Environmental Impact Assessment of Onyeama Coal Mine in Enugu,
Southeastern Nigeria
*Ezemokwe, D.E1, Idogwu, C. N2, Orazulike, D.M3, Ezemokwe, I .U4
1,2
Projects Development Institute (PRODA), P.M B 1609 Enugu, Enugu State *Corresponding Authors: deezemokwe@gmail.com
3
Geology Programme, Abubakar Tafawa Balewa University, Bauchi, Bauchi State
4
Dept of Environmental Studies, Abubakar Tafewa Balewa University, Bauchi, Bauchi State
Abstract – Heavy-metal concentration levels in water, coal wastes, soil and
background soil were determined with a view to assessing the degree of contamination and environmental impact due to coal mining activities around Onyeama coal mine. A total of 58 samples comprising 11 water, 11 coal wastes, 22 soils and 14 background soils were collected and analyzed. Various physico
-chemical characteristics of water analyzed include pH, alkalinity, total hardness, total dissolved solids (TDS), sulphate, chloride, calcium and magnesium. Chemical analysis of water, coal wastes, soil and background soil samples were undertaken to determine concentrations of Cd, Cr, Ni, Cu, Co, Pb, Zn, As, Mn and Fe using an Atomic Absorption Spectrophotometer. The Enrichment Factor (EF) and Pollution Index (PI) results indicate significant enrichments of Cd, Pb and Ni in all the media examined compared with other elements studied. In water, the concentrations of Fe (3.13 mg/l), Cd (0.33 mg/l), Ni (1.30 mg/l), Cr (0.12 mg/l) and As (0.07 mg/l) exceeded the recommended values (1.0, 0.003, 0.02, 0.05 and 0.01mg/l respectively) for potable water. In coal waste samples, Cd (2.52mg/kg) is high with health risk level of 5. Cu (2.81mg/kg), Co (1.57 mg/kg) and As (0.19 mg/kg) moderately polluted the environment. In soil, high mean concentration levels are recorded for Cd (5.56 mg/kg) and Pb (3.15 mg/kg), moderate to low levels for Cr (1.88 mg/kg), Cu (1.70 mg/kg), Co (0.44mg/kg), Mn (0.99mg/kg) and As (0.16 mg/kg). Concentration of metals in the four media examined indicated that the level of pollution is in descending order as shown: soil medium >>>coal wastes medium >> water medium> background soil medium. Reference to World Health Organization standards, the observed trend in the concentration of the metals in the media, will pose health problems to humans and may impact adversely on the ecological, agricultural as well as underground water systems.
Key Words – Enrichment factor; Pollution Index;Heath Risk Level;Heavy metals; Toxic elements; WHO.
1
Introduction
coal mining is dominant among all mining activities for environmental degradation. Toxic pollutants contained in coals and others formed during combustions are released into the air, water and the soil. Some of the pollutants are known to cause cancer, while some impair reproduction (Keating, 2001). Environmental impact assessment in the study area, before, during and after the coal mining, was at low ebb. Against this background, this study is intended to investigate the impact of coal mining within Onyeama coal mine area on the environment. Specifically, the study sought to: (i) evaluate the content of the effluents from the tunnels and water from the nearby Ekulu river and determine whether the waters meet the standards of the World Health Organization (WHO) values and other standard limits for potable water; (ii) determine the concentration of heavy metals in soil in the vicinity of coal mines with a view to providing information on the degree of contamination so as to enable the assessment of possible environmental impacts that could occur due to coal mining activities; (iii) determine the compositions of coal waste dumps and their effects on the ground water quality and on the environment (iv) assess the distribution of heavy-metals in the background soil sediments far away from mined area (as control) to determine their contribution to abnormal elemental concentrations.
2
Materials and Methods
The research involved integrated geological, hydrogeological and chemical studies. Field study involved the application of precise techniques in sample collection to ensure that data from each analysis performed on the samples were reproducible. A total of 58 samples comprising 11 water, 11 coal wastes, 22 soils and 14 background soils were systematically collected and chemically analyzed. The coal wastes and soil samples were oven dried at 1050C for 24 hours to remove moisture. Each sample was crushed in a mortar and mechanically sieved to increase surface area so as to enhance efficiency of subsequent chemical attack. A 0.2 g of each sample was weighed and kept in dried crucibles. Total digestion method was applied. Total digestion method releases all elements in a sample (Crock et al, 1983). Samples were dissolved in acid mixture of 5 ml nitric acid, 3 ml perchloric acid and 2 ml hydrofluoric acid. The cooled solution was made up to 250 ml in a volumetric flask with de-ionized water. The solutions were analyzed for Cd, Cr, Cu, Mn, Ni, Pb, Fe, Zn, As, and Co using an Atomic Absorption Spectrophotometer (AAS) model 210 VGP. Water samples were analyzed for total hardness, total dissolved solids, chloride, alkalinity, sulphate, Ca, Mg, Cd, Cr, Cu, Mn, Ni, Pb, Fe, Zn and As.
