydrogeochemical character of groundwater is partly due to the chemical (ionic) inputs from precipitation, chemical weathering, dissolution of the parent rock and cation (base) exchange processes (Tijani 1994). This study investigated the quality and hydrochemical parameters in groundwater samples collected from Iwo, Ikonifin and Ife-Odan areas of Osun State, Nigeria.

Materials and methods The study area The study area comprises of Iwo, Ikonifin and Ife-Odan, all of which are within Osun and Oyo State, Southwest Nigeria Iwo and Ikonifin fall within Osun State while Ife-

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Odan is a settlement in Oyo State located in boundary with Ikonifin. Osun State is located between latitude 7.822568 N and longitude 4.130516 E, southwestern Nigeria. Osun State generally is underlain by basement complex which results in an inselberg landscape that is gently undulating with flat sloped ridges in some parts. Elevations gradually increase northward from 150 to 500 m. Inselberg summits may range between 300 and 700 m in area of Ife-Odan, one of the study areas. The climate of the area is tropical with distinct wet and dry seasons. The mean temperature varies between 25 and 30 °C, while the mean annual rainfall reaches between 1,000 and 1,500 mm (FORMECU 1998). The vegetation of the study area grades from tropical forest in the area of Iwo to derived Savannah in the areas of Ikonifin and Ife-Odan. The map of Nigeria showing Osun State as well as Oyo State, indicating the study area, is shown in Fig. 1. The geology of the study area The study area falls within Osun State which is entirely underlain with Precambrian basement complex rocks. The basement complex rock is dominated by undifferentiated quartzo-feldspathic biotite and hornblende-bearing gneisses, schists and migmatites. The study area is characterized by ridge forming quartzites that are often micaceous and sometimes grade into muscovite–quartz–schist (Jones and Hockey 1964). The Nigerian Basement Complex forms a part of the Pan-African mobile belt and lies between the West African and Congo Cratons and south of the Touareg Shield (Black 1980). It is intruded by the Mesozoic calcalkaline ring complexes (younger granite) of the Jos Plateau and lies unconformably overlain by cretaceous and younger sediments. The Nigerian Basement was affected by the 600 Ma Pan-African orogeny and occupies the re-activated region which resulted from the plate collision between the passive continental margin of the West African Craton and the active pheurasian continental margin (Dada 2006). The basement rocks are believed to be the result of at least four major orogenic cycles of deformation, metamorphic and remobilization corresponding to the Liberian (2,700 Ma), the euburrean (2,000 Ma), the Kiberian (1,100 Ma) and the Pan-African cycles (600 Ma). The three first cycles were characterized by intense deformation and isoclinical folding accompanied by regional metamorphism, which was further followed by extensive migmatizition, granitization and gneissification which produced syntectonic granites and homogenous gneisses. Late tectonic emplacement of granites and granitoids is associated contact metamorphism accompanied by end stages of the last deformation. The end of the orogeny was marked by faulting and fracturing (Gandu et al. 1986; Rahaman 1989) according to some geological and petrological investigations, which classified

Environ Earth Sci

Fig. 1 Map of Nigeria showing 36 states of Nigeria and map of Osun State showing the study area. Source: Fadipe et al. (2011). Key: study area—

the Nigeria Basement Complex into six major groups of rocks, namely migmatite—gneiss—quartzite complex; slightly migmatized to non-migmatized meta-sediment and meta-igneous rocks; charnockitic, gabbroic and dioritic rocks; the older granite suites; metamorphosed to un-metamorphosed calc-alkaline volcanic and hypabyssal rocks; unmetamorphosed dolerite dykes, basic dyke and syenite dyke (Ayodele and Oguniyi 2013). Land use Osun State occupies a total land area of 9,491 km2. There are 11 forest reserves in Osun State which covers 91,268 ha

of land. The forest reserve and land ratio is 1:10 (FORMECU 1998). Lands are leased to farmers for a considerable number of years by the government. Land made available this way would be able to accommodate trees with long rotation age. Five important incentives for forest conservation in Southwest Nigeria include land tenure review, long term lease of land market service, land for arable farming and prizes for the best managed woodland (Faleyimu and Oyebade 2012). Other incentives are economic incentive, technical assistance, giving of grants to stakeholders, loan incentives and giving of tree seedlings (Faleyimu et al. 2010). All these motivations have impacted on forest conservation in the study area.

