Mineralogical Magazine, October 2005, Vol. 69(5), pp. 719±736
Aqueous exposure and uptake of
arsenic by riverside communities affected by
mining contamination in the R|¨o Pilcomayo basin, Bolivia
J. ARCHER1, K. A. HUDSON-EDWARDS1,*, D. A. PRESTON2, R. J. HOWARTH3 AND K. LINGE4
School of Earth Sciences, Birkbeck, University of London, Malet St., London WC1E 7HX, UK
School of Geography, University of Leeds, Leeds LS2 9JT, UK
Department of Earth Sciences, University College London, Gower St., London WC1E 6BT, UK
NERC ICP Facility, School of Earth Sciences and Geography, Kingston University, Penrhyn Road,
Surrey KT1 2EE, UK
1
2
3
4
ABS TR AC T
The headwaters of the RõÂo Pilcomayo drain the Cerro Rico de PotosõÂ precious metal-polymetallic tin
deposits of southern Bolivia. Mining of these deposits has taken place for around 500 years, leading to
severe contamination of the Pilcomayo's waters and sediments for at least 200 km downstream.
Communities living downstream of the mines and processing mills rely on the river water for irrigation,
washing and occasionally, cooking and drinking, although most communities take their drinking water
from springs located in the mountains above their village. This investigation focuses on arsenic
exposure in people living in riverside communities up to 150 km downstream of the source. Sampling
took place in April±May 2003 (dry season) and was repeated in January±March 2004 (wet season) in
five communities: El Molino, Tasapampa, Tuero Chico, Sotomayor and Cota. Cota was the control in
2003 and again in 2004; a nearby city, Sucre, and several locations in the UK were also used as
controls in 2004. Drinking, irrigation and river waters, hair and urine samples were collected in each
community, digested where appropriate andÿanalysed
for As using ICP-MS. Arsenicÿ1concentrations in
drinking watersÿ1 ranged 0.2 ÿ112 mgÿ1l 1, irrigation water 0.6
ÿ329 m g l , river waters
0.9ÿ12,800 mg l , hair 37ÿ2110 mg kg and urine 11ÿ891 mg lÿ1. All but one drinking water
sample ÿwas
found to contain As below the World Health Organization recommended guideline of
10 mg l 1, although a number of irrigation and river water concentrations were above Canadian and
Bolivian guidelines. Many As concentrations in the hair and urine samples from this study exceeded
published values for non-occupationally exposed subjects. Analysis of mean concentration values for
all media types showed that there were no statistically significant differences between the control
locations and the communities exposed to known As contamination, suggesting that the source of As
may not be mining-related. Arsenic concentration appears to increase as a function of age in hair
samples from males and females older than 30 years. Male volunteers over the age of 35 showed
increasing urine-As concentrations as a function of age, whereas the opposite was true for the females.
K EY WORDS :
arsenic, mining, water, hair, urine, human exposure, Bolivia, Pilcomayo.
Introduction
ARSENIC (As) is a human poison. Excessive uptake
via the skin, lungs and gastrointestinal tract can
lead to a wide range of pathologies, including
* E-mail: k.hudson-edwards@geology.bbk.ac.uk
DOI: 10.1180/0026461056950283
#
2005 The Mineralogical Society
gastrointestinal discomfort, vomiting, convulsions, skin lesions, blackfoot disease, cancer and
death (Hughes, 2002; Wright and Welbourn,
2002). According to the World Health
Organization (WHO) (2001), pigmentation
changes in the skin are the ®rst manifestations
of chronic exposure to As. These are followed by
hyperkeratosis, which in turn may be followed by
J. ARCHER ET AL.
cancer, although this usually takes more than 10
years to develop.
Water is one of the major pathways for human
exposure to As. High groundwater
concentrations
of As (190ÿ740 mg lÿ1) in West Bengal have
been linked to high concentrations in human hair
and urine, which in turn have been related to skin
lesions and cancers (Chatterjee ., 1995; Das
., 1995, 1996; Samanta
., 2004). In
Wisconsin, by contrast, individuals drinking
water for over 20 years with
much lower
concentrations of As (2 mg lÿ1 or more) were
more likely to report a history of depression, high
blood pressure, circulatory problems and bypass
surgery compared ÿto1 others drinking water
containing <2 mg l of As (Zierold
.,
2004). Similarly, Knobeloch and Anderson
(2003) have reported that ÿlong-term
ingestion of
water containing >5 mg l 1 of As signi®cantly
increases the risk of skin cancer. Human
populations exposed to As will not necessarily
react in the same manner: health effects will
depend on the As bioavailability and exposure,
and on nutritional status, diet, age and sex.
Present-day and historic mining activities have
released large quantities of As-bearing waters and
sediments to ¯uvial environments (Miller, 1997;
Foster ., 1998; Hudson-Edwards ., 1999).
These contaminate river and ground water either
directly or indirectly, through release of As from
contaminated sediments, for tens to hundreds of
km downstream of source areas. This contamination has the potential to severely affect plants,
micro-organisms, water supply and soils, and as a
consequence, the food chain. Humans are
susceptible to As through drinking contaminated
water or eating crops grown on contaminated soils
using contaminated irrigation water. Studies of
human As exposure and uptake in rivers affected
by mining-related As contamination are rare. In
some non-¯uvial areas affected by mining, Ascontaminated wastes, soils and waters have been
linked to elevated human hair and urine
concentrations (Farago and Kavanagh, 1999;
Matshullat . 2000), but in others, few cases
of As toxicity have been reported (Hamilton,
2000).
