Environ. sci. Technol. 1994, 28, 877-881
Arsenic Species in Groundwaters of the Blackfoot Disease Area, Taiwan
Shun-Long Chen, Shlaan I?.Dzeng, and Mo-Hslung Yang'
Institute of Nuclear Science, National Tsing Hua University, Hsinchu, Taiwan, Republic of China
Kong-Hwa Chlu, Guan-Mlng Shleh, and Chlen M. Wai'
Department of Chemistry, University of Idaho, Moscow, Idaho 83843
The groundwaters collected from three wells in the
Blackfootdisease (BFD) area in southwest Taiwan contain,
on the average, 671 i 149 r g of total dissolved arsenic/L.
The arsenic contents in the well waters of Hsinchu, a city
in the northwest of the island where no BFD has ever been
reported, are less than 0.7 pg/L. The predominant arsenic
species in the well waters of the BFD area is As3+with an
average As3+/As5+ ratio of 2.6. The methyl arsenicals,
monomethylarsinic acid and dimethylarsonic acid, are
below detection limits (C1 pg/L), and the insoluble
suspended arsenic accounts for about 3% of the total
arsenic in the water. Ultrafiltration experiments indicate
that the dissolved arsenic species can be roughly divided
into two main groups, one with molecular mass <lo00 and
the other with molecular mass >300 000 Da. The results
obtained from the BFD area are compared with similar
arsenic studies conducted in the United States. The
importance of arsenic speciation in environmental water
studies and the possible cause of BFD are discussed.
Introduction
Blackfoot disease (BFD) is a peripheral vascular disease
found in a limited area on the southwest coast of Taiwan.
The BFD area consists mainly of four villages located about
20 km north of Tainan. The symptoms of BFD start with
spotted discoloration on the skin of the extremities,
especially the feet. The spots change from white to brown
and eventually to black, hence the name BFD. The
affected skin gradually thickens, cracks, and ulcerates.
Amputation of the affected extremities is often the final
resort to save the BFD victims. The disease, first observed
in the southwest coast area of Taiwan in the 1930s and
was reported to correlate with the
peaking in the 1950~1,
consumption of groundwater by local inhabitants (1).
Outbreak of the disease increased rapidly around 1950
when the number of deep artesian wells drilled by local
villagers for drinking reached a maximum. A map of the
BFD area, its geological descriptions, and early investigations of arsenic in the artesian wells of this area were
reported by Tseng et al. (1). The number of patients
suffering from this disease has been decreasing since 1956
after purified tap water was made available to the local
dwellers. In 1975, a total of 1141 BFD patients were
identified in this area (2). The cause of BFD is still
unknown, but it is generally attributed to the high
concentrations of arsenic found in the deep well waters
(1).
According to the US.Code of Federal Regulations (CFR)
published in 1992,the maximum contaminant level (MCL)
of arsenic in community water systems is 0.05 mg/L (3).
This is also the permissible level of arsenic in bottled water
according to the CFR (4). The CFR standard is actually
based on the interim MCL of arsenic in drinking water
0013-938X/94/09280877$04.50/0
0 1994 American Chemlcal Soclety
recommended by the US. Environmental Protection
Agency (U.S. EPA). The U.S.EPA is in the process of
revising the MCL of arsenic in drinking water, and the
new MCL is expected to be lower than the interim MCL
value (5). The chemical form of arsenic in drinking water
is not specified by the CFR, although it is well-established
that the toxicity of arsenic depends on its chemical form.
