Journal of Geology and Mining Research Vol. 2(7), pp. 183-196, December 2010 Available online http://www.academicjournals.org/jgmr ISSN 2006 – 9766 ©2010 Academic Journals Full Length Research Paper

Integrating geographic information system (GIS) and hydrochemistry for heavy metal pollution studies: The

case of Ubeji and Omadino areas of Delta State, Southern Nigeria

A. W. Mode, N. G. Onokwai, O. S. Onwuka, A. C. Ekwe* and I. A. Oha

Department of Geology, University of Nigeria, Nsukka, Enugu State, Nigeria.

Accepted 21 June, 2010

Hydrochemical studies have been carried out on water and soil samples from the industrial areas of Ubeji and Omadino in Warri South Local Government Area of Delta State in order to access the extent of the heavy metal pollution around the area. A total of twenty samples: 4 boreholes, 4 hand-dug wells, 4 rivers, 8 soils and an effluent from the refinery were obtained and the heavy metal content and metal ion concentrations were determined using atomic absorption spectrophotometer (AAS). Results show that cadmium (Cd) levels ranged from 0.04 – 0.12 mg/l, zinc (Zn) ranged from 0.002 – 2.06 mg/l, chromium (Cr), from 0.003 – 0.29 mg/l, lead (Pb), from 0.002 - 0.02 mg/l, nickel (Ni), from 0.007 – 0.13 mg/l and cobalt (Co) ranged from 0.01 – 1.04 mg/l. Na+ levels ranged from 0.45 – 5.36 mg/l, K+, from 0.20 – 1.37 mg/l, Ca2+ and Mg2+ ranged from 0.01 – 2.32 mg/l and 0.01 – 1.25 mg/l respectively. Chloride (Cl-) levels ranged from 12 – 32 mg/l, SO4

2-, from 1.00 – 4.00 mg/l, NO3-, from 0.04 – 0.05 mg/l while HCO3

-, arsenic (As), mecury (Hg) and barium (Ba) were below detectable limits. Groundwater in Ubeji and Omadino areas based on chemical quality in comparison with World Health Organisation (WHO) standards is unsuitable for drinking because heavy metals of interest exceed permissible limits. Generally, higher metal concentrations were obtained in Omadino compared to Ubeji, thus the trend of contamination is further away from the supposed source. Key words: Effluent, heavy metal pollution, Omadino, Ubeji, water quality.

INTRODUCTION In the past four decades, there had been substantial increase in oil and gas exploration, refining and product marketing in the Nigerian Niger Delta. One refinery is located in Warri, a coastal town in the Niger Delta and refining for specific application carries with it potential problems of raw materials transport, handling/storage in large volumes, and chemical production processes. These activities present points at which chemical substances may be lost to the environment as a result of leaks, spills or other short and long term events. Often, these substances constitute contaminants and are either *Corresponding author. E-mail: amobiekwe@yahoo.com, amobi.ekwe@unn.edu.ng.

trapped in the soil or infiltrate through the soil and eventually percolate to the groundwater, or they could be transported into surface water bodies. These contaminants generally, may contain different heavy metal and hydrocarbon components that may be deleterious to humans and the environment. The environmental impacts of these activities have been of concern to the scientific community, government regulatory agencies, oil company operators as well as host communities whose most eloquent testimony of resistance to the general pollution of the environment by the activities of oil companies is violent protest and militancy. Several workers have presented results on the health and environmental implications of heavy metals in soils and water resources in Warri area (Ogunlaja and Ogunlaja, 2007; Olomukoro and Azubuike, 2009;

184 J. Geol. Min. Res.

� Figure 1. Map of the study area.

Emoyan et al., 2006; Ayenimo et al., 2005; Olobaniyi and Owoyemi, 2006). Ohimain et al., 2008 evaluated the changes in water chemistry in the Warri River due to dredging of an oil well access canal.