In order to determine the impacts of miningcontaminated water on riverside communities,
and ultimately, to develop management and
remediation strategies, it is important to evaluate
the level of exposure and uptake of As by human
resident populations, and their current contaminant and water management strategies. This paper
et al
al
et
Study area
et
al
et
et al
presents the results of an investigation of the
aqueous pathways, exposure and uptake of As in
residents living in communities along a miningcontaminated river system in Bolivia.
al
et al
et al
720
The RõÂo Pilcomayo (20ëS 65ëW) rises at an
elevation of ~5200 m in the central Andes and
¯ows in a southeasterly direction for ~670 km
until reaching the semi-arid/semi-tropical Chaco
Plains, where it forms Argentina's northern
boundary with Paraguay. The Pilcomayo
basin
covers an2 area of 272,000 km2, of which
98,100 km lies in Bolivia. In the lower reaches,
the Pilcomayo enters the Chaco2 Plains where it
has constructed a 210,000 km , low-declivity,
fan-shaped body of sediment (Iriondo, 1993;
Wilkinson and Mohler, 1995). The RõÂo
Pilcomayo traverses Ordovician, Silurian,
Cretaceous, Tertiary and Quaternary volcanic
and sedimentary rocks that are intruded by
dacites, quartz porphyries and adamellites.
The climate is dominated by distinct wet
(November to April) and dry seasons (May to
October). Average monthly rainfall is ~100 mm
during peak wet season and 5 mm during dry
season (PROVISA, 1989). Discharges are 3equally
diverse, with average discharges
of 80 m sÿ1 at
3
ÿ
1
low stage and 3600 m s in ¯ood (Wilkinson
and Mohler, 1995). The chemical composition of
Pilcomayo river water is variable throughout the
year, and is controlled by variations in discharge
during the wet and dry seasons and the weathering
of evaporitic minerals (halite, gypsum), carbonates (calcite, dolomite) and pyrite from mine
tailings that are ejected into the river (see below)
(Smolders ., 2004).
The headwaters of the RõÂo Pilcomayo in
Bolivia drain precious metal-polymetallic ore
deposits at PotosõÂ (Cunningham
., 1991;
Fig. 1). Mining of these deposits since 1540 and
ejection of mine tailings into the river has resulted
in As contamination of water, sediment and soil
of the basin for at least 200 km downstream of the
mines (JICA, 1999; Schollaert, 2000; HudsonEdwards
., 2001; Smolders
., 2002;
Miller
., 2004). The banks of the RõÂo
Pilcomayo are populated by many Andean
communities who rely on the river water for
irrigation and washing, and on alluvial soils for
growing crops. It is therefore highly likely that
these communities are being directly exposed to
As. Preliminary studies carried out in 2001 to
et al
et al
et al
et
al
et al
AS UPTAKE BY RIVERSIDE COMMUNITIES, BOLIVIA
FIG. 1. Location of the RõÂo Pilcomayo basin, Bolivia, showing the mining area at PotosõÂ and the villages sampled for
this study (adapted from Miller ., 2004).
et al
investigate the risks of this exposure revealed that
many drinking, irrigation and river waters were
enriched in As above recommended guidelines,
and thus, that water may be a pathway of human
As exposure, but no samples were taken to
evaluate the level of human As uptake at this
time (Miller ., 2004).
et al
Methods and materials
Sampling took place during both dry (AprilÿMay
2003) and wet seasons (JanuaryÿMarch 2004) in
the uppermost 150 km of the RõÂo Pilcomayo that
was shown previously to be the most highly
contaminated of the whole river system (HudsonEdwards ., 2001; Miller ., 2004). Sample
collection took place in ®ve villages: El Molino,
et al
et al
721
Tasapampa, Tuero Chico, Sotomayor and Cota
(Fig. 1). Four of these are located on the banks of
the RõÂo Pilcomayo and one, Cota, is a control
located adjacent to a tributary known not to ¯ow
through any mining districts or to be affected by
mining-related dust. During the wet season,
additional samples were taken at Sucre, a city
located ~40 miles north of Tuero Chico, and three
locations in the UK (Aberdeen, London and
Surrey) to provide extra controls. A research
ethics proposal was submitted and approved by
the Research Ethics Committee of Birkbeck
College, University of London, prior to sample
collection.
Samples of drinking, irrigation and river water,
hair and urine were collected in all the villages
(Table 1). Drinking waters were taken from taps
J. ARCHER ET AL.
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722
AS UPTAKE BY RIVERSIDE COMMUNITIES, BOLIVIA
and storage tanks. The taps chosen for sampling
were all located in public places (e.g. medical
centres, schools and/or the main square of each
village) and storage tanks were the principal tanks
used by each village for storage of all potable
water. Taps were allowed to run freely for 3 min
prior to sample collection. Irrigation waters were
collected from canals serving cultivated land, and
river water was collected from the banks of the
RõÂo Pilcomayo, adjacent to each village. Water
samples collected in 2004 were taken from the
same taps, tanks and locations as those sampled
during the 2003 ®eldtrip. However, collection of
irrigation water samples was problematic during
both ®eldtrips, but particularly during the wet
season, as many villagers relied on rainfall to
irrigate their crops. As a result, only two samples
from El Molino and two from Cota were collected
in 2004. UK water samples comprised potable tap
water only and were treated in an identical fashion
to the Bolivian water samples. All water samples
were 30 ml in volume, and were collected
un®ltered so as to most closely represent those
consumed and used by inhabitants. They were
acidi®ed with 0.6 ml of concentrated nitric acid
and stored in acid-washed HDPE bottles below
4ëC. Field blanks were opened and acidi®ed in the
same manner as samples. Field duplicates and
blanks form 14% and 13%, respectively, of the
total number of sample sets collected.
Hair and urine samples were collected within
two to three days of the water samples from
between 4 and 11 individuals in each village (see
Table 2 for volunteer details). Bolivian volunteer
selection was conducted on a ®rst come-®rst
served basis, although only volunteers who were
non-smokers, apparently healthy and permanent
residents of the villages were used in the study.