Arsenic is known to exist in natural waters in different
oxidation states depending on the redox environment.The
trivalent inorganic species arsenite is more toxic to the
biological systems than the pentavalent species arsenate
(6). Organoarsenicals such as monomethylarsinic acid
(MMA) and dimethylarsonic acid (DMA) also exist in the
natural environments, but their toxicities are lower than
the inorganic arsenic species (5). Information on the
distribution of arsenic species is therefore important to
assess its toxicity in drinking water. The distribution of
arsenic species and other trace and minor elements in well
waters of the BFD area have not been reported in the
literature. This information is of fundamental importance
for understanding the cause of BFD and the potential
hazards of arsenic in the aquatic environment. Recently,
we have conducted a systematic study of arsenic species
and other minor and trace elements in the well waters of
a representative village (Putai) in the BFD area in
southwest Taiwan for a period of 1 year. The metal
contents in the well waters of the BFD area are compared
with those obtained from another city in Taiwan where
no BFD case has ever been reported. Correlations between
the arsenic species and other elements in the well waters
and the occurrence of BFD in Taiwan are discussed.
Experimental Section
Reagents. Stock solutions (1000 mg/L) of arsenite,
arsenate, DMA, and MMA were prepared from sodium
arsenite (E. Merck), disodium hydrogen arsenate (E.
Merck), sodium dimethylarsinate trihydrate (E. Merck),
and disodium methylarsonate (Chem Service), respectively, and stored at 4 "C until use. Working standards
for each arsenic species (usually in the range 0.1-0.8 mg/
L) were prepared fresh daily in 0.2% (v/v) sulfuric acid
solution. Stock solutions of other elements were prepared
from the E. Merck Titrisol standard solutions (1.000 f
0.002 g) by diluting to 1 L with deionized water. The
counterion of eluent in the pairing ion chromatography
(PIC) was 5 X 10-3 M tetrabutylammonium phosphate
(PIC-A, Waters) in 5% methanol solution. All acids and
bases used in this work were of superpure grade (E.Merck).
The NIST standard reference material SRM 1643b (trace
elements in water) and the ICP multi-element standard
solution from E. Merck (QC 11355) were used as the
references for quality control of analytical data.
Sampling and Pretreatment Procedure. Groundwater samples were collected from three deep wells in the
BFD endemic district, Putai, Taiwan. These wells were
Envlron. Sci. Technol., Vol. 28,
No. 5, 1994 877
previously used by local dwellers as sources of drinking
water before tap water was made available to this area.
Groundwater samples were also collected from three wells
in another city Hsinchu, which is about 200 km north of
Putai and is the hometown of National Tsing Hua
University. No BFD case has ever been reported in the
Hsinchu area. Water samples were collected from the wells
of these two locations every two months for 1 year (from
July 1991 to May 1992).
High-density polyethylene bottles were used as containers for groundwater collection. The bottles were
precleaned with 10% nitric acid and then rinsed with
deionized water. The well water was allowed to run
through the pumping pipe for at least 10 min prior to
sample collection. One liter of the collected water was
filtered through a 0.45-pm Millipore membrane immediately after collection. The water was acidified by adding
2 mL of sulfuric acid and was stored at 4 "C for arsenic
speciation studies. The preservation of arsenic species in
water by sulfuric acid was reported in the literature (7).
Another 5 L of the water was also filtered through a 0.45pm Millipore membrane, adjusted to pH <2 by nitric acid,
and stored at 4 "C for ICP-AES, ICP-MS,HPIC, or GFAAS
analysis. The insoluble fraction collected on the membrane
was washed with deionized water and dried in a desiccator
for neutron activation analysis (NAA).
Analytical Methods. A Perkin-Elmer Model 5100PC
atomic absorption spectrometer equipped with an HGA300 graphite furnace atomizer was used to determine total
As, Se, Cd, Pb, and Cu. A mercury/hydride generation
system (MHS-10) was also used for total As, Se, and Hg
determination in conjunction with the AAS according to
the procedures recommended by EPA (8). The detection
limit for total As using the hydride generation method is
0.7 pg/L. A simultaneous ICP-AES (Therm0 Jarrell Ash
Model ICAP 9000) was used for the determination of Ba,
Ca, Cr, Fe, K, Mg, Mn, Na, P, Sr, and Zn. A one-MW
TRIGA nuclear reactor with a steady neutron flux of 6 X
1012 n cm-2 s was used for the irradiation of filter
membranes to determine insoluble arsenic. A highresolution ORTEC Ge(Li) detector and an EG&G ORTEC
ADCAM (Model 950) multichannel analyzer were used
fortheanalysisof7~As(559keV,t~p=l.lday)
afterneutron
activation. The details of NAA of arsenic are given in the
literature (9).
