Effects of mining activities on water quality of Bulyanhulu

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Assessment of effects of selected mine pollutants on the water quality
of the Bulyanhulu River,Tanzania.
Grace Nkuli a,*, Zvikomborero Hoko a, Shepherd. Misi a, Richard. J. Kimwagab
a
Department of Civil Engineering, University of Zimbabwe, P.O. Box MP 167, Mt Pleasant, Harare,
Zimbabwe.
b
Department of Civil Engineering, University of Dar es Salaam, P.O. Box 35131, Dar es Salaam, Tanzania.
Abstract
A study was carried out in Tanzania to assess the water quality impact of gold mining
at Bulyanhulu Gold Mine (BGM) on Bulyanhulu River. About 40,000 people use the
river water for agricultural and domestic purposes. BGM discharges effluent from
waste management facilities intermittently to the river. Samples were collected from
Bulyanhulu River during the period January to March 2008. Parameters studied
included pH, SO4, Fe, Ni and Zn. The water quality analysis was done according to
standard methods. The pH was found to be 7.0 ± 0.2 on average for all points against
a limit of 6.5-8.5 based on Tanzanian guidelines for drinking water quality. Mean SO4
concentrations for all sampling points were 69.6 ± 30.2 mg/l compared to 600 mg/l
and 250 mg/l suggested in the Tanzanian and WHO guidelines for drinking water. Fe
values were 3.0 ± 1.7 mg/l compared to 1mg/l and 0.3 mg/l for Tanzanian and WHO
guidelines. Results for Ni were 0.4 ± 0.3 mg/l against limits of 0.05 mg/l (Tanzania)
and 0.02 mg/l (WHO). Zn was found to be 1.8 ± 0.8 mg/l against maximum values of
0.2 mg/l (Tanzania) and 3 mg/l (WHO). The elevated concentrations of Fe, Ni and Zn
compared to guidelines may be attributed to weathering of sulphide ore bodies at the
mine, chemicals used in the process plant, disposal of batteries and old metal scraps
around the mine. Statistical analysis indicated a significant variation (p<0.05) of Fe,
Ni and Zn between two successive points upstream and downstream the mine. These
elements may potentially have high toxicological effects in the aquatic biota and
human beings especially in communities around the mine. It was concluded that the
river is polluted by mining activities with respect to Fe, Zn and Ni and therefore not
suitable for human consumption. It is recommended the effluent of the effluent
control ponds should be treated by precipitation of metals to reduce their mobility
through seepage. Lime and caustic soda should be added to neutralize the drainage
water and avoid release of pollutants from the sulphides ore.
Keywords: Bulyanhulu River, water quality, Bulyanhulu Gold Mine, mining effects, mine effluents.
Corresponding author. Tel: +263912300599: Email address: [email protected] Sub theme: Water and Environment.
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1. Introduction
Mining is a major economic activity in many developing countries (Tauli-Corpuz,
1997). Both small and large-scale mining operations are inherently disruptive to the
environment, producing enormous quantities of waste that can have deleterious
impacts for decades (UNEP, 1997). Mining activities that affect water quality include
the disposal of waste rock, tailings deposition, and effluent discharges from different
stages of mineral processing (Dock, 2005). According to Ripley (1996) effluent
released from gold mines consist of heavy metals mainly from pyrite (FeS 2) and
chalcopyrite (CuFeS2). Koryak (1997) argues that the effluent produced from waste
rock dumps has a potential to cause acid mine drainage (AMD) in stream and river
waters. Studies on brook trout by Mc Kim and Benoit (1971) showed that water
polluted by gold mining activities due to AMD had concentrated heavy metals such as
As, Fe, Zn, Cu and Pb. Iron concentration of 0.3 mg/l had effects on fish population,
while zinc concentration of 0.18 mg/l greatly reduced egg production of the fathead
minnow (Mc Kim and Benoit, 1971). Low pH values of less than 5 affected behaviors
and reproduction of aquatic organisms in West Virginia streams (Mount, 1973).
