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INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 2, No 2, 2011
© Copyright 2010 All rights reserved Integrated Publishing Association
Research article ISSN 0976 – 4402
Received on September, 2011 Published on November 2011 1048
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its
Control on Mercury Methylation in Stream Sediments Corpus, T.J.
1, David, C.P.
1, Murao, S.
2, Maglambayan, V.
3
1- National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon
City, Philippines
2- Institute for Geo-Resources and Environment, National Institute of Advanced Industrial
Science and Technology, Tsukuba City, Japan
3- Exploration Division, Philex Mining Corporation, Pasig City, Philippines
doi:10.6088/ijes.00202020062
ABSTRACT
Elevated mercury (Hg) concentrations have been found in the Ambalanga Catchment,
Benguet, where small-scale gold mining (SSM) is the main source of livelihood. To
determine the distribution of total mercury (THg) and methylmercury (MeHg), and the
possible physical controls on Hg methylation in the watershed, stream sediment sampling in
the eight subbasins of the Ambalanga Catchment was conducted on two periods: low-flow
(LF) stage in November 2001 and high-flow (HF) stage in July 2003. Results revealed high
THg concentrations in three subbasins (Acupan, Dalicno, and Sangilo) in the 2001 period and
six subbasins (Acupan, Dalicno, Sangilo, Surong, Gold Creek, and Upper Ambalanga) in
2003. The increase in contaminated subbasins is attributed to the increase in river discharge
which resulted in increased erosion of contaminated sediments. Significantly high
concentrations of MeHg were found in two subbasins (Acupan and Lucbuban) in 2001 and
four subbasins (Acupan, Dalicno, Sangilo, and Upper Ambalanga) in 2003. The high MeHg
may be driven by the enhancement of the methylation process in areas with large amounts of
fine-grained sediments that accumulated in lower hydrologic gradient (and ensuing increased
organic activity) close to and at some distance downstream from the point sources.
Keywords: Methylmercury, Total mercury, Background concentration, Methylation,
Channel morphology, Benguet
1. Introduction
Small-scale mining (SSM) in many Third World countries employs Hg amalgamation to
recover gold from river sediments, soil, alluvium, and lode ores (Lacerda, 1997; Lin et al.,
1997; Miguel, 2000; Avocat et al., 2001; Stamenkovic et al., 2004). Hg amalgamation has
been one of the main sources of Hg pollution in the aquatic environment (Lacerda, 1997;
Akagi et al., 2000). Transport of Hg in the stream is primarily in a particulate (solid) phase
which accounts for 70-90 % of total Hg transported in streams impacted by mine tailings
(Rytuba, 2000). Both Hg and MeHg are adsorbed onto iron oxy-hydroxide substrate and clay
particles or colloids (Rytuba, 2000; Miguel, 2000).
MeHg is the most toxic form of Hg commonly found in the environment (Enger and Smith,
1998; Winch et al., 2008). It is the form of Hg that is of greatest concern for the environment
and human health, as it is highly toxic and bioconcentrates up the food web, eventually
accumulating in fish, top predators, and humans (Wolfe et al., 1998; USEPA, 2001b). When
ingested in sufficient amounts by humans, Hg causes damage to the brain, kidney, and
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1049
nervous system, and in extreme cases, death (USEPA, 1994; Lacerda, 1997; Enger and Smith,
1998; Cortes-Maramba et al., 2006). Hg methylation is primarily a result of anaerobic
microbial activity, which is typically enhanced in sediments with high organic matter
(Compeau and Bartha, 1985; Nevado et al., 2009). Stamenkovic et al. (2004) reported that
both pond/wetland and channel sites exhibited high potential for Hg methylation, for higher
rates would be expected at sites with slower water. Seasonal changes in sediment organic
content and the fraction of KOH-extractable THg may be important in controlling net Hg (II)-
methylation rates (Flanders et al., 2010). They also observed that the highest sediment MeHg
concentrations were in habitats with large amounts of fine-grained sediment driven by lower
hydrologic gradient.
Since the 1970s, artisanal miners in the Ambalanga Watershed have been employing Hg
amalgamation to extract gold from its ore, and later dumping the Hg-contaminated mine
tailings directly into the Ambalanga River. SSM in the Ambalanga Catchment presents
potential risks to the local community and the environment because of the unregulated
amalgamation practice and discharging of mine tailings into the river system. Floresca et al.
