Journal of Environmental Protection, 2011, 2, 1227-1239
doi:10.4236/jep.2011.29141 Published Online November 2011 (http://www.scirp.org/journal/jep)
Assessment of Mercury Pollution in Rivers and
Streams around Artisanal Gold Mining Areas of
the Birim North District of Ghana
Vincent K. Nartey1, Raphael K. Klake1, Ebenezer K. Hayford2, Louis K. Doamekpor1,
Richard K. Appoh3
1Department of Chemistry, Faculty of Science, University of Ghana, Legon, Ghana; 2Department of Earth Science, Faculty of Sci-
ence, University of Ghana, Legon, Ghana; 3Environmental Science Programme, Faculty of Science, University of Ghana, Legon,
Ghana.
Received August 19th, 2011; revised September 25th, 2011; accepted October 28th, 2011.
ABSTRACT
Artisanal gold mining in local communities is on the increase . This has led to concern s about mercury pollution result-
ing from these mining activities. This study was conducted to assess the level of mercury pollution in rivers and streams
around artisanal gold mining areas of the Birim North District of Ghana. Rivers, streams, sediments and boreholes
were sampled to determine total mercury levels during the wet and dry seasons and to explore the potential impact of
the mercury levels on water quality in the area. The results show that the total mercury concentrations measured up-
stream were significantly lower than concentrations in samples taken downstream. Also, the total mercury concentra-
tions measured in the stream water samples in both seasons exceeded the WHO guideline limit (1.0 µg/L) for drinking
water. However, one downstream total mercury concentration exceeded the guideline limit in the dry season. The total
mercury concentrations in sediments upstream and downstream in both seasons exceeded the US-EPA guideline value
of 0.2 mg/kg. The boreholes in the study area have total mercury concentrations exceeding the WHO guideline limit
during both seasons. Total mercury concentrations in the boreholes in the wet season were lower than the dry season.
Keywords: Mercury Pollution, Artisanal Gold mining, Birim North District, Ghana
1. Introduction
Mining has played a major role in the socio-economic
and infrastructural development of most developing coun-
tries, particularly in Africa and especially Ghana which
is the second largest gold producer in Africa [1].
Gold mining can be on large-scale and small-scale.
The technique used depends on the scale, the type of de-
posit and its location [2]. Small scale mining has been on
the increase in developing countries like Ghana. Mineral
production from small-scale mining accounts for appro-
ximately one-sixth of global mineral output [3]. Direct
employment by the small-scale mining sector in Ghana
as at the end of 2006 was about 600,000 [1]. In 2007,
about 239,331 ounces representing 9.6 % of total gold
production was recorded by the small-scale gold mining
sector in Ghana [1].
Artisanal mining encompasses small, medium, infor-
mal, legal and illegal miners who use rudimentary tech-
niques for mineral extraction and often operate under ha-
zardous, labor-intensive and highly disorganized condi-
tions. Despite these factors, artisanal mining is an essen-
tial activity in many de veloping countries, particularly in
regions where economic alternatives are critically limited.
In recent years, this sector has experienced unprece-
dented growth worldwide. In Ghana, where poverty rates
remain high, small-scale mining has become the best
earning opportunity for the economically active popula-
tion [4].
The methods for extracting gold have varied during
the years. Starting with simple small hand op erations like
gravity panning, there are now diverse techniques some
of which are amalgamation and cyanide leaching [5].
The earlier methods of extracting visible gold without
mercury or cyanide have less serious environmental im-
pacts than the present methods. In all, artisanal gold min-
ing is estimated to release up to 1350 tons of mercury to
the global environment annually [6]. About 5.0 tons of
mercury is released from small-scale mining operations
in Ghana each year [3]. Mercury emissions from these

Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas 1228 of the Birim North District of Ghana
activities are derived from poor practices, lack of know-
ledge about mercury toxicity and insufficient access to
appropriate techniques. Environmental and health im-
pacts resulting from the misuse of mercury and their ef-
fects on water bodies require coordinated actions and
global responses. These responses can only come after
there has been enough data on the level of mercury re-
sulting from artisanal mining.
Available literature shows that there have not been
past studies on the effects of artisanal mining on the le-
vels of mercury in artisanal mining areas. To understand
the scope and depth of the problems associated with ar-
tisanal mining, there is the need to study the levels of
mercury in a location where artisanal mining takes place.
One of these is the Birim area of Ghana. Most of the
communities in the area get their domestic water supply
from bore holes, rivers and streams. It is therefore im-
perative that the levels of mercury in these sources be
known. Fishing is also a common phenomenon in these
rivers and streams. The levels of mercury in these fishes
can be used to safeguard the health of over a million
people that rely on these rivers and streams for their fish
supply. Knowledge of the mercury levels will also en-
courage remedial measures to be taken before the water
is used for any purpose. The first objective of this study
was to determine the levels of total mercury in rivers,
streams, sediments and boreholes. Secondly, to compare
the temporal and spatial variations in streams sediments
and rivers. Thirdly to compare the levels of mercury in
these samples with WHO guideline values.