The present study attempts to give a wider scope of data presentation in order to elicit the water characterisation and show a three dimensional (3D) distribution of some heavy metals in Ubeji and Omadino areas of the Warri industrial area in the Niger Delta. Location and description of the study area The study area (Ubeji and Omadino communities) is situated in Warri South Local Government Area of Delta State. It lies between latitudes 5°30´N and 5°38´N and longitudes 5°38´E and 5°45´E (Figure 1) and covers an area of about 66 km2. The two communities are located within the oil rich Niger Delta province of Nigeria. Climatologically, the study area has a mean annual rainfall of 3200 mm and mean temperature of about 28°C. Topography is flat, with an average elevation of about 13 m above sea level. The flat and low relief

features often encourage flooding after rain events. The drainage pattern is dendritic with major tributaries emptying into the Forcados River. The vegetation of the area is tropical rain forest type, comprising abundant trees and grasses. It consists of coastal fresh water forest on the barrier beach ridges, mangrove swamps of tidal zone and fresh water swamp forest in the region beyond the limit of tidal influence.

Geologically, the area is underlain by a quaternary to recent alluvium, the Somebreiro - deltaic plain sand (Olobaniyi and Efe, 2006). This formation, is highly aquiferous and consists of fine to medium and coarse-grained unconsolidated sands with occasional intercalations of gravelly beds, peat or lenses of plastic clay. It is generally in excess of 100 m in thickness. Below the Somebreiro - deltaic plain sands are the three stratigraphic units (Benin, Agbada and Akata Formations) that constitute the Niger Delta. The soils in the study area exhibits a wide range of colours from milky white through brown to very dark brown; and they vary in types and texture from loamy to sandy and clayey types according to the United States Department of Agriculture (USDA) classification. The soils of the area are extremely rich in

Mode et al. 185

� Figure 2. Map of study area showing sampling locations.

nutrients, as evidenced by the existence of luxuriant trees and grasses typical in the study area.

The area is accessible through a network of well maintained secondary roads that connect to the Warri Port expressway. Several footpaths off the minor roads connect to spot locations where samples were collected. MATERIALS AND METHODS Sample collection A total of twenty-one (21) samples; eight ground water samples (4 boreholes and 4 hand-dug wells), four surface water samples (rivers), eight soil samples and an effluent sample from the refinery were collected for analysis (Figure 2). The spatial coordinates (longitude, latitude and elevation) of the sampling points were collected with the e-Trex GPS, a powerful geographic information system tool. The water samples were stored in 1-l bottles and labelled appropriately according to site of collection while, soils were stored in polyethylene bags and were labelled accordingly. The depth to water in the dug wells varied from as low as 2 - 16 m while soil samples were taken from shallow depths of about 0.3 m. Sample preparation and analysis The metal ions concentrations were determined using the atomic absorption spectrophotometer (Perkin-ElmerAA53110) for the cations (Na+, K+, Ca2+, and Mg2+) and visible spectrophotometer (WPA5110) for the anions (Cl-, SO4

2-, HCO3- and NO3

-). 20 g each of the soil samples were dried in an oven at 105°C at constant

weight and weighed into digestion tubes. After the addition of 20 ml concentrated hydrochloric acid, the samples were digested for 3 h at 100°C in an aluminium heating block. The digestion mixture was cooled to room temperature and 1 ml hydrogen peroxide carefully added. The digestion tubes were heated for a further 30 min. The digestion mixture was diluted to the mark with distilled water and transferred into 50 ml polypropylene bottles for analysis. For elemental analysis a Chem Tech Analytical 2000 atomic absorption spectrophotometer (AAS) was used. The analyses were carried out using an air–acetylene flame at optimum recommended instrument operating conditions. The calibration standards were prepared from 1000 ppm stock solutions to obtain calibration standards for Cd, Co, Ni, Zn and Cr. PRESENTATION, ANALYSES AND DISCUSSION OF RESULTS Various presentation modes have been employed to display the water chemistry results and to aid the interpretation. They include: stiff diagram, Schoeller diagram, circular diagram and bar graphs. Water chemistry data Table 1 shows analytical results for metal ion concentration; cations (Na+, K+, Ca2+, and Mg2+) and anions(Cl-, SO4