Children below the age of 11 and adults over the
age of 56 were not included. Volunteers of both
sexes were included, though females were often
more willing volunteers; thus for some villages
the number of female volunteers sometimes
substantially outweighs male (Table 2). This is
particularly true for Tuero Chico. Volunteers used
the same drinking water sources and ate crops and
livestock grown and reared in the same area.
Where possible the sample volunteers were the
same for both ®eldtrips, although in 2004 some of
the original volunteers were unavailable.
Volunteers from the UK were selected from
non-smoking, healthy individuals who used the
same water source for drinking, cooking and
washing. They were requested to refrain from
drinking alcoholic beverages and consuming ®sh
or sea vegetables for one week prior to sample
collection. Hair from the occipital region of the
head was tied with cotton before being cut with
stainless steel scissors. Samples were then placed
into zip-lock bags and stored in a cool, dark
container. Grey hairs were discarded from the
samples. Volunteers providing hair samples were
also asked to provide a 30 ml urine sample. The
urine samples comprised the ®rst void of the day
and were acidi®ed and stored in acid-washed
HDPE bottles below 4ëC until digestion/analysis
~3 months later. Creatinine (C4H7N3O) measurements were taken prior to digestion or analysis in
order to standardize all urine samples
(Matschullat ., 2000).
et al
TABLE 2. Hair and urine volunteer information.
2003
No. of samples
Mean age (years)
Range
No. of males
No. of females
2004
No. of samples
Mean age (years)
Range
No. of males
No. of females
El Molino
Tasapampa
Tuero Chico Sotomayor
5
33.2
12ÿ44
3
2
6
26.7
16ÿ42
3
3
11
39.5
21ÿ55
1
10
7
23.4
16ÿ34
2
5
5
29.4
11ÿ50
1
4
5
34.0
13ÿ45
3
2
4
25.5
17ÿ33
2
2
11
40.1
22ÿ56
1
10
5
25.8
19ÿ35
2
3
4
34.8
16ÿ51
1
3
723
Cota
Sucre
6
33.0
24ÿ45
4
2
UK
10
28.9
25ÿ34
7
4
J. ARCHER ET AL.
Questionnaires requesting information about
lifestyle, occupation, diet, health and water
management techniques were also undertaken in
each village and in the UK. Health status
information for the community was obtained
during interviews with medical personnel in
each village. In Tasapampa, Tuero Chico and
Cota, the health workers interviewed were
residential nurses working alone, whereas in El
Molino and Sotomayor the interviews were
carried out with a residential doctor and nurse.
A total of 23 families was questioned regarding
water use. These families included the hair and
urine volunteers. Sample volunteers were also
questioned as to what they had consumed during
the two days prior to urine sample collection.
In the laboratory, hair samples were washed
according to the method described in IAEA
(1977) and 50 mg of the youngest 3ÿ4 cm of
hair separated for digestion. Hair and un®ltered
waters collected during the 2003 dry season visit
were all digested in open acid-washed glass
boiling tubes. Hair samples were digested using
a reagent mixture of concentrated HNO3 and
H2O2, whereas the un®ltered waters were digested
using only concentrated HNO3. Urine samples
were ®ltered. Hair, urine and un®ltered waters
collected during the 2004 wet season were
digested using a newly acquired microwave
digestion instrument. The reagents used to digest
the hair and un®ltered waters were the same as
above, but smaller volumes were used. The urine
was digested using the same reagents as those
used for the hair. The digests were ®ltered and
made up to 25 ml volume with deionized
ultrapure water.
All samples were analysed for As using
quadrupole ICP-MS (a Plasmaquad PQ2+ in
2003 and an Agilent 7500c in 2004), with external
calibration
using As solutions diluted from a
10 mg lÿ1 stock standard (SPEX CertiPrep,
USA). Suppression tests were carried out before
the analysis to determine the correct dilution
factor required for each sample media. To
determine the accuracy of the digestion and
analysis, reference materials were included in
every analysis batch. The reference materials used
were TMDA-52.2 (Lake Ontario water),
Seronorm201205 (urine) and GBW09101 human
hair (LGC Promochem, Teddington, UK).
Table 3 contains the measured As concentration
in reference materials, blanks and duplicates. This
table also shows average detection limits for each
sampling medium for each year. Detection limits
improved by approximately an order of magnitude in 2004 compared to 2003, due to improved
sample preparation procedures and the use of the
more sensitive Agilent 7500c ICP-MS.
Statistical methods
Mean analyte concentration and standard deviation values for all groups were calculated using
Cohen's (1959, 1961) technique to correct for the
presence of any determinations below analytical
method detection limits. Pairwise and multiple
comparisons between means for the various
groups (e.g. differences between towns or
seasons) were made using Analysis of Means
(ANOM; Ott, 1967; Nelson, 1974, 1983, 1993).
This is a very effective graphical technique.
Group means and standard deviations are ®rst
calculated for each of the groups to be compared.
From these, the grand mean and pooled standard
deviation over all the groups are then obtained.
Upper and lower decision limits are then
calculated for each group, taking into account
group sizes and the statistical signi®cance level of
the required result. If one or more group means
fall outside the upper or lower decision limits (e.g.
Fig. 2), then the mean(s) for that group(s) is (are)
statistically signi®cantly different from the rest at
the chosen level of signi®cance (`signi®cantly'
FIG. 2. ANOM spatial analysis for log-transformed As
concentrations in 2004 river water. Thin black bar,
group mean; thick dark grey bar, lower 95% decision
limit; thick light grey bar, upper 95% decision limit
(95% decision limits are bounds such that if one or more
group means fall beyond the limits there is a 95%
probability that it is different from the groups, that are
not statistically different from each other, which fall
between the lower and upper bounds).