2. Materials and Methods
2.1. The Study Area
The Birim North District is within latitude 6.15oN -
6.35oN and longitude 0.20oW - 1.05oW. It is located in
the western end of the Eastern Region of Ghana. The dis-
trict with its capital at New Abirem is bordered by Kwa-
hu West District to the north; Asante-Akyem South,
Amansie East and Adansi South districts all to the west;
Birim South District to the south; and Atiwa and Kwae-
bibirem districts to the east (Figure 1).
The district covers an estimated total land area of
1,250 km2 representing about 6.47% of the total land
area of the Eastern Region. It is the second largest dis-
trict in terms of land area after the Afram Plains District,
in the Eastern Region [7].
2.2. Climate
The district lies within a wet semi-equatorial climatic
zone and therefore experiences a double maxima rainfall
pattern. The first rainfall season starts from late March
and ends in early July. The second season also starts from
mid August and ends in late October. The amount of
rainfall received in the district is between 1500 and 2000
mm per annum. Temperatures range between a minimum
of 25.2˚C and a maximum of 27.9˚C. The district has a
relative humidity of abou t 55.0% - 59.0% throughout the
year [7].
2.3. Relief and Drainage
The district is mostly u ndulating and hilly in na ture. The
hilly areas are underlain by lava flows and schist. The
lower areas of the district are also underlain by phyllite
and greywacke. The lower areas have relatively low rain-
fall compared with the hilly areas. The highest point in
the district is the Kwasiakwasi Mountain (N 06o28'09.6"
& W 00o54'44.3") located in the Kwasiakwasi Forest
Reserve and rises to a height of about 800 m above sea
level. The Kwasiakwasi Forest Reserve is the source of
streams such as Nyanoma, Nkwasua and Aprokuma.
The district is drained mainly by two rivers, the Pra
and its tributary the Birim. The tributaries of these rivers
in the district include the Nwi, Suten, Maman g, Adeche-
nsu, Sukrang, Nkwas ua, Nyanoma, Afosu, etc. All these
rivers flow generally from the northeast to the southwest
to join the Pra, which flows southwards and enters the
sea at Shama in the Western Region. The Pra River
serves as the boundary between the district and all the
three districts in the Ashanti Region bord ered to the west.
Also, the Birim Rive r serves as the southe rn boundary of
the district [7].
2.4. Geology and Hydrogeology
The geology of the study area consists mainly of Pro-
terozoic rocks of the Birimian (Upper and Lower Biri-
mian) and Tarkwaian systems. Dixcove Granitoids Com-
plex has intruded both the Birimian and Tarkwaian sys-
tems in many places in the district [8]. The Upper Biri-
mian rocks consist of black slates, sericite schist and
phyllites, with subordinate grey, sandy phyllites and gre-
wackes. The lower Birimian rocks also consist of black
phyllites, metasiltstones, metagreywackes, tuffaceous se-
diments, tuffs and hornstones [8].
The Tarkwaian system is chiefly sandstone, quartzite,
phyllite, shale and conglomerate and is resting on and
derived from the Birimian system [8]. The sandstone (a
quartzite) consists of variable amounts of feldspar, seri-
cite, chlorite, ferriferous carbonate, magnetite or hema-
tite and epidote. The Tarkwa Phyllite consists of chlori-
toid and magnetite or hematite with sericite and chlorite
[9]. The conglomerates consist of silicified Birimian green-
stone and hornstone with minor jasper, quartz, quartz-
porphyry, tourmaline-quartz rocks with Birimian phyl-
lites and schists in a matrix w ith q uartz, feldspar, ch lorite,
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Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas
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1229
Figure 1. Map of the Study Area.

Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas 1230 of the Birim North District of Ghana
carbonate, epidote, magnetite, chert and gondite [9].
The district lies almost wholly in the main mine ral de-
posit area of the Eastern Region, accounting for the many
small scale mining operations in gold and diamond.
Groundwater is the main source of domestic water sup-
ply in the study area. Most of the towns/villages rely on
groundwater with the exception of New Abirem and
Afosu where surface water taken from the Pra and Afosu
Rivers is treated and distributed. The underground water
reserve is rich, despite the scarcity and inadequacy of
potable water in many communities. Borehole yields in
the study area are in the range of 1 - 5 m3/hr. The rock
underlying the area lack primary porosity since they are
crystalline. Groundwater occurrence is therefore associ-
ated with the development of second ary porosity through
fissuring and weathering.
