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Potential heavy metal pollution of soil and water resources from artisanal mining in Kokoteasua, Ghana
Groundwater for Sustainable Development 8 (2019) 450–456
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Research paper
Potential heavy metal pollution of soil and water resources from artisanal mining in Kokoteasua, Ghana
T
Ebenezer Gyamfia,∗, Emmanuel Kwame Appiah-Adjeia,b, Kwaku Amaning Adjeia a b
Regional Water and Environmental Sanitation Centre, Civil Engineering Department Kwame Nkrumah University of Science and Technology, Kumasi, Ghana Geological Engineering Department, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
A R T I C LE I N FO
A B S T R A C T
Keywords: Groundwater Artisanal mining Heavy metals Pollution indices Ghana
Effluents and mine waste from artisanal mining in Kokoteasua, a community in Ghana, are discharged directly to the environment without prior treatment and have the potential of polluting the soil and water resources that the populace rely on for their daily water need. Therefore, this study has assessed the impact of the artisanal mining activities on the soil and water resources in the community. The method employed involved mapping the water supply points in the community and sampling the water supply points and the soil (at 20 cm and 40 cm depths) to determine their heavy metal levels (i.e. Fe, Pb, Zn, As, Mn, Cu, and Hg). The water quality was assessed using the World Health Organisation (WHO) guideline values for drinking water while pollution indices were used to evaluate the levels of soil pollution. The results, generally, indicated that groundwater in the community is potable but unsuitable for drinking in isolated locations due to high levels of As and Zn. The stream, however, recorded high levels of Mn, Fe, and pH above the acceptable WHO drinking water guidelines. Again, the study found the soil to be extremely polluted with all the measured heavy metals (except Hg) from contamination factor, enrichment factor, geo-accumulation index and pollution load index assessments. Thus, the artisanal mining needs to be regulated to protect the water resource and soil from further pollution.
1. Introduction Groundwater constitutes about 97% of the available freshwater on earth and forms an important component of the water cycle (Delluer, 1999). It serves as a source of potable water for agriculture, industry and domestic use as well as in helping to maintain soil moisture, wetlands and stream flows in many parts of the world (Oladeji et al., 2012). Qiu (2010) estimated that groundwater constitutes about 70% and 40% of the total water resources used respectively for domestic and irrigation purposes in China. Nickson et al. (2005) also estimated that about one-third of global population depend on groundwater as their source of potable water. In Ghana, groundwater serves as the main source of sustainable water supply for the populace living in rural communities and emerging communities in the urban areas (Duah and Xu, 2006). Groundwater of good quality is very important to these communities because it is their main source of potable water for drinking and domestic purposes. Commonly, anthropogenic activities such as farming, indiscriminate waste disposal and mining among others significantly influence groundwater quality either directly or indirectly (Teaf et al., 2006). For instance, mining activities generate waste such as waste rock, tailings
∗
and effluents at the various stages of processing the ore, which have the potential to leach through the soil into aquifers and directly pollute groundwater (Johnson and Hallberg, 2005). A typical pollution of groundwater from effluents of mine waste is reported by Obiadi et al. (2016) at a coal mine in the Enugu area of Nigeria, which contaminated surface water and shallow groundwater with high levels of acidity, iron, and sulphate. Studies by Mallo (2011) also found that effluents from mines usually have very low pH, which causes acid mine drainage and ends up in water bodies including groundwater. Oladipo et al. (2014), similarly, found evidence of heavy metal contamination of groundwater as a result of illegal mining activities in Zamfara State, Nigeria. Ghana is known to be one of the major gold producers globally, and the mining sector is believed to contribute significantly to the gross foreign earnings of the country. Artisanal gold mining has been on the increase in the country and it is said to be a major contributor of metals in water resources due to indiscriminate use of Mercury (Hg) and other harmful chemicals in the mining activities (Donkor et al., 2006). Globally, small-scale mining is noted to be a major contributor to the pollution of water resources because it makes use of huge volumes of water thereby polluting the water resources (Cunningham et al., 2005; Owens et al., 2005). Most artisanal mining operators have no
Corresponding author. E-mail address: gyamfi[email protected] (E. Gyamfi).
https://doi.org/10.1016/j.gsd.2019.01.007 Received 26 July 2018; Received in revised form 24 December 2018; Accepted 21 January 2019 Available online 02 February 2019 2352-801X/ © 2019 Elsevier B.V. All rights reserved.
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pyroclastic rocks, which are also associated with the hornblende-rich ‘belt-type’ Granitoid (Kesse, 1985; Nude et al., 2012). High-sulphide type Gold mineralization constitutes the gold ore in the area while pyrites and arsenopyrites are the pathfinders (Osae et al., 1995). The mineralization has Fe, As, Pd, Sb, Cu, Zn, S and Au as the key geochemical signatures, and are used to classify the ore (Oberthu et al., 1994). Gold mineralization in the area is structurally controlled.
concession of their own and, thus, operates illegally. Therefore, their operations are naturally furtive and clandestine, thereby operating uncontrollably within the concessions of large-scale mining companies or in areas that are prohibited from mining such as around forest reserves, water bodies or environmentally sensitive areas (Appiah, 1998). As a result, their operations are often not regulated leading to the use of unsafe chemicals in extracting the gold. These chemicals are usually discharged uncontrollably into the ecosystem (Meech et al., 1998) and leads to contamination of the environment. Several methods have been used to analyze the quality of soil and water at places with significant mining activities. Awadh (2013) used the geo-accumulation (Igeo) index to assess soil contamination in such an area by comparing the heavy metal concentrations to their crustal levels and found that the concentrations in the soil were above the crustal levels; thus, signifying that the soil has been contaminated. Likuku et al. (2013), on the other hand, used enrichment factor, pollution load index, the degree of contamination and geo-accumulation index to evaluate heavy metal concentration in the soils. Again, Boateng et al. (2012) used geo-accumulation index, pollution load index and contamination factor to assess the geochemical impact on the soil quality of a reclaimed tailings dam. In analysing the water quality in such environments, the World Health Organisation (WHO) guidelines for assessing suitability of drinking water (WHO, 2011) are commonly utilised. For instance, Oladipo et al. (2014) analysed the concentration of heavy metals in groundwater at Zamfara State, Nigeria, by comparing the measured parameters in the groundwater samples with the WHO guideline values and water quality standards from the Federal Environmental Protection Agency, Nigeria (1998). Similarly, Abdul-Rahaman et al. (2014) analysed possible groundwater contamination in a mining community in Ghana by determining the concentration of heavy metals in the water and comparing them with the WHO guideline values for drinking water. In recent times, artisanal mining has been on the rise in Kokoteasua, a community within the Obuasi Municipality in Ghana. Unfortunately, the waste rock, tailings and effluents from the mining activities are directly discharged into the environment and stream in the area. These have the potential of polluting the surface water and shallow aquifers that the populace relies on as their main source of water supply and, thus, pose a serious threat to their health if not curbed. Therefore, this study aims to assess the effect of artisanal mining on the quality of soil and water resources in a typical artisanal community using Kokoteasua as a case study.