Alkalinity of water was determined by titrimetric method. Titrimetric method according to Bryant, (2005) is applicable to drinking, domestic, saline and surface waters as well as industrial wastes. It is suitable for all concentration ranges.10ml of unfiltered portion of each water sample was titrated potentiometrically with 0.01M HCI solution using methyl orange as indicator. Chloride was determined by titrating 10ml of the sample with a standard solution of 0.1N silver nitrate solution using solution of potassium chromate as indicator. Total solids (TS) and total dissolved solids (TDS) were determined by volumetric method. Filtrations were done with Whatman Grade A filter paper (Ageman and Chau, 1976 and Taliadouri, 1995).Hardness of water was determined by calculation method. Hardness as sum of CaCO3 equivalents (mg/l) obtained by multiplying concentration (mg/l) found of cations by a given factor. The water samples were quantitatively analyzed for trace metals: lead (Pb), zinc (Zn), nickel (Ni), copper (Cu), cadmium (Cd), cobalt (Co), iron (Fe), manganese (Mn), chromium (Cr) and arsenic (As) using Buck Scientific Absorption Spectrophotometer (AAS) model 210 VGP. Concentration of the trace elements were extrapolated from plotted curve (Vogel, 2007).
3
Results
Results of chemical analysis of water samples (mg/l) are shown in Table 1 Trace metals analysis of Water samples in mg/l are shown in Table 2.
Concentrations of metals in coal waste samples from Onyeama mine area in milligrams per kilogram (mg/kg) are presented in Table 3. The metal concentrations shown in Table 3 (mg/kg) were used to calculate the Enrichment Factors (EF) as well as Pollution Index (Pi) of each metal in the coal waste samples shown in Tables 6 and 9 respectively. Concentration levels of metals in the surrounding soils and Background soil are shown in Tables 4 and 5 respectively. Enrichment factors (EF) of soil are shown in Table 7 and its pollution Index (Pi) in Table 10.The EF of Background soil samples is presented in Table 8 and its Pi in Table 11.
Based on the value of the enrichment factor (EF), the health risk level is inferred. The pollution condition can be divided into six health risk levels (HRL), according to Liao and Chao (2006) and Sutherland (2002).When the enrichment factor (EF) is less than 1; it indicates that there is no contamination, the HRL is 0. When the EF is equal to one or two, it indicates that the pollution level is minimal and the HRL is 1.When the enrichment factor lies between 20-40, it indicates high level of pollution and the health risk level is 4. The Pollution index (Pi) was calculated using the Liao and Chao, (2006) formula as shown below:
Pi = Ci/Si … (1)
Where Pi = Pollution index
Ci = concentration of heavy metal in the medium
Si = relevant standard for this metal (Rudnick and Gao, 2003)
Table 12 shows compared Enrichment (EF), Pollution Idex (Pi) and High Risk (HRL) levels of the examined media.
Table 1. Chemical Analysis of Water Samples (mg/l)
Sample ID
Total hardness as
CaCO3
Total solids (TS)
Total dissolved solids (TDS)
Cl Ca Mg Alk Sulphate
D- 1 104.00 401.00 120.00 61.70 50.15 20.00 100.00 215.00
D- 2 520.00 120.00 21.80 35.40 17.10 19.40 75.00 NIL
D- 3 340.00 650.00 100.00 74.00 33.00 8.60 67.00 100.00
D- 4 220.00 320.00 110.00 141.00 21.30 5.40 NIL 490.00
D- 5 440.00 310.00 73.00 160.30 9.75 16.80 110.00 160.00