Groundwater circulation in the study area is mainly
localized due to the numerous mountains and hills that
act as groundwater divides. Its flow is therefore mostly
restricted to joints, fractures or other openings within the
crystalline rock formations. In general, there are two
types of aquifers: weathered rock aquifers and fractured
rock aquifers. These aquifers tend to be either confined
or semi-confined. Groundwater in the mining area is
known to be vulnerable to pollution from mining and this
may have serious effect on human health.
2.5. Sampling Sites
Even though the Birim North District has many rivers
and streams, the artisanal gold mining areas where the
study was conducted is drained by the Pra, Nwi, Suten,
Sereman, Nyanoma, Nkwasua, Aprokuma and Tainsu ri-
vers. Out of these, Pra, Nwi, Suten, Nyanoma, Nkwasua
and Tainsu were selected because of their strategic loca-
tions in relation to the artisanal mining activities and
their potential impact on domestic water supply in the
area. The six boreholes sampled are located in the areas
affected mostly by the mining activities. The sampling
sites were given different designations as shown in Ta-
ble 1. All the bore- holes have yields ranging from 1 - 3
m3/hr (Figure 2).
2.6. Sampling Methodology
Environmental Data Sampling
Sampling was designed to cover a 12 month period. The
samples were collected between the months of April,
2009 and February, 2010. April, June and August were
considered wet periods whilst October, December and
February were considered as dry periods even though
some rains occurred in the month of February.
Water and sediment sampling points were immedi-
ately upstream of the artisanal gold mining areas and
near discharge areas of all the rivers/streams. The sam-
pling points upstream of the artisanal gold mining areas
were located at least 2 km from the artisanal gold mining
area to prevent any possible contamination. The sam-
pling points near the discharge areas were also located
about 100 m upstream of the junction with the receiving
water body. In the case of River Nwi, a first order tribu-
tary of River Pra, samples were taken about 1km up-
stream of its first tributary in the mining area and also
100 m upstream of the confluence with River Pra. Water
and sediment samples from River Pra were taken about 2
km upstream before it enters the mining area and about 2
km downstream of the mining area. Two boreholes were
selected at each mining town/village and water samples
taken.
At each river/stream sampling point, about 300 cm3 of
water were taken from the centre of the stream/river at a
depth of about 10 to 20 cm below the water surface.
Sediment samples weighing about 300 g were also scooped
below the water surface from the centre of the stream/
river. These were cleaned of wood pieces, pebbles, shells,
leaves, etc. The borehole water samples were collected
directly from the well heads. The borehole pipe should
have been emptied by pumping before taking the sample
but because these boreholes are almost continuously
working throughout the day, the samples were collected
directly. The water samples were kept in pre-labelled
polypropylene bottles which have been rinsed with
10.0% HNO3. About 3 cm3 of concentrated HNO3 was
added to the water samples before its cap was fitted in
order to stabilize the mercury content, because trace
mercury is relatively stable at lower pH [10]. The sedi-
ment samples were put in pre-labelled transparent poly-
thene bags. The bags were tied, put into a second poly-
thene bag and sealed with duct tape. All the samples
were stored in an ice chest with ice to maintain a low
temperature (<4˚C) during transportation to the Envi-
ronmental Chemistry Laboratory of the Water Research
Institute for total mercury analysis.
2.7. Laboratory Analyses
The laboratory analyses were undertaken according to
procedures outlined by APHA, AWWA and WEF 1998)
[11]. Total mercury analysis was done at the Environ-
mental Chemistry Laboratory of the Water Research In-
stitute by Cold-Vapour Atomic Absorption Spectroscopy
(CVAAS).
2.7.1. Water Analyses
About 100 cm3 each of the water samples was transferred
into 125 cm3 conical flask. Approximately 5 cm3 of con-
centrated HNO3 was added and heated in a water bath at
95˚C for about one hour. It was filtered, cooled and
transferred into a 100 cm3 volumetric flask and diluted to
the mark. A working solution of 0.1 mg/L was prepared
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Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas 1231
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Figure 2. Hydrogeological Map of the Study Area Showing Sampling Points.

Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas 1232 of the Birim North District of Ghana
Table 1. Geographical Location of Sampling Sites.