Knight (2001) reported livestock and human death in less than 24 hours after using
water from a stream near Geita Gold Mine in Tanzania, the deaths were linked to
pollution from the mine. This was reported to be due to overflow of mining waste
from the 82-hectare effluent dam into nearby streams. Work by Kahatano et al. (1995)
found high levels of Pb, Cu, Zn and Hg in water of some streams and rivers in the
Lake Victoria gold fields. Possible sources of these metals include mining activities
and industrial discharges (Kishe and Mahiwa, 2001). According to Shuttle (2005) the
ores mined at Bulyanhulu gold mine (BGM) are mainly pyrite and chalcopyrite.
Malunga (2007) reported that there have been a number of accidental effluent
discharges from BGM effluent control ponds to the environment in years 2002 and
2004 to 2007 due to heavy rainfalls. In 2005 approximately 450,000m3 of effluent was
discharged into the river (Malunga, 2007). There is lack of information regarding the
water quality of Bulyanhulu River despite its importance for supporting activities
such as agriculture and domestic uses.
Philips et al. (2001) and BOT (2002) have documented positive aspects of
mining, which include; creation of employment; contribution to Government revenue;
foreign currency earnings and increase of Gross Domestic Product (GDP). The
contribution of the mining sector to the GDP in Tanzania increased to 3.8% in 2007
from 3.5% registered in 2005 (URT, 2007). Tanzania is endowed with abundant
mineral resources of international value including gold, diamonds, tanzanite e.t.c. The
major gold fields are located within the Lake Victoria Gold field (Kikula, 2002).
The purpose of the study was to assess and analyse the levels of pH, SO4, Fe, Ni
and Zn pollution in the Bulyanhulu River as a result of the mining activities at
Bulyanhulu Gold Mine and to compare the levels to standard and guideline values of
Tanzania and the World Health Organization respectively.
2. Study area description
Bulyanhulu Gold Mine is an underground mine located approximately 45 km
south of Lake Victoria at an elevation of 1,200 meters above sea level. It is some 75
km from Kahama District in Shinyanga Region of Tanzania. The mine was
commissioned in March 2001 and has a design capacity to process an average of
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2,500 dry tones of gold-bearing ore per day with 11 - 14 g/t gold content and around
0.5 % copper feed (Shuttle, 2005). The Bulyanhulu gold mine (BGM) is located in the
Lake Victoria Gold Field (LVGF). Lake Victoria gold fields (Fig.1) are the largest
and richest in gold in Tanzania and have a long history of gold mining, which dates
back to the 1920’s, and consequently mining has profound environmental impacts on
the Lake Victoria catchment areas (Kahatano et al., 1995). The surface drainage from
the BGM area is towards the Bulyanhulu River, which is the only major surface water
body in the area. BGM waste dump and tailing’s runoff flows into effluent ponds. The
purpose of the ponds is to collect and settle fine materials from effluents that flow
from waste rock dump and tailing storage facility. This is meant to minimize
contamination of groundwater and the river downstream of the mine. A large amount
of the effluent in the ponds is recycled within the mine for different purposes such as
dust suppression. However some of the effluent at times overflow over the walls of
ponds during heavy rainfall events and flow into the river while part of this overflow
infiltrate into the ground. The river downstream the mine is used for irrigation of
crops (mainly vegetables and maize), and domestic use including drinking without
treatment for some 20,000 to 40,000 people (Norecol and Moore, 1997). The main
livelihood activities around the mine are agriculture (including livestock farming) and
artisanal mining.
Fig.1. Map showing the location of Lake Victoria Gold Fields in Tanzania (Source: Malunga, 2007)
The Bulyanhulu area is generally flat and has few rock outcrops. The area is
typically represented by extensive lateritic and saprolitic weathering profiles that have
been developed to a depth of between 50 to 80 m (Norecol and Moore, 1997). The
surface geology of the mine site is relatively simple, comprising an upper zone of
transported soils overlying residual soils. In areas of high ground, the upper
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transported layer comprise of clayey, silt sands and organic topsoil, and is typically
less than 1m thick. According to (Norecol and Moore, 1997) copper exists as
chalcopyrite and chalcocite and gold occurs as liberated grains and as fine particles
locked in pyrite. Sulphur and iron levels at approximately 10% each are also high in
gold ores (Norecol and Moore, 1997).
3. Materials and Methods
According to Schmitz (1995) sampling operations are broken down into four
components namely; selection of sampling stations, selection of water quality
parameters, sampling frequency, collection and analysis methods.
3.1 Location of sampling sites
Four sampling points were selected and named as W1, W2, W3 and W4.