(1995) estimated the tonnage and gold grades of mine tailings produced by the small-scale
gold miners (averaging 430 tonnes/month at a grade range of 3.45 to 12.07 g/t Au). Mining
practices, gold-recovery processes, and problems encountered by small-scale miners in the
area have been documented by Caballero (1996), Cabria et al. (2002), Maglambayan and
Murao (2002), and Baluda (2002). Mercury contamination is cited as one of the pressing
environmental problems in these small-scale operations.
2. Materials and Method
2.1 Sample Collection
Sampling of stream sediments was conducted on two occasions: in November 2001 and July
2003. Sampling sites are on second- and third-order tributaries that drain mineralized areas
with known SSM activities and are located downstream of the gold-processing plants. A
control site not influenced by SSM in the Lucbuban Subbasin was also selected to establish
the Hg background level in the area. Lucbuban was selected since the catchment is barren of
gold mineralization and has no SSM and gold-processing history.
Thirty-seven sediment samples were collected comprising 17 sites in the November 2001
sampling period and 20 in July 2003 (Figure 1). Stream sediments were gathered from low-
velocity river channels where fine sediments accumulate. Fresh hand gloves were worn and
replaced at every sample site to avoid possible contamination. Polypropylene bottles (125-ml)
served to contain the composited sediments samples hand-grabbed from five randomly-
selected points. Fine fractions (minus 63 µm) were later collected by wet-sieving through a
0.063 mm nylon-mesh sieve by washing with deionized water. After air-drying, the sample
fractions were pulverized using porcelain mortar and pestle.
2.2 Analytical Procedure
All analytical procedures were carried out at laboratories in the U.S. and in Canada. Frontier
Geosciences Inc. in Seattle conducted the analysis for THg and MeHg concentrations for the
2001 samples. The sediments were digested using cold aqua regia. Analysis was done by
SnCl2 reduction, dual amalgamation, and cold vapor atomic fluorescence spectrometre (CV-
AFS) detection using modified EPA method 1631 (USEPA, 1999). Meanwhile, the MeHg in
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1050
sediments was prepared by bromide/methyl extraction and analyzed by aqueous phase
ethylation, isothermal GC separation and CV-AFS detection using modified EPA method
1630 (USEPA, 2001a).
Figure 1: Sampling location map showing the eight subbasins of the Ambalanga Catchment.
Two laboratories in Canada performed analyses in the July 2003 sediment samples. Total Hg
on fine sediment fractions was examined by ACME Analytical Laboratories Ltd. in
Vancouver, while the MeHg concentrations by Norwest Labs in Surrey. At ACME, the
samples were digested with 6 ml of HCl- HNO3-H2O (1:1:1) at 95°C for 1 hour and the
solutions were diluted to 20 ml. The THg was extracted with methyl isobutyl ketone (MIBK)
followed by ICP-MS technique.
At the Norwest Labs, samples for MeHg analysis were extracted into methylene chloride to
avoid possible methylation artifact effects followed by flameless atomic absorption
spectrometry method modified from Kennedy and Crock (1987). Samples for THg in
sediments were digested with 45% NaOH and L-cysteine and were reduced by SnCl2. CdCl2
is added to the SnCl2 (known as the Magos’ reagent) followed by cold vapor atomic
absorption spectrometry using a 5100 Perkin-Elmer instrument.
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1051
3. Results and Discussion
3.1 Hg Concentrations in Stream Sediments - November 2001
Hg distribution in sediments is widely variable in 2001 (0.005-1.86 ng/g MeHg and 1.18-
2,600 ng/g THg). Among the eight subbasins studied, Lucbuban was selected as a control site
(MAU1-E) for background concentration. Showing the highest Hg concentration among the
four sites represents the background concentration (42 ng/g) in the area. This is consistent
with the global background range in sediments at 10-50 ng/g (Gustin et al., 1994). In the
2001 period, three subbasins (Acupan, Dalicno, and Sangilo) revealed high concentrations for
THg and two subbasins (Acupan and Lucbuban) for MeHg (Figure 2). In general, high
concentrations for both THg and MeHg are coincident, although the absolute MeHg values
are comparatively low. Although MeHg levels are invariably low, reported values of >0.10
ng/g MeHg have been considered anomalous. In subbasins with elevated THg concentrations,
the background has been exceeded by a factor of 4 to 86.