Sampling Site Designation Name of Area GPS Position
Rivers/Streams
Upstream of Nyanoma Stream NYU Nyahnoma Hill N 06° 26' 50.2"
W 00 o 53' 45.3"
Downstream of Nyanoma Stream NYD Sakapia N 06o 26' 25.4"
W 00o 54' 00.4"
Upstream of Nkwasua Stream NKU Nkwasua Hill N 06o 26' 51.1"
W 00o 54' 44.4"
Downstream of Nkwasua Stream NKD Noyem N 06o 26' 27.4"
W 00o 54' 50.5"
Upstream of Tainsu Stream TAU Nyafoman N 06o 26' 27.5"
W 00o 55' 51.2"
Upstream of of Suten St ream SUU Sakapia N 06o 25' 51.6"
W 00o 53' 55.8"
Downstream of Suten Stream SUD Nyafoman N 0 6o 26' 07.0"
W 00o 56' 28.7"
Upstream of Nwi River NWU Mampong N 06o 28' 57.2"
W 00o 55' 00.8"
Downstream of Nwi River NWD Amenam N 06o 24' 59.2"
W 01o 00' 18.2"
Upstream of Pra River PRU Jamasi N 06o 33' 31.0"
W 00o 57' 11.8"
Downstream of Pra River PRD Prasokuma N 06o 24' 00.3"
W 01o 02' 26.2"
Boreholes
Borehole at Akoasi 1 AKB 1 Akoasi N 06o 27' 54.3"
W 00o 53' 42.0"
Borehole at Akoasi 2 AKB 2 Akoasi N 06o 27' 51.2"
W 00o 53' 13.6"
Borehole at Noyem 1 NOB 1 Noyem N 06o 27' 09.6"
W 00o 55' 57.4"
Borehole at Noyem 2 NOB 2 Noyem N 06o 27' 06.5"
W 00o 55' 44.4"
Borehole at Nyafoman 1 NYB 1 Nyafoman N 06o 25' 57.2"
W 00o 56' 40.7"
Borehole at Nyafoman 2 NYB 2 Nyafoman N 06o 25' 48.2"
W 00o 56' 42.5"
Artisanal Mining/Processing Sites
Sakapia Site NYP N 06o 26' 31.3"
W 00o 54' 00.7"
Noyem New Site NKP N 06o 26' 34.4"
W 00o 54' 44.3"
Nyafoman Site 1 TAP N 06o 26' 31.3"
W 00o 56' 42.5"
Nyafoman Site 2 NWP N 06o 26' 32.9"
W 00o 56' 00.6"
Nyafoman Site 3 SUP N 06o 26' 05.7"
W 00o 56' 34.1"
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Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas
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from a commercially prepared solution of 10 mg/L. A
calibration standard solution of 2.0, 5.0 and 10.0 µg/L
were prepared from the working solution in 50 cm3 vo-
lume with the addition of 1 cm3 each of concentrated
HNO3 and 1.0 g each of NaCl. The samples and refer-
ence materials were prepared using the same methodo-
logy.
A 50 cm3 volume of blank and the calibration stan-
dards were transferred into flasks and 1.0 cm3 of 5.0%
stannou s chlorid e was then add ed. The ab sorban ce sign al
was noted at both 30 s and 60 s for the blank and each
calibration solution. A graph of absorbance against con-
centration was generated. The procedure was repeated
for the samples alongside reference materials and the
corresponding absorbance extrapolated from the graph to
obtain the concentrations.
2.7.2. Sediment Analyses
The sediment samples were dried at a temperature of
80˚C for about 12 hr. The cooled samples were ground,
homogenised and sieved using 180 µm aperture pore size
sieve net. About 0.2 g of the dry samples were weighed
into teflon tubes and 2 cm3 of concentrated HNO3 slowly
added. One reference material (SD-M-2/TM marine sedi-
ment, IAEA) and two blanks were also treated in the
same manner. The Teflon tubes were tightly closed,
shaken and placed in stainless steel bombs. The stainless
steel bombs were placed on a hot plate and heated at a
temperature of 150˚C continuously for six hours.
The samples together with the blank and reference
material were allowed to cool to room temperature be-
fore releasing the pressure by opening the bomb. The
samples were transferred into graduated polypropylene
tubes. The Teflon tubes were rinsed three times with
deionised water and the rinsed solution added to the
samples in the polypropylene tubes. Solutions were then
diluted with deionised water to 50 cm3 and mixed tho-
roughly. The particles were then allowed to settle over-
night and the digested sample analysed using Unicam
969 Atomic Absorption Spectrometer (AAS).
2.8. Quality Control
Quality control samples including blanks and certified
reference materials were prepared according to APHA,
AWWA and WEF (1998) [11]. Certified reference mate-
rials were digested along with the samples to check the
accuracy of the method. The reference material for the
sediment samples was SD-M-2/TM marine sediment
(IAEA) and that of the water samples was NIVA 0736,
though not digested. A quality control standard was run
routinely during the sample analysis to monitor instru-
ment drift and overall quality o f the analysis. Analysis of
all blanks and certified reference materials showed no
inherent bias in the method of analysis for total mercury.
3. Results and Discussions
All statistical analyses were performed using SPSS (ver-
sion 17.0) for windows. Comparisons were made be-
tween upstream means and downstream means for both
stream water and sediment samples. Comparisons were
also made between wet and dry season means for stream
water, borehole water and sediment samples. The paired
sample t-test was used to test for differences in the
means of mercury concentrations in the upstreams and
downstreams of the rivers/streams as well as differences
between wet and dry periods. A probability value of p <
0.05 was considered as statistically significant in this
study.