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Field sampling and laboratory analysis A total of 20 groundwater samples from dug wells collected between January and March 2009 from three different communities (Iwo, Ikonifin and Ife-Odan) in the study area were analyzed. The physicochemical parameters such as pH, temperature, electrical conductivity (EC) and redox potential (EH) were determined on the field, while both the cations and other anions were analyzed in the laboratory. The position of each well was known with the aid of geographical positioning systems (GPS), eTrex Legend model (USA mode). The temperature was measured using a celsius thermometer; EC and Eh were measured using Thermo Orion model 105 conductivity meter and 2000 VWR Scientific portable pH meter. The anions SO42-, Cl-, NO3and PO43- were determined using colorimetric methods. Similarly, NH4? ion concentration was determined using colorimetric methods. The analysis of metals in groundwater sample was achieved using atomic absorption spectrophotometer (Bulk Scientific model). Sample treatment Water samples meant for physicochemical parameters not determined on site were kept in ice chest, transferred to the laboratory and analyzed within 5 days. The water samples meant for metal analysis were preserved with 5 mL concentrated nitric acid per liter and digested with aqua regia before analysis. Blank digestion was also carried out to ensure accuracy. Quality assurance To ensure that quality assurance was observed, the sampling polyethylene bottles were thoroughly washed with 10 % nitric acid, rinsed with distilled water and with the groundwater itself before final collection of the sample. The reagents used for groundwater preservation in the field and laboratory analysis were of analytical grade. The quality assurances taken for toxic metals include reagent and blank analyses, determination of spiked samples and recovery. Analysis of samples was carried out in triplicate. The recovery for spikes ranged from 99 to 112 % of the concentration matrix. This demonstrates the capability of the method to yield accurate results (Table 1). The digestion procedure is appropriate, because the blanks are not contaminated and the spikes are not lost due to volatilization. Analytical methods The digested water sample was aspirated and atomized in a flame. A light beam from a hollow cathode lamp whose

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Table 1 Operating conditions and recovery study for metal determination using AAS Cd

Mn

Pb

Wavelength (nm)

228.8

279.5

283.3

Flame

Air–acetylene

Air–acetylene

Air–acetylene

Nebulizer

Universal

Universal

Universal

Calibration

Non-linear

Linear

Linear

De-ionized water

Not detected

Not detected

Not detected

Spiked added (mgL-1)

0.5

0.5

0.5

Number of samples

5

5

5

Spiked results (mgL-1)

0.503 ± 0.001

0.507 ± 0.004

0.509 ± 0.001

% Recovery

100.6

101.5

101.8

cathode is made of the element to be determined is directed through the flame into a monochromator and onto a detector that measures the amount of light absorbed. Absorption depends upon the presence of free unexcited ground state atoms in the flame. Since the wavelength of the light beam is characteristic of only the metal being determined, the light energy absorbed by the flame is a measure of the concentration of that metal in the sample. The wavelengths used are shown in Table 1. Data analysis The generated data were compared with international standards and also subjected to statistical analysis using Pearson correlation method for the purpose of establishing significant variations and water elemental reaction changes.

Results The operating conditions and recovery study for metal determination using AAS are shown in Table 1. The % recovery ranged between 100.6 and 101.8 %, which showed a good analytical working range. The range of physicochemical parameters analyzed for the groundwater samples is shown in Table 2. Some of the groundwater samples were slightly basic (pH [6.0). The values of electrical conductivity is generally low \100 lSCm-1, while the groundwater redox potential in the study area generally ranges between -6.0 and 53.3 mV. The dissolved oxygen content ranged between 2.1 and 6.2 mgL-1, the SO42- concentration from 10.6 to 21.0 mgL-1, the chloride from 75.6 to 136.68 mgL-1 and the NO3- from 0.43 to 6.01 mgL-1. The concentration ranges of elements are: Na (1.1–2.0 mgL-1), K (0.16–0.7 mgL-1), Cu (0.1–0.48 mgL-1), Pb (0.06–0.75 mgL-1), Mn

Environ Earth Sci Table 2 Range of physicochemical parameters in wells from all locations

NA not available, EC electrical conductivity, RP redox potential, DO dissolved oxygen

Parameters

Min

Maximum

Mean

WHO World Health Organization (2011)

Nigerian standard NIS 554:2007

Temp (°C)

28

30.1

28.91

NA

NA

pH

6.2

7.5

6.44

6.5–8.5

6.5–8.5

EC (lScm-1)

28

82

58.61

250

1,000

RP (mV)

-8

53

26.9

NA

NA

DO (mgL-1)

2.1

5.8

3.58

NA

NA

HCO32- (mgCaCO3L-1)

140

280

160

NA

NA

SWL (m)

2

6

3.5

NA

NA

Depth (m)

18

55

30.4

NA

NA

SO42-

10.6

21

15.2

250

100

Cl-

75.6

136.68

99.72

250

250

NO3NH4?