Figure 2: High THg levels in Acupan, Dalicno, and Sangilo Subbasins and MeHg peaks
at Acupan and Lucbuban in 2001. Note that concentrations are in log scale.
In this study, Hg concentrations in sediments are grouped into four classes: 1) high MeHg-
high THg, 2) low MeHg-high THg, 3) high MeHg-low THg, and 4) low MeHg-low THg
(Figure 3). The first class is demonstrated only in the Acupan Subbasin, showing the highest
concentrations for both MeHg (0.18-1.86 ng/g) and THg (618-2600 ng/g) from four sites
(BAT-1E to BAT-4E). The high Hg concentrations are one order of magnitude above the
background level. The highest THg level (BAT-1E) was collected downstream of the Acupan
SSM area. Another elevated concentration (BAT-4E) in the Acupan Subbasin is evident
(Figure 2). This may have been distributed from the contaminated sediments coming from the
Dalicno Subbasin and the Upper Ambalanga Subbasin through a diversion tunnel located
upstream of and not far from BAT-4E. In terms of milling production, contribution from
Acupan accounts for 35%, assaying at 9.29 g/t Au in the Acupan proper, and with the highest
number of ball mills (40%) in the study area (Floresca et al., 1995).
Two subbasins (Dalicno and Sangilo) reflected low MeHg and high THg levels. THg
concentrations are considered significant, which are 30 and 7 times above background
concentration, respectively. Floresca et al. (1995) reported ten ball mills (11%) in Dalicno
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1052
with 3% share in milling production, and with moderately high assays of the mine tailings
(6.75 g/t Au). However, no recorded processing and production history was obtained for
Sangilo. This suggests that the source of the high Hg concentrations (7-times above local
background level) comes from SSM activity, by the release of mine tailings into the river
system during ore-processing. Also, the depressed MeHg concentrations could be a function
of the low organic content and probably the short distance (<1 kilometre) from the source
area to the sampling site. This may have hindered the methylation process to its full extent.
Likewise, moderately-elevated concentrations are manifested in two subbasins (Surong at
SUR-1E and MAN-1E, and Gold Creek) and at site AMB-1E. The moderate THg
concentrations could be attributed to the fact that most of the ore feed is from the peripheral,
low- to medium- grade quartz-calcite veins. For another, the tailings are mainly dumped into
small ponds located at some distance from the river system. What is at risk is the likelihood
of contaminating the groundwater adjacent to processing plants.
Figure 3: Elevated MeHg and THg levels in Acupan, Dalicno, and Sangilo Subbasins
on both sampling events.
As shown in Figure 2, there is a general downstream decreasing trend in concentrations of
THg along Batuang (Acupan) - Ambalanga River, starting from BAT-1E to BAT-4E and
dropping drastically at AMB-1E. In comparison, the MeHg concentrations indicated a
general inverse trend, increasing downstream, although of comparatively low values, over the
THg concentrations, and decreasing abruptly at AMB-1E.
Relatively high MeHg concentrations (0.16 ng/g at site PIT-1E and 0.17 ng/g at TUK-1E)
with corresponding low THg levels are also observed (Figure 2). Site PIT-1E is located in
the headwaters of the Acupan Subbasin, upstream of ore-processing plants. The elevated
MeHg concentration at PIT-1E is probably due to the Hg associated with the occurrence of
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1053
gold veins (although no processing plants were observed) in the vicinity that was enhanced
by the probable higher availability of organic matter. Site TUK-1E in the Lucbuban
Subbasin is positioned immediately downstream at the confluence of Tukok and Sapuan
Creeks, both exhibiting very low levels of MeHg and THg. What could have caused the
relatively high MeHg in TUK-1E could then be the unusual abundance of fine-grained
sediments and organic matter that reacted with natural Hg concentrations, causing
methylation under abnormal conditions.
Figure 4: MeHg and THg concentrations in 2003 are high at Acupan, Dalicno, Sangilo,
and Upper Ambalanga Subbasins and moderate at Surong and Gold Creek.