D- 6 100.00 110.00 90.80 80.05 33.40 NIL 75.00 90.30
D- 7 95.00 440.00 520.00 27.90 12.12 9.60 35.00 700.00
D- 8 47.90 120.00 87.90 42.75 16.70 3.40 105.00 120.30
D- 9 76.00 312.00 63.40 106.00 4.75 6.70 75.00 225.00
D-11 115.00 420.00 320.00 35.40 8.01 2.43 100.00 20.00
Total 2207.90 3378.00 1646.90 917.86 225.51 106.73 748.00 2260.30
Average 200.71 307.09 149.71 83.44 20.50 10.57 82.44 226.03
Table 2. Trace Metals Analysis of Water Samples (mg/l)
Sample ID Cd Cr Cu Mn Ni Pb Co Fe Zn As pH
D- 1 0.32 0.02 0.03 0.02 0.60 0.03 0.13 0.64 0.87 ND 5.0
D- 2 0.45 0.01 0.05 0.03 0.37 0.01 0.11 0.88 1.02 0.01 5.5
D- 3 0.18 ND 0.04 0.05 0.98 0.05 0.42 0.61 0.99 0.10 5.5
D- 4 0.16 ND 0.07 0.11 0.10 0.10 0.07 0.37 1.29 ND 6.5
D- 5 0.14 0.04 0.03 0.02 1.11 0.02 0.17 0.45 1.06 ND 6.0
D- 6 0.40 0.02 0.03 0.08 1.55 0.07 0.10 0.42 1.12 ND 5.5
D- 7 0.47 0.01 0.12 0.03 1.10 0.03 0.05 0.96 0.90 0.01 4.5
D- 8 0.56 0.01 0.07 0.07 0.11 0.04 0.15 0.83 0.78 ND 5.0
D- 9 0.35 ND 0.06 0.10 0.86 0.06 0.19 0.81 1.06 ND 5.5
D-10 0.31 ND 0.08 0.02 0.19 0.08 0.06 0.35 0.57 ND 5.5
D-11 0.46 0.02 0.04 0.49 0.07 0.10 0.12 0.97 0.03 0.09 5.0
Table 3. Enrichment Factors (EF) of Coal Waste Samples
Sample ID
Enrichment Factors (EF)
Cd Cr Cu Mn Ni Pb Co Fe Zn As
D- 12 Nil Nil Nil Nil Nil Nil 16.05 0.99 0.46 12.30
D- 13 Nil Nil Nil 1.37 15.81 28.27 34.35 0.99 3.48 0.00
D- 14 221.30 2.19 25.88 0.64 Nil 49.18 Nil 1.00 0.07 0.00
D- 15 190.50 2.73 Nil 0.63 35.97 30.64 5.71 0.99 0.09 26.97
D- 16 110.21 1.31 28.34 1.14 1.73 44.15 30.61 0.99 2.12 9.79
D- 17 123.29 1.61 6.22 Nil 17.09 18.34 1.68 0.99 1.86 6.45
D- 18 107.80 3.78 Nil 1.27 Nil 36.65 13.47 1.00 0.07 21.56
D- 19 19.15 1.12 Nil 0.42 7.69 20.61 8.54 0.99 1.05 22.37
D- 20 309.29 3.17 13.21 0.21 6.29 55.02 53.53 0.99 5.43 13.70
D- 22 99.17 1.80 Nil Nil 16.00 56.25 17.46 1.00 2.24 0.00
Total 1680.81 22.35 73.65 5.29 149.42 414.88 196.06 10.92 22.65 113.14
Average 186.75 2.48 18.41 0.66 18.67 41.48 19.60 0.94 2.05 16.16
Table 4. Concentration (mg/kg) of Metals in Soil Samples (Onyeama Mine Area)
Sample ID
Concentration of Metals in mg/kg
Cd Cr Cu Mn Ni Pb Co Fe Zn As pH
D- 23 1.37 1.50 1.25 1.50 3.78 3.50 0.75 241.25 1.12 ND 6.5
D- 24 2.50 1.12 1.25 4.62 2.62 1.62 0.75 253.75 0.25 0.15 4.5
D- 25 1.75 1.25 5.00 3.12 3.50 1.25 1.62 1092.50 Nil 0.25 4.5
D- 26 2.87 1.12 3.75 0.50 6.00 1.50 0.25 192.50 1.12 ND 4.5
D- 27 2.12 1.37 Nil 6.12 Nil 1.00 1.25 192.25 0.87 0.12 4.5
D- 28 3.12 2.62 1.25 1.50 Nil 0.75 0.12 523.75 1.12 0.25 6.5
D- 29 1.75 1.12 1.25 0.12 Nil 0.87 1.25 202.50 0.12 012 5.0
D- 30 8.00 1.50 0.87 0.12 15.37 2.00 0.12 1205.00 14.87 0.25 4..5
D- 31 10.25 0.872 1.50 0.25 18.50 3.87 0.13 752.50 10.75 0.25 4.5
D- 32 13.87 1.62 0.25 0.63 7.37 4.00 0.13 926.25 1.37 0.12 4.5
D- 33 5.37 2.13 4.12 0.13 12.75 3.12 0.13 780.00 15.87 0.25 4.5
D- 34 9.37 0.87 1.37 0.75 5.12 3.62 0.13 1093.75 5.25 0.12 5.5
D- 35 8.75 1.75 0.50 0.37 16.00 4.12 1.87 1100.00 6.50 ND 4.5
D- 36 9.75 1.50 1.00 0.25 8.37 2.25 0.13 1315.00 15.25 0.12 5.0
D- 37 4.25 3.25 2.87 0.25 1.12 4.12 0.25 937.50 12.00 ND 5.0
D- 38 4.87 2.75 1.75 0.12 4.00 4.62 0.12 575.00 3.37 0.12 5.5
D- 39 1.00 1.62 1.12 0.12 14.50 3.50 0.12 1438.75 8.25 0.25 5.5
D- 40 4.25 2.00 2.00 0.25 10.87 1.75 0.25 1312.50 2.50 0.12 4.4
D- 41 5.12 2.00 1.12 0.25 8.25 3.87 0.12 1190.00 3.97 0.25 5.5
D- 42 6.25 5.62 0.62 ND 3.25 2.25 0.12 1081.25 5.62 0.12 6.5