0.43 0.02

6.01 0.6

2.51 0.21

50 1.5

50 1.5

0.52

2.8

1.82

NA

NA

9

114

33.5

NA

NA

PO43-1

TDS (mgL )

(0.03–0.35 mgL-1) and Cd (0.01–0.04 mgL-1) (Table 3). Some samples had greater concentrations of Pb and Cd than the WHO-recommended limit in drinking water. Figure 2 shows the pipers plot of the study area with Na and K as the most dominant cations, while HCO¯3 and CO32- are the most dominant anions. Table 4 shows the results of Duncan multiple range test for the physicochemical parameters. There was no significant difference in the mean value of temperature, pH, Cl-, NO3-, NH4?, TDS, HCO32-, RP and EC. However, significant differences were recorded in the mean values of DO, depth, SO42-, PO43- and TDS in the three locations. The DO was significantly higher in Ife-Odan, which can be attributed to a relatively shallow depth in comparison to other locations (Table 4). Among the trace elements, the mean concentration value of Pb2? was the only one to be significantly higher in Ife-Odan and Ikonifin (Table 5). The Pearson correlation of physicochemical parameters showed that significant correlations existed between EC and HCO32(R = 0.88), EC and static water level (SWL) (R = 0.55), Cl- and TDS (R = 0.54), and NO3- and NH4? (R = 0.65) (Table 6). In addition, significant correlation existed between K and Ca (R = 0.52), K and Mn (R = 0.69), K and Cd (R = 0.59), Na and Mg (R = 0.51), Ca and Mn (R = 0.51), Cu and Cd (R = 0.52), and Mn and Cd (R = 0.88) (Table 7). The piper plot showed the geochemistry of anions and cations, indicating that CO32-, HCO¯3, Na? and K? were the dominant ions (Fig. 2).

Discussion Conductivity values of groundwater are an indication of the presence of dissolved solids and contaminants, especially

Table 3 Range of metal concentrations (mgL-1) measured from the study area Elements

Min

Max

Mean

WHO World Health Organization (2011)

Nigerian standard NIS 554:2007

Na

1.1

2

1.51

NA

200

K

0.16

0.7

0.41

NA

NA

Ca

0.1

0.86

0.25

NA

NA

Mg

0.11

0.83

0.32

NA

0.2

Cu

0.1

0.48

0.3

2

1

Pb

0.06

0.75

0.37

0.01

0.01

Mn

0.03

0.35

0.18

5

0.20

Cd

0.01

0.04

0.02

0.003

0.003

electrolytes; however, these do not give information about the specific chemical. The values recorded in this study (Table 2) fall below the WHO-recommended value of 250 lScm-1, thereby implying the absence of salt intrusion from any external sources. It has been observed that the electrical conductivity of the groundwater signifies intrusion and miscibility of seawater with upland aquifer (Howsam 1989). The low values recorded in the study area are far below those reported by Orebiyi et al. (2010) in the shallow groundwater of Abeokuta, which is relatively closer to Lagos. It therefore implies that there is no likelihood of saline intrusion into the study area, which is farther from the coast. The alkalinity indicates the level of carbonates, bicarbonates and hydroxyl group in water samples (Williams et al. 2009). Since hydroxides are not common to natural water, no phenolphthalein alkalinity was recorded for all the analyzed water samples; however,

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Fig. 2 Piper plot showing the geochemistry of the ions in groundwater of the study area

the trend of low alkalinity and moderate pH reported in this work contradicts that reported for the groundwater of Lagos City, Nigeria, where low alkalinity and low pH values were recorded (Yusuf 2007). Globally, bicarbonate (HCO3-) is the dominant inorganic carbonate species in most rivers and many groundwaters (Maybeck 2003; Eby 2004). The dominance of HCO3- in the analyzed samples from the study area with a range of 140–280 mgL-1 is comparable to the values reported by Duvbiama and Egbuna (2013) in groundwater from Akure, Southwest Nigeria. A pH range of 6.2–7.5 was recorded in the groundwater of the study area, which is very close to 6.5–8.5 recommended by WHO. The normal values of pH do not have any undesirable effect on human health. The importance of the physicochemical properties generally lies in the fact that they are related to the chemical properties, that is, the dissolved substances. The solubility limits of many minerals depend on the temperature and the pH (Jordana and Batista 2004). Along the flow path, if any of those properties changes, some solid phases can become unstable and dissolve other phases, leading to newly formed minerals. These chemical reactions imply a change in the chemical composition of the groundwater along the flow path. The values of redox potentials (EH) recorded for the three locations (Iwo, Ikonifin and Ife-Odan) were mainly positive with the exception of some locations in Iwo which recorded negative values as low as -8 mV. These wells are likely to have activities of reducing