724
AS UPTAKE BY RIVERSIDE COMMUNITIES, BOLIVIA
TABLE 3. ( ) Reference, ( ) blank and ( ) duplicate As data and
( ) detection limit values for all sampling
media for 2003 and 2004. All As concentrations are in mg lÿ1 for waters and urine and mg kgÿ1 for hair.
a
b
2003
a
mean
% rsd
certified value
tolerance limits
range
% bias
c
Waters
d
2004
2003
30.7
25.4
18.9%
1.0%
25.5
25.5
25.6ÿ35.8 22.3ÿ28.4
20.4
ÿ0.6
Hair
2004
2003
549
20.8%
590
0ÿ1990
520ÿ660
ÿ7.0
615
2.2%
590
451ÿ778
520ÿ660
4.2
164
4.6%
184
68ÿ260
ÿ10.7
2004
0.075
0.005
0.077
0.005
0.072
0.005
2003
0.001
0.007
0.017
0.008
0.014
0.008
Urine
2004
180
0.8%
184
175ÿ185
ÿ2.3
b
Sample
blank 1
sd
blank 2
sd
blank 3
sd
Waters
2003
2004
0.032
0.096
0.016
0.002
0.022
0.087
0.045
0.003
0.030
0.081
0.060
0.006
2003
0.015
0.006
0.011
0.003
0.008
0.004
Hair
Urine
2004
0.064
0.004
0.064
0.006
0.068
0.003
c
Sample no.
3D/I
3D/I/D
% bias
4E/R
4E/R/D
% bias
2003
320
324
ÿ1.1
543
579
ÿ6.4
% rsd
1.2
2.6
2.3
0.9
Sample no. 2004
6B/D
0.231
6B/D/D
0.335
% bias
ÿ31
6D/D
0.323
6D/D/D
0.316
% bias
2.2
% rsd
19.1
3.9
10.4
16.1
d
Media
Waters
Hair
Urine
2003
3.18
141
3.00
2004
0.111
22.3
0.698
implies `statistically signi®cant with 95% con®dence' hereafter). If they all lie within the
decision limits, then there are no statistically
signi®cant differences between the groups.
Robust regression, which down-weights
outliers, was used when ®tting standard linear
regression models (Rousseeuw and Leroy, 2003).
725
Mahon's (1996) revision of the York (1967)
errors-in-variables regression method was used
where it was necessary to incorporate errors in
both and when ®tting a functional regression
model to data drawn from two different populations (As concentrations in hair or urine as a
function of As concentrations in water). Nonx
y
J. ARCHER ET AL.
linear trends were identi®ed using Cleveland's
(1979) LOESS technique. This applies a locallyweighted smooth to the data: a window,
centred on each successive coordinate in turn,
is passed across the data and a locally-weighted
regression is used to predict the value within the
window. The ensemble of these points produces
the desired smooth curve. This and the 95%
con®dence limits were obtained using
(Insightful Corporation).
xy
x
y
S-Plus
Verif|cation of in-house reference materials
It can be assumed that in the case of replicate
analysis of homogeneous reference materials,
analytical error conforms to the normal distribution (Thompson and Howarth, 1980). With regard
to Table 3, statistical tolerance limits (Hahn and
Meeker, 1991) can be calculated such that one can
be 95% certain that 99% of all the possible values
of individual observations drawn from the
sampled distributions will fall between their
lower and upper bounds. These limits (Table 3)
all enclose the certi®ed values
for As (although
the 2003 water at 25.5 mÿg1lÿ1 is just below the
lower limit of 25.6 mg l ). This difference is
small and has been deemed reasonable for the
purposes of this investigation. If the argument is
based on a con®dence interval for the mean of the
observed distribution, a similar conclusion is
reached. Arsenic concentrations found in the
blanks are all low, and precisions are also
acceptable for the purposes of this study.
Results
Lifestyle, health and water management
Most of the inhabitants of the study area depend
on farming and livestock for their livelihood. The
methods used to work the land are largely
traditional, with most agricultural tasks performed
by hand using simple tools and livestock for
ploughing and some transport. Vegetables grown
in the ®elds are eaten by the farmers and their
extended families or sold to other inhabitants of
the community and in nearby cities (Sucre and
PotosõÂ). The communities are relatively poor and
their mostly vegetarian diet re¯ects this: meat
consumption is generally reserved for special
occasions. Dairy products are seldom consumed
and most protein intake comes from eggs and
pulses. Fish is not consumed. Consumption of
potable water increases slightly from an average
of two litres per day during the dry season to 2.25
726
litres per day during the wet season when the
annual temperatures are at their highest.
Information on community health, gleaned
from medical staff, revealed that the commonest
complaints are diarrhoea, nausea and vomiting in
all ®ve villages. Health workers also reported
stunted growth in children from Sotomayor and
Tuero Chico, and headaches and tiredness in
Tasapampa and Tuero Chico. Amongst these
reports there were no obvious symptoms that
could be expressly related to arsenic toxicity
alone, i.e. no mention of skin thickening,
ulceration or changes in pigmentation.
The long dry season means that water management is very important in the communities. Each
village has an elected water committee that
manages water distribution and the maintenance
of the system. Drinking water is taken from what
are believed to be uncontaminated springs or
streams located in the mountains surrounding
each of the ®ve villages. This water is transferred
by plastic pipe to the main concrete supply tank
above each village. All villages rely on a single
spring, except Sotomayor, which has access to
three. The tanks are covered, and regional
government agencies sometimes provide chlorine
and disinfectants to be mixed with water prior to
consumption, although this is rarely done. Most
households have access to a private tap supplied
by water from the main tank. Those without a
private tap collect water in plastic containers from
communal taps located in either local schools,
health centres or the village main square. Some
families collect rainwater to provide potable water
when, on occasion, none is available from the taps
during the dry season. No family reported taking
water from the RõÂo Pilcomayo for cooking or
drinking. Irrigation water is collected from either
an uncontaminated tributary or a spring, except in
Tuero Chico and Sotomayor, where water from
the RõÂo Pilcomayo is used during the dry season.