According to WEGS (2002) the topography of Bulyanhulu gold mine (BGM) area
generally drains in the direction of the Bulyanhulu River. Close proximity (600m) of
the river to gold mining activities renders it susceptible to pollution through leachates,
seepage and runoff. Sampling point W1, which was located 4 km upstream west of
the mining area was meant to establish the water quality before the influence of BGM
activities. The layout of the area and the sampling points are shown in Fig. 2.
Fig.2. Location of the sampling sites (W1=1st point 4km upstream of the mine. W2= 2 nd point 600m
downstream the mine. W3 = 3rd point 6km downstream the mine and W4 = 4 th point 40km downstream
the mine.)
3.3 Parameter selection
Parameters of interest in this study were pH, SO4, Fe Zn and Ni as toxic
parameters that might be influenced by gold mining activities. Some of these
parameters may be detrimental to aquatic, fauna, flora and human health in the local
4
area as suggested by McBride (1994). Most of these parameters have not been
studied within the Lake Victoria gold field (LVGF). The field reports by NEMC
(1994) and Kahatano et al. (1995) dealt with the environmental impacts of mine
activities, mainly due to Pb, Cu, Cr, Zn and Hg on some streams and rivers in the
LVGF.
3.4 Sample collection and analysis
Ten sampling campaigns were made in the period January to March 2008 at
regular intervals of one week. Water samples were collected in well-labelled sterile
500ml white polyethylene bottles. Samples were collected below the water surface
with the containers facing the direction of the flow in order to obtain a representative
sample. The pH was measured using the HACH spectrometer equipment (2001).
Sulphates were measured using the UV-V Spectrometer according to APHA (2000)
while the analyses of Fe, Ni and Zn was done by using an Inductively Coupled
Plasma-Optical Emission Spectrometer as recommended by APHA (2000).
3.5 Methods of data analysis
Microsoft Excel was used for statistical data analyses to obtain paired t-test and
standard deviations for each parameter measured. The pared t-test was used to
compare the differences of water quality between two successive points.
4. Results and Discussion
4.2 River water quality results
The summary results of the water quality analysis for the four sampling sites on
the Bulyanhulu River for all ten sampling campaigns are presented in Table 1. The p
values, at 95% confidence level, for comparison of each parameter studied at different
sampling points of the river are as in Table 2. Detailed results for each parameter are
presented in the sub-sections that follow. Results were compared to Tanzania water
law-Mining regulations for receiving water (portable/groundwater) maximum
permissible concentration as suggested in RMPC (2006). Results were also compared
to the World Health Organisation WHO (1996) guidelines for drinking water quality.
Table 1
Bulyanhulu River water quality results for the ten sampling campaigns (14th Jan to
17th Mar 2008).
Sampling
points
pH
SO4
Fe
Ni
Zn
pH unit
mg/l
mg/l
mg/l
mg/l
7.0-7.3
48.0-99.0
2.5-3.9
0.2-0.7
0.8-1.6
(7.2 ± 1.4%)
(48.8 ± 26%)
(3.2 ± 16%)
(0.4 ± 50%)
(1.3 ± 15%)
W2
7.0-7.3
49.0-99.0
2.2-3.9
0.2-0.9
1.8-3.2
(7.2 ± 1.4%)
(69.4 ± 23%)
(3.2 ± 19%)
(0.6 ± 50%)
(2.7 ± 15%)
W3
7.0-7.3
16.0-165.0
1.6-7.2
0.3-0.7
0.4-3.7
(7.1 ± 1.4%)
(80.0 ± 58%)
(4.7 ± 34%)
(0.5 ± 20%)
(1.6 ± 63%)
W4
6.5-7.1
<0.1
0.1-1.3
0.0-0.6
1.2-3.6
(6.7 ± 3.0%)
0.7 ± 43%)
(0.2 ± 50%)
(2.0 ± 35%)
The range, average and standard deviation expressed as a % of the average are based on 10 values for
the ten sampling campaigns for each parameter. W1=1st point 4km upstream of the mine. W2= 2nd
W1
5
point 600m downstream the mine. W3 = 3rd point 6km downstream the mine and W4 = 4 th point 40km
downstream the mine.)