2.2. Mapping and sampling Water supply points in the community including boreholes, handdug wells, springs, and stream were mapped with the aid of a Geographic Position System (GPS). These supply points were plotted on the topographic map of the area and further used in creating a buffer map to show the number of supply points within 100 m, 200 m, 300 m and beyond 400 m radius from the active mining area based on government regulation on minimum required distance from active mining to water points. The drainage map was also used to determine the flow direction and its linkage to the mineral processing sites where effluents are discharged directly to the stream; it as well aided in planning the sampling points for the study shown in Fig. 1. The samples were taken at the upstream, downstream and close to the active mining and processing zones in the study area to evaluate the quality of the water resources and soil around the active mining and processing areas where effluents are directly discharged to the environment. The samples upstream were mainly to serve as control points. In total, fourteen (14) water samples were taken within the study area from fourteen (14) sampling points on two occasions; i.e. in April (prior to the rainy season) and November (after rainy season). The sampling points included six (6) from boreholes, two (2) from hand-dug wells, two (2) from springs, one (1) from a pit at the artisanal mining site where groundwater is pumped out and three (3) from the stream. The water samples were acidified with nitric acid (HNO3) to keep it in oxidation state and set the pH of both the samples and standards equal. The sampling, storage and transportation of the water to the laboratory were done following standard protocols (APHA, 1995) to ensure consistency and data quality. In addition, twenty (20) soil samples were taken from ten (10) different locations at depths of 20 cm and 40 cm with the aid of a hand augur for the study (Fig. 1). These soil samples were put in plastic bags and sent to the laboratory for measurement of their heavy metal concentrations. 2.3. Laboratory analysis and pollution indices
2. Methodology In drinking water quality assessments, priority is usually given to parameters which are known to be of concern to human health and potability when present in significant concentrations in the water source (Ponsadailakshmi et al., 2018). Therefore, heavy metals (i.e. Fe, Pb, Zn, As, Cu, Mn, and Hg) in both the water and soil samples were measured in the laboratory using the ICP-OES analyzer following standard procedures (McComb et al., 2014). The ICP was first initialized and the plasma allowed to stabilize for 15 min. Tuning was then done to determine if the ICP is in good condition to start analysing samples. To achieve this, the tuning solution was first analysed and the intensities observed by the instruments were monitored against the expected intensities of the tuning solution. The instrument was tuned using a 10 ppb solution, which contains Li, Pb, Tl, and Y. The instrument was calibrated before analysing the samples with a blank and appropriate calibration standard. Calibration standards of 1, 10, 50 and 100 ppb were used to calibrate the instrument and only R2 above 0.999 was accepted. The calibration was verified with a 10 ppb and 50 ppb standard followed by the analysis of the samples with appropriate internal standard (i.e. Sc, Ge, In, Rh, Tb, Lu and Ir). The measured concentration of the heavy metals in the water samples were compared with the WHO guideline values for drinking water (WHO, 2011). However, pollution indices such as the
2.1. Study area description Kokoteasua (KTS), shown in Fig. 1, is a suburb of Obuasi Municipality and is located in the southern part of Ashanti Region of Ghana at about 64 km from Kumasi. The municipality is bounded to the east by the Adansi South District, west by Amansie Central District, north by the Adansi North District and south by Upper Denkyira District of Central Region (Bempah et al., 2013). It is, precisely, located within latitudes 1°39′54″ to 1°40′18″ W and longitudes 6°12′54″ to 6°12′34″ N. The topography of the area is gently undulating to hilly. Annual rainfall in the area ranges from 1250 mm to 1750 mm whereas the mean annual temperature is 25.5 °C with relative humidity peaking between 75% and 80% (Boateng et al., 2012). The area is underlained by meta-sedimentary and meta-volcanic rocks of the Birimian formation (Kesse, 1985; Nude et al., 2012). The meta-sedimentary rocks occupy the north-western half of the area and comprise low-grade metamorphosed rocks that are associated with mica-rich ‘basin’ type Granitoid (Kesse, 1985; Nude et al., 2011). The meta-volcanic group is separated from the meta-sedimentary group by the main Obuasi mineralized shear zone and is dominated by basalts intercalated with 451
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Fig. 1. The Kokoteasua area in Ghana with the study sampling points.
Contamination factor (CF), Enrichment Factor (EF), Geo-accumulation index (Igeo) and Pollution Load Index (PLI) were used to evaluate the metal pollution of the heavy metal concentrations in the soil. These indices helped in assessing the presence and intensities of anthropogenic contaminants in the surface soil. The contamination factor (CF), as expressed in equation (1), is the ratio of the measured concentration of an element to the background concentration of that same element, and represents the individual impact of each trace metal on the sediments (Olatunji et al., 2009). It was used to evalute the level of contamination of the measured parameters in the soil. Mathematically, the CF is expressed as:
CF =
Cm Cb
Table 1 Classes of pollution indices on (a) CF (b) EF and (c) Igeo.
(1)
where Cm is the measured concentration of the element and Cb is the background concentration of that same element. The Martin and Meybeck classification (shown in Table 1a) was used to classify the degree of heavy metal contamination of the soil. The enrichment factor (EF), which is also used to evaluate the anthropogenic effect on the soil by computing the difference between metals from anthropogenic source and that of a geogenic source (BuatMenard and Chesselet, 1979; Ismaeel and Kusag, 2012), was used to evaluate how the soil is enriched with the measured parameters. In computing the EF, Al was used as a reference element to standardize the heavy metal concentration (Taylor, 1964). Mathematically, EF is computed using the relation in equation (2):
EF =
Cm Cmref / Cb Cbref
Class
EF Values
Soil Quality
0 1 2 3 6
<2 2–5 5–20 20–40 > 40
Depletion to minimal enrichment Moderate enrichment Significant enrichment Very high enrichment Extremely high enrichment
Class
Igeo Value
Soil Quality
0 1 2 3 4 5 6
<0 0–1 1–2 2–3 3–4 4–5 >5
Unpolluted Unpolluted to moderately polluted Moderately polluted Moderately to heavily polluted Heavily polluted Heavily to extremely polluted Extremely polluted
CF
Contamination Levels
Cf < 1 1 ≤ Cf < 3 3 < Cf < 6 Cf > 6
Low contamination Moderate contamination Considerate contamination Very high contamination
heavy metal contamination in sediments by comparing the present concentration with previous times when there were little or no industrial activities. It was computed as:
Igeo = log 2
(2)
Cn 1.5Bn
(3) −1
Where Cm is the measured concentration of the element and Cb is background concentration of the measured element. Cmref is the measured concentration of the reference element while Cbref is the background concentration of the reference element. The Buat-Menard and Chesselet (1979) classification shown in Table 1b was used to classify the level of enrichment of the soil. Geo-accumulation index (Igeo), as expressed in equation (3) was further used to characterize the
where Cn is the measured concentration in mg kg of the metal and Bn is the geochemical background value of the metal in mg kg−1. Due to the conceivable variations in the background values, the factor 1.5 was used for small anthropogenic impact on a given metal in the environment. Muller's classification shown in Table 1c was used to classify the pollution of the soil based on the computed Igeo values. The pollution load index (PLI) was also used in this study to 452
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gold from the concentrated ore in the area. This may be because the Hg is scooped for reuse several times, by the miners, till it is used up before the effluents are discharged to the environment. Fig. 3(a) shows the computed Igeo values and indicate that, based on Muller (1969), the soil is extremely polluted with all the analysed heavy metals since all the Igeo values were greater than 5. The computed EF (Fig. 3(b)) also showed that the soil is moderately enriched with Mn, significantly enriched with Cu, Fe, and Zn, very highly enriched with Pb and extremely enriched with As based on the BuatMenard and Chesselet (1979) scheme. The high As concentration in the area conform to work done by Nude et al. (2011) in the Obuasi municipality. Again, the As enrichment in soils within 200 m radius is higher as compared to the soils beyond 200 m radius. The CF for Cu, Fe, Mn, and Zn, based on Martin and Meybeck (1979) classification scheme, were low in the soil (Fig. 3(c)) since they were less than 1. However, the soil was moderately and highly contaminated with Pb and As respectively. The high CF values for As conforms to work done by Boateng et al. (2012) in Obuasi area and is due to its association with the ore mined in the study area. Thus, its contamination of the soil could be due its rapid weathering from exposure of the ore to the environment through the mining activities. The As concentration was higher at the depth of 20 cm than the 40 cm depth. Likewise, the CF of the metals were far higher at the depth of 20 cm in comparison to the 40 cm depth. The PLI values for both depths of investigations for all the heavy metals, except As, were below 1 and denotes perfection (Tomlinson et al., 1980). However, the PLI for As in the soil at both the 20 cm and 40 cm depths were above 1 and showed that the soil quality is deteriorated with high levels of As; this seems to be in conformity with studies by Boateng et al. (2012). Generally, the level of pollution of the soil in the study area decreased with depth as well as away from the active mining site.
Table 2 Methods used for analysing the physicochemical parameters. Parameters
Standard Methods
pH Conductivity and Total Dissolved Solids Total Suspended Solids
Probe Method Probe Method Sension 5 (Hach)
Alkalinity Turbidity Colour Fluoride Chloride Sulphide Nitrate Salinity Phosphorus (Total) Sulphate Biochemical Oxygen Demand (BOD)
Photometric Method 8006 (Non-Filterable Residue) Titration Method 2320B Absorptometric Method 8237 (FAU) APHA PlatinumeCobalt Standard Method 8025 4500-F- D SPADNS Method 8029 4500-Cl- B Argentometric Method 4500-S2- F Iodometric Method AOAC Official Method 973.50 2520 B Electrical Conductivity Method 4500-P E. Ascorbic Method 4500-SO42- E. Turbidimetric Method 5210 B 5-Day BOD Test
measure the level of contamination of the soil. The PLI for a single site is the nth root of not less than 5 contamination factors (CF) as expressed in equation (4). The contamination factors represent the individual impact of each trace metal on the sediments. The PLI was computed for the soil at 20 cm and 40 cm depths. Mathematically, the PLI proposed by Tomlinson et al. (1980) is given as: 1
PLI = (CF 1 ∗ CF 2 ∗ CF 3 ∗ ⋯ ∗ CFn )
n
(4)
where, CF = Contamination factors and n = the number of contamination factors and sites respectively. PLI < 1 denotes perfection, PLI = 1 means only baseline levels of pollutants are present and PLI > 1 indicates deterioration of site quality (Tomlinson et al., 1980). On the other hand, Table 2 shows the various standard methods used for analysing the physicochemical parameters.