3.2 Hg Concentrations in Stream Sediments - July 2003
Concentrations of Hg in sediments increased significantly during the 2003 sampling episode
relative to 2001. Four subbasins showed elevated concentrations for MeHg and six for THg,
with their respective peaks coincident with one another (Figure 4). Of these, Hg levels in
three subbasins (Acupan, Dalicno, and Sangilo) are significant. These drain the center of the
Acupan gold deposit, while the other three (Surong, Gold Creek, and Upper Ambalanga)
have moderate Hg levels, peripheral to or at some distance from Acupan, Atok Big Wedge,
and Kelly gold deposits, respectively.
The distribution of Hg concentrations during the HF stage is classified into three: both high
for MeHg and THg, low MeHg but high THg concentrations, and both low for MeHg and
THg (Figure 3). High concentrations for both MeHg (150-1000 ng/g) and THg (161-3600
ng/g) are demonstrated in four subbasins (Acupan, Dalicno, Sangilo, and Upper Ambalanga)
and at stations AMB1-E and AMB2-E. THg levels exceeded the background concentration
by a factor of 4 to 86. Except for those which registered below detection limit (<40 ng/g),
MeHg concentrations are greater than background concentration by 4 to 24 times.
Similarly, a consistent decreasing trend in THg concentrations along the Batuang River
(Acupan Subbasin) - lower Ambalanga River System is observed (BAT1-E at 3,600 ng/g to
AMB2-E at 1065 ng/g) (Figure 5). The decrease in THg levels at AMB1-E and AMB2-E
does not follow the trend as observed in the BAT series samples. This shows that the source
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1054
of Hg is not only from Acupan but also from other subbasins upstream, although their
contributions are not as high as those coming from the Acupan Subbasin.
Figure 5: A consistent decreasing downstream trend for THg and general decreasing
levels for MeHg in 2003 along Batuang (Acupan) - lower Ambalanga River.
The concentrations of MeHg and THg at the farthest station (AMB2-E) are still high,
considering that the site is 7 kilometres downstream of BAT1-E. Hg concentrations
downstream of AMB2-E are expected to decrease further as there is no current SSM activity
in the location. Based on the estimated average concentration gradient of 340 ng/g per
kilometre, THg concentration is estimated to reach its background concentration for another 3
kilometres downstream from AMB2-E, or 10 kilometres from BAT1-E, by way of
attenuation process.
Although the trend of MeHg concentrations is generally decreasing downstream, the
concentrations at BAT2-E and BAT3-E are slightly higher than that of BAT1-E (460 ng/g).
This is almost consistent with the trend during the 2001 sampling. The same development is
observed from BAT4-E to AMB1-E and AMB2-E. This suggests that, as the contaminated
sediments are released from the source site, the process of methylation starts to work.
The concentration increases downstream until it reaches a certain distance where a maximum
is achieved. Afterwards, it abruptly decreases. The higher the THg concentrations in the
sediments, the more active the methylation process will be. This, in turn, produces more
MeHg wherever there is an abundance of organic matter present in the sediments. Compeau
and Bartha (1985) suggested that Hg methylation is primarily a result of anaerobic microbial
activity, which is typically enhanced in sediments with high organic matter. Overall, the
background concentration has been exceeded by a factor of 72 (BAT1-E) and 25 (AMB2-E).
The consistent decreasing trend of the Hg concentration downstream suggests that the main
source of Hg is at BAT1-E, the center of SSM activity in the Acupan Subbasin. Much of the
contaminated tailings have been transported from the source area, particularly from the
Acupan Subbasin.
Hg concentrations in Dalicno (DAL1-E) reflected high THg (3193 ng/g) and MeHg (640
ng/g), elevated compared to the background level by 64- and 13-fold, respectively. The
Sangilo Subbasin revealed the same Hg distribution pattern as in the Dalicno Subbasin yet of
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1055
relatively lower Hg concentrations. Not surprisingly, low MeHg-high THg concentrations
define the Gold Creek Subbasin and Manganese Creek in the Surong Subbasin-the former
draining the Atok Big Wedge gold mine, and the latter the Sierra Oro Gold Mine which is
peripheral to the main Acupan deposit.