Table 2
Significance test (p) values between upstream and downstream sampling sites
Parameters
Sampling points
W1 and W2
0.870029857
0.012636865
0.381383842
0.249418502
1.45565E-08
pH
SO4
Fe
Ni
Zn
W1 and W3
0.127646181
0.060067033
0.014382977
0.602530434
0.323816032
W2 and W3
0.23909873
0.515410442
0.043165809
0.39065011
0.003562742
The significance test was performed on average values for the study period for each parameter at the
two sites compared. P values in bold (p<0.05) indicate that there is a significance difference between
the two paired points at 95 % confidence level.
4.2.1 pH
The pH results for all the sampling campaigns for the study sites are presented in
Fig. 3. The pH values for all sampling points were found to be in the range of 6.5 to
7.3 (Table 1). All the values of pH for all sampling points complied with the
prescribed guidelines for drinking water quality of 6.5 to 8.5. The RMPC (2006)
recommended pH for drinking water ranges from 6.5 to 8.5. There were no significant
differences (p>0.05) at 95% confidence level between (W1 and W2), (W1 and W3)
and between (W2 and W3) meaning that the mining activities were not affecting the
pH of the river during the study period. This is perhaps due to the buffer capacity of
the river. The standard deviation of pH levels during the entire study period at
different sampling points ranged from 1.4% to 3.0% indicating slight variations
among sampling days at each sampling point.
9
8
7
pH
6
5
4
3
2
1
0
W1
1/14/2008
2/11/2008
3/10/2008
W2
S ampling points
1/21/2008
2/18/2008
3/17/2008
W3
1/29/2008
2/25/2008
RMPC-pH
W4
2/4/2008
3/3/2008
Fig.3. Variation of pH among river sampling points for the period of 14 th Jan to 17th Mar 2008.
(RMPC-pH = receiving water (portable/groundwater) maximum permissible concentration guideline
and W1-W4 = river points.)
6
At pH values less than 7.0 corrosion of water pipes may occur, resulting in the
release of metals into drinking water. This can be toxic and may pose health problems
if concentrations of such metals exceed recommended limits (Anderson et al., 2000).
For rivers where aquatic life is expected, the pH has to be within the range of 6.5
to 8.7 (EPA, 1996). Low pH from acid pollution can potentially damage aquatic biota
by increasing abnormal behaviors and reducing the reproductive capacity (Mount,
1973). Studies in Norway and Sweden indicated that extinction of fish populations
often resulted from chronic reproductive failures due to acidification induced effects
on sensitive growth development stages of the fish (Brungs et al., 1998). However the
impact of pH on aquatic life was not investigated in this study. At present it appears
that the pH level in the river is still acceptable for aquatic life. The most possible
environmental impact of pH involves synergistic effects. Synergy involves the
combination of 2 or more substances, which produce effects greater than their
individual effect, for example; water with iron of a given concentration will become
more toxic to fish as water becomes more acidic (Annon, 2004).
The required pH level by Tanzania guidelines for irrigation water ranges from 6.5
to 9.0 as given in (RMPC3, 2006). All sample for all points had values within the
guideline and hence suitable for irrigation. In agriculture soil pH outside the required
range directly affect the availability of essential nutrients to plants and the adaptability
of a given crop (Rowe and Magid, 1995). At low pH levels less than 5.5 the nutrients
may form precipitates with metals present such as aluminum, which causes nonproductivity in acidic soils, but soils at pH 5.5 to 8.0 precipitates the iron and
eliminate the toxicity (Rowe and Magid, 1995).
Generally, it can be said that the mining activities were not impacting on the pH
levels in the river during the period of study.
4.2.2 Sulphates
Fig. 4. presents a plot of the sulphate results. Sulphate levels ranged from 0 to
165 mg/l. All samples were below the Tanzania and WHO maximum allowable limits
for drinking water quality of 600 mg/l and 250 mg/l respectively. Sulphate values
showed an increasing trend in the downstream direction from W1 to W3. Point W4
measured values below the method detection limit of <0.05 mg/l, this could be due to
natural purification of the river and dilution as this point is located on the shore of
Lake Victoria that receives water from different sources hence enhancing the dilution
effect. Significant differences in sulphate levels (p<0.05) were observed between W1
and W2 points. The sulphate levels could be linked to anthropogenic sources such as
agricultural land use activities in the study area. There was no significant variation
(p>0.05) between the points (W1 and W3) and (W2 and W3) and hence the effect of
mine activities with regard to sulphate on water quality may be considered
insignificant. There was a large standard deviation variation (23% to 58%) of sulphate
levels among sampling days at each point.