3.3. Water quality Table 3 shows the physicochemical parameters measured during the two sampling seasons. Generally, all the measured physicochemical parameters (i.e. temperature, true colour, salinity, total hardness, conductivity, TDS, fluoride, nitrate, chloride, sulphate, phosphorus and sulphide) were all within the acceptable WHO guideline values for drinking water except pH, turbidity, total suspended solids (TSS) and alkalinity. Also, there was generally no significant variation in the concentration of the parameters in the November and April periods. The pH ranged from 5.6 to 7.6 in November and 5.8 to 6.9 in April with about 47% and 65%, respectively, of the samples below the lower limit of the permissible guideline values for drinking water (WHO, 2011), which indicates that the water in the community is slightly acidic. This is consistent with the slightly acidic pH of water in mining communities of the country from similar studies (Bhattacharya et al., 2012; Ewusi et al., 2017; Dorleku et al., 2018) and may be due to the release of mine waste and chemicals used in extracting and processing the ore into the environment. Similarly, the turbidity, TSS, and alkalinity values ranged from 0 to 24 mg/l, 100–470 mg/l and 0–25 NTU respectively with about 18%, 53% and 18% respectively of them above the acceptable WHO (2011) guideline values for drinking water. The turbidity issues were mainly associated with the stream water close to the processing site and extreme downstream of the processing site. Table 4 shows the concentration of heavy metals in the water samples in both November and April sampling months. Generally, heavy metals of varying concentrations were detected in the various water samples in the study area, especially in the hand-dug wells and boreholes, but they did not vary significantly over the months. A comparison of the concentration of the heavy metals As, Cu, Pb, and Zn with the WHO (2011) guideline values for drinking water showed most of the metals were below detectable limits (DL). Nonetheless, they could still be present in the water, albeit in very low concentrations,
3. Results and discussions 3.1. Groundwater supply points Overall, six (6) boreholes, two (2) hand-dug wells, two (2) springs, a stream and pumped water from the pits were mapped in the study area as shown on Fig. 2. The water in the community is mainly for drinking and other domestic purposes such as washing and bathing. As shown on Fig. 2, two (2) of the groundwater supply points are located within a 100 m buffer radius from the artisanal mining site whereas five (5) and seven (7) are within the buffer radii of 200 m and 300 m respectively. All the groundwater supply points are, however, within a 400 m radial distance. According to government regulations (MWRWH, 2011), there should be a 100 m minimum buffer distance between a mining activity and a source of drinking water. Thus, the chemicals used in the blasting and processing of the mined ore pose a direct risk to the quality of the four groundwater supply points located within 100 m radius of the mining site. 3.2. Heavy metal pollution of soil The concentrations of the heavy metals Cu, Pb, Zn, Mn, As and Fe in the soil ranged from 10.1 to 36 mg/kg, 6.5–42.5 mg/kg, 16.4–95.8 mg/ kg, 43.0–595.5 mg/kg, 55.2–1200 mg/kg and 6570.9–49,558.1 mg/kg, respectively, and generally decreased with depth. These concentrations were similar to values obtained in the Obuasi area by previous researchers (Antwi-Agyei et al., 2009; Boateng et al., 2012) who investigated the soil up to a depth of 50 cm. Hg, on the other hand, was very low (below the detectable limit of < 0.0001 mg/kg) in the soil although it is the chemical used by the artisanal miners in extracting 453
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Fig. 2. Buffer zones for water supply points to the mining site in the study area.
Fig. 3. Computed (a) Igeo, (b) EF and (c) CF in the soil at 20 cm and 40 cm depths (Note: As values in (b) and (c) are × 102).
Table 3 Chemical parameters for the two sampling seasons. Parameter
pH Cl− HCO3− Na+ K+ PO42SO42Ca2+ Mg2+
NOVEMBER
APRIL
WHO Guideline Values
Min
Max
Mean
SD
% outside W H O Values
Min
Max
Mean
SD
% outside W H O Values
5.6 1.9 65.9 0.1 0.1 0.1 0.1 0.1 0.1
7.6 141 573 573 88.0 6.9 43.0 27.0 17.0
6.5 20.6 312 47.4 10.0 0.9 12.3 5.7 2.9
0.6 31 177 136 21 2.1 14 8.7 4.9
47.1 – – – 23.6 – – – –
5.8 1.7 1.2 1.5 0.3 0.2 0.8 1.8 1.8
6.9 20.7 124 27.2 4.3 0.3 19.8 37.2 16.7
6.4 11.3 63.4 11.0 1.1 0.1 6.1 12.1 4.6
0.4 4.3 40 5.7 0.9 0.1 5.6 11 3.5
64.7 – – – – – – – –
454
6.5–8.5 250 600 200 12 – 250 75 100
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Table 4 Heavy metals concentration (mg/l) in the water samples in both sampling seasons. ID
SP1 SP2 BH1 BH2 BH3 BH4 BH5 BH6 HDW1 HDW2 STS1 STS2 STS3 DL WHO
November
April
As
Cu
Fe
Mn
Pb
Zn
As
Cu
Fe
Mn
Pb
Zn
< 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.06 < 0.05 < 0.05 0.21 0.05 0.01
< 0.02 < 0.02 < 0.02 < 0.02 0.02 < 0.02 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.02 1.0
< 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 0.3 < 0.1 0.15 1.30 4.19 4.02 0.1 0.3
< 0.02 < 0.02 < 0.02 0.05 < 0.02 0.05 0.20 < 0.02 < 0.02 0.21 0.05 5.31 3.48 0.02 0.5
< 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.02 0.01
< 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.06 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.05 0.01
< 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.06 < 0.05 < 0.05 0.06 0.05 0.01
< 0.02 0.03 0.24 0.36 0.06 0.05 0.02 0.08 < 0.02 < 0.02 < 0.02 0.21 0.32 0.02 1.0
< 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 0.23 < 0.1 0.92 0.62 0.98 0.53 0.1 0.3
0.17 0.02 < 0.02 0.13 0.16 0.05 0.02 0.08 0.09 0.06 0.08 0.13 0.19 0.02 0.5
< 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.05 0.03 0.02 0.01
< 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.09 < 0.05 0.11 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.05 0.01
Sanitation Centre, Kumasi for supporting this research through their ACE World Bank Project under Grant Number IDA 54230-GH. The authors also acknowledge the useful comments and suggestions of the anonymous reviewers, which helped to improve the paper.
since the DL were above the permissible limits for drinking water. There were, however, isolated cases where the levels of As, Pb and Zn were above the guidelines for drinking water (WHO, 2011) in locations downstream of the processing site in both sampling months. Similarly, the concentrations of Fe and Mn in the stream were mostly above the acceptable guidelines for drinking (WHO, 2011) and decreased away from the processing site in both November and April. This was not surprising since the water pumped directly from the mine pits into the stream during mining contained extremely high levels of Fe and Mn above the permissible levels for drinking. These two metals are common contaminants of groundwater in mining communities of the country (Bhattacharya et al., 2012; Dorleku et al., 2018) since they are key associations of the gold-bearing rocks mined in the country including the study community. Thus, weathering of the rocks, facilitated by its exposure to the atmosphere through the mining activities, may be releasing the metals to the surface stream. Like in the soil, Hg was not detected, at all, in all the water supply points of the community.