During the wet season the communities frequently
rely on rainfall alone to irrigate their ®elds.
Almost all families questioned about water
quality stated that drinking water is often very
turbid during the wet season and therefore
regarded as `cleaner' during the dry season.
Families in Tasapampa, Tuero Chico, Sotomayor
and Cota regard the RõÂo Pilcomayo and its
tributaries as `dirtiest' during the wet season,
but those in El Molino (closest to the mines)
believed the opposite, claiming that the river
smells bad and the water turns to `sludge' during
the dry season. Community members in
AS UPTAKE BY RIVERSIDE COMMUNITIES, BOLIVIA
was determined in water from one tap. This very
high As concentrations was found in a 2003 water
sample from a tap which, when sampled again in
2004, was foundÿ1 to be much lower in concentration (2.21 mg l ).ÿ1A Bolivian agricultural water
standard (50 mg l ; Bolivian agricultural waters
standard, 1995) andÿ1 a Canadian irrigation water
standard (100 mg l ; Peterson, 1999) were used
for the irrigation and river water assessment.
Almost all river waters displayed As concentrations in excess of these standards; the exception is
Cota, the control village, where concentrations
were less than all other village concentrations.
Irrigation waters collected in 2003 show that As
concentrations
for Tuero Chico (average
273 mg lÿ1) are double that of the Canadian
standard, and that the As concentration for
Sotomayor match the standards. Arsenic concentration in irrigation waters collected in 2004 are
all well below the Bolivian and Canadian
Tasapampa, Tuero Chico and Sotomayor reported
¯ooding to be an occasional problem (once in ®ve
years on average), affecting a small number of
®elds closest to the river. Overall, these ¯oods are
regarded as positive phenomena by the communities as they supply fertile silt to the ®elds. Many
families surveyed did not perceive the use of
contaminated river water for irrigation as a threat
to health.
Water analysis
The WHO recommended guideline for ÿAs1
concentrations in drinking water (10 mg l ;
WHO, 1996, 1998) was used to assess the
quality of the drinking waters sampled (Fig. 3).
Arsenic concentrations in the drinking waters of
the communities in this study all fall below this
concentration, with the exception of El Molino,
where a very high As concentration (112 mg lÿ1)
FIG. 3. As concentrations in: ( ) drinking water; ( ) irrigation water; and ( ) river water samples.
a
b
727
c
J. ARCHER ET AL.
standards (Fig. 3). Overall, the river waters
contain the greatest concentrations of As followed
by the irrigation waters and the drinking water
samples.
Analysis of means (ANOM) was used to assess
the magnitudes of apparent differences between
As concentrations in the different groups of water
data. Because there was evidence that, in general,
analyte concentrations were lognormally distributed and that group standard deviation tended to
increase as a function of group mean, all data
were log-transformed prior to ANOM statistical
analysis. The ANOM results for 2004 river water
(Fig. 2) illustrate the use of this test. For the
purposes of display, the back-transformed logarithmic group means and 95% decision limits are
shown plotted on a logarithmic-scaled ordinate.
ANOM was used to compare the group means for
the water samples for all locations.
As stated above, only group mean concentration values which fall beyond their corresponding
upper or lower decision limits can be regarded
(with 95% con®dence) as having a statistically
signi®cant different mean concentration
compared to those for other groups which lie
within the ANOM limits. There are no signi®cant
differences between the mean As village concentrations in the 2003 river waters. River waters
collected in 2004 show Cota as possessing mean
As concentrations that are signi®cantly low
compared to those from the other four sample
villages (Fig. 2). Conversely, the 2004 river water
samples collected in El Molino and Sotomayor
contain mean As concentrations that are signi®cantly high compared to the other three villages.
Because of the small numbers of samples taken
from each location, the standard deviations are
relatively large, which in turn results in a wide
decision limit range. Despite this, there is a
similarity between the trends seen in the 2003 and
the 2004 river water data, with the average As
concentrations decreasing in the order: El Molino
> Sotomayor > Tuero Chico > Tasapampa > Cota.
In the drinking waters the average As
concentration for El Molino is signi®cantly
higher than the other villages in both 2003 and
2004. The highest to lowest trend in average As
concentrations for the other villages is similar to
that seen in the river waters. Interestingly, Sucre
is the only one of the three controls to show an
average drinking water-As concentration that is
signi®cantly lower than the sample villages. There
are no signi®cant differences between Cota, the
UK and the remaining villages.
Mean As concentrations in irrigation water
samples show a different pattern to that seen in
the river and drinking waters. In the 2003 data,
only Tuero Chico shows As concentrations that
are signi®cantly higher than the others and El
Molino shows As concentrations that are signi®cantly lower. El Molino and Cota were the only
villages from which irrigation waters were
collected in 2004. ANOM on the data shows
that El Molino has a signi®cantly higher mean As
concentration in irrigation water than Cota.
ANOM was also used for comparisons between
As concentration means in the waters for 2003
and 2004. There were no signi®cant differences
between mean As concentration for irrigation and
river for the dry (2003) and wet (2004) seasons.
The mean As drinking water concentration is
signi®cantly higher in the dry season than the wet
season. There appears to be a pattern, repeated
consistently in many of the individual villages, in
which dry season concentrations are higher than
wet season concentrations, although not necessarily with a statistically-signi®cant difference in
magnitude (recall that the ANOM decision limits
tend to be relatively broad, mainly as a result of
the small number of observations in each group).
Hair and urine
728
Hair grows at an average rate of approximately
1.1ÿ1.5 cm per month (Akagi
., 1995;
Boischio and Cerichiari, 1998). Because the hair
lengths sampled for this study were between 3 and
4 cm, the concentrations in Fig. 4 represent As
expelled via the body from up to four months
previously. The 2003 samples therefore re¯ect As
exposure during the wet season, and the 2004
samples, the middle to end ofIIIthe dry season/early
wet season. The 1/2 for As and its metabolites
(including AsV) to leave the body via the kidneys
as urine are reported by Crecelius (1977) as 10
and 30 h, respectively. The urine-As concentrations presented herein therefore represent the
expulsion of As consumed during the preceding
24 h. Arsenic concentration in 2003 urine samples
represent dry season As exposure and urine 2004
data represent wet season exposure.