Sulphates are corrosive to concrete structures, pipes and asbestos-cement pipes,
although at low levels (less than 350 mg/l) the rate of attack is typically very slow.
Sulphate levels above the recommended limit (600mg/l) in drinking water are
associated with taste effects, diarrhea and gastrointestinal irritation (ATSDR, 2005).
Ripley (1996) suggests that sulphuric acid is formed when air and water react
with sulphur bearing minerals such as pyrite, commonly associated with gold ore.
Acid formation in water has an effect of lowering the pH. As a result high sulphate
levels are normally associated with low pH (Anderson et al., 2000). The resulting
acidic condition kills aquatic animals and plants rendering the water unfit for aquatic
7
life (Nemerow and Avijiti, 1991). A study by Haraguchi (2005) on effects of sulphate
discharge on river water chemistry found that water discharged from canals after
pyrite oxidation into the main stream of the Sebangau River and Kahayan River in
Indonesia had lower pH (less than 4.5) compared to the main stream water of the
rivers, implying sulphuric acid loading, which resulted in a reduction of total
abundance of fish, benthic invertebrate populations and acidification of soil. In this
study sulphates appear not to be affecting pH, as there was no significant difference in
pH between upstream and downstream points (section 4.2.1). The aquatic life use
standard for sulphate defined by EPA (1996) is 500 mg/l. The sulphate levels in the
river sampling points are not yet of serious concern for aquatic life as all points had
values below recommended guidelines for aquatic life water quality.
According to the Tanzanian guidelines for irrigation water quality, the required
value is 600 mg/l. All sampling points were found to be within the recommended
value and therefore, suitable for irrigation. Sulphate levels above the guideline value
could affect sensitive crops by limiting the uptake of calcium and increasing the
adsorption of sodium and potassium resulting in a disturbance in the cationic balance
within the plant (Rowe and Magid, 1995).
From the analysis, it can be concluded that, at present the local surface water
quality of the Bulyanhulu River is not significantly affected by mining activities that
are often associated with increased sulphate levels.
700
600
SO 4 (mg/l)
500
400
300
200
100
0
W1
W2
W3
W4
1/29/2008
2/25/2008
RMPC-SO4
2/4/2008
3/3/2008
WHO
Sampling points
1/14/2008
2/11/2008
3/10/2008
1/21/2008
2/18/2008
3/17/2008
Fig.4. Sulphate variation among river water sampling points for the period of 14 th Jan to 17th Mar 2008.
(RMPC-SO4 = receiving water (portable/groundwater) maximum permissible concentration guideline,
WHO = World Health Organization drinking water quality guidelines and W1-W4 = river points.)
4.2.3 Iron
Results for iron are presented in Fig. 5. The iron range was 0.1 to 7.2 mg/l. Some
97% of all samples had values higher than the 0.3 mg/l WHO drinking water
guidelines limit. The 3% of samples, which had values less than 0.3mg/l, were from
W4. The recommended Tanzanian guideline for drinking water quality is 1 mg/l. Of
the total samples 80% did not meet the Tanzanian guidelines. Site W4 had iron
values that met both limits except for 2 sampling days. Low iron values at site W4
could be as a result of self purification and dilution in the river as at this point the lake
receives water from different tributaries. Iron showed an increasing trend from W1 to
8
W3 (upstream to downstream). There were significant differences (p<0.05) in the iron
concentration at (W1 and W3) and (W2 and W3) points while variation in iron levels
between W1andW2 were insignificant (p>0.05) at 95% confidence level. High levels
of iron could be linked to mining activities. Relatively high levels of iron were also
measured upstream of the mine at river point (W1) and this could possibly be
attributed to iron mineralization associated with the natural geology around the gold
mining area, which constitute of pyrites and chalcopyrite (Kahatano et al., 1995;
Ripley, 1996; Shuttle, 2005). Iron is naturally released into the environment from
weathering of sulphide ores (pyrite FeS2) and igneous, sedimentary and metamorphic
rocks (Hem, 1989). The standard deviation of iron levels among the 10 sampling days
at different sampling points ranged from 16% to 43% indicating moderate variations
among points.