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.gsd.2019.01.007. References Abdul-Rahaman, I., Freeman, L., Ampadu, B., 2014. Investigating soil and water contamination of trace metals in Tarkwa-Nsuaem municipality, Ghana. Int, J. Plant. Soil Sci. 5 (4), 217–226. Antwi-Agyei, P., Hogarh, J.N., Foli, G., 2009. Trace elements contamination of soils around gold mine tailings dams at Obuasi, Ghana. Afr. J. Environ. Sci. Technol. 3 (11), 353–359. APHA, 1995. In: Standard Methods for the Examination of Water and Waste Water, nineteenth ed. American Public Health Association, Washington, DC. Appiah, H., 1998. Organization of small-scale mining activities in Ghana. J. S. Afr. Inst. Min. Metall 98 (7), 307–310. Awadh, S.M., 2013. Assessment of the potential nickel and lead in the road-side dust in the Karkh city along the highway between Ramadi and Rutba, West of Iraq. Merit Res. J. Environ. Sci. Toxicol. 1 (7), 126–135. Bempah, C.K., Ewusi, A., Obiri-Yeboah, S., Mensah, F., Boateng, J., Voigt, H.-J., 2013. Distribution of arsenic and heavy metals from mine tailings dams at Obuasi municipality of Ghana. Am. J. Eng. Res. 2 (5), 61–70. Bhattacharya, P., Sracek, O., Eldvall, B., Asklund, R., Barmen, G., Jacks, G., Koku, J., Gustafsson, J.-E., Singh, N., Brokking Balfors, B., 2012. Hydrogeochemical study on the contamination of water resources in a part of Tarkwa mining area, Western Ghana. J. Afr. Earth Sci. 66–67, 72–84. https://doi.org/10.1016/j.jafrearsci.2012.03. 005. Boateng, E., Dowuona, G.N., Nude, P.M., Foli, G., Gyekye, P., Jafaru, H.M., 2012. Geochemical assessment of the impact of mine tailings reclamation on the quality of soils at AngloGold concession, Obuasi, Ghana. Res. J. Environ. Earth Sci. 4 (4), 466–474. Buat-Menard, P., Chesselet, R., 1979. Variable influence of atmospheric flux on the trace metal chemistry of oceanic suspended matter. Earth Planet. Sci. Lett. 42, 398–411. Cunningham, W.P., Cunningham, M.A., Saigo, B., 2005. Environmental Science: a Global Concern, eighth ed. McGraw-Hill, Boston. Delluer, J., 1999. The Handbook of Groundwater Hydrology. CRC Press LLC, London. Donkor, A.K., Nartey, V.K., Bonzongo, J.L., Adotey, D.K., 2006. Artisanal mining of gold with mercury in Ghana. West Afr. J. Appl. Ecol. 9, 2–18. Dorleku, M.K., Nukpezah, D., Carboo, D., 2018. Effects of small-scale mining on heavy metal levels in groundwater in the Lower Pra Basin of Ghana. Appl. Water Sci. 8, 126. https://doi.org/10.1007/s13201-018-0773-z. Duah, A.A., 2006. Groundwater contamination in Ghana. In: Xu, Y., Usher, B. (Eds.), Groundwater Pollution in Africa. Taylor & Francis Group plc., London, pp. 57–64. Ewusi, A., Apeani, B., Ahenkorah, I., Nartey, R.S., 2017. Mining and metal pollution: assessment of water quality in the Tarkwa mining area. Ghana Mining Journal 17 (2), 17–31. Ismaeel, W.A., Kusag, A.D., 2012. Enrichment factor and geo-accumulation index for heavy metals at industrial zone in Iraq. IOSR J. Appl. Geol. Geophys. 3 (1), 26–32. Johnson, B.D., Hallberg, K.B., 2005. Acid mine drainage remediation options. Sci. Total Environ. 338, 3–14.
4. Conclusions The study has evaluated heavy metals in the water resources and soil at Kokoteasua community in Obuasi where artisanal mining has been on the rise in recent times. The results indicate that there are twelve water supply points for the community comprising six boreholes, two hand-dug wells, two springs, a stream and a pumped water from the mining pit. Out of these, four are within the 100 m unacceptable minimum buffer radius from a mine to water supply points whereas the rest are all within 400 m radius of the mine site. The water quality assessment results indicate that groundwater in the community is generally suitable for drinking in comparison to the WHO guideline values for drinking water except in isolated locations where the levels of As and Zn are unsuitable. On the other hand, the stream in the community is not suitable for drinking due to higher levels of turbidity, total suspended solids, Pb, Mn, and Fe above the acceptable drinking water standard. Similarly, the soil in the community is heavily polluted with Fe, Pb, Zn, Cu, Mn and As. The levels of the heavy metal pollution, however, decreases with depth (from 0 – 20 cm to 20–40 cm) in the community. Thus, indicating that artisanal mining in the community is polluting the soil and surface stream; hence, there is the need to regulate it to control the pollution and protect the water resources from further pollution and its associated health implications on the populace. Acknowledgment The authors thank the Regional Water and Environmental 455
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Obiadi, I.I., Obiadi, C.M., Akudinobi, B.E., Maduewesi, U.V., Ezim, E.O., 2016. Effects of coal mining on the water resources in the communities hosting the iva valley and okpara coal mines in Enugu state, Southeast Nigeria. Sustain. Water Resour. Manag. 2 (3), 207–216. Oladeji, O.S., Adewoye, A.O., Adegbola, A.A., 2012. Suitability assessment of groundwater resources for irrigation around Otte village, Kwara state, Nigeria. Int. J. Appl. Sci. Eng. Res. 1 (3), 437–445. Oladipo, M.O., Njinga, R.L., Elele, U.U., Salisu, A., 2014. Heavy metal contaminations of drinking water sources due to illegal gold mining activities in Zamfara state-Nigeria. J. Chem. Biochem. 2 (1), 31–44. Olatunji, A.S., Abimbola, A.F., Afolabi, O.O., 2009. Geochemical assessment of industrial activities on the quality of sediments and soils within the Lsdpc industrial estate, Odogunyan, Lagos, Nigeria. Glob. J. Environ. Res. 3 (3), 252–257. Osae, S., Kase, K., Yamamoto, M., 1995. A geochemical study of the Ashanti gold deposit at Obuasi, Ghana. Earth Sci. 2, 81–90. Owens, P.N., Batalla, R.J., Collins, A.J., Gomez, B., Hicks, D.M., Horowitz, A.J., Kondolf, G.M., Marden, M., Page, M.,J., Peacock, D.H., Petticrew, E.L., Salomons, W., Trustrum, N.A., 2005. Fine-grained sediment in river systems: environmental significance and management issues. River Res. Appl. 21, 693–717. Ponsadailakshmi, S., Sankari, G.S., Prasanna, S.M., Madhurambal, G., 2018. Evaluation of water quality suitability for drinking using drinking water quality index in Nagapattinam district, Tamil Nadu in Southern India. Groundw. Sustain. Dev. 6, 43–49. Qiu, J., 2010. China faces up to groundwater crisis. Nature 466, 308. https://doi.org/10. 1038/466308a. Taylor, S.R., 1964. Abundance of chemical elements in the continental crust. Geochim. Cosmochim. Acta 28, 1273–1285. Teaf, C., Merkel, B., Mulisch, H.M., Kuperberg, M., Wcislo, E., 2006. Industry, mining and military sites: potential hazards and information needs. In: Schmoll, O., Howard, G., Chil, J., Chorus, I. (Eds.), Protecting Groundwater for Health. IWA Publishing, London, pp. 309–336. Tomlinson, D.L., Wilson, J.G., Harris, C.R., Jeffrey, D.W., 1980. Problem in the assessment of heavy metals levels in Estuaries and the formation of a pollution index. Helgol. Mar. Res. 33, 566–575.
Kesse, G.O., 1985. The Mineral and Rock Resources of Ghana. Balkema Publishers, Accra. Likuku, A.S., Mmolawa, K.B., Gaboutloeloe, G.K., 2013. Assessment of heavy metal enrichment and degree of contamination around the copper-nickel mine in the Selebi Phikwe region, eastern Botswana. Environ. Ecol. Res. 1 (2), 32–40. Mallo, S.J., 2011. The Menace of acid mine drainage: an impending challenge in the mining of Lafia-Obi coal, Nigeria. Cont. J. Eng. Sci. 6 (3), 2141–4068. Martin, J.M., Meybeck, M., 1979. Elemental mass balance of materials carried by major world rivers. Mar. Chem. 7 (3), 173–206. McComb, J.Q., Rogers, C., Han, F.X., Tchounwou, P.B., 2014. Rapid screening of heavy metals and trace elements in environmental samples using portable X-ray fluorescence spectrometer: a comparative study. Water, Air, Soil Pollut. 225 (12), 2169. https://doi.org/10.1007/s11270-014-2169-5. Meech, J.A., Veiga, M.M., Troman, D., 1998. Reactivity of mercury from gold mining activities in darkwater ecosystems. Ambio 27 (2), 92–98. Muller, G., 1969. Index of geo-accumulation in sediments of the rhine river. Geojournal 2, 108–118. MWRWH, 2011. Riparian Buffer Zone Policy for Managing Freshwater Bodies in Ghana. Ministry of Water Resources, Works, and Housing, Accra. Nickson, R.T., McArthur, J.M., Shrestha, B., Kyaw-Nyint, T.O., 2005. Arsenic and other drinking water quality issues, Muzaffargarh district, Pakistan. Appl. Geochem. 20, 55–68. Nude, P.M., Foli, G., Yidana, S.M., 2011. Geochemical assessment of the impact of mine spoils on the quality of stream sediments within the Obuasi mines environment, Ghana. Int. J. Geosci. 2 (3), 259–266. Nude, P.M., Asigri, J.M., Yidana, S.M., Arhin, E., Foli, G., Kutu, J.M., 2012. Identifying pathfinder elements for gold in multi-element soil geochemical data from the WaLawra Belt, Northwest Ghana: a multivariate statistical approach. Int. J. Geosci. 3 (1), 62–70. WHO (World Health Organization), 2011. Guidelines for Drinking-Water Quality. WHO press, Geneva. Oberthu, T., Vetter, U., Mumm, A.S., Welser, T., Amanor, J.A., Gyapong, W.A., Blenkinsop, T.G., 1994. The Ashanti gold mine at Obuasi: mineralogy, geochemical, stable isotopes and fluid inclusion studies on the metallogenesis of the deposite. Geol. Jahrb. 100, 31–129.