In both sampling periods, Hg levels in the Lucbuban Subbasin are of background range (0.01-
42 ng/g). The subbasin was selected as background control since the area does not contain
any processing plants, does not perform any SSM activities, has no gold mineralization, and
is underlain by unaltered and unmineralized Itogon quartz diorite.
Higher concentrations and wider distribution of Hg were more significant during the 2003
sampling than in the 2001. This can be explained with more Hg-contaminated mine tailings
that are dumped over the steep banks of the river adjacent to the processing plants. Additional
mine tailings, organic matter and other contaminated sediments under conditions of higher
discharge and turbidity, can be effectively eroded and transported downstream.
3.3 MeHg Concentrations in Stream Sediments
High MeHg concentrations have been observed on both sampling periods, particularly during
the HF event. The methylated Hg could be a function of THg, geology, river discharge,
sediment grain size, organic content, and channel morphology. In the three subbasins
(Acupan, Dalicno, and Sangilo) where MeHg are highest, MeHg coincides with the drainage
at the center of the gold-rich Acupan vein system. As can be expected, the most number of
ball mills are located here - hence higher ore milling and mine tailings production. Of the 94
ball mills recorded in the area, 48 of these (or 51%) are located in the three subbasins, which
account for about 39 % (or 167 tonnes) of the total tailings production per month.
In the 2003 period, four subbasins showed high MeHg concentrations and six subbasins with
elevated THg levels. Others reported MeHg levels below detection limit. MeHg levels are
positively correlated with THg as supported by its correlation analysis (R2 = 0.6599).
Because of higher volume of Hg-contaminated tailings in the sediments, there is more Hg
available during methylation process. For instance, Hg availability from tailings in the
Acupan Subbasin reported 3.84-12.4 g/t THg, reflecting a range of 8- to 253-fold above the
background, indicative of anthropogenic origin.
Seasonal variation indicates differences in discharge with 52.5 m3/s in the 2003 period
against 6.7 m3/s in 2001, or about 8-fold higher in 2003. The higher discharge during periods
of HF and flood events (e.g., 2003) would translate to a higher carrying capacity, effectively
eroding and transporting larger volumes of mine tailings downstream from SSM wastes
dumped along the river banks.
Rytuba (2000) suggested that MeHg concentrations are relatively low at the discharge point
but increases significantly in mine drainage as it flows through and reacts with calcines (mine
tailings). This trend is clearly illustrated at Acupan and Surong Catchments and at stations
AMB1-E to AMB2-E during the HF period (Figure 5). As an example, the initial MeHg level
at BAT1-E (460 ng/g) increases and peaks about 1 kilometre downstream at BAT2-E (1,000
ng/g). MeHg progressively drops in concentrations, until the background level at BAT4-E is
reached, which is about 3 kilometres downstream of BAT1-E. This suggests that methylation
process starts at the source area and continues downstream up to a certain distance, until the
maximum level of methylation has been achieved. In contrast, the highest THg level is shown
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1056
at the point source (BAT1-E at 3,600 ng/g), followed downstream by consistently decreasing
concentrations.
Channel morphology also plays a significant role. Stamenkovic et al. (2004) and Flanders et
al. (2010) reported that both pond/wetland and channel margins/sites exhibited high potential
for Hg methylation, for higher rates would be expected at sites with slower water or lower
hydrologic gradient. In many instances, sediment samples collected below the water line
were taken in sites with slow flow. It is where gentle to relatively flat river slopes can be
expected where water flow tends to slow down. This therefore serves as a temporary sink for
Hg and organic matter conducive to methylation activity.
4. Conclusion
Hg availability in sediments is largely drawn from anthropogenic Hg associated with
contaminated mine tailings. Sediment sampling on two periods (November 2001 and July
2003) revealed elevated MeHg and THg concentrations attributed to anthropogenic sources.