8
7
Fe (mg/l)
6
5
4
3
2
1
0
W1
W2
W3
W4
1/29/2008
2/25/2008
RMPC-Fe
2/4/2008
3/3/2008
WHO
Sampling points
1/14/2008
2/11/2008
3/10/2008
1/21/2008
2/18/2008
3/17/2008
Fig.5. Iron variation among sampling points for the period of 14th Jan to 17th Mar 2008. (RMPCFe = receiving water (portable/groundwater) maximum permissible concentration, WHO = World
Health Organization drinking water quality and W1-W4 = river points.)
Iron is essential for the production of heme (required for hemoglobin and
myoglobin), oxygen and blood transport, cellular respiration and the function of many
enzymes involved in electron transport (Dock, 2005). In human health, iron levels
above recommended values are associated with microbial growth, color (brown
staining) and taste (ATSDR, 2005).
According to Tolgyessy (1993) the forms of occurrence of dissolved and nondissolved iron depend on pH and the presence of complex-forming inorganic and
organic substances. Annon (2004) points out that low pH of less than 4 increases
solubility of iron due to reducing conditions in the environment, thus effecting the
release hydrogen ions, which increases acidity in the environment. This also promotes
leaching of dissolved ionic metal ions such as Pb, Zn, Cu, Fe, Cd, and Ni. In this
study the pH in all river sampling points ranged from 6.5 to 7.3 indicating the water
was around near neutral conditions, the probable occurrence of iron at this pH range
could be less than 3 mg/l as suggested by Tarimo (2007). Therefore, the high levels of
iron may be linked to pollution by the mine. The iron guideline value suitable for
aquatic life is less than 0.3 mg/l (EPA, 1996). Most mayfly nymphs cannot survive in
streams with iron concentration greater than 0.3 mg/l. For example, Warnick (1989)
found iron levels of 0.3 mg/l of iron toxic to mayflies, stoneflies and caddis flies. Fish
9
population however, can tolerate iron concentrations up to 1.0 mg/l (Warnick, 1989).
The potential survival of the fly species in the Bulyanhulu River is very minimal since
most samples (97% of the total) had iron values higher than 0.3 mg/l.
The Tanzania maximum allowable limit for irrigation water according to RMPC3,
(2006) is 0.1 mg/l. Only 33% of the total water samples for the entire sampling period
were found to be within this guideline value. Rowe and Magid (1995) state an
allowable limit of iron for irrigation as 5 mg/l. For this limit of 5mg/l, 85% of the total
water samples would be suitable for irrigation. Iron is not toxic to plants in aerated
soils, but contribute to soil acidification and loss of essential phosphorus and
molybdenum at high levels above 5 mg/l (Rowe and Magid, 1995).
Higher proportions of dissolved metals such as iron are found in groundwater
than in surface water because of the greater exposure to soluble materials in geologic
strata (Todd, 1959). High levels of heavy metals such as iron upstream of the mine
could therefore be attributed by surface water-groundwater interaction in the river
channel. Keith et al. (2001) suggested that the elevation of iron in most rivers is via
base flow. This supports the inference that the geological condition of the area may be
influencing the iron levels in the water.
It can be concluded that there is a significant variation of iron levels between the
points upstream and downstream of the mine implying that the mining activities were
affecting water quality with respect to iron.
4.2.4 Nickel
Fig. 6. presents results for nickel, which ranged from 0 to 0.9 mg/l. The
maximum permissible level of nickel in the Tanzanian standards and WHO guidelines
is 0.05 mg/l and 0.02 mg/l respectively. About 75% of water samples were above the
Tanzania allowable limit and 83 % above the WHO threshold value. The differences
in nickel values at (W1 and W2), (W1 and W3), and (W2 and W3) were insignificant
(p>0.05) at 95% confidence level however. Nickel in mining areas is often associated
with acid mine drainage since the nickel ore often occurs in sulphide form and
associated with other sulphide minerals (Lupankwa et al., 2004). In the study area Ni
ore occurs in sulphide form as nickel sulphide (NiS) according to Chimimba (1987)
and this could explain why there were high levels of Ni at most sampling points. Low
nickel levels were measured at W4 and this could be due to adsorption or dilution
occurring. The standard deviation during the sampling period at each point varied
from 20% to 50%.