Also, the results of the water samples were compared
with the WHO guideline value (1.0 µg/L) for drinking
water [12] and that of the sediment samples were com-
pared with the US EPA guideline value of 0.2 mg/kg
[13]. Finally, comparisons were made with results from
studies conducted elsewhere with similar characteristics.
The results of total mercury analysis for the study pe-
riod are presented in Tables 2-4, Figures 3-5. A com-
parison is made between the upstream and downstream
means as well as the wet season and dry season means.
The results are compared with studies conducted with
similar characteristics. Also, the results of the water sam-
ples were compared with the WHO guideline value (1.0
µg/L) for drinking water [12] and that of the sediment
samples are compared with the US EPA guideline value
of 0.2 mg/kg [13]. Th e con c entration s falling abov e th ese
safe limits are identified and discu ssed.
Although there are clear guidelines of limit values for
maximum metal concen trations in water, air and food, as
yet there is no equivalent consensus of permissible levels
of metals in soils and sediment. This arises primarily as a
result of great uncertainties of metal dose-relatio nships in
soil and sediment media and has resulted in bewildering
and sometimes contradictory guideline values [14].
3.1. Total Mercury in River/Stream Water
All the total mercury concentrations recorded in the wet
season were lower than the corresponding dry season
concentrations with the exception of the upstream of the
River Nwi where the dry season total mercury concentra-
tion (0.311 µg/L) was lower than the wet season total
mercury concentration (0.358 µg/L), Table 2. The dif-
ference in total mercury concentration between the wet
and dry seasons was significant at 5.0%, since probabil-
ity calculated (0.001) is less than 0.05.
This reveals systematic seasonal variations in total
mercury concentrations. The increase in total mercury

Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas 1234 of the Birim North District of Ghana
Table 2. Comparison of Mean Concentrations of Total Mer-
cury (µg/L) in Stream/River Water Samples with Known
Artisanal Gold Mining Sites in the World .
This Study Wet Dry Mean
NYU 0.250 0.383 0.317
NYD 0.578 0.672 0.625
NKU 0.146 0.331 0.239
NKD 0.282 0.987 0.635
TAU 0.113 0.349 0.231
TAD 0.872 1.343 1.108
SUU 0.167 0.412 0.290
SUD 0.541 0.694 0.618
NWU 0.358 0.311 0.335
NWD 0.674 0.822 0.748
PRU 0.045 0.248 0.147
PRD 0.370 0.643 0.507
Table 3. Comparison of Mean Concentrations of Total Mer-
cury in Borehole Water Samples with Known Artisanal
Gold Mining Sites in the World.
This Study Wet Dry Mean
AKB1 0.283 0.473 0.378
AKB2 0.383 0.437 0.410
NOB1 0.237 0.439 0.338
NOB2 0.078 0.390 0.234
NYB1 0.619 0.482 0.551
NYB2 0.146 0.301 0.224
Sampling Sites Hg Levels (ug/L) Reference
Borehole (Adaase) 4.00 [14].
Adaase Borehole No. 162 2.00 [14].
Dokyiwa Borehole No.
238 <1.00 [14].
Dokyiwa Borehole No.
291 1.00 [14].
Ntonnsua Borehol e 1.00 [14].
New Bidiem Borehole No.
110 1.00 [14].
New Bidiem Borehole No.
201 <1.00 [14].
Akatakyieso Borehole 1.00 [14].
Other Nations with Active AGM
Paniki (Indonesia) 0.095 [16].
Kumahukur (Indonesia) 0.090 [16].
Malayalang (Indonesia) 0.070 [16].
Koka (Indonesia) 0.095 [16].
Table 4. Comparison of Mean Concentrations of Total
Mercury(mg/Kg) in Stream / River Sediment Samples with
Known Artisanal Gold Mining Sites in the World.
This Study Wet Dry Mean
NYU 0.507 0.891 0.699
NYD 1.628 2.184 1.906
NKU 0.381 1.212 0.797
NKD 1.852 4.745 3.299
TAU 0.732 1.881 1.307
TAD 2.323 4.886 3.605
SUU 0.411 0.390 0.401
SUD 1.308 3.769 2.539
NWU 0.396 0.381 0.389
NWD 0.758 2.807 1.783
PRU 0.134 0.405 0.270
PRD 0.401 1.415 0.908
Sampling Sites Hg Levels (mg/kg) Reference
R. San (Sansu) 2.600 [14].
R. Kwame Tawia
(Dokyiwa) 0.260 [14].
R. Fena (Hia No. 2) 0.280 [14].
R. Fena
(Fenaso Faaman) 0.290 [14].