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Research paper
Potential heavy metal pollution of soil and water resources from artisanal mining in Kokoteasua, Ghana
T
Ebenezer Gyamfia,∗, Emmanuel Kwame Appiah-Adjeia,b, Kwaku Amaning Adjeia a b
Regional Water and Environmental Sanitation Centre, Civil Engineering Department Kwame Nkrumah University of Science and Technology, Kumasi, Ghana Geological Engineering Department, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
A R T I C LE I N FO
A B S T R A C T
Keywords: Groundwater Artisanal mining Heavy metals Pollution indices Ghana
Effluents and mine waste from artisanal mining in Kokoteasua, a community in Ghana, are discharged directly to the environment without prior treatment and have the potential of polluting the soil and water resources that the populace rely on for their daily water need. Therefore, this study has assessed the impact of the artisanal mining activities on the soil and water resources in the community. The method employed involved mapping the water supply points in the community and sampling the water supply points and the soil (at 20 cm and 40 cm depths) to determine their heavy metal levels (i.e. Fe, Pb, Zn, As, Mn, Cu, and Hg). The water quality was assessed using the World Health Organisation (WHO) guideline values for drinking water while pollution indices were used to evaluate the levels of soil pollution. The results, generally, indicated that groundwater in the community is potable but unsuitable for drinking in isolated locations due to high levels of As and Zn. The stream, however, recorded high levels of Mn, Fe, and pH above the acceptable WHO drinking water guidelines. Again, the study found the soil to be extremely polluted with all the measured heavy metals (except Hg) from contamination factor, enrichment factor, geo-accumulation index and pollution load index assessments. Thus, the artisanal mining needs to be regulated to protect the water resource and soil from further pollution.
1. Introduction Groundwater constitutes about 97% of the available freshwater on earth and forms an important component of the water cycle (Delluer, 1999). It serves as a source of potable water for agriculture, industry and domestic use as well as in helping to maintain soil moisture, wetlands and stream flows in many parts of the world (Oladeji et al., 2012). Qiu (2010) estimated that groundwater constitutes about 70% and 40% of the total water resources used respectively for domestic and irrigation purposes in China. Nickson et al. (2005) also estimated that about one-third of global population depend on groundwater as their source of potable water. In Ghana, groundwater serves as the main source of sustainable water supply for the populace living in rural communities and emerging communities in the urban areas (Duah and Xu, 2006). Groundwater of good quality is very important to these communities because it is their main source of potable water for drinking and domestic purposes. Commonly, anthropogenic activities such as farming, indiscriminate waste disposal and mining among others significantly influence groundwater quality either directly or indirectly (Teaf et al., 2006). For instance, mining activities generate waste such as waste rock, tailings
∗
and effluents at the various stages of processing the ore, which have the potential to leach through the soil into aquifers and directly pollute groundwater (Johnson and Hallberg, 2005). A typical pollution of groundwater from effluents of mine waste is reported by Obiadi et al. (2016) at a coal mine in the Enugu area of Nigeria, which contaminated surface water and shallow groundwater with high levels of acidity, iron, and sulphate. Studies by Mallo (2011) also found that effluents from mines usually have very low pH, which causes acid mine drainage and ends up in water bodies including groundwater. Oladipo et al. (2014), similarly, found evidence of heavy metal contamination of groundwater as a result of illegal mining activities in Zamfara State, Nigeria. Ghana is known to be one of the major gold producers globally, and the mining sector is believed to contribute significantly to the gross foreign earnings of the country. Artisanal gold mining has been on the increase in the country and it is said to be a major contributor of metals in water resources due to indiscriminate use of Mercury (Hg) and other harmful chemicals in the mining activities (Donkor et al., 2006). Globally, small-scale mining is noted to be a major contributor to the pollution of water resources because it makes use of huge volumes of water thereby polluting the water resources (Cunningham et al., 2005; Owens et al., 2005). Most artisanal mining operators have no
Corresponding author. E-mail address: gyamfi[email protected] (E. Gyamfi).
https://doi.org/10.1016/j.gsd.2019.01.007 Received 26 July 2018; Received in revised form 24 December 2018; Accepted 21 January 2019 Available online 02 February 2019 2352-801X/ © 2019 Elsevier B.V. All rights reserved.
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pyroclastic rocks, which are also associated with the hornblende-rich ‘belt-type’ Granitoid (Kesse, 1985; Nude et al., 2012). High-sulphide type Gold mineralization constitutes the gold ore in the area while pyrites and arsenopyrites are the pathfinders (Osae et al., 1995). The mineralization has Fe, As, Pd, Sb, Cu, Zn, S and Au as the key geochemical signatures, and are used to classify the ore (Oberthu et al., 1994). Gold mineralization in the area is structurally controlled.
concession of their own and, thus, operates illegally. Therefore, their operations are naturally furtive and clandestine, thereby operating uncontrollably within the concessions of large-scale mining companies or in areas that are prohibited from mining such as around forest reserves, water bodies or environmentally sensitive areas (Appiah, 1998). As a result, their operations are often not regulated leading to the use of unsafe chemicals in extracting the gold. These chemicals are usually discharged uncontrollably into the ecosystem (Meech et al., 1998) and leads to contamination of the environment. Several methods have been used to analyze the quality of soil and water at places with significant mining activities. Awadh (2013) used the geo-accumulation (Igeo) index to assess soil contamination in such an area by comparing the heavy metal concentrations to their crustal levels and found that the concentrations in the soil were above the crustal levels; thus, signifying that the soil has been contaminated. Likuku et al. (2013), on the other hand, used enrichment factor, pollution load index, the degree of contamination and geo-accumulation index to evaluate heavy metal concentration in the soils. Again, Boateng et al. (2012) used geo-accumulation index, pollution load index and contamination factor to assess the geochemical impact on the soil quality of a reclaimed tailings dam. In analysing the water quality in such environments, the World Health Organisation (WHO) guidelines for assessing suitability of drinking water (WHO, 2011) are commonly utilised. For instance, Oladipo et al. (2014) analysed the concentration of heavy metals in groundwater at Zamfara State, Nigeria, by comparing the measured parameters in the groundwater samples with the WHO guideline values and water quality standards from the Federal Environmental Protection Agency, Nigeria (1998). Similarly, Abdul-Rahaman et al. (2014) analysed possible groundwater contamination in a mining community in Ghana by determining the concentration of heavy metals in the water and comparing them with the WHO guideline values for drinking water. In recent times, artisanal mining has been on the rise in Kokoteasua, a community within the Obuasi Municipality in Ghana. Unfortunately, the waste rock, tailings and effluents from the mining activities are directly discharged into the environment and stream in the area. These have the potential of polluting the surface water and shallow aquifers that the populace relies on as their main source of water supply and, thus, pose a serious threat to their health if not curbed. Therefore, this study aims to assess the effect of artisanal mining on the quality of soil and water resources in a typical artisanal community using Kokoteasua as a case study.