Human health exposure to nickel is regarded as one of the most causes of human
skin sensitization and allergic contact dermatitis (Dock, 2005). Experimental studies
have documented that nickel is an animal carcinogen and water-insoluble salts such as
crystalline nickel sulphide and subsulphide are the most potent compounds (Dock,
2005). Dissolution of nickel particles within the cell could lead to high concentration
of intercellular nickel, which damage the genetically inactive heterochromatin and the
damage may involve cross liking of oxidized amino acids to DNA (Dock, 2005).
Other effects of nickel pointed out by ATSDR (2005) include the disturbance of
respiratory system and asthma, birth defects, vomiting and damage to
deoxyribonucleic acid (a component of genes) at high concentrations.
EPA (1996) recommends that aquatic water use levels for nickel should not be
more than 0.1 mg/l. In this study only 33 % of the total samples collected were found
to be within the recommended value and therefore, this could affect the aquatic
10
species found in the river. Lawrence et al. (2004) reported negative effects of nickel
on phototropic organisms such as algae and cyanobacteria.
The required nickel level by Tanzania guidelines for irrigation water is 0.1 mg/l.
Again in the study only 33% of all the samples met the recommended value and thus
at most points the water was not suitable for irrigation. According to Rowe and Magid
(1995) the recommended nickel value for irrigation water is 0.2 mg/l. Above this
threshold value nickel becomes toxic to a number of plants and its toxicity reduces at
neutral or alkaline pH levels. In this study only 38% of the samples met the 0.2 mg/l
value suggested by Rowe and Magid (1995).
In conclusion, there was insignificant variation of nickel concentrations between
the points upstream and downstream the mine. The mine was therefore not having a
significant impact on the river water quality. The fact that nickel values between
points upstream and downstream of the mine had no significant variation suggests that
the geology of the area is affecting the nickel levels.
1.00
0.90
0.80
Ni (mg/l)
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
W1
W2
W3
W4
S ampling points
1/14/2008
2/11/2008
3/10/2008
1/21/2008
2/18/2008
3/17/2008
1/29/2008
2/25/2008
RMPC-Ni
2/4/2008
3/3/2008
WHO
Fig.6. Nickel variation among river water sampling points for the period of 14 th Jan to 17th Mar
2008. (RMPC-Ni = receiving water (portable/groundwater) maximum permissible concentration
guideline, WHO = world health organization guideline for drinking water and W1-W4 = river points.)
4.2.5 Zinc
The results for zinc are shown in Fig. 7. Zinc levels ranged from 0.8 to 3.7 mg/l.
Values of Zn were all (100 %) above the Tanzanian acceptable level of 0.2 mg/l while
93% of samples were found to be within the 3.0 mg/l WHO guideline limit for
drinking water quality. The point upstream of the mine (W1) measured low values of
zinc compared to other points downstream. There were significant differences
(p<0.05) in zinc levels between (W1 and W2) and (W2 and W3) sampling points
while the variation in zinc levels between W1 and W3 were insignificant (p>0.05) at
95 % confidence level. High values of zinc in the study area could be related to
anthropogenic sources including mining activities, galvanized scraps, cast metal (ZnPb), brass (Zn-Cu), dry cells, vulcanized rubber and zinc oxides (white pigment),
which were scattered around the mine area. This was also noted by Kahatano et al.
(1995) around some rivers in the Lake Victoria Gold Fields. The standard deviation
ranged from 15% to 63% showing a wide variation of zinc during the study period at
the four sampling points.
11
In humans, zinc is required as a co-factor for a great number of enzymes
catalyzing the metabolism of proteins and nucleic acids and has also been shown to
play an important role in a variety of eukaryotic transcription factors (Dock, 2005).
Zinc deficiency cause growth retardation and delayed sexual maturation. Excess zinc
intake in diets can lead to deficiencies in iron, calcium and copper as it competes for
their binding sites in tissues thereby reducing growth, causing anemia, kidney
damage, fainting, nausea and stomach disorder (Vernet, 1989).