To determine if the As concentrations in hair
and urine collected during this investigation are
relatively high or low compared with the rest of
the world, they have been compared to `reference
concentrations' derived from studies of nonoccupationally exposed reference populations in
Sweden, the UK, Japan and Italy (Minoia .,
et
al
T
et al
AS UPTAKE BY RIVERSIDE COMMUNITIES, BOLIVIA
FIG. 4. As concentrations in all human hair and urine samples. Reference lines represent published reference
concentrations derived from studies of non-occupationally exposed populations: ( ) urine; ( ) hair.
a
1990; White and Sabbioni, 1998; Rodushkin and
Axelsson, 2000; Morton ., 2002; Sera .,
2002). Figure 4 shows the As concentration in
each sample for all 2003 and 2004 data, together
with the reference concentrations. Many samples
from each village lie above at least one of the
reference concentrations. Villages where As
concentrations exceed all the reference values
are found in the 2003 hair data for El Molino,
Tuero Chico, Sotomayor and Cota; in the 2004
hair data for El Molino, Tuero Chico, Sotomayor
and Sucre; in the 2003 urine data for El Molino,
Sotomayor and Cota; and in the 2004 urine data
for El Molino, Tasapampa, Tuero Chico,
Sotomayor, Sucre and the UK. The villages of
Tuero Chico, Sotomayor and particularly, El
Molino, show consistently high As concentrations
compared to the reference values in most, if not
all, of the hair and urine data. In the 2003 hair
data, two As concentrations in El Molino
and one
in Sotomayor exceed 400 mg kgÿ1, which is
almost double
the highest reference value of
230 mg kgÿ1 (Sera
., 2002). Arsenic
concentrations in some of the 2004 hair samples
show the greatest differences between Bolivian
concentrations and the other studies. Individual
As concentrations in the 2004 hair samples from
El Molino and Tuero Chico reached
concentrations of 1300 and 2110 mg kgÿ1, respectively,
which is considerably higher than the aforementioned highest
published reference value
(230 mg kgÿ1; Sera
., 2002). In the 2003
urine data, two Asÿ1 concentrations from El Molino
(89 and 95 mg l ) exceed the highest reference
concentration of 31.1 mg lÿ1 (Minoia ., 1990)
by approximately three times.
ANOM was also applied to log-transformed
hair- and urine-As concentrations. No signi®cant
et al
et
et al
al
et al
et al
729
b
differences are exhibited between mean As
concentrations in 2003 hair samples from each
of the ®ve villages, including the control village
Cota. In the 2004 hair data, only El Molino and
Tuero Chico are signi®cantly higher. Mean As
concentrations in 2004 hair from two of the three
controls, Cota and Sucre, are not signi®cantly
different to the other villages. However, the third
control, the UK, has a mean As concentration that
is signi®cantly lower than all the other villages.
Interestingly, the downstream pattern seen in the
hair samples for 2003 is similar to the trend
exhibited by both the river and drinking water
data, although the 2004 hair data do not follow
this trend, as the Tuero Chico mean ÿAs
concentration is very high (617 mg kg 1).
Arsenic concentrations in the 2003 urine
samples from El Molino and Sotomayor are
signi®cantly higher than those from Tasapampa,
Tuero Chico and Cota. The mean As concentration in 2003 urine from Tuero Chico is
signi®cantly lower than the other villages.
Arsenic concentrations for the UK and the other
two controls, Sucre and Cota, show no signi®cant
difference from the other villages in the 2004
data. The downstream pattern of As concentration
in the 2004 urine data is repeated in the 2003
urine data, but this differs from that seen in the
previous ANOM data for hair and waters.
There are no signi®cant differences between
the pooled mean urine-As concentrations for all
villages, in either 2003 or 2004. The 2003 urineAs concentration does appear to be higher than
the 2004 concentration and this pattern is repeated
in most of temporal pairs for individual villages.
The same mean As concentrations in hair shows
that As concentrations are signi®cantly lower in
the 2003 samples. There is no correlation between
J. ARCHER ET AL.
hair and urine data from 2003 and 2004; nor is
there between 2003 and 2004 hair; nor 2003 and
2004 urine.
Errors-in-variables functional regression
between log-transformed As concentrations in
the hair and urine and those in the drinking waters
(Fig. 5) shows increasing trends in all cases,
although only that for the
2003 urine is
statistically signi®cant ( 2 = 0.87 at 90%
con®dence). The UK has been omitted from this
analysis since it is the As pathways operating in
the Bolivian communities which are under
investigation here.
Robust linear regression analysis of As
concentration in the hair and urine as a function
of age did not show any statistically signi®cant
trends. However, LOESS suggests the presence of
non-linear trends in the data (Fig. 6). In the hair
data, females show an increase in As concentration with age and males show a small initial
r
decrease followed by an increase in As concentration in males >26. Male and female As
concentrations in urine remain relatively static
up to the age of around 35 after which
concentrations in the males appear to increase,
but decrease in females. We believe that, while
relatively low-magnitude, these are real
phenomena since the method is non-parametric
and the independent ®ts to male and female data
indicate correlated and inverse patterns of change
in the older population in the case of hair and
urine-As concentrations.
When As concentration as a function of sex is
analysed using ANOM, there appears to be no
signi®cant difference between males and females
in the 2003 data. In the 2004 data, however, the
hair-As concentrations are signi®cantly higher for
females compared to males. By contrast, the 2004
urine-As concentrations are signi®cantly lower for
females compared to males.