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microorganisms, going on as supported by low dissolved oxygen (3.3 mgL-1) and low sulfate concentrations (14.6 mgL-1). In addition, the nitrate concentration being as low as 0.36 mgL-1 is also a pointer to the reducing characteristics of the water. The concentrations of anions (SO42-, Cl-, NO3-, PO43-) and NH4? in the groundwater of the study area were below the recommended limit of WHO (Table 2). The maximum value for SO42- is 21 mgL-1. Water with SO42- concentration [250 mgL-1 is objectionable for some industries, while water containing about 500 mgL-1 tastes bitter (Ezeigbo 1988). The chloride present may be due to atmospheric precipitation and subsequent release of ions from the underlying basement rock (Olayinka et al. 1998). The nitrate values are lower than the WHO-recommended limit of 10 mgL-1 in drinking water; however, the possible source of nitrate in water is mainly anthropogenic (improper disposal of waste and agricultural sources). There is no specific limit recommended by WHO for NH4? and PO43- in drinking water, but the values for PO43- recorded in this study may appear too high and the source may be due to agricultural activities in the study area. The depth was significantly higher in Ikonifin which was reflected in the values of redox potential. Deep groundwater is commonly found to be reducing, because depletion of oxygen occurs. Although the SO42- and Clare within WHO limits in drinking water, the significantly high values of PO43- and SO42- recorded from groundwater of Ife-Odan and Iwo occur as a result of runoff from agricultural sources. The trend of cation concentration Na? [ Ca2? [ Mg2? [ K? (Table 3) is very similar to that reported by Boboye (2008) in Iddo area of Southwest Nigeria. The values of Na? were greater than those of K?, which was in line with the observation that the concentration of K should normally be around one-tenth that of Na? and \10 mg/L for potable groundwater (Adediji and Ajibode 2005). The major sources of K? in groundwater are weathered orthoclase and microcline; feldspars and biotite in most cases are also from potassium-based chemicals. The maximum values of 0.83 mgL-1 Mg2? recorded for the analyzed groundwater is far below the WHO limit. It is possible that the source of Mg2? in the analyzed groundwater is the chemical weathering of mafic minerals in the bedrock (i.e., olivine, biotite) and other related minerals which constitute the basement rocks in the area. Besides the role of percolating water from runoff as a participant in the chemical reactions, its role as a carrier of weathered (soluble) products usually results in the leaching of cations in the silicate minerals (Malomo et al. 1993). All the samples have concentration of manganese within the range of WHO-recommended 0.01–0.35 mgL-1. Manganese makes water distasteful with no specific toxic

Environ Earth Sci Table 4 Distribution of physicochemical parameters in wells from Ife-Odan, Iwo and Ikonifin DO Mean ± SE