Zinc has been associated with impairment of river and stream water quality for
many years. High values of zinc that exceed 5 mg /l in the aquatic environment affect
the movements of fish in streams and may also have acute physiological effects on
fish (EPA, 1996). Skidmore (1992) demonstrated that acute exposure of rainbow trout
to zinc caused a severe inflammatory reaction in fish gills followed by circulatory
breakdown, tissue destruction, respiratory collapse and death. The State of Texas
(2005) also reported that the Neeches River was not meeting its requirements for
aquatic uses due to high levels of zinc, which were associated with reduction in
aquatic species diversity and abundance (Peplow, 2000). Although the species
diversity or impact of aquatic system was not studied in this study, it is important to
note that the relatively high levels of zinc at all points downstream of the mine may
potentially affect aquatic life and the health of the population that depend on the river.
4
3.5
Zn (mg/l)
3
2.5
2
1.5
1
0.5
0
W1
W2
W3
W4
S ampling points
1/14/2008
2/11/2008
3/10/2008
1/21/2008
2/18/2008
3/17/2008
1/29/2008
2/25/2008
RMPC-Zn
2/4/2008
3/3/2008
WHO
Fig.7. Zinc variation among river water sampling points for the period of 14 th Jan to 17th Mar
2008. (RMPC-Zn = receiving water (portable/groundwater) maximum permissible concentration
guideline, WHO = world health organization guideline for drinking water and W1-W4 = river points.)
The Tanzanian guideline value of 0.2 mg/l for irrigation water was not met in 100
% of total samples. Rowe and Magid (1995) point out that nickel levels above 0.2
mg/l are toxic to many plants at widely varying concentrations. The toxicity reduces
at higher pH values above 6 and in fine textured or organic soil. Lenntech (2004)
found that zinc - rich soils with zinc levels above 5 mg/l have limited number of plant
species that survive on them as zinc interferes with work of microorganisms and the
respiration of the earthworms, soil aeration, decomposition, soil fertility, plant
growth, development and productivity. Thus zinc toxicity reduces plant species
abundance and biodiversity. In this study it appears that the zinc levels in the river are
not acceptable for irrigation use.
12
Zinc contamination in mining areas may be related to mine waste dumps that
could be from the decomposition of carbon-zinc batteries disposal. The batteries are
used in underground mines for lighting. Zinc-carbon batteries are composed of a
manganese dioxide and carbon cathode, a zinc anode, and zinc chloride as the
electrolyte. Zinc contamination could also be caused by oxidation of sphalerite (ZnS)
from mineralized veins and oxidation of zinc fillings used to precipitate gold in the
cyanidation process in Tanzania (Kahatano et al., 1995). Effluents from mine ponds
into streams and rivers contain high levels of heavy metals, which cause danger to
species especially those dependent on streams and rivers. Ntengwe and Maseka
(2006) found out that almost all fish species in the Chambishi and Mwabishi streams
in Zambia exhibited stunted growth due to mine effluents containing high levels of Zn
and Ni. Studies in Tanzania by Tarimo (2007) found out that discarded batteries
polluted soils and water by increasing heavy metal content. During the rain season,
mine wastes are leached and add heavy metal ions such as Zn, Cu and Ni to the water
resources. Such phenomenon was also observed in Sweden by Linda (2002) that
weathering, leaching and soil erosion in gold mining areas contribute to water and soil
pollution due to release of heavy metal ions.
It can be concluded that the zinc values in the river points downstream of the
mine are significantly affected by mining activities. This can be deduced from the
significant differences between upstream and downstream points.
4. Conclusions and Recommendations
4.1 Conclusions
Based on the results of this study it was concluded that the Bulyanhulu River is
significantly affected by mining activities with respect to Ni, Fe and Zn, which makes
its water unsuitable for human consumption, aquatic life and irrigation use.
4.2 Recommendations
The following recommendations were made;




It is recommended that the mine should treat the effluent of the effluent
control ponds by precipitating out metals thus reducing their mobility through
seepage. Construction of additional ponds with adequate retention times that
can enhance the removal and retention of metals is also suggested.
It is recommended that lime and caustic soda should be added to the effluent
control ponds to neutralize the acid mine drainage and to elevate pH.
Further research should be conducted in both seasons wet and dry to assess the
seasonal variation of the pollutants.
The impact of the mine pollution on aquatic life should be investigated.
Acknowledgements
This paper presents part of the research results of an MSc study by Grace Nkuli at
the University of Zimbabwe under a WaterNet scholarship. The authors would like to
express their sincere gratitude to Bulyanhulu Gold mine (BGM) management for
allowing the research and also for providing assistance during the study.
13
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