D- 43 14.37 1.87 3.75 ND 13.12 1.87 0.12 655.00 8.50 0.37 4.5
D- 44 1.50 3.00 0.87 ND ND 7.25 0.12 648.75 8.62 0.37 4.5
TOTAL 122.45 41.44 37.46 21.96 154.56 69.38 9.84 17711.74 123.06 3.52 110.4
Table 5. Concentrations (mg/kg) of Metals in Background Soil Samples
Sample ID
Concentration of Metals in mg/kg
Cd Cr Cu Mn Ni Pb Co Fe Zn As pH
BG- 45 0.37 2.37 2.00 6.37 0.75 3.75 0.25 831.25 6.25 0.25 6.0
BG- 46 1.12 5.12 1.12 9.12 1.62 3.50 0.87 1113.75 7.25 0.25 6.0
BG- 47 1.62 2.12 0.62 Nil 11.87 2.62 0.37 1127.50 2.62 0.12 6.0
BG- 48 1.50 Nil 3.75 4.00 6.62 1.37 0.25 1177.50 3.50 0.12 6.0
BG- 49 Nil 3.62 0.87 Nil 11.00 2.25 0.87 1173.75 Nil 0.25 5.0
BG- 50 0.25 3.75 2.25 0.50 11.12 0.50 0.37 1080.04 5.00 0.37 6.0
BG- 51 0.72 1.12 1.87 0.62 0.87 3.25 Nil 648.75 6.00 0.37 5.0
BG- 52 1.12 Nil 0.12 1.37 4.00 4.75 0.37 1190.00 4.00 Nil 6.0
BG- 53 1.12 Nil 0.75 0.87 10.12 1.87 0.62 1313.75 1.87 0.25 6.0
BG- 54 2.50 3.00 1.00 3.37 2.62 2.25 1.12 1451.25 4.37 0.12 6.0
BG- 55 4.62 4.00 0.12 0.87 6.75 1.75 Nil 587.50 3.62 0.25 6.0
BG- 56 4.75 Nil 0.37 5.50 10.37 3.50 Nil 937.50 2.87 Nil 5.0
BG- 57 5.25 1.50 2.50 6.62 1.50 0.87 0.37 976.50 7.00 0.12 6.0
BG- 58 6.12 1.37 2.87 5.62 6.36 4.12 0.62 1625.00 7.00 0.37 6.0
Total 30.59 27.97 20.21 44.83 85.57 36.35 6.08 15234.100 61.85 2.77 81
Average 2.18 1.99 1.44 3.20 6.11 2.59 0.43 1088.00 4.41 0.19 5.7
Table 6. Enrichment Factors (EF) of Coal Waste Samples
Sample ID
Enrichment Factors (EF)
Cd Cr Cu Mn Ni Pb Co Fe Zn As
D- 12 Nil Nil Nil Nil Nil Nil 16.05 0.99 0.46 12.30
D- 13 Nil Nil Nil 1.37 15.81 28.27 34.35 0.99 3.48 0.00
D- 14 221.30 2.19 25.88 0.64 Nil 49.18 Nil 1.00 0.07 0.00
D- 15 190.50 2.73 Nil 0.63 35.97 30.64 5.71 0.99 0.09 26.97
D- 16 110.21 1.31 28.34 1.14 1.73 44.15 30.61 0.99 2.12 9.79
D- 17 123.29 1.61 6.22 Nil 17.09 18.34 1.68 0.99 1.86 6.45
D- 19 19.15 1.12 Nil 0.42 7.69 20.61 8.54 0.99 1.05 22.37
D- 20 309.29 3.17 13.21 0.21 6.29 55.02 53.53 0.99 5.43 13.70
D- 21 500.10 4.64 Nil 0.45 48.76 75.77 14.66 0.99 5.78 0.00
D- 22 99.17 1.80 Nil Nil 16.00 56.25 17.46 1.00 2.24 0.00
Total 1680.81 22.35 73.65 5.29 149.42 414.88 196.06 10.92 22.65 113.14
Table 7. Enrichment Factors (EF) of Soil Samples (Onyeama Mine Area)
Sample ID
Enrichment Factors (EF)
Cd Cr Cu Mn Ni Pb Co Fe Zn As
D- 23 126.99 3.09 12.87 0.41 17.81 88.48 10.42 0.99 4.32 0.00
D- 24 220.33 2.19 12.24 1.22 11.74 38.93 9.91 0.99 0.99 12.69
D- 25 35.81 0.06 0.02 0.19 3.64 6.97 4.97 0.99 Nil 6.14
D- 26 333.39 2.89 48.40 0.52 35.44 47.52 1.47 0.99 0.06 0.00
D- 27 241.60 3.47 Nil 0.17 Nil 31.08 21.36 0.99 4.13 16.41
D- 28 133.24 2.48 5.93 0.78 Nil 8.73 0.76 0.99 1.99 12.81
D- 29 193.25 2.74 15.33 0.37 Nil 26.20 20.70 0.99 0.05 15.90
D- 30 148.20 0.61 1.79 0.00 14.48 10.10 0.33 0.99 11.48 5.56
D- 31 304.42 0.57 4.95 0.02 27.93 31.34 0.57 0.99 13.30 8.91
D- 32 334.72 0.86 0.67 0.01 9.04 26.32 0.47 0.99 1.37 3.47
D- 33 153.94 1.35 13.12 0.04 18.58 24.39 0.55 0.99 18.95 8.60
D- 34 191.58 0.39 3.11 0.02 5.31 20.17 0.39 0.99 4.46 2.94
D- 35 177.91 0.79 1.12 0.01 16.54 22.84 5.70 1.00 5.50 0.00
D- 36 165.76 0.56 1.88 0.01 7.23 10.43 0.33 0.99 10.80 2.44
D- 37 101.29 1.72 7.60 0.01 1.35 31.59 0.89 0.99 11.91 0.00
D- 38 189.28 2.47 7.55 0.00 7.90 48.97 0.69 0.99 5.70 5.59
D- 39 15.53 0.55 1.93 0.01 11.45 14.82 0.27 0.99 5.33 4.66
D- 40 72.39 0.75 3.78 0.00 9.41 8.12 0.63 1.00 1.77 2.45
D- 41 79.75 2.83 2.33 0.01 7.87 19.80 0.33 0.99 3.02 5.63