During the 2001 episode, two subbasins (Acupan and Lucbuban) showed high MeHg levels
and three subbasins (Acupan, Dalicno, and Sangilo) demonstrated elevated THg
concentrations. In the 2003 period, four catchments (Acupan, Dalicno, Sangilo, and Upper
Ambalanga) exhibited high MeHg levels and six subbasins (Acupan, Dalicno, Sangilo,
Surong’s Manganese Creek, Gold Creek, and Upper Ambalanga) showed high THg
concentrations. In general, four basins (Acupan, Dalicno, Sangilo, and Upper Ambalanga)
have high values for both MeHg and THg, and the two subbasins (Surong and Gold Creek)
contained moderate THg levels. On both sampling occasions, the local background level has
been exceeded by 4- to 86-fold.
A positive correlation between THg and MeHg is indicated as supported by its R2 value of
0.6599. This explains the higher MeHg concentrations driven by higher volume of Hg-
contaminated tailings transported during the HF period. Subbasins with high MeHg and THg
are centered on the Acupan gold-rich deposit, where the most number of ball mills are located
such that higher milling and mine tailings are produced. More elemental Hg is utilized, thus
more Hg availability for methylation. With the 8-fold higher discharge in HF over the LF
period, flashing out of more Hg-contaminated mine tailings dumped into river banks is
justified. Flanders et al. (2010) suggested that higher amounts of fine-grained sediments
building up in pools and channel margins have the highest MeHg levels which seem to favor
Hg methylation.
Overall, the methylation process can be explained by physical characteristics in the area such
as Hg availability from anthropogenic sources, discharge, sediment grain size, and channel
morphology which indirectly increase organic activity resulting to increased methylation of
available Hg.
Acknowledgement
This paper is part of the master’s thesis of the first author at the University of the Philippines.
This work could not have been done if not for the help of the National Institute of Advanced
Industrial Science and Technology, Tsukuba City, Japan; the Environmental Agency of
Japan; the University of the Philippines-National Institute of Geological Sciences especially
Rushurgent Working Group and Dr. Joselito Duyanen; the University of the Philippines
Diliman-Office of the Vice-Chancellor for Research and Development; and the Mines and
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1057
Geosciences Bureau-Cordillera Administrative Region, Baguio City for providing support
during the course of sampling. The management and staff of Benguet Corporation are
appreciated for their assistance and their permission to conduct sampling in the study area.
Dr. James Rytuba of the United States Geological Survey, Menlo Park California is thanked
for his sound advice and for facilitating the sample analysis in different U.S. laboratories. A
review by an anonymous reader is much appreciated.
5. References
1. Akagi, H., Castillo, E.S., Cortes-Maramba, N., Francisco-Rivera, A.T. and Timbang,
T.D. (2000), Health assessment for mercury exposure among schoolchildren residing
near a gold processing and refining plant in Apokon, Tagum, Davao del Norte,
Philippines. The Science of the Total Environment, 259, pp 31-43.
2. Avocat, R., Milian, J.F. and Bertoni, C. (2001), The impact of artisanal gold mining
on surface water quality. Mining Environmental Management, January 2001, pp 18-
23.
3. Baluda, R.P. (2002), Small-scale gold mining in the Baguio Mineral District,
Philippines. In: Small-scale Mining in Asia: observations towards a solution of the
issue, S. Murao, V. Maglambayan and N. de la Cruz (eds.), Mining Journal Book Ltd,
London, pp. 11-15.
4. Caballero, E.J. (1996), Gold from the Gods: Traditional small-scale miners in the
Philippines. Giraffe Books, Quezon City, Philippines.
5. Cabria, H., Maglambayan, V.B., Tanno, K. and Murao, S. (2002), Pocket mining at
Itogon, Philippines. In: Small-scale Mining in Asia: observations towards a solution
of the issue, S. Murao, V. Maglambayan and N. de la Cruz (eds.), Mining Journal
Book Ltd, London, pp. 27-30.
6. Compeau, C.C. and Bartha, R.A. (1985), Sulfate reducing bacteria: principal
methylators of mercury in anoxic estuarine sediment. Applied and Environmental
Microbiology, 50, pp 498-502.
7. Cortes-Maramba, N., Reyes, J.P., Rivera, A.T.F., Akagi, H., Sunio, R. and
Panganiban, L.C. (2006), Health and environmental assessment of mercury exposure
in a gold mining community in Western Mindanao, Philippines. Journal of
Environmental Management, 81, pp 126–134.
8. Enger, E.D. and Smith, B.F. (1998), Environmental Science: a study of
interrelationships. 6th Edition. WCB/McGraw-Hill, New York.