HCO32Mean ± SE

SWL Mean ± SE

Depth Mean ± SE

34.2 ± 5a

4.96 ± 0.34b

224 ± 32.86a

3.9 ± 0.67a

28.4 ± 6.12a

3.4 ± 0.4a

228 ± 9.27a

3.5 ± 0.68a

29.6 ± 3.61ab

Temp Mean ± SE

pH Mean ± SE

Ife-Odan

28.56 ± 0.32a

6.72 ± 0.13a

28.8 ± 0.3a

6.6 ± 0.07a

50.79 ± 2.63a

39.6 ± 3.97a

a

a

a

a

Iwo Ikonifin

29.36 ± 0.1

EC Mean ± SE

RP Mean ± SE

Locations

6.44 ± 0.12

Locations

SO42Mean ± SE

Ife-Odan

17.3 ± 0.62b

58.0 ± 11.82a 53.02 ± 6.05

33.8 ± 7.34

a

3.58 ± 0.55

NO3Mean ± SE

ClMean ± SE 107.12 ± 8.08a a

Iwo

16.6 ± 1.04

93.62 ± 11.85

Ikonifin

12.4 ± 1.84a

106.51 ± 5.18a

2.57 ± 0.9

200 ± 13.93

NH4? Mean ± SE

2.47 ± 1.05a

b

a

PO43Mean ± SE

0.29 ± 0.05a

a

0.244 ± 0.12

2.08 ± 0.4

0.18 ± 0.08a

43.4 ± 3.21b TDS Mean ± SE

1.93 ± 0.08b

a

2.92 ± 0.53a

3.5 ± 0.45

a

33.2 ± 11.96a

b

33.8 ± 10.05a

0.79 ± 0.14a

62.38 ± 14.1a

a, b

No significant difference among the mean values bearing the same superscript in a column at P B 0.05. Significant difference exist among the mean values bearing different superscript in a column at P B 0.05 Table 5 Distribution of metal concentrations (mgL-1) measured from Ife-Odan, Iwo and Ikonifin Locations

Na Mean ± SE

K Mean ± SE

Ca Mean ± SE

Mg Mean ± SE

Cu Mean ± SE

Pb Mean ± SE

Mn Mean ± SE

Cd Mean ± SE

Ife-Odan

1.28 ± 0.07a

0.42 ± 0.11a

0.55 ± 0.13a

0.34 ± 0.10a

0.36 ± 0.01a

0.53 ± 0.04b

0.2 ± 0.07a

0.022 ± 0.01a

Iwo

1.79 ± 0.04a

0.43 ± 0.09a

0.24 ± 0.04a

0.44 ± 0.14a

0.25 ± 0.06a

0.26 ± 0.11a

0.1 ± 0.01a

0.012 ± 0.00a

a

a

a

a

a

b

a

0.02 ± 0.00a

Ikonifin

1.91 ± 0.04

0.4 ± 0.03

0.16 ± 0.04

0.49 ± 0.12

0.31 ± 0.03

0.6 ± 0.06

0.2 ± 0.04

a, b No significant difference among the mean values bearing the same superscript in a column at P B 0.05. Significant difference exist among the mean values bearing different superscript in a column at P B 0.05

Table 6 Pearson correlation for physico-chemical parameters Temp Temp

pH

EC

RP

DO

HCO32-

SWL

Depth

SO42-

Cl-

NO3-

NH4?

TDS

1

pH

-0.39

EC

-0.53

0.05

RP

-0.07

-0.70

1 1 0.18

1

DO

-0.4

0.09

0.17

0.19

1

HCO32-

-0.49

-0.09

0.88

0.48

0.18

SWL

-0.32

0.08

0.55

0.36

0.27

0.54

1

Depth

0.12

-0.11

0.48

-0.03

-0.23

0.26

0.34

SO42Cl-

-0.05 -0.22

0.41 0.12

-0.37 -0.09

-0.06 0.32

0.29 0.46

-0.13 0.12

-0.27 0.23

-0.60 -0.28

1 0.59

1

NO3-

0.21

-0.07

-0.54

-0.19

-0.02

-0.54

-0.58

-0.19

0.04

-0.45

NH4?

-0.13

0.49

-0.14

-0.63

-0.01

-0.27

-0.48

-0.27

0.19

-0.54

0.65

1

PO42-

-0.17

0.34

-0.01

0.03

0.21

0.27

-0.11

-0.49

0.70

0.19

0.18

0.46

0.54

-0.11

-0.05

0.45

-0.07

0.22

0.2

0.08

0.26

0.54

-0.32

-0.52

TDS

PO42-

1 1

1 1 0.13

1

P \ 0.05

effects (Longe and Enekwechi 2007; Nwidu et al. 2006). In this study the maximum concentration of Ca recorded is 0.86 mg/L and calcium salts have been observed as one of the most commonly occurring inorganic chemicals in nature. Though the human body requires *0.7–2.0 g of calcium per day as food element, excessive amounts can lead to the formation of kidney or gallbladder stones. Calcium

toxicity is rare, but overconsumption may lead to deposit of calcium phosphates in the soft tissue of the body which can cause depression. It plays a vital role in building healthy teeth and bones. It is vital to every cell in the body, for nucleus function, nerve transmission, blood clotting and many others. If deficient, it is mobilized from bones causing osteoporosis (Chapman-Nowakofski and Tussing

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Environ Earth Sci Table 7 Pearson correlation for metals Na