R. Fena (Adaase) 0.290 [14].
R. Fena (Adaase) 1.460 [14].
River Kwabrafo
( Kwabrafoso) 1.440 [14].
River Supu
(Ntonnsua) 3.020 [14].
Lower Pra River 0.026 [15].
Upper Pra River 0.018
Offin River 0 .023 [15].
Other Nations with Active AGM
South-western Amazon
Basin (Brazil) 0.122 [17].
Talawan Watershed
(Indonesia) 6.820 [18].
Mindanao Island
(Philippines) 21.03 [19].
concentration during the dry season could be attributed
to two things. The first is increased mining activities
during the dry season with corresponding increase in
mercury use. The other reason is the evaporation of sur-
face water resulting in increased mercury concentrations.
During the study period, there was no evidence of in-
creased mining activities. Increase in total mercury con-
centration can therefore be wholly attributed to evapora-
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Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas
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1235
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
NYU NYD NKU NKDTAUTADSUUSUD NWUNWD PRUPRD
Sampling Points
Total Mercury (ug/L)
Wet Season
Dry Seas on
WHO Guide l i ne
Figure 3. Total Mercury Analysis of Stream/River Water Samples (NYU) = Upstream of Nyanoma Stream, (NYD) = Down-
stream of Nyanoma Stream, (NKU) = Upstream of Nkwasua Stream, (NKD) = Downstream of Nkwasua Stream, (TAU) =
Upstream of Tainsu Stream, (TAD) = Downstream of Tainsu Stream, (SUU) = Upstream of Suten Stream, (SUD) = Down-
stream of Suten Stream, (NWU) = Upstream of Nwi River, (NWD) = Downstream of Nwi River, (PRU) = Upstream of Pra
River, (PRD) = Downstream of Pra River.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
AKB1 AKB2 NOB1 NOB2 NYB1 NYB2
Sampling Points
Total Mercury (ug/L)
Wet Season
Dry Season
WHO Guideline
Figure 4. Total Mercury Analysis of Borehole Water Samples (AKB1) = Borehole at Akoasi 1, (AKB2) = Borehole at Akoasi 2,
(NOB1) = Borehole at Noyem 1, (NOB2) = Borehole at Noyem 2, (NYB1) = Borehole at Nyafoman 1, (NYB2) = Borehole at
Nyafoman 2.

Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas 1236 of the Birim North District of Ghana
0.0
1.0
2.0
3.0
4.0
5.0
6.0
NYU NYD NKU NKDTAUTADSUUSUDNWUNWD PRUPRD
Sampling Points
Total Mercury (mg/kg)
Wet Seas on
Dry Seas on
US-EPA Guideline
Figure 5. Total Mercury Analysis of Stream/River Sediment Samples (NYU) = Upstream of Nyanoma Stream, (NYD) =
Downstream of Nyanoma Stream, (NKU) = Upstream of Nkwasua Stream, (NKD) = Downstream of Nkwasua Stream, (TAU)
= Upstream of Tainsu Stream, (TAD) = Downstream of Tainsu Stream, (SUU) = Upstream of Suten Stream,( SUD) = Down-
stream of Suten Stream, (NWU) = Upstream of Nwi River, (NWD) = Downstream of Nwi River, (PRU) = Upstream of Pra
River, (PRD) = Downstream of Pra River.
tive effects. Also, during the dry season, river mixing is
very minimal and this prevents mercur y in bottom layers
of the rivers from coming to the surface to be volatilized.
None of the wet season total mercury concentrations
exceeded the WHO guideline value (1.0 µg/L) for drink-
ing water [12]. Even though that of the downstream of
Tainsu River (0.872 µg/L) was considerably close. The
lowest total mercury concentration recorded during the
dry season was 0.248µg/L in the River Pra.
The total mercury concentrations were higher in all the
downstreams of the rivers/streams than the correspond-
ing upstream. The difference is significant at 5.0% since
probability calculated (0.001) is less than 0.05. This su-
ggests that the gold recovery activities contribute immen-
sely to the level of mercury in these water bodies, result-
ing in increased mercury concentrations downstream of
each of the rivers/streams.
None of the upstream total mercury concentrations
exceeded the WHO guideline value (1.0 µg/L) for drink-
ing water [12]. The lowest upstream total mercury con-
centration of 0.045 µg/L was recorded in the Pra River
during the rainy season whilst the highest (0.412 µg/L)
was recorded in the River Suten during the dry season.
The lowest downstream total mercury concentration of
0.282 µg/L was recorded in the Nkwasua River during
the wet season and the highest (1.343 µg/L) which ex-
ceeds the WHO guideline value (1.0 µg/L) for drinking
water was recorded in River Tainsu during the dry sea-
son.