FIG. 5. As concentration in human hair and urine as a function of its concentration in drinking water. Data points
represent mean values with and error bars representing 1 standard deviation. All data have been transformed to
logs to base 10: ( ) hair 2003; ( ) hair 2004; ( ) urine 2003; ( urine 2004.
x
y
a
b
c
730
d)
AS UPTAKE BY RIVERSIDE COMMUNITIES, BOLIVIA
excessive and likely to lead to poisoning (Arnold
., 1990). Hair samples taken in 2004 from El
Molino (1300ÿ1 mg kgÿ1) and Tuero Chico (907 and
2110 mg kg ) have concentrations approaching,
or in excess of, the 1000 mg kgÿ1 criterion.
Similarly, in Utah, USA, some inhabitants
showing hyperkeratosis exhibited highest average
urine-As concentrations of 0.175 to 0.211 mg lÿ1,
and highest average hair-As concentrations of 1.09
Discussion
et al
Although the Pilcomayo village hair- and urine-As
concentrations exceed those in non-occupationally
exposed populations, it is also important to verify if
they approach concentrations in persons exhibiting
signs of As toxicity. Arsenic concentrations in hair
that are ÿregarded
as `normal' are 80 to
250 mg kg 1, with 1000 mg kgÿ1 considered
FIG. 6. As concentration in human hair and urine as a function of age. LOESS regression lines and the respective
95% con®dence limits are shown: ( ) female hair; ( ) male hair; ( ) female urine; ( ) male urine.
a
b
731
c
d
J. ARCHER ET AL.
to 1.21 mg kgÿ1 (Southwick ., 1983). Urine
As concentrations in this study all lie below this
range. The As range in the American hair samples
is exceeded by one individual in El Molino and
another in Tuero Chico. Average As concentrations
in biological media from individuals living in West
Bengal, some of whom
have As-related skin
lesions, are 3.43ÿ1mg kgÿ1 (Samanta .,ÿ2004)
and 6.75 mg kg (rangeÿ11.18ÿ31.0 mg kg 1) ÿfor1
hair and 0.43 mg l (0.03 ÿ2.00 mg l ÿ1;
Chatterjee
., 1995) and 259.5 ng mg
creatinine (range 20.5ÿ2890 ng mgÿ1 of creatinine; Tokunaga ., 2005) for urine. In total,
~10% of the individuals in the current investigation
showed hair or urine concentrations in excess of
published averages from studies where people are
known to show symptoms of As poisoning.
A lack of correlation between the hair and urine
data can be explained by the different time
periods for As expulsion that these media
represent (Crecelius, 1977; Akagi
., 1995;
Boischio and Cerichiari, 1998). The lack of
correlation for the 2003 and 2004 hair and urine
data may be due to different amounts of As uptake
in the wet and dry seasons. Similar seasonal
effects on urinary inorganic As concentrations
were reported by Hinwood . (2004) for areas
affected by gold mining in Australia. The broad
spread of results for hair and urine concentrations
is not unexpected when analysing samples from
human volunteers who vary considerably in such
characteristics as age, sex and health status.
Differences in As uptake based on age and sex
and the associated differences in lifestyle and
occupation could be considered as confounding
factors in this study, but strenuous attempts have
been made to limit these. For example, the age
range of 11 to 56 years old is broad, but most of
the male (79%) and female (81%) volunteers for
this study were involved in the same farming
activities using the same methods. The crops
grown and consumed, and their preparation and
cooking methods, are also virtually identical
amongst community members. Some of the
female members are housewives caring for
babies and small children, but they usually
return to farming once the children begin to
attend school. Because the Bolivian communities
are relatively remote and poor, they do not have
access to a wide range of different food and
beverage products, so members of these communities eat and drink the same limited number of
products. Volunteers in this study were chosen
based on their non-smoking habits so as to
et al
et al
et
al
et al
et al
et al
732
eliminate this potentially confounding factor
from the study. Average weekly alcohol
consumption was not recorded for individuals,
but apart from special occasions, moderate
amounts of alcohol only are consumed in the
communities. Some community members in
Tasapampa, Tuero Chico and Sotomayor
described crossing the RõÂo Pilcomayo for
various purposes and some of the teenage
volunteers also described swimming in the river
during very hot weather, but accurate measurement of these activities was not possible. In a
relatively small sample population such as this,
these confounding factors can bias the results and
so any conclusions should be treated with some
caution.
It is unclear whether drinking water is a
pathway for human As uptake in the Pilcomayo
study villages. The consistent mutually increasing
relationship between drinking water-As and hairand urine-As concentrations (Fig. 5) suggests that
it may be so, but the drinking water-impacted As
hair, and to a lesser extent, urine concentrations,
are likely to be older than the actual drinking
water As concentrations used for this plot. El
Molino is the only village to have As concentrations in drinking water above WHO recommended guidelines, with all the other study
villages showing concentrations well below such
guidelines. Whether this will lead to health effects
is uncertain. The recorded health problems of
stunted growth, widespread anaemia, headaches
and tiredness have been attributed by local health
workers to Pb poisoning, sunstroke and the
relatively common chagas disease, rather than
As accumulation. Because As poisoning can take
up to 10 years to be expressed, some of these
health problems could still be related to As
accumulation. Some believe that drinking water
with As concentrations much lower than the
WHO and
US EPA recommended guideline
(10 mg lÿ1) can have an adverse effect on
human health. A study in Wisconsin, USA,
found that individuals drinking
water for over
20 years containing 2 mg lÿ1 of As or greater
were more likely to report a history of depression,
high blood pressure, circulatory problems and
bypass surgery compared
to others drinking water
containing <2 mg lÿ1 of As (Zierold ., 2004).