D- 42 191.66 2.58 1.42 0.00 3.41 12.68 0.37 0.99 3.02 5.63
D- 43 490.49 2.41 14.22 0.00 22.77 17.40 0.61 0.99 12.08 15.15
TOTAL 3953.29 34.55 163.59 3.80 232.10 614.90 82.31 21.80 133.51 147.62
Average 179.09 1.57 7.43 0.17 10.55 27.95 3.74 0.99 6.06 6.91
Table 8. Enrichment Factors (EF) of Background Soil Samples
Sample ID
Enrichment Factors(EF) of Metals
Cd Cr Cu Mn Ni Pb Co Fe Zn As
BG- 45 9.95 1.41 5.97 0.51 1.02 27.51 1.00 0.99 7.00 8.07
BG- 46 22.47 2.28 2.49 0.54 1.65 19.15 2.61 0.99 6.06 6.02
BG- 47 32.13 0.93 1.36 ND 11.97 14.17 1.10 0.99 2.16 2.85
BG- 48 28.45 ND 7.90 0.22 6.38 7.08 0.71 0.99 2.76 1.95
BG- 49 NB 1.53 1.83 ND 10.64 11.67 2.48 0.99 ND 5.71
BG- 50 5.17 1.72 5.17 0.03 11.70 2.82 1.14 0.99 4.31 9.19
BG-51 24.81 0.85 7.16 0.06 1.52 30.55 ND 0.99 8.61 15.30
BG-52 21.01 ND 0.25 0.07 3.81 24.31 1.04 0.99 3.12 ND
BG-53 19.04 ND 1.41 0.04 8.74 8.67 1.58 0.99 1.32 5.10
BG- 54 38.50 1.02 1.71 0.15 2.05 9.45 2.58 0.99 2.80 2.21
BG- 55 175.86 3.38 0.50 0.09 13.06 18.16 ND 0.99 5.74 11.42
BG- 56 113.20 ND 0.97 0.39 12.56 22.75 ND 0.99 2.85 ND
BG- 57 120.22 0.76 6.36 0.45 1.74 5.43 1.27 0.99 6.67 3.29
BGS- 58 84.04 0.41 4.37 0.23 4.44 15.43 1.27 0.99 4.00 6.09
Total 694.85 14.29 47.45 2.74 91.28 217.15 16.78 13.86 54.41 77.20
Average 49.63 1.02 3.38 0.19 6.52 15.51 1.19 0.99 3.88 5.51
Table 9. Pollution Index (Pi) of Metals in Coal Waste Samples
Sample ID
Pollution Index (Pi) of Metals
Cd Cr Cu Mn Ni Pb Co Fe Zn As
D- 12 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04
D- 13 0.00 0.00 0.00 0.00 0.03 0.05 0.06 0.00 0.00 0.00
D- 14 59.37 0.01 0.18 0.00 0.00 0.35 0.00 0.00 0.00 0.00
D- 16 20.25 0.00 0.13 0.00 0.00 0.21 0.15 0.00 0.00 0.04
D- 17 34.37 0.01 0.04 0.00 0.12 0.13 0.01 0.00 0.01 0.04
D- 18 18.75 0.01 0.00 0.00 0.00 0.17 0.06 0.00 0.00 0.10
D- 19 4.75 0.00 0.00 0.00 0.05 0.13 0.05 0.00 0.00 0.14
D- 20 40.62 0.01 0.04 0.00 0.00 0.19 0.18 0.00 0.01 0.04
D- 21 56.25 0.01 0.00 0.00 0.14 0.22 0.04 0.00 0.01 0.00
D- 22 23.50 0.00 0.00 0.00 0.07 0.26 0.08 0.00 0.00 0.00
Total 234.36 0.06 0.39 0.00 0.54 1.82 0.75 0.00 0.03 0.50
Average 25.85 0.00 0.03 0.00 0.04 0.16 0.06 0.00 0.00 0.04
Table 10. Pollution Index of Metals in Soil Samples (Onyeama Mine Area)
Sample
ID
Pollution Index (Pi) of Metals
Cd Cr Cu Mn Ni Pb Co Fe Zn As
D- 23 17.12 0.01 0.04 0.00 0.06 0.31 0.03 0.00 0.01 0.00
D- 24 31.25 0.00 0.04 0.00 0.04 0.14 0.03 0.00 0.00 0.06
D- 25 21.87 0.00 0.18 0.00 0.05 0.11 0.08 0.01 0.00 0.10
D- 26 35.87 0.00 0.13 0.00 0.10 0.13 0.01 0.00 0.01 0.00
D- 27 26.50 0.01 0.00 0.00 0.00 0.09 0.06 0.00 0.01 0.04
D- 28 39.00 0.01 0.04 0.00 0.00 0.06 0.00 0.00 0.01 0.10
D- 29 21.87 0.00 0.04 0.00 0.00 0.07 0.06 0.00 0.00 0.04
D- 30 100.00 0.00 0.03 0.00 0.26 0.18 0.00 0.00 0.20 0.10
D- 31 128.12 0.00 0.05 0.00 0.31 0.35 0.00 0.00 0.14 0.10
D- 32 173.37 0.01 0.00 0.00 0.12 0.36 0.00 0.00 0.01 0.04
D- 33 67.12 0.01 0.15 0.00 0.20 0.28 0.00 0.00 0.22 0.10
D- 34 117.12 0.00 0.05 0.00 0.08 0.32 0.00 0.01 0.07 0.04
D- 35 109.37 0.00 0.01 0.00 0.27 0.37 0.09 0.01 0.09 0.00
D- 36 121.87 0.00 0.03 0.00 0.14 0.20 0.00 0.01 0.21 0.04
D- 37 53.12 0.02 0.10 0.00 0.01 0.37 0.01 0.01 0.16 0.00
D- 38 60.87 0.02 0.06 0.00 0.06 0.42 0.00 0.00 0.04 0.04
D- 39 12.50 0.01 0.04 0.00 0.24 0.31 0.00 0.02 0.11 0.10
D- 41 64.00 0.01 0.04 0.00 0.13 0.35 0.00 0.01 0.05 0.10
D- 42 78.12 0.04 0.02 0.00 0.05 0.20 0.00 0.01 0.07 0.04