Other downstream total mercury concentrations which
were significant but lower than the WHO guideline value
(1.0 µg/L) for drinking water [12] included Nkwasua
(0.987 µg/L) during the dry season, Tainsu (0.872 µg/L)
during the wet season and Nwi (0.822 µg/L) during the
dry season.
In both the wet and dry seasons, trends in total mer-
cury concentrations showed peak values at the down-
stream of River Tainsu. This may be d ue to the proximity
of a gold processing site to the downstream of the river.
There were very significant variations in the total mer-
cury concentrations among the downstream sampling po-
ints (range = 0.282 – 1.343 µg/L) th an the upstream sam-
pling points (rang e = 0.045 – 0.412 µg/L) indep endent of
the sampling time. These variations were most likely the
result of the intensity of processing activities that take
place along the individual rivers.
In comparing with other studies conducted in Ghana
and other countries, the data available did not differenti-
ate between wet and dry periods and therefore the com-
parisons are made between the means only. Table 2
gives the comparative resu lts for water samples from the
study area, other artisanal gold mining areas in Ghana
with similar geology and three other known artisanal
gold mining sites in the world. The Rivers Fena, Kwa-
C opyright © 2011 SciRes. JEP

Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas 1237
of the Birim North District of Ghana
brafo, Kwame Tawia, Supu, San, Buama and Jimi are all
located in the Offin Sub-basin of the Pra Basin. The ri-
vers in the Talawan watershed (Indonesia) include Lotta,
Pancuran IX, ‘Sea’, Malalayang, Paal II, Perumnas and
Kilu. The Mutum Parana, Prainha, Humaita, Porto Velho
and Cachoreira Rivers are all located in the South-west-
ern Amazon Basin where most gold mining activities in
Brazil occur.
A comparison of the data from this stud y with that ob-
tained by others at the River Pra basin in previous studies
revealed that all the total mercury concentrations repor-
ted were relatively higher than those recorded at all the
sampling points in this study [15,16]. The differences
could be attributed to factors such as the length of time
that gold processing has taken place in the rivers/streams,
the period of sampling, the sample collection/handling
procedures as well as analytical tools employed.
The total mercury concentrations in the river/stream
water samples collected from the study area were rela-
tively higher than values recorded) at the Talawan Wa-
tershed (Indonesia) [17]. Also , the total mercury concen-
trations in the South-western Amazon Basin (Brazil)
were relatively lower compared to the study area whereas
that of the Philippines (Mindanao Island, 754.00 µg/L)
far exceeds levels recorded in the study area.
3.2. Total Mercury in Borehole Water
In wet and dry seasons, trends in total mercury concen-
trations showed peak values at NYB1. This could be as a
result of the proximity of NYB1 to the downstream of
River Suten which also serves as a gold processing site.
The mean mercury values for both seasons were 0.291
µg/L (wet) and 0.420 µg/L (dry). The total mercury con-
centrations measured in the wet season were lower than
the corresponding dry season concentrations with the
exception of NYB1 where the wet season total mercury
concentration (0.619 µg/L) was higher than the dry sea-
son total mercury concentration (0.482 µg/L). NYB1
recorded the highest dry season total mercury concentra-
tion of 0.482 µg/L whilst the lowest of 0.301 µg/L was
recorded at NYB2. The lowest wet season total mercury
concentration of 0.078 µg/L was measured at NOB2 and
the highest 0.619 µg/L at NYB1. The difference in total
mercury concentrations between the two seasons was
insignificant at 5.0%, since probability calculated (0.096)
is greater than 0.05.
None of the total mercury concentrations exceeded the
WHO guideline value (1.0 µg/L) for drink ing water [12].
Measured total mercury concentrations in this study
ranged from 0.078 µg/L to 0.619 µg/L in the wet season
and from 0.301 µg/L to 0.482 µg/L in the dry season.
This shows that there are variations among the various
sampling sites in the total mercury concentrations meas-
ured in the wet season more than those measured in the
dry season.
Table 3 gives the comparative results for borehole
water samples from the study area, other mining areas in
Ghana and artisanal gold mining sites located in the Ta-
lawan watersh e d of Ind o nesia.
A comparison of the data from this stud y with that ob-
tained in a study at Obuasi and its surrounding commu-
nities show that all the total mercury concentrations re-
ported were relatively higher than that recorded at all the
sampling points in this study [15]. The differences could
be attributed to factors such as the depth of the boreholes,
soil type, proximity to gold processing sites as well as
the length of time that gold mining has taken place in the
areas. The mean total mercury concentrations in the
borehole water samples collected from the study area
were also relatively higher than all the known sites in In-
donesia.