2-, HCO3- and NO3

-). Sodium levels ranged from 0.45 to 5.36 mg/l and are generally higher in

186 J. Geol. Min. Res.

Table 1. Analytical results for soil and water samples in mg/l. Sample Cd Hg Zn Cr Na Pb Ni K Ca Mg Co NO3 SO4 Cl BH1 UBEJI BDL BDL 0.351 0.009 3.518 BDL BDL 0.702 2.326 1.248 0.053 4 15 BH2 UBEJI BDL BDL BDL 0.010 5.358 BDL BDL 0.959 0.419 0.341 0.041 3 22 BH1 OMADINO BDL BDL BDL 0.010 1.841 BDL 0.006 1.370 0.011 0.028 0.051 12 BH2 OMADINO BDL BDL 0.011 0.012 2.285 BDL 0.135 0.689 1.051 0.266 0.017 32 WELL 1 UBEJI BDL BDL BDL 0.010 0.451 BDL 0.028 0.109 0.011 0.012 0.06 2 16 WELL 2 UBEJI BDL BDL 0.002 0.008 0.569 BDL BDL 0.717 1.484 0.328 0.023 0.04 3 19 WELL 2C OMADINO BDL BDL BDL 0.004 1.263 BDL BDL 0.204 0.284 0.108 0.01 0.06 2 19.8 WELL 2 OMADINO BDL BDL BDL 0.004 2.690 BDL BDL 1.187 1.351 0.252 0.027 0.05 1 14 RIVER 2C OMADINO BDL BDL BDL BDL 0.000 0.006 0.017 RIVER 1C OMADINO BDL BDL BDL 0.003 0.003 BDL 0.011 RIVER 1 UBEJI BDL BDL BDL BDL BDL 0.048 0.021 RIVER 2 UBEJI BDL BDL BDL 0.012 0.002 BDL 0.011 EFFLUENT BDL BDL 0.062 0.290 BDL 0.042 0.066 S1 UBEJI 0.0619 BDL 0.548 BDL 0.002 0.013 1.043 S2 UBEJI BDL BDL 0.382 BDL 0.014 BDL 0.667 S2 OMADINO 0.041 BDL 2.059 0.024 0.019 BDL S3C OMADINO 0.1243 BDL 0.145 0.045 BDL 1.063 S2C OMADINO 0.039 BDL 0.008 0.65 boreholes than wells. Its concentration is highest in Ubeji borehole 2 (UB2). Potassium concentration follows the same trend as sodium, ranging from 0.20 – 1.37 mg/l with the exception of Omadino well 1 (OW2) which is slightly higher than some boreholes. Calcium and magnesium concentrations ranged from 0.01 – 2.32 mg/l and 0.01 – 1.25 mg/l respectively, recording higher values in some wells than boreholes and are highest in Ubeji borehole 1 (UB1). Chloride values are higher in boreholes than wells, and ranged from 12 – 32 mg/l, with highest values in Omadino borehole 2 (OB2). Sulphate values ranged from 1.00 – 4.00 mg/l, nitrate levels from 0.04 – 0.05 mg/l while bicarbonate were not detected at all.

The origin of these metal ions and their presence in such concentration in the study area is related to the hydrogeologic conditions of the study area. The area is a coastal area and this accounts for the fairly high concentration of chloride (Cl-) ions. Mercado (1985) inferred that the dominant clay type particularly in the hydromorphic soils of the Niger Delta is montmonrillonite clay in association with sediments high in organic matter content. This could possibly explain the presence of Ca2+ and Na+ in the groundwater of Ubeji and Omadino areas. Stiff diagrams Pattern diagrams represent chemical analyses by four parallel axes, with concentrations in mmol of cations plotted to the left of a vertical zero axis and anions to the right. The resulting points when connected form an irregular polygonal pattern; waters of similar quality

define a distinctive shape. In the stiff diagrams (Figures 3 and 4), absolute

concentrations in meq/l are used for rapid comparison of result of each groundwater sample. The samples from Ubeji area show nearly similar shape which is indicative of homogeneity in source except for well 1, which has very low cation concentration compared to the others. Samples from Omadino area equally show similarity in shape with the exception of borehole 2, whose chloride peak is more pronounced, probably because of its nearness to the coast.