D- 43 179.62 0.01 0.13 0.00 0.22 0.17 0.00 0.00 0.11 0.14
D- 44 18.75 0.02 0.03 0.00 0.00 0.05 0.00 0.00 0.11 0.14
Total 1530.55 0.19 1.28 0.00 2’52 4.99 0.38 0.10 1.66 1.36
Average 69.57 0.00 0.05 0.00 0.11 0.22 0.01 0.00 0.07 0.06
Table 11. Pollution Index (Pi) of Metals in Background Soil Samples
Sample ID
Pollution Index (Pi) of Metals
Cd Cr Cu Mn Ni Pb Co Fe Zn As
BG- 45 4.62 0.01 0.07 0.00 0.01 0.34 0.01 0.01 0.08 0.10
BG- 46 14.00 0.03 0.04 0.00 0.02 0.31 0.04 0.01 0.10 0.10
BG- 47 20.00 0.01 0.02 0.01 0.20 0.23 0.01 0.01 0.03 0.04
BG- 48 18.75 0.00 0.13 0.00 0.11 0.12 0.01 0.01 0.04 0.04
BG- 49 0.00 0.02 0.03 0.01 0.18 0.20 0.04 0.01 0.00 0.10
BG- 50 3.12 0.02 0.08 0.01 0.18 0.04 0.01 0.01 0.06 0.14
BG- 51 9.00 0.00 0.06 0.00 0.01 0.29 0.00 0.00 0.08 0.14
BG- 52 14.00 0.00 0.00 0.00 0.06 0.43 0.01 0.01 0.05 0.00
BG- 53 14.00 0.00 0.02 0.01 0.17 0.17 0.03 0.01 0.02 0.10
BG- 54 31.25 0.02 0.03 0.00 0.04 0.20 0.05 0.01 0.06 0.04
BG- 55 57.75 0.02 0.00 0.00 0.11 0.15 0.00 0.00 0.05 0.10
BG- 56 59.37 0.00 0.01 0.01 0.17 0.31 0.00 0.01 0.03 0.00
BG- 57 65.62 0.01 0.09 0.00 0.02 0.07 0.01 0.01 0.03 0.04
BG- 58 76.50 0.01 0.10 0.00 0.10 0.37 0.03 0.02 0.09 0.14
Total 138.23 0.15 0.79 0.05 1.38 3.23 0.25 0.13 0.72 1.08
Average 27.73 0.01 0.03 0.00 0.09 0.14 0.01 0.00 0.05 0.07
Table 12. Compared EF, Pi and HRL of Coal waste, Soil and Background soil media
Media Cd Cr Cu Mn Ni Pb Co Fe Zn As
Coal Waste
EF 137.7 1.9 16.9 0.04 19.1 28.0 13. 0.9 1.99 14.9
Pi 28.19 0.00 0.05 0.00 0.06 0.17 0.0 0.0 0.00 0.05
HRL 5 2 3 0 3 4 3 0 2 3
Soil
EF 179.0 2.57 7.43 0.17 10.5 27.9 3.7 0.9 6.6 6.9
Pi 72.9 0.01 0.06 0.00 0.19 0.37 0.0 0.0 0.0 0.07
HRL 5 2 3 0 3 4 2 0 3 3
Back-ground
Soil
EF
Pi 49.63 1.02 3.38 0.19 6.52 15.5 1.1 0.9 3.88 5.51
HRL 5 1 2 0 3 3 1 0 2 3
HRL means Health Risk Level
4
Discussion
4.1 Characteristics of Water Medium
Determined trace metal concentrations for Water samples are shown in Table 2. It is seen from these data that the concentration trend of metals in water medium follows the order: Fe > Ni > Zn > Pb > Cd > Co > Cr > Cu > Mn > As. The concentration of toxic elements such as Mn (0.01 – 0.50 mg/l) with average of 0.09 mg/l, Pb (0.01 – 6.30 mg/l) with average of 0.53 mg/l, Cr (0.02 – 0.80 mg/l) with average 0.09 mg/l, Cd (0.16 – 0.56 mg/l) with average 0.34 mg/l and As (< 0.01 – 0.10 mg/l) with 0.05 average are high (Table 2) compared with WHO (2011) permissible limits. According to Gurdeep (2006), toxic metals such as cadmium, arsenic and lead are more soluble at low pH (Table 2) as a result of secondary reactions between iron sulphate compounds in nearby clays and shales. Obtained results indicate that cadmium, copper and arsenic, in some locations (Table 2) are below detection limits. However, high arsenic (As) value 0.10 mg/l is in excess of its normal load and thus demands special attention. In a situation like this, Huttan (1987) noted that high Arsenic (As) has an effect on the liver by causing a disease called cirrhosis. In Chile and Taiwan, 0.2 mg/l arsenic in drinking water and taken for a long time has been calculated as threshold for skin cancer (Finkelman, 1999).
Mean values of Pb (0.05 mg/l), Zn (0.88 mg/l), Cd (0.34 mg/l), As (0.05 mg/l) and Ni (0.64mg/l) as shown in Table 2 are at significant levels and exceed public health standards. Trace metals at these levels in drinking water, according Huttan (1987) are highly toxic and undesirable, do not support aquatic life, destroy mining equipment and result in land damage which poses environmental problems.