Two methods were used to determine arsenic species in
water samples. One method of arsenic speciation was done
using the pairing ion high-performance liquid chromatography (PIC-HPLC, Waters Model 501) coupled to a
hydride generation AAS. The technique of PIC-HPLC
separation of arsenic species is given in the literature (10,
11). Usually, 100 pL of water sample was loaded into the
sample loop and then injected on a separation column.
The polystyrene divinylbenzene reversed-phase columns
Dionex NG-1 and NS-1 were used as the guard column
and the separation column, respectively. The arsenic
species were eluted from the separation column with a
solution consisting of 5 X 10-3 M tetrabutylammonium
phosphate in 5% methanol solution adjusted to pH 7.3 at
a flow rate of 1 mL/min. Under these conditions, the
elution times for As3+,DMA, MMA, and As5+are 2.1,3.2,
4.0, and 6.3 min, respectively. The effluent was mixed
with 1 M HC1 and 4 % w/v sodium borohydride on-line,
and the arsine generated was determined by AAS at 193.7
nm. The detection limits for As3+,As5+,MMA, and DMA
678
Envlron. Scl Technol.,Vol. 28, No. 5, le94
Allowing well water to flow through
the pumpinq,tube for 10 min
,
,
5 L water sample
1 L water sample
I
I
0.45pm millipore filtration
at the sampling site
0.45 &m millipore
I
filtration
Adding 2 mL H p ,
I
I
fraction
retained by
the f iltsr
I
NAA for
insoluble
tb
by PIC-HGAAS
I
I
1 L adjusted
to pH<Z with
"0, and
stored at 4'C
1
4L
(unacidified)
for ultranitration
I
0.1 L
(unacidified)
for anion
determination
by HPIC
speciation
by solvent
extraction
Multielemental
Filtrate
analysis by
adjusted to
ICP/rnS,
pHc2 with HN03
ICP/MS, or GFAAS,
1
total As
As determination
determination
by ICP/MS
by HGAAS or NAA
Flgure I. Procedures of sampling, pretreatment, and analysis of the
groundwaters collected from the BFD area.
using this method are 0.7, 1.5, 1.0, and 1.0 pg/L, respectively. Another method of arsenic speciation involved a
solvent extraction procedure using ammonium pyrrolidinedithiocarbamate (APDC) as a ligand for complexation with As3+followed by NAA of the extracted complex.
The pentavalent As5+was determined by reduction to As3+
with sodium thiosulfate and potassium iodide followed by
the extraction of the trivalent species. The difference in
arsenic concentration between the two aliquots with and
without reduction was used to calculate the As5+concentration. The detailed procedure of arsenic speciation by
APDC extraction is given in the literature (9).
The ultrafiltration technique was used to further
characterizethe distribution of dissolved arsenic in water.
The well waters were first filtered through a 0.45-pm
Millipore membrane. The filtered water (unacidified) was
separated into five aliquots for size distribution studies.
An ultrafiltration apparatus (Model XX42PRK60, Millipore, Waters) with four different membranes (Millipore
Pellicon minicassette, 1,5, 10, and 300 kDa) was used to
differentiate the molecular sizes of the dissolved arsenic
in water. One aliquot was used as the reference, and the
other four aliquots were each filtered through a different
membrane to determine the dissolved arsenic in each size
fraction by ICP-MS (Perkin-Elmer,Sciex Elan 5000).The
procedure of ultrafiltration technique for size differentiation is described in the literature (12). Anions in the
water samples were determined by HPIC (Dionex Model
4500i) following the procedures recommended by the EPA
(8). The overall procedures of arsenic speciation and
chemicalanalysis of other trace elements in the well waters
are illustrated in Figure 1.