Ionic concentrations of samples from Omadino differ significantly from those of Ubeji. As revealed by the shapes, they contain more chloride, little or no sulphate, calcium and magnesium are low or absent and sodium is relatively moderate. Circular diagrams Circular diagrams with a special scale for the radii so that the area of a circle is proportional to the ionic concentration of the analysis and sectors within the circle show the fractions of the different ions expressed in milli-equivalents per litre are used in representing and comparing water quality analyses. A visual description of the relative concentration /abundance in meq/l of the chemical parameters is presented in Figures 5 and 6. The samples from Ubeji and Omadino areas reveal an overall order of cationic concentration in groundwater as Na+ > Ca2+ > Mg2+, while Cl- > SO4 is

the order of anionic concentration. HCO3 is below detectable limits.

Mode et al. 187

� Figure 3. Stiff diagrams for Ubeji groundwater samples.

�

Figure 4. Stiff diagrams for Omadino groundwater samples.�

188 J. Geol. Min. Res.

NaCaMgClHCO3SO4

LegendUbeji Ubeji

NaCaMgClHCO3SO4

Legend

Ubeji

NaCaMgClHCO3SO4

LegendUbeji

NaCaMgClHCO3SO4

Legend

� Figure 5. Circular diagrams for Ubeji groundwater samples.

Ubeji

NaCaMgClHCO3SO4

LegendOmadino

NaCaMgClHCO3SO4

Legend

Omadino

NaCaMgClHCO3SO4

LegendOmadino

NaCaMgClHCO3SO4

Legend

Omadino

� Figure 6. Circular diagrams for Omadino groundwater samples.

Schoeller diagram The Schoeller diagram is widely employed in comparing water analyses results. The principal ionic concentrations, expressed in milli-equivalents per litre, are plotted on six equally spaced logarithmic scales and

the points plotted are joined by straight lines which not only show absolute values of each ion but also the concentration differences among various groundwater analyses.

It is used to assess the homogeneity or heterogeneity of chemical properties of groundwater. The Schoeller plot

Mode et al. 189

� Figure 7. Schoeller plot for Ubeji and Omadino groundwater samples.

100%

80%

60%

40%

20%

0%

Conce

ntr

atio

ns

Na K Ca Mg NO3 SO4 Cl HCO3

Major Ions

UW2UW1UB 2UB 1

� Figure 8. Bar graphs for ionic concentrations in Ubeji groundwater samples.

(Figure 7) provides a visual description of the relative concentrations in milli-equivalents per litre of ions in the samples from the study areas. The diagram reveals the order of cationic and anionic concentration, showing approximately the same trend with the exception of a few samples. Schoeller plot of the same trend indicates that the groundwater has undergone similar patterns of

geochemical evolution (Bajjali, 2006). Bar graphs The simplest form of presentation of a chemical data for visual inspection is a bar graph. Figures 8 and 9 show the

190 J. Geol. Min. Res.

0Na K Ca Mg NO3 SO4 Cl HCO3

Major Ions

2.5

2

1.5

1

0.5

Conc

entra

tions OW2

OW1OB 2OB 1

� Figure 9. Bar graphs for ionic concentrations in Omadino groundwater samples.

Table 2. Heavy metal concentrations in Ubeji soil samples in meq/l.

LOC US1 US2 US3 US4 Cd 0.001 0 0 0 Hg 0 0 0 0 Zn 0.017 0.011 0.032 0.017 Cr 0.011 0 0.059 0.020 Pb 0.000 0.000 0.001 0.003 Co 0.035 0.023 0.034 0.032 Ni 0.000 0 0.003 0 As 0 0 0 0 Ba 0 0 0 0

bar graphs of the concentration and distribution profiles obtained for metal ions in Ubeji and Omadino groundwater samples. Heavy metals Soils, groundwater and surface water samples obtained from Ubeji and Omadino were analyzed for the presence of Cd, Hg, Zn, Cr, Pb, As, Ba and Co. From Table 1, Cd levels ranged from 0.04 to 0.12 mg/l and is present only in soils, Zn concentrations ranged from 0.002 to 2.06 mg/l and is generally more significant in the soils. Cr ranged from a concentration of 0.003 to 0.29 mg/l, lead levels ranged from 0.002 to 0.02 mg/l. Ni concentrations range from 0.007 to 0.13 mg/l while cobalt is present in all samples significantly and ranged from 0.01 to 1.04 mg/l. Heavy metal concentrations in milli-equivalents per litre

Table 3. Heavy metal concentrations in Omadino soil samples in meq/l.