K

Ca

Na

1

K

-0.25

1

Ca

-0.79

0.52 -0.6

Mg

Cu

Pb

Mn

Cd

1

Mg

0.51

Cu

-0.39

0.45

-0.37 0.22

-0.39

1

Pb

0.04

-0.06

0.24

0.49

0.14

1

Mn

-0.33

0.69

0.51

-0.27

0.47

0.38

1

Cd

-0.37

0.59

0.47

-0.22

0.52

0.37

0.88

1

1

P \ 0.05

2001). The piper’s diagram showed the distribution of dominant cations and anions in the groundwater of the study area. It can be seen that the dominant cations are K? and Na?, while the dominant anions are HCO¯3 and CO32showing that they are from natural sources. This shows that sylvite (KCl), halite (NaCl), dolomite CaMg[CO3]2, quartz (SiO2), anhydrite (CaSO4) and calcite are likely to be the main minerals which are dissolved in groundwater and participate in the water–rock reaction. The water sample characterized by Ca and Na–HCO3 water type suggests cation exchange process in the geogenic reaction (Oke and Tijani 2012). Among the heavy metals and other elements, Pb was found to have exceeded the WHO limit of 0.01 from all locations, while the values recorded from Ife-Odan were significantly higher than those from other locations. This can be attributed to vehicular activities in the area. All the three locations serve as transit points where heavy trucks carrying finished products take a rest overnight before continuation of their journey to the northern part of the country. In the process, most of the trucks broke down and repair work was carried out on them. Pollution from leaking fuel and brake pads might have released Pb into the environment which would percolate into the soil and contaminate the groundwater in the area. Elevated lead concentration may also be attributed to anthropogenic influence, such as small-scale entrepreneur activities which include open-air solid waste combustion, saw mills, wood works, quarrying, filling stations and auto repair workshops (Adepelumi et al. 2001; Adekunle et al. 2007). A concentration of lead higher than in the present study within the range of 0.61–14 lg/L has been reported in boreholes and dug wells in Nigeria (Asubiojo et al. 1997). Lead occurs at the highest concentration near roadsides and its amounts decrease with increasing distances from the road and with increasing depth in soil (Bretzel and Calderisi 2009). If the contaminants are bound strongly to the soil and their desorption does not occur, groundwater pollution may not be a problem (Businelli et al. 2009). However, if desorption occurs easily, the

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contaminant could become mobile and contaminate water supplies. In humans, exposure to lead can result in a wide range of biological effects depending on the level and duration of exposure. Various effects occur over a broad range of doses, with developing fetuses and infants being more sensitive than adult. High levels of exposure may result in toxic biochemical effects in humans, which in turn would cause problems in the synthesis of hemoglobin, affect the kidneys, gastrointestinal tract, joints and reproductive system and cause acute or chronic damage to the nervous system. Cadmium concentration is higher in all sampling locations than the WHO-recommended limit (0.005 mgL-1) in drinking water. The violation of WHO limit for Cd in groundwater is similar to that reported in previous studies (Oluyemi et al. 2009). The source of Cd is the decayed debris that had accumulated as rocks and undergone mineralization through bacterial processes (Garrett et al. 2008). These rocks led to a steady accumulation of small amounts of Cd in agricultural soils where fertilizers were applied, which resulted in leaching to groundwater (Garrett et al. 2010). The correlation analysis (P \ 0.05) of physicochemical parameters showed that EC and HCO32- (R = 0.88), EC and static water level (SWL) (R = 0.55), Cl- and TDS (R = 0.54), and NO3- and NH4? (R = 0.65) (Table 6) have some characteristics in common. However, relationships exist between K? and Ca2? (R = 0.52), K? and Mn2? (R = 0.69), K? and Cd2? (R = 0.59), Na2? and Mg (R = 0.51), Ca and Mn (R = 0.51), Cu and Cd2? (R = 0.52), and Mn2? and Cd2? (R = 0.88) (Table 7).

Conclusion The physicochemical properties and the anions of the groundwater examined are within the WHO-recommended limit in drinking water. The lead concentrations in groundwater of the study areas were higher than the recommended limit in drinking water which may be attributed to activities of motor mechanics. It is likely that lead percolated into the soil and contaminated the groundwater. Lead is weakly bound to the soil and thereby allows easy mobility. The source of Cd is likely due to decayed debris that had accumulated as rocks and undergone mineralization through bacterial processes. These rocks lead to a steady accumulation of small amounts of Cd in soils which result in leaching to groundwater. The dominant cations according to the results of piper plots include Na? and K?, which shows that the sources of pollution is from water–rock interaction, while the dominant anions are CO32- and HCO¯3 which indicates sources from the bedrock. Concerted effort should be made by the state and local government to treat the water before consumption.

Environ Earth Sci

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