2.2. Mapping and sampling Water supply points in the community including boreholes, handdug wells, springs, and stream were mapped with the aid of a Geographic Position System (GPS). These supply points were plotted on the topographic map of the area and further used in creating a buffer map to show the number of supply points within 100 m, 200 m, 300 m and beyond 400 m radius from the active mining area based on government regulation on minimum required distance from active mining to water points. The drainage map was also used to determine the flow direction and its linkage to the mineral processing sites where effluents are discharged directly to the stream; it as well aided in planning the sampling points for the study shown in Fig. 1. The samples were taken at the upstream, downstream and close to the active mining and processing zones in the study area to evaluate the quality of the water resources and soil around the active mining and processing areas where effluents are directly discharged to the environment. The samples upstream were mainly to serve as control points. In total, fourteen (14) water samples were taken within the study area from fourteen (14) sampling points on two occasions; i.e. in April (prior to the rainy season) and November (after rainy season). The sampling points included six (6) from boreholes, two (2) from hand-dug wells, two (2) from springs, one (1) from a pit at the artisanal mining site where groundwater is pumped out and three (3) from the stream. The water samples were acidified with nitric acid (HNO3) to keep it in oxidation state and set the pH of both the samples and standards equal. The sampling, storage and transportation of the water to the laboratory were done following standard protocols (APHA, 1995) to ensure consistency and data quality. In addition, twenty (20) soil samples were taken from ten (10) different locations at depths of 20 cm and 40 cm with the aid of a hand augur for the study (Fig. 1). These soil samples were put in plastic bags and sent to the laboratory for measurement of their heavy metal concentrations. 2.3. Laboratory analysis and pollution indices
2. Methodology In drinking water quality assessments, priority is usually given to parameters which are known to be of concern to human health and potability when present in significant concentrations in the water source (Ponsadailakshmi et al., 2018). Therefore, heavy metals (i.e. Fe, Pb, Zn, As, Cu, Mn, and Hg) in both the water and soil samples were measured in the laboratory using the ICP-OES analyzer following standard procedures (McComb et al., 2014). The ICP was first initialized and the plasma allowed to stabilize for 15 min. Tuning was then done to determine if the ICP is in good condition to start analysing samples. To achieve this, the tuning solution was first analysed and the intensities observed by the instruments were monitored against the expected intensities of the tuning solution. The instrument was tuned using a 10 ppb solution, which contains Li, Pb, Tl, and Y. The instrument was calibrated before analysing the samples with a blank and appropriate calibration standard. Calibration standards of 1, 10, 50 and 100 ppb were used to calibrate the instrument and only R2 above 0.999 was accepted. The calibration was verified with a 10 ppb and 50 ppb standard followed by the analysis of the samples with appropriate internal standard (i.e. Sc, Ge, In, Rh, Tb, Lu and Ir). The measured concentration of the heavy metals in the water samples were compared with the WHO guideline values for drinking water (WHO, 2011). However, pollution indices such as the
2.1. Study area description Kokoteasua (KTS), shown in Fig. 1, is a suburb of Obuasi Municipality and is located in the southern part of Ashanti Region of Ghana at about 64 km from Kumasi. The municipality is bounded to the east by the Adansi South District, west by Amansie Central District, north by the Adansi North District and south by Upper Denkyira District of Central Region (Bempah et al., 2013). It is, precisely, located within latitudes 1°39′54″ to 1°40′18″ W and longitudes 6°12′54″ to 6°12′34″ N. The topography of the area is gently undulating to hilly. Annual rainfall in the area ranges from 1250 mm to 1750 mm whereas the mean annual temperature is 25.5 °C with relative humidity peaking between 75% and 80% (Boateng et al., 2012). The area is underlained by meta-sedimentary and meta-volcanic rocks of the Birimian formation (Kesse, 1985; Nude et al., 2012). The meta-sedimentary rocks occupy the north-western half of the area and comprise low-grade metamorphosed rocks that are associated with mica-rich ‘basin’ type Granitoid (Kesse, 1985; Nude et al., 2011). The meta-volcanic group is separated from the meta-sedimentary group by the main Obuasi mineralized shear zone and is dominated by basalts intercalated with 451
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Fig. 1. The Kokoteasua area in Ghana with the study sampling points.
Contamination factor (CF), Enrichment Factor (EF), Geo-accumulation index (Igeo) and Pollution Load Index (PLI) were used to evaluate the metal pollution of the heavy metal concentrations in the soil. These indices helped in assessing the presence and intensities of anthropogenic contaminants in the surface soil. The contamination factor (CF), as expressed in equation (1), is the ratio of the measured concentration of an element to the background concentration of that same element, and represents the individual impact of each trace metal on the sediments (Olatunji et al., 2009). It was used to evalute the level of contamination of the measured parameters in the soil. Mathematically, the CF is expressed as:
CF =
Cm Cb
Table 1 Classes of pollution indices on (a) CF (b) EF and (c) Igeo.
(1)
where Cm is the measured concentration of the element and Cb is the background concentration of that same element. The Martin and Meybeck classification (shown in Table 1a) was used to classify the degree of heavy metal contamination of the soil. The enrichment factor (EF), which is also used to evaluate the anthropogenic effect on the soil by computing the difference between metals from anthropogenic source and that of a geogenic source (BuatMenard and Chesselet, 1979; Ismaeel and Kusag, 2012), was used to evaluate how the soil is enriched with the measured parameters. In computing the EF, Al was used as a reference element to standardize the heavy metal concentration (Taylor, 1964). Mathematically, EF is computed using the relation in equation (2):
EF =
Cm Cmref / Cb Cbref
Class
EF Values
Soil Quality
0 1 2 3 6
<2 2–5 5–20 20–40 > 40
Depletion to minimal enrichment Moderate enrichment Significant enrichment Very high enrichment Extremely high enrichment
Class
Igeo Value
Soil Quality
0 1 2 3 4 5 6
<0 0–1 1–2 2–3 3–4 4–5 >5
Unpolluted Unpolluted to moderately polluted Moderately polluted Moderately to heavily polluted Heavily polluted Heavily to extremely polluted Extremely polluted
CF
Contamination Levels
Cf < 1 1 ≤ Cf < 3 3 < Cf < 6 Cf > 6
Low contamination Moderate contamination Considerate contamination Very high contamination
heavy metal contamination in sediments by comparing the present concentration with previous times when there were little or no industrial activities. It was computed as:
Igeo = log 2
(2)
Cn 1.5Bn
(3) −1
Where Cm is the measured concentration of the element and Cb is background concentration of the measured element. Cmref is the measured concentration of the reference element while Cbref is the background concentration of the reference element. The Buat-Menard and Chesselet (1979) classification shown in Table 1b was used to classify the level of enrichment of the soil. Geo-accumulation index (Igeo), as expressed in equation (3) was further used to characterize the
where Cn is the measured concentration in mg kg of the metal and Bn is the geochemical background value of the metal in mg kg−1. Due to the conceivable variations in the background values, the factor 1.5 was used for small anthropogenic impact on a given metal in the environment. Muller's classification shown in Table 1c was used to classify the pollution of the soil based on the computed Igeo values. The pollution load index (PLI) was also used in this study to 452
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gold from the concentrated ore in the area. This may be because the Hg is scooped for reuse several times, by the miners, till it is used up before the effluents are discharged to the environment. Fig. 3(a) shows the computed Igeo values and indicate that, based on Muller (1969), the soil is extremely polluted with all the analysed heavy metals since all the Igeo values were greater than 5. The computed EF (Fig. 3(b)) also showed that the soil is moderately enriched with Mn, significantly enriched with Cu, Fe, and Zn, very highly enriched with Pb and extremely enriched with As based on the BuatMenard and Chesselet (1979) scheme. The high As concentration in the area conform to work done by Nude et al. (2011) in the Obuasi municipality. Again, the As enrichment in soils within 200 m radius is higher as compared to the soils beyond 200 m radius. The CF for Cu, Fe, Mn, and Zn, based on Martin and Meybeck (1979) classification scheme, were low in the soil (Fig. 3(c)) since they were less than 1. However, the soil was moderately and highly contaminated with Pb and As respectively. The high CF values for As conforms to work done by Boateng et al. (2012) in Obuasi area and is due to its association with the ore mined in the study area. Thus, its contamination of the soil could be due its rapid weathering from exposure of the ore to the environment through the mining activities. The As concentration was higher at the depth of 20 cm than the 40 cm depth. Likewise, the CF of the metals were far higher at the depth of 20 cm in comparison to the 40 cm depth. The PLI values for both depths of investigations for all the heavy metals, except As, were below 1 and denotes perfection (Tomlinson et al., 1980). However, the PLI for As in the soil at both the 20 cm and 40 cm depths were above 1 and showed that the soil quality is deteriorated with high levels of As; this seems to be in conformity with studies by Boateng et al. (2012). Generally, the level of pollution of the soil in the study area decreased with depth as well as away from the active mining site.
Table 2 Methods used for analysing the physicochemical parameters. Parameters
Standard Methods
pH Conductivity and Total Dissolved Solids Total Suspended Solids
Probe Method Probe Method Sension 5 (Hach)
Alkalinity Turbidity Colour Fluoride Chloride Sulphide Nitrate Salinity Phosphorus (Total) Sulphate Biochemical Oxygen Demand (BOD)
Photometric Method 8006 (Non-Filterable Residue) Titration Method 2320B Absorptometric Method 8237 (FAU) APHA PlatinumeCobalt Standard Method 8025 4500-F- D SPADNS Method 8029 4500-Cl- B Argentometric Method 4500-S2- F Iodometric Method AOAC Official Method 973.50 2520 B Electrical Conductivity Method 4500-P E. Ascorbic Method 4500-SO42- E. Turbidimetric Method 5210 B 5-Day BOD Test
measure the level of contamination of the soil. The PLI for a single site is the nth root of not less than 5 contamination factors (CF) as expressed in equation (4). The contamination factors represent the individual impact of each trace metal on the sediments. The PLI was computed for the soil at 20 cm and 40 cm depths. Mathematically, the PLI proposed by Tomlinson et al. (1980) is given as: 1
PLI = (CF 1 ∗ CF 2 ∗ CF 3 ∗ ⋯ ∗ CFn )
n
(4)
where, CF = Contamination factors and n = the number of contamination factors and sites respectively. PLI < 1 denotes perfection, PLI = 1 means only baseline levels of pollutants are present and PLI > 1 indicates deterioration of site quality (Tomlinson et al., 1980). On the other hand, Table 2 shows the various standard methods used for analysing the physicochemical parameters.