4.2 Characteristics of Coal Waste Medium
Coal waste dumps piled at their present locations, present ugly sites and wastage of useful lands meant for agriculture. In their present form, the piles have destroyed approximately 17,110 square meters of arable land. Also, due to large areas these dumps occupy; wind blows particulate matter contents from them, into the atmosphere. Again, due to high unrecovered coal content of these coal waste dumps, they are subject to high risk of combustion, particularly during the harmattan periods. According to Edwards (1981), coal dumps piled in the open air as found in these Onyeama mined areas, change much during the process of weathering and rain leaching. That the changed condition may turn the reducing environment into oxidized one. Thus, a lot of hazardous wastes can enter the farmland, surface and ground water body causing severe threat to life of the local people and live stocks.
Coal waste dumps are known to contain diverse amounts of trace elements in their overall composition (Thomas, 1992). Heavy metal concentrations of the coal waste dumps is presented in Table 3. L
It is seen that coal waste dumps are characterized by elevated concentrations of Cadmium, Nickel, Iron and Manganese. The elemental concentration sequence in coal waste dumps follows the order: Fe > Ni > Cu > Mn > Cd > Pb > Co > Cr > Zn >As (Table 3) Concentrations of Cd (< 0.38 – 4.50mg/kg) with average 2.52 mg/kg, Ni (< 0.13 – 8.63 mg/kg) with average 4.23 mg/kg, Mn (< 0.75 – 5.62 mg/kg) with average 3.26 mg/kg, Fe (133.75 – 498.75 mg/kg) and average 313.97mg/kg and Cu (< 1.25 – 3.75 mg/kg) averaging 2.81 mg/kg (Table 3) are considered limited when compared with established standards. However, studies have shown that special attention should be paid if some of these ions are in coal mine drainage due to their high toxicity (Huttan, 1987).
contaminates surface and underground water resources. It implies that coal mining dumps can be a long term source of groundwater contamination, lasting for decades and increasing with time. This probability is quite high, since Ekulu River that truncates the study areas may have been contaminated by Cd, Cr, Mn and Ni toxic elements.
Cu was not detected in many coal waste dump samples (Table 3). In sites Cu was detected, the range is < 1.25 – 3.75 mg/kg) with average 2.81 mg/kg. Cu contamination is not considered significant within the coal waste dumps.
Enrichment factors (EF) of coal waste dump samples is presented in Table 6.The (EF) trend in descending order is Cd > Pb > Ni > Cu > As > Co> Zn > Cr > Fe > Mn. Calculated Pollution Index of Coal waste samples is shown in Table 9.The avareage values of Cr, Mn, Fe and Zn shows 0. 00 pollution level. It implies thy had no effet on the environment.Those of Ni, Co, As and Cu indicated intermediate level of comtamination.Only Pb and Cd showed high level of contamination. The table 12 indicates high level of pollution by Cd and Pb with health risk level (HRL) of 5 and 4 respectively. Ni, Cu, Co and As moderately contaminated the environment with HRL of 3. Cr and Zn show low level of pollution with HRL of 2. Fe and Mn indicate minimal level with HRL of 1.