3.3. Total Mercury in River/Stream Sediments
Sediments represent an important component of aquatic
ecosystems because of the niche and food source they
provide for benthic aquatic organisms. The protection of
sediment quality is therefore viewed as a logical and
needed extension of water quality protection. All the
total mercury concentrations measured in the dry season
were higher than the corresponding wet season concen-
trations with the exception of the upstream of Rivers Nwi
and Suten, Table 4. In the case of the upstream of River
Nwi, the wet season total mercury concentration was
0.396 mg/kg an d the dry season total mercury con centra-
tion was 0.381 mg/kg. Also, the wet season total mercury
concentration of the upstream of River Suten was 0.411
mg/kg whereas the dry season concentration was 0.390
mg/kg. The difference in total mercury concentration
between the wet and dry seasons was significant at 5.0%
since probability calculated (0.003) is less than 0.05.
Two reasons may have contributed to this seasonal
variation in total mercury concentration. The first is in-
creased mining activities during the dry season with cor-
responding increase in mercury use. The other reason is
the evaporation of surface water resulting in increased
mercury concentrations in the water and sediments. Dur-
ing the study period, there was no evidence of increased
mining activities. In crease in total mercury concentration
can therefore be wholly attributed to evaporative effects.
Also, during the dry season, river mixing is very minimal
and this prevents mercury in bottom layers of the sedi-
ments from coming to the surface to be volatilized.
The total mercury concentration s of the upstreams and
downstreams of all the rivers/streams during both the wet

Assessment of Mercury Pollution in Rivers and Streams around Artisanal Gold Mining Areas 1238 of the Birim North District of Ghana
and dry seasons exceeded the US EPA guideline value of
0.2 mg/kg with the exception of the upstream of the Pra
River (0.134 mg/kg) during the wet season. The total
mercury concentrations were lower in all the upstreams
of the rivers/streams than the corresponding downstreams.
The difference is significant at 5.0% since probability
calculated (0.001) is less than 0.05. This may be as a
result of the dumping of contaminated tailings and waste
water into the water bodies, resulting in increased mer-
cury concentrations in the sediments downstream of each
of the rivers/streams.
The highest upstream total mercury concentration of
1.881 mg/kg was recorded in the Tainsu stream during
the dry season whilst the lowest (0.134 mg/kg) was re-
corded in the Pra River during the rainy season. The
highest downstream total mercury con centratio n of 4.886
mg/kg was recorded in the Tainsu stream during the dry
season and the lowest (0 .401 mg/kg) was recorded in the
Pra River during the wet season. Other downstream total
mercury concentrations which were very significant in-
clude Nkwasua (4.745 mg/kg) and Suten (3.769 mg/kg)
during the dry season.
In both the wet and dry seasons, trends in total mer-
cury concentrations showed peak values at the down-
stream of Tainsu and Nkwasua streams, Figure 5. This
could be attributed to the fact that the downstream of
both streams are very close to gold processing sites. There
were very significant variations in the total mercury con-
centrations among the downstream sampling points
(range = 0.401 - 4.886 mg/kg) more than the upstream
sampling points (range = 0.134 - 1.881 mg/kg) indepen-
dent of the sampling time. The differences in intensity of
processing activities that take place along the individual
rivers may have accounted for this.
Generally, metals in sediments do not have immediate
implications for human health as long as humans do not
consume these sediments directly, but they can have se-
rious consequences when they enter the food chain. Ta-
ble 4 gives the comparative results for sediment samples
from the study area, other mining areas in Ghana with
similar geology and three other known artisanal gold
mining sites located in Brazil, Indonesia and Philipp ines.
A comparison of the data from this stud y with another
on the Upper and Lower Pra [16]. revealed that the total
mercury concentrations measured at all sampling points
in this study exceeded the concentrations in the Upper
Pra (0.018 mg/kg), the Lowe r Pra (0.026 mg/kg) and the
Offin (0.023 mg/kg) Rivers. Another comparison with a
study showed differential variation among the total mer-
cury concentrations [15]. The difference could probably
be due to differences in the length of time that gold pro-
cessing has taken place in the rivers/streams, sediment
grain size, organic matter content, sampling seasons, the
sample collection/handling procedures as well as analy-
tical tools employed.
Compared with other active AGM sites in the world,
the mean mercury values obtained in the study sediments
were higher than that of Brazil, but lower than that of the
Philippines and Indonesia.
4. Acknowledgements
Our sincere thanks go to Mr. Felix Okyere Amoah of
Land-tech Engineering Ltd. for helping pick all the GPS
coordinates and also Mr. H. Komladzei of the Map
Room of the Water Research Institute fo r drawing all the
maps in this work. W e also appreciate the role played by
Messrs Michael Dzorleku and Michael Afram Danquah
of the Environmental Chemistry Laboratory of the W ater
Research Institute in the analyses. The role played by the
field assistants Messrs Agyarko Ayeh Asiedu and Daniel
Asomani is acknowledged
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