3.3. Water quality Table 3 shows the physicochemical parameters measured during the two sampling seasons. Generally, all the measured physicochemical parameters (i.e. temperature, true colour, salinity, total hardness, conductivity, TDS, fluoride, nitrate, chloride, sulphate, phosphorus and sulphide) were all within the acceptable WHO guideline values for drinking water except pH, turbidity, total suspended solids (TSS) and alkalinity. Also, there was generally no significant variation in the concentration of the parameters in the November and April periods. The pH ranged from 5.6 to 7.6 in November and 5.8 to 6.9 in April with about 47% and 65%, respectively, of the samples below the lower limit of the permissible guideline values for drinking water (WHO, 2011), which indicates that the water in the community is slightly acidic. This is consistent with the slightly acidic pH of water in mining communities of the country from similar studies (Bhattacharya et al., 2012; Ewusi et al., 2017; Dorleku et al., 2018) and may be due to the release of mine waste and chemicals used in extracting and processing the ore into the environment. Similarly, the turbidity, TSS, and alkalinity values ranged from 0 to 24 mg/l, 100–470 mg/l and 0–25 NTU respectively with about 18%, 53% and 18% respectively of them above the acceptable WHO (2011) guideline values for drinking water. The turbidity issues were mainly associated with the stream water close to the processing site and extreme downstream of the processing site. Table 4 shows the concentration of heavy metals in the water samples in both November and April sampling months. Generally, heavy metals of varying concentrations were detected in the various water samples in the study area, especially in the hand-dug wells and boreholes, but they did not vary significantly over the months. A comparison of the concentration of the heavy metals As, Cu, Pb, and Zn with the WHO (2011) guideline values for drinking water showed most of the metals were below detectable limits (DL). Nonetheless, they could still be present in the water, albeit in very low concentrations,
3. Results and discussions 3.1. Groundwater supply points Overall, six (6) boreholes, two (2) hand-dug wells, two (2) springs, a stream and pumped water from the pits were mapped in the study area as shown on Fig. 2. The water in the community is mainly for drinking and other domestic purposes such as washing and bathing. As shown on Fig. 2, two (2) of the groundwater supply points are located within a 100 m buffer radius from the artisanal mining site whereas five (5) and seven (7) are within the buffer radii of 200 m and 300 m respectively. All the groundwater supply points are, however, within a 400 m radial distance. According to government regulations (MWRWH, 2011), there should be a 100 m minimum buffer distance between a mining activity and a source of drinking water. Thus, the chemicals used in the blasting and processing of the mined ore pose a direct risk to the quality of the four groundwater supply points located within 100 m radius of the mining site. 3.2. Heavy metal pollution of soil The concentrations of the heavy metals Cu, Pb, Zn, Mn, As and Fe in the soil ranged from 10.1 to 36 mg/kg, 6.5–42.5 mg/kg, 16.4–95.8 mg/ kg, 43.0–595.5 mg/kg, 55.2–1200 mg/kg and 6570.9–49,558.1 mg/kg, respectively, and generally decreased with depth. These concentrations were similar to values obtained in the Obuasi area by previous researchers (Antwi-Agyei et al., 2009; Boateng et al., 2012) who investigated the soil up to a depth of 50 cm. Hg, on the other hand, was very low (below the detectable limit of < 0.0001 mg/kg) in the soil although it is the chemical used by the artisanal miners in extracting 453
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Fig. 2. Buffer zones for water supply points to the mining site in the study area.
Fig. 3. Computed (a) Igeo, (b) EF and (c) CF in the soil at 20 cm and 40 cm depths (Note: As values in (b) and (c) are × 102).
Table 3 Chemical parameters for the two sampling seasons. Parameter
pH Cl− HCO3− Na+ K+ PO42SO42Ca2+ Mg2+
NOVEMBER
APRIL
WHO Guideline Values
Min
Max
Mean
SD
% outside W H O Values
Min
Max
Mean
SD
% outside W H O Values
5.6 1.9 65.9 0.1 0.1 0.1 0.1 0.1 0.1
7.6 141 573 573 88.0 6.9 43.0 27.0 17.0
6.5 20.6 312 47.4 10.0 0.9 12.3 5.7 2.9
0.6 31 177 136 21 2.1 14 8.7 4.9
47.1 – – – 23.6 – – – –
5.8 1.7 1.2 1.5 0.3 0.2 0.8 1.8 1.8
6.9 20.7 124 27.2 4.3 0.3 19.8 37.2 16.7
6.4 11.3 63.4 11.0 1.1 0.1 6.1 12.1 4.6
0.4 4.3 40 5.7 0.9 0.1 5.6 11 3.5
64.7 – – – – – – – –
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6.5–8.5 250 600 200 12 – 250 75 100
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Table 4 Heavy metals concentration (mg/l) in the water samples in both sampling seasons. ID
SP1 SP2 BH1 BH2 BH3 BH4 BH5 BH6 HDW1 HDW2 STS1 STS2 STS3 DL WHO
November
April
As
Cu
Fe
Mn
Pb
Zn
As
Cu
Fe
Mn
Pb
Zn
< 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.06 < 0.05 < 0.05 0.21 0.05 0.01
< 0.02 < 0.02 < 0.02 < 0.02 0.02 < 0.02 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.02 1.0
< 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 0.3 < 0.1 0.15 1.30 4.19 4.02 0.1 0.3
< 0.02 < 0.02 < 0.02 0.05 < 0.02 0.05 0.20 < 0.02 < 0.02 0.21 0.05 5.31 3.48 0.02 0.5
< 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.02 0.01
< 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.06 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.05 0.01
< 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.06 < 0.05 < 0.05 0.06 0.05 0.01
< 0.02 0.03 0.24 0.36 0.06 0.05 0.02 0.08 < 0.02 < 0.02 < 0.02 0.21 0.32 0.02 1.0
< 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 0.23 < 0.1 0.92 0.62 0.98 0.53 0.1 0.3
0.17 0.02 < 0.02 0.13 0.16 0.05 0.02 0.08 0.09 0.06 0.08 0.13 0.19 0.02 0.5
< 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.05 0.03 0.02 0.01
< 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.09 < 0.05 0.11 < 0.05 < 0.05 < 0.05 < 0.05 < 0.05 0.05 0.01
Sanitation Centre, Kumasi for supporting this research through their ACE World Bank Project under Grant Number IDA 54230-GH. The authors also acknowledge the useful comments and suggestions of the anonymous reviewers, which helped to improve the paper.
since the DL were above the permissible limits for drinking water. There were, however, isolated cases where the levels of As, Pb and Zn were above the guidelines for drinking water (WHO, 2011) in locations downstream of the processing site in both sampling months. Similarly, the concentrations of Fe and Mn in the stream were mostly above the acceptable guidelines for drinking (WHO, 2011) and decreased away from the processing site in both November and April. This was not surprising since the water pumped directly from the mine pits into the stream during mining contained extremely high levels of Fe and Mn above the permissible levels for drinking. These two metals are common contaminants of groundwater in mining communities of the country (Bhattacharya et al., 2012; Dorleku et al., 2018) since they are key associations of the gold-bearing rocks mined in the country including the study community. Thus, weathering of the rocks, facilitated by its exposure to the atmosphere through the mining activities, may be releasing the metals to the surface stream. Like in the soil, Hg was not detected, at all, in all the water supply points of the community.