LOC OS1 OS2 OS3 OS4 Cd 0 0.001 0.000 0 Hg 0 0 0 0 Zn 0.013 0.063 0.004 0.018 Cr 0.053 0 0.001 0.055 Pb 0.000 0.000 0.000 0.000 Co 0.015 0.022 0.036 0.025 Ni 0.011 0 0 0 As 0 0 0 0 Ba 0 0 0 0

for soil and water samples from Ubeji and Omadino areas are presented in Tables 2 and 3.

In the study area, the chromium levels are higher in the boreholes than wells and completely below detectable limits in surface water which suggests that the contamination is probably from depth. The Cr concentration is highest in the soil samples and does not reconcile with the suspicion that the contamination is from depth. The high Cr concentration in the boreholes as opposed to wells may be as a result of the filtering capacity of the soils, contaminant transport and a function of solubility of the metal. Its absence (below detectable limits) in the rivers may be due to dilution in concentration resulting from the large volume of water in the rivers or due to settling at the sediments of the rivers which usually acts as sinks of contaminants in aquatic systems (Adams et al., 1992; Burton and Scott, 1992; Mucha et al., 2003). Cd is completely absent in both groundwater

Mode et al. 191

Table 4. Heavy metal concentrations in Ubeji water samples in meq/l.

LOC UB1 UB2 UW1 UW2 UR1 UR2

Cd 0 0 0 0 0 0

Hg 0 0 0 0 0 0

Zn 0.0108 0 0 0.001 0 0

Cr 0.0003 0.0004 0.0004 0.0003 0 0

Pb 0 0 0 0 0 0

Co 0.0018 0.0012 0.0004 0.0008 0.0007 0.0004

Ni 0 0 0.0009 0 0.0016 0

As 0 0 0 0 0 0

Ba 0 0 0 0 0 0

Table 5. Heavy metal concentrations in Omadino water samples in meq/l. LOC OB1 OB2 OW1 OW2 OR1 OR2

Cd 0 0 0 0 0 0

Hg 0 0 0 0 0 0

Zn 0 0.0004 0 0 0 0

Cr 0.0004 0.0004 0.0001 0.0002 0 0

Pb 0 0 0 0 0 0

Co 0.0017 0.0006 0.0009 0.0003 0.0004 0.0006

Ni 0.0002 0.0046 0 0 0 0.0002

As 0 0 0 0 0 0

Ba 0 0 0 0 0 0

and surface water samples but present in some of the soil samples (US1, OS2 and OS3) in low concentration. Its absence in surface and groundwater is probably a function of the retaining capacity of the soils.

Ni is generally higher in water than soils particularly in Omadino borehole (OB2). Co is present in all the samples collected from the study area including the effluent sample from the refinery. Its levels are higher in the soil samples than in water, though present in water in significant quantities. Zn concentrations recorded higher in soils consistently than in water, Zn occurred only in three groundwater samples from Ubeji (UB1, UW2, and OB2) (Tables 4 and 5) and is completely absent in surface water. Pb is entirely absent in both ground and surface water but present consistently in all soil samples. Ba, As and Hg are below detectable limits.

The effluent sample (Table 1) from the refinery contains the heavy metals of interest in significant concentrations with the exception of Hg and Cd. Hg and Cd are possibly not petroleum-related heavy metals or are not constituents of the several chemicals used for the

industrial activities in the Warri Refinery and Petrochemical Co. Ltd. Spatial distribution of heavy metals within the study area A geographic information system (GIS) software (SURFER 8) was used to plot three-dimensional distribution of heavy metal concentration in water and soil samples obtained from the study area. These spatial plots reveal the trend of distribution of the metals in groudwater as concentration in milli-equivalents per litre vary from one sampling point to another. Zn and Ni show similarity in trend (Figure 10). Their concentration increases gradually away from the north further south of Omadino from river-2 to borehole-2 and eventually drops in extreme south of borehole-1. Cr also increases away from north towards south, where it peaks at borehole-2 while Co generally decreases away from south towards north of Omadino.

192 J. Geol. Min. Res.

� Figure 10a. Spatial distribution of Zn in Omadino.

� Figure 10b. Spatial distribution of Ni in Omadino.