9. Flanders, J.R., Turner, R.R., Morrison, T., Jensen, R., Pizzuto, J., Skalak, K. and
Stahl, R. (2010), Distribution, behavior, and transport of inorganic and
methylmercury in a high gradient stream. Applied Geochemistry, 25, pp 1756-1769.
10. Floresca, P.A. Jr, Ramirez, R.P. and Quitoriano, E.R. (1995), Evaluation of BGO tails
potential, Benguet Corporation, September 13, 1995.
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1058
11. Gustin, M.S., Taylor, G.E. and Leonard, T.L. (1994), High levels of mercury
contamination in multiple media of the Carson River Drainage Basin of Nevada:
implications for risk assessment. Environmental Health Perspectives, 102: pp 772-
778.
12. Kennedy, K.R. and Crock, J.G. (1987), Determination of mercury in geological
materials by continuous-flow cold-vapor atomic absorption spectrophotometry.
Analytical Letters, 20, pp 899-908.
13. Lacerda, L.D. (1997), Global mercury emissions from gold and silver mining. Water,
Air, & Soil Pollution, 97, pp 209-221.
14. Lin, Y., Guo, M. and Gan, W. (1997), Mercury pollution from small gold mines in
China. Water, Air, & Soil Pollution, 97, pp 233-239.
15. Maglambayan, V.B. and Murao, S. (2002), Problems of small-scale mining around
Baguio City, Philippines. In: Small-scale Mining in Asia: observations towards a
solution of the issue, S. Murao, V. Maglambayan and N. de la Cruz (eds.), Mining
Journal Book Ltd, London, pp 3-7.
16. Miguel, J.M. (2000), Mercury pollution in sediments of Hijo River draining the gold
processing plants in Tagum, Davao del Norte. MSc thesis, University of the
Philippines, Diliman, Quezon City.
17. Nevado, J.J.B., Martín-Doimeadios, R.C.R. and Moreno, M.J. (2009), Mercury
speciation in the Valdeazogues River–La Serena Reservoir system: Influence of
Almadén (Spain) historic mining activities. The Science of the Total Environment,
407, pp 2372-2382.
18. Rytuba, J.J. (2000), Mercury mine drainage and processes that control its
environmental impact. The Science of the Total Environment, 260, pp 57-71.
19. Stamenkovic, J., Gustin, M.S., Marvin-DiPasquale, M.C., Thomas, B.A. and Agee,
J.L. (2004), Distribution of total and methyl mercury in sediments along Steamboat
Creek (Nevada, USA). The Science of the Total Environment, 322, pp 167-177.
20. US Environmental Protection Agency (1994), Information Fact Sheet: Hazards to
consumers using metallic mercury in the home environment, Office of Pollution
Prevention and Toxics, July 1994.
21. US Environmental Protection Agency (1999), Method 1631, Revision B: Mercury in
water by oxidation, purge and trap, and cold vapor atomic fluorescence spectrometry,
EPA no. 821-R-99-005, May 1999.
22. US Environmental Protection Agency (2001a), Method 1630: Methyl mercury in
water by distillation, aqueous ethylation, purge and trap, and CVAFS, United States
Environmental Protection Agency, EPA no. 821-R-01-020, January 2001.
Small-scale Gold Mining in the Ambalanga Catchment, Philippines: Its Control on Mercury Methylation in
Stream Sediments
Corpus, T.J., David, C.P., Murao, S., Maglambayan, V.
International Journal of Environmental Sciences Volume 2 No.2, 2011 1059
23. US Environmental Protection Agency (2001b), South Florida ecosystem assessment:
phase I/II– Everglades stressor interactions: hydropatterns, eutrophication, habitat
alteration, and mercury contamination. Athens, GA, USA.
24. Winch, S., Praharaj, T., Fortin, D. and Lean, D.R.S. (2008), Factors affecting
methylmercury distribution in surficial, acidic, base-metal mine tailings. The Science
of the Total Environment, 392, pp 242-251.
25. Wolfe, M.F., Schwarzbach, S. and Sulaiman, R.A. (1998), Effects of mercury on
wildlife – a comprehensive review. Environmental Toxicology and Chemistry, 17, pp
146–60.