Similarly, Knobeloch and Anderson (2003)
reported that long-term
ingestion of water
containing >5 mg lÿ1 of As signi®cantly increases
the risk of skin cancer. The Pilcomayo communities have, however, been using the same sources
et al
AS UPTAKE BY RIVERSIDE COMMUNITIES, BOLIVIA
of drinking water for decades, suggesting that if
As toxicity were present, it would have revealed
itself before now (although it is possible that the
medical staff in the area may not be fully trained
in the recognition of As toxicity symptoms).
The source of As in the drinking water in the
Pilcomayo Basin is probably not directly miningrelated, given that communities use tributary
waters unaffected by mining activity, and that
the drinking water-As concentrations in most of
the study villages are not statistically different
from those of the control village Cota. The only
exception to this is El Molino, where one of the
four tap waters sampled in 2003 contained an
anomalously high As concentration, despite the
fact that another of the other taps receiving water
from the same tank, and sampled on the same day,
showed a far lower concentration. In 2004 the
water sampled from the tap which had previously
shown a high As concentration containedÿ1 far less
As (below the recommended 10 mg l guideline). The same 2003 tap water was analysed
®ltered (0.2 mm) and found toÿ1 contain far lower
As concentrations (2.09 mg l ), suggesting that
the As was associated with particulate matter.
Further sampling from this tap should allow
con®rmation of whether this tap water is highly
contaminated or had simply discharged an
anomalous particulate, in¯ating the As concentration. Smolders . (2004) showed that there is a
geologically signi®cant chemical weathering
control on the major element chemistry of the
RõÂo Pilcomayo, suggesting that it is possible that
the As is derived from natural weathering of
bedrock in the catchment.
In the irrigation waters, Tuero Chico and
Sotomayor have average As concentrations that
are well above guidelines. This is due to the fact
that both villages use Pilcomayo waters to irrigate
their crops during the dry season, whereas the
other villages use water from uncontaminated
tributaries. Villagers claim that they do not drink
from the irrigation canals, but they do eat
vegetables grown in the irrigated ®elds.
Consequently, vegetables grown in Tuero Chico
and Sotomayor may represent another exposure
pathway by which As reaches the human body.
This may explain why the results from the ANOM
tests show that Tuero Chico 2004 hair-As
concentrations deviate from the trend noted in
the drinking and river water and 2003 hair data.
The increase of hair-As concentration as a
function of age (in individuals over 30; Fig. 6)
suggests that either adults of >30 y are exposed to
and/or consume greater quantities of As, or that
As may be accumulating in the bodies of those
who are >30 y old, resulting in greater excretion
via hair. This trend is repeated in the male urine
data. The counterpart downward trend seen in the
female urine data can not be explained at present.
Conclusions
The lack of statistically signi®cant differences
between the controls and the other communities
suggest that the mining-contaminated RõÂo
Pilcomayo should not be held solely responsible
for As contamination in this area of Southern
Bolivia. Natural chemical weathering of bedrock
may play a signi®cant role in exposing local
communities to As.
The results of the study have not clearly shown
that drinking water is an As exposure pathway.
Even if it is, the fact that all but one drinking
water sample were found to contain As below the
WHO recommended guideline of 10 mg lÿ1
suggests that there are other pathways through
which As enters the human body in the Pilcomayo
communities, including ingestion of vegetables
grown using contaminated irrigation water,
ingestion of meat from livestock reared drinking
contaminated water, and inhalation of contaminated dust, as have been shown for other areas
(e.g. Lee and Chon, 2003). Analysis of these
media was outside of the scope of this study, but
should certainly be attempted in the future.
Around 10% of the sample population possessed
hair- or urine-As concentrations equal to concentrations from other studies where symptoms of As
toxicity have been observed, but the long-term
effects of this apparent exposure are currently
unknown. The human populations sampled in this
study were relatively small compared to the total
population in the river catchment area; therefore
any future investigations into As exposure in the
riverside communities should include a larger
sampling program encompassing a greater proportion of the population.
et al
Acknowledgements
733
This work was funded by NERC through a
studentship to J. Archer (number NER/S/A/
2002/11010) and ICP support (OSS/253/0204),
and through a travel grant awarded by the Society
for Latin American Studies. Special thanks go to
Teresa Bohorquez, Rosmary Herobas, David
Gomez, Evelyn Rossa and Mary Rossa for
J. ARCHER ET AL.
Chakraborti, D. (1995) Arsenic in groundwater in six
assisting with health surveys and arranging
districts of West Bengal, India: the biggest arsenic
interviews with community members, and to
calamity in the world. Part 2: arsenic concentration
Dario Urquizo, Mamerto Ortiz, Juan Vedia
in drinking water, hair, nails, urine, skin-scale and
Partes, Luis Salazar, Riberto Vilasques and
liver tissue (biopsy) of the affected people.
,
Pastor Quispe for giving permission to work in
120, 917ÿ924.
their communities. The authors are grateful to
D., Samanta, G., Mandal, B.K., Chowdhury, T.R.,
Carlos Aliaga Arriola and Elizabeth Romero for Das,Chanda,
C.R., Chowdhury, P.P., Basu, G.K. and
advice and help with water sampling in Sucre. We
Chakraborti, D. (1996) Arsenic in groundwater in six
thank A. Osborn and S. Houghton for analytical
districts of West Bengal, India.
assistance using Wolfson Laboratory for
5ÿ16.
Environmental Geochemistry facilities (UCL- Farago, M.E. and Kavanagh,, 18P., (1999)
High arsenicBirkbeck, University of London), and F. Barry
containing
soils
in
SW
England
and
human
exposure
at the NERC ICP-MS Facility at Kingston
assessment.
Pp.
181
ÿ
184:
University.
(H. Armannsson, editor). Balkema,
Analyst
Environmental
Geochemistry and Health
Geochemistry
of
the
Earth's Surface
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[
]
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Earth and Planetary
Science Letters
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Journal of Public Health
Manuscript received 2 February 2005:
revised 7 July 2005
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