At Ubeji (Figure 10), the concentration of Zn increases away from south further north and gradually declines in the extreme north while Ni increases from north to south and changed erratically to zero in the extreme south. Cr concentration trends centrally while Co decreases from north to south and gradually changes increasing towards the north.

From the map of the study area (Figure 1), Omadino is located north of Ubeji and as seen from the spatial distribution of the heavy metals in ground water, concentration generally increased in Ubeji towards the north, that is, towards Omadino and in Omadino further south. This plots buttress the inference that contamination is more significant in Omadino compared

Mode et al. 193

� Figure 10c. Spatial distribution of Co in Omadino.

� Figure 10d. Spatial distribution of Cr in Omadino.

to the seat of the refinery - Ubeji. Water quality There is a growing awareness on the importance of water

quality, including both chemical characteristics, due to dissolved material and physical characteristics, such as temperature, taste and suspended solids. Given the increasing usage and pollution of water sources by human activities, it may be argued that the problems of water quality are now often more difficult and demanding

194 J. Geol. Min. Res.

� Figure 10e. Spatial distribution of Zn in Ubeji.

� Figure 10f. Spatial distribution of Ni in Ubeji.

than those of water quantity. The ionic component concentration of the groundwater samples from the study

area when compared with that of World Health Organisation (WHO) standards (Table 6), are within the

Mode et al. 195

2E-0054E-0056E-0058E-0050.00010.000120.000140.000160.000180.00020.000220.000240.000260.000280.00030.000320.000340.000360.00038

3

42

5

6

9

Boreholes

Shallow wells

Rivers

� Figure 10g. Spatial distribution of Cr in Ubeji.

Table 6. World Health Organization (WHO) drinking water standards (1993). Element/Compound Recommended limit (mg/l) Mandatory limit (mg/l) Unofficial (mg/l) Arsenic (As) 0.01 0.05

Barium (Ba) 1

Bicarbonate (HCO3) 1000

Cadmium (Cd) 0.01

Calcium 75 200

Chloride (Cl-) 200 250

Chromium (Cr) 0.05

Cobalt (Co) None

Lead (Pb) 0.05

Magnesium 50 150

Mercury (Hg) 0.005

Nickel (Ni) None

Nitrate (NO3) 45

Sodium (Na) 200

Sulphate (SO4) 200 400

Zinc (Zn) 5

acceptable limits. For the heavy metal concentrations, the values of various parameters ranged between desirable and maximum permissible limits. For example, zinc is within the acceptable limit, while nickel, chromium and cobalt exceed tolerance limits. Assessing the chemical

quality of the groundwater in Ubeji and Omadino areas of Warri with reference to WHO standards for drinking water, the water is not completely suitable because of the high Co, Cr and Ni contents. These heavy metals can cause serious damage to the organs when consumed.

196 J. Geol. Min. Res. CONCLUSION AND RECOMMENDATIONS From the results of the analyses of heavy metal concentration in water and soils from the study area, we found out that Co and Cr concentrations are generally more significant in Ubeji and Omadino areas while the concentrations of Ni, Pb and Zn within the same area are quite low. Results show that contamination is more pronounced in boreholes than hand dug wells and shows little or no contamination in surface water. The absence of contaminants on surface water could be attributed to solubility and contaminant transport. The soils which were sampled few meters away from water sampling points have relatively higher concentrations of heavy metals and such insoluble metals like lead was consistently present in the soils. These heavy metals (Pb and Cd) were completely below detectable limits for groundwater in all the wells. The chemical quality of groundwater in Ubeji and Omadino areas in comparison with WHO standards defies its suitability for drinking. World Health Organization recommends that Pb, Ni, Co and Cd should be absent in drinking water. Results from this study indicate that Omadino is relatively polluted in comparison to Ubeji, thus, the general trend of contamination is further north. We therefore recommend that other advanced imaging tools like crosshole electrical tomography be employed in the area to ascertain the extent and direction of the pollution plumes. ACKNOWLEDGEMENTS We specially acknowledge the help of Prof. S. A. Braide, Shell Professor of Environmental Studies, Institute of Pollution Studies (IPS), Rivers State University of Science and Technology (RSUST), Port Harcourt and Mr.

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