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.gsd.2019.01.007. References Abdul-Rahaman, I., Freeman, L., Ampadu, B., 2014. Investigating soil and water contamination of trace metals in Tarkwa-Nsuaem municipality, Ghana. Int, J. Plant. Soil Sci. 5 (4), 217–226. Antwi-Agyei, P., Hogarh, J.N., Foli, G., 2009. Trace elements contamination of soils around gold mine tailings dams at Obuasi, Ghana. Afr. J. Environ. Sci. Technol. 3 (11), 353–359. APHA, 1995. In: Standard Methods for the Examination of Water and Waste Water, nineteenth ed. American Public Health Association, Washington, DC. Appiah, H., 1998. Organization of small-scale mining activities in Ghana. J. S. Afr. Inst. Min. Metall 98 (7), 307–310. Awadh, S.M., 2013. Assessment of the potential nickel and lead in the road-side dust in the Karkh city along the highway between Ramadi and Rutba, West of Iraq. Merit Res. J. Environ. Sci. Toxicol. 1 (7), 126–135. Bempah, C.K., Ewusi, A., Obiri-Yeboah, S., Mensah, F., Boateng, J., Voigt, H.-J., 2013. Distribution of arsenic and heavy metals from mine tailings dams at Obuasi municipality of Ghana. Am. J. Eng. Res. 2 (5), 61–70. Bhattacharya, P., Sracek, O., Eldvall, B., Asklund, R., Barmen, G., Jacks, G., Koku, J., Gustafsson, J.-E., Singh, N., Brokking Balfors, B., 2012. Hydrogeochemical study on the contamination of water resources in a part of Tarkwa mining area, Western Ghana. J. Afr. Earth Sci. 66–67, 72–84. https://doi.org/10.1016/j.jafrearsci.2012.03. 005. Boateng, E., Dowuona, G.N., Nude, P.M., Foli, G., Gyekye, P., Jafaru, H.M., 2012. Geochemical assessment of the impact of mine tailings reclamation on the quality of soils at AngloGold concession, Obuasi, Ghana. Res. J. Environ. Earth Sci. 4 (4), 466–474. Buat-Menard, P., Chesselet, R., 1979. Variable influence of atmospheric flux on the trace metal chemistry of oceanic suspended matter. Earth Planet. Sci. Lett. 42, 398–411. Cunningham, W.P., Cunningham, M.A., Saigo, B., 2005. Environmental Science: a Global Concern, eighth ed. McGraw-Hill, Boston. Delluer, J., 1999. The Handbook of Groundwater Hydrology. CRC Press LLC, London. Donkor, A.K., Nartey, V.K., Bonzongo, J.L., Adotey, D.K., 2006. Artisanal mining of gold with mercury in Ghana. West Afr. J. Appl. Ecol. 9, 2–18. Dorleku, M.K., Nukpezah, D., Carboo, D., 2018. Effects of small-scale mining on heavy metal levels in groundwater in the Lower Pra Basin of Ghana. Appl. Water Sci. 8, 126. https://doi.org/10.1007/s13201-018-0773-z. Duah, A.A., 2006. Groundwater contamination in Ghana. In: Xu, Y., Usher, B. (Eds.), Groundwater Pollution in Africa. Taylor & Francis Group plc., London, pp. 57–64. Ewusi, A., Apeani, B., Ahenkorah, I., Nartey, R.S., 2017. Mining and metal pollution: assessment of water quality in the Tarkwa mining area. Ghana Mining Journal 17 (2), 17–31. Ismaeel, W.A., Kusag, A.D., 2012. Enrichment factor and geo-accumulation index for heavy metals at industrial zone in Iraq. IOSR J. Appl. Geol. Geophys. 3 (1), 26–32. Johnson, B.D., Hallberg, K.B., 2005. Acid mine drainage remediation options. Sci. Total Environ. 338, 3–14.
4. Conclusions The study has evaluated heavy metals in the water resources and soil at Kokoteasua community in Obuasi where artisanal mining has been on the rise in recent times. The results indicate that there are twelve water supply points for the community comprising six boreholes, two hand-dug wells, two springs, a stream and a pumped water from the mining pit. Out of these, four are within the 100 m unacceptable minimum buffer radius from a mine to water supply points whereas the rest are all within 400 m radius of the mine site. The water quality assessment results indicate that groundwater in the community is generally suitable for drinking in comparison to the WHO guideline values for drinking water except in isolated locations where the levels of As and Zn are unsuitable. On the other hand, the stream in the community is not suitable for drinking due to higher levels of turbidity, total suspended solids, Pb, Mn, and Fe above the acceptable drinking water standard. Similarly, the soil in the community is heavily polluted with Fe, Pb, Zn, Cu, Mn and As. The levels of the heavy metal pollution, however, decreases with depth (from 0 – 20 cm to 20–40 cm) in the community. Thus, indicating that artisanal mining in the community is polluting the soil and surface stream; hence, there is the need to regulate it to control the pollution and protect the water resources from further pollution and its associated health implications on the populace. Acknowledgment The authors thank the Regional Water and Environmental 455
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Obiadi, I.I., Obiadi, C.M., Akudinobi, B.E., Maduewesi, U.V., Ezim, E.O., 2016. Effects of coal mining on the water resources in the communities hosting the iva valley and okpara coal mines in Enugu state, Southeast Nigeria. Sustain. Water Resour. Manag. 2 (3), 207–216. Oladeji, O.S., Adewoye, A.O., Adegbola, A.A., 2012. Suitability assessment of groundwater resources for irrigation around Otte village, Kwara state, Nigeria. Int. J. Appl. Sci. Eng. Res. 1 (3), 437–445. Oladipo, M.O., Njinga, R.L., Elele, U.U., Salisu, A., 2014. Heavy metal contaminations of drinking water sources due to illegal gold mining activities in Zamfara state-Nigeria. J. Chem. Biochem. 2 (1), 31–44. Olatunji, A.S., Abimbola, A.F., Afolabi, O.O., 2009. Geochemical assessment of industrial activities on the quality of sediments and soils within the Lsdpc industrial estate, Odogunyan, Lagos, Nigeria. Glob. J. Environ. Res. 3 (3), 252–257. Osae, S., Kase, K., Yamamoto, M., 1995. A geochemical study of the Ashanti gold deposit at Obuasi, Ghana. Earth Sci. 2, 81–90. Owens, P.N., Batalla, R.J., Collins, A.J., Gomez, B., Hicks, D.M., Horowitz, A.J., Kondolf, G.M., Marden, M., Page, M.,J., Peacock, D.H., Petticrew, E.L., Salomons, W., Trustrum, N.A., 2005. Fine-grained sediment in river systems: environmental significance and management issues. River Res. Appl. 21, 693–717. Ponsadailakshmi, S., Sankari, G.S., Prasanna, S.M., Madhurambal, G., 2018. Evaluation of water quality suitability for drinking using drinking water quality index in Nagapattinam district, Tamil Nadu in Southern India. Groundw. Sustain. Dev. 6, 43–49. Qiu, J., 2010. China faces up to groundwater crisis. Nature 466, 308. https://doi.org/10. 1038/466308a. Taylor, S.R., 1964. Abundance of chemical elements in the continental crust. Geochim. Cosmochim. Acta 28, 1273–1285. Teaf, C., Merkel, B., Mulisch, H.M., Kuperberg, M., Wcislo, E., 2006. Industry, mining and military sites: potential hazards and information needs. In: Schmoll, O., Howard, G., Chil, J., Chorus, I. (Eds.), Protecting Groundwater for Health. IWA Publishing, London, pp. 309–336. Tomlinson, D.L., Wilson, J.G., Harris, C.R., Jeffrey, D.W., 1980. Problem in the assessment of heavy metals levels in Estuaries and the formation of a pollution index. Helgol. Mar. Res. 33, 566–575.
Kesse, G.O., 1985. The Mineral and Rock Resources of Ghana. Balkema Publishers, Accra. Likuku, A.S., Mmolawa, K.B., Gaboutloeloe, G.K., 2013. Assessment of heavy metal enrichment and degree of contamination around the copper-nickel mine in the Selebi Phikwe region, eastern Botswana. Environ. Ecol. Res. 1 (2), 32–40. Mallo, S.J., 2011. The Menace of acid mine drainage: an impending challenge in the mining of Lafia-Obi coal, Nigeria. Cont. J. Eng. Sci. 6 (3), 2141–4068. Martin, J.M., Meybeck, M., 1979. Elemental mass balance of materials carried by major world rivers. Mar. Chem. 7 (3), 173–206. McComb, J.Q., Rogers, C., Han, F.X., Tchounwou, P.B., 2014. Rapid screening of heavy metals and trace elements in environmental samples using portable X-ray fluorescence spectrometer: a comparative study. Water, Air, Soil Pollut. 225 (12), 2169. https://doi.org/10.1007/s11270-014-2169-5. Meech, J.A., Veiga, M.M., Troman, D., 1998. Reactivity of mercury from gold mining activities in darkwater ecosystems. Ambio 27 (2), 92–98. Muller, G., 1969. Index of geo-accumulation in sediments of the rhine river. Geojournal 2, 108–118. MWRWH, 2011. Riparian Buffer Zone Policy for Managing Freshwater Bodies in Ghana. Ministry of Water Resources, Works, and Housing, Accra. Nickson, R.T., McArthur, J.M., Shrestha, B., Kyaw-Nyint, T.O., 2005. Arsenic and other drinking water quality issues, Muzaffargarh district, Pakistan. Appl. Geochem. 20, 55–68. Nude, P.M., Foli, G., Yidana, S.M., 2011. Geochemical assessment of the impact of mine spoils on the quality of stream sediments within the Obuasi mines environment, Ghana. Int. J. Geosci. 2 (3), 259–266. Nude, P.M., Asigri, J.M., Yidana, S.M., Arhin, E., Foli, G., Kutu, J.M., 2012. Identifying pathfinder elements for gold in multi-element soil geochemical data from the WaLawra Belt, Northwest Ghana: a multivariate statistical approach. Int. J. Geosci. 3 (1), 62–70. WHO (World Health Organization), 2011. Guidelines for Drinking-Water Quality. WHO press, Geneva. Oberthu, T., Vetter, U., Mumm, A.S., Welser, T., Amanor, J.A., Gyapong, W.A., Blenkinsop, T.G., 1994. The Ashanti gold mine at Obuasi: mineralogy, geochemical, stable isotopes and fluid inclusion studies on the metallogenesis of the deposite. Geol. Jahrb. 100, 31–129.
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