4.3 Characteristics of Soil Medium
Heavy metal pollution in soils depends largely on human activities on the earth surface. Pollution in soils is a widely documented problem by soil scientists. In Nigeria, many researchers have recorded high levels of heavy metal ions in the soils, rivers and ground water in different areas according to (Njoku and Onyeka, 2007) and (Nwajei and Iwegbu, 2007). In order to interpret the level of pollution of metals in soils, only their concentration values are considered (Xie et al, 2005).
4.4 Characteristics of Background Soil Medium
Fifteen (14) background control soil samples were collected at distances between ten and fifteen kilometers away from areas of mining activities. The samples were believed not contaminated as a result of coal mining. Table 5 shows concentrations (mg/kg) of metals determined from the background soil samples. Table 5 shows Cd (< 0.37-6.12 mg/kg), Cr (< 1.12 - 5.12 mg/kg), Cu (0.12-3.75 mg/kg), Mn (< 0.50 – 6.62 g/kg), Ni (0.75 -11.87 mg/kg), Pb (0.50 - 4.75 mg/kg), Zn (< 1.87-7.25 mg/kg), Co (< 0.25-1.12mg/kg), As (< 0.12 – 0.37 mg/kg) and Fe (587.50 – 1625.00 mg/kg). The concentration sequence in descending order is: Fe > Ni > Zn > Mn > Pb > Cd > Cr > Cu > Co>As. The average values of these metals (Table 5 ) are, Cd (2.18 mg/kg), Cr (1.19 mg/kg), Cu (1.44 mg/kg), Mn (3.20 mg/kg), Ni (6.11 mg/kg), Pb (2.59 mg/kg), Zn (4.41 mg/kg), Co (0.43 mg/kg), As (0.19 mg/kg) and Fe (1088.00 mg/kg).
Chromium, Manganese, Cobalt and Arsenic were below detectable limits in some locations. Average concentrations of these metals, Cr (1.99 mg/kg), Mn (3.20 mg/kg), Co (0.43 mg/kg) and As (0.19 mg/kg), table 5 were very low when compared with established limits of Rudnick and Gao (2003), Shacklette and Boerngen (1979) and Bowen (1979). They therefore pose no risk to health and the environment.
Soil pH ranged from 5.0- 6.0 and averaged 5.7 Table 5.
Table 8 shows the enrichment factors (EF) in background soil and thre table also indicates the enrichment trend of the metals in this order: Cd > Pb > Ni > As > Zn > Cu > Cr > Fe> Co > Mn. Tables 11 and 12 show that Fe, and Mn have zero health risk levels (HRL) and indicate pollution condition as absent according to (Liao and Chao, 2006). Cobalt and Chromium, each has HRL of 2 and this indicates low level pollution condition. Nickel, Arsenic, Zinc and Copper are at intermediate levels of pollution with HRL of 3. Cadmium and Lead show respective HRL of 5 and 3.Their pollution level is considered high.
5
Conculsions
environment with HRL of 3 while Cr and Zn had low effect with HRL of 2. Fe and Mn indicated minimal level effect with HRL of 1. (iv) Compared pollution index results of the studied media (water, soil and coal wastes) with the background (control) soil medium, contamination levels indicated as follows: In water medium, Cd (heavy),Pb (high),Co (intermediate), Cr (low) Cu (unpolluted), Mn (unpolluted) and As (unpolluted). In coal waste medium, Cd (heavy),Pb (high) Cr (low), Cu (intermediate), Mn (unpolluted), Co (intermediate) and As (intermediate). In soil medium, Cd (heavy), Cr (low), Cu (intermediate), Mn (unpolluted), Co (low) and As (intermediate).In background soil medium, Cd (heavy), Cr (low), Cu (low), Mn (unpolluted), Co (low) and As (intermediate). Interpretation of all the field and geochemical data revealed that Onyeama coal mining exhibited characteristics that moderately affect the environment and therefore, there is health safety risk. Detected heavy metal pollutants had negative impacts on the geological, ecological, agricultural, surface and underground water conditions of the studied area.
6
Recommendation
Initial planning and workable design of operations are very vital to minimizing pollution associated with coal mining activities. It follows therefore; before mining begins, a mining plan, mine closure and restoration plans must be prepared and approved by scheduled authority. These plans should clearly define the sequence, nature of extraction and management of waste matters. The plans should be updated regularly (5 – 8 years) as mining progresses. Restoration plan has been applied already in the United States of America and the United Kingdom. The result in these places shows that it is a good way to minimize environmental disturbances after mining activity might have ceased. It is further recommended that the coal waste dumps be compacted to promote stability, limit the amount of oxygen in the piles which can lead to combustion. Compaction can also limit the amount of rain water infiltration and precipitation that seep into the piles which increase leaching of metals into the surface and ground water.
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