Results and Discussion
The total dissolved arsenic and the distribution of As3+,
As5+,MMA, DMA, and insoluble arsenic in the well waters
of Putai are given in Table 1. The concentrations of the
arsenic species given in Table 1are the averages of triplicate
bimonthly samples obtained from each of the three wells
in Putai during the 1-yearstudy period. The concentration
ranges of the arsenic species are given in parentheses. The
average concentrationsof the soluble arsenic found in each
Table 1, Average Concentrations and Ranges of Arsenic
Species in Well Waters of Putai, Taiwan ( d L P
1
total soluble As 734 i 92
(662-897)
As3+
365 f 42
(318-434)
As5+
346 f 43
(303-420)
insoluble As
7.6 f 1.8
(5.0-9.7)
well no.
2
3
av. of all
samples
748 & 45
(687-810)
593 & 41
(542-634)
115 f 60
(33-174)
28.2 f 18.9
(15.0-53.2)
583 f 132
(470-754)
451 f 122
(358-683)
128 f 36
(89-190)
29.8 f 13.2
(16.7-44.0)
671 f 149
(470-897)
462 f 129
(318-683)
177 f 109
(33-420)
21.9 12.4
(5.0-53.2)
*
MMA and DMA are below detection limits (<1 pg/L).
of the three wells over the 12-month period are 583 f 133,
734 f 92, and 748 f 45 pg/L. The total amounts of
dissolved arsenic were determined by the hydride generation-atomic absorption spectrometry (HGAAS)and by
NAA of the filtered water samples directly. The total
dissolved arsenic in the water collected from each individual well shows some variation. The variation of the
average value is about 25% from 583 pg/L for the low
arsenic well to 748 pg/L for the high arsenic well. Averaging
over the three wells, the total dissolved arsenic concentration is 671 f 149 pg/L, with a range of 470-897 pg/L
for all the well waters (a total of 54 samples) collected
from the Putai area. The average value of the dissolved
arsenic in all the well waters analyzed by this study is
about 13 times greater than the CFR’s MCL for arsenic
in drinking water. The main arsenic species found in the
well waters of the BFD area are As3+ and As5+,with a total
average ratio of As3+/As5+about 2.6. The individual wells
show a variation of As3+/As5+ratio from about 1.1to 5.2.
The high concentration of As3+ species present in these
waters reflects the reduced environment of the aquifer,
which may be caused by the low oxygen fugacity or the
presence of other reducing agents, or both, in the groundwater system. According to the information provided by
the local dwellers, the depth of the wells chosen for this
study is estimated to be around 150 m. This estimate was
based on the number of bamboo tubes and their average
length used in drilling the wells some 40 years ago. The
methyl arsenicals (MMA and DMA) are below detection
(<1pg/L) in the well waters, and the insoluble suspended
arsenic is about 3% relative to the total soluble arsenic.
The sum of As3+and As5+accounts for about 95 % of the
total dissolved arsenic according to the datagiven in Table
1. Some other soluble forms of arsenic, not detectable by
our speciation techniques, are probably also present in
the well waters. In comparison with the arsenic contents
in the well waters of Hsinchu where no BFD has ever been
reported, the BFD waters are about 3 orders of magnitude
higher. The average total arsenic in the well waters of
Hsinchu is less than 0.7 pg/L (n = 54). The insoluble
suspended arsenic and the soluble MMA and DMA in the
well waters of Hsinchu were not detectable (<1 pg/L).
The chemical forms of the inorganic arsenic species
present in natural waters depend on the pH and the redox
potential of the aquatic system. The pH values of the
well waters collected from the Putai area are in the range
of 8.1 f 0.4. The chemical forms of As3+ and As5+ at pH
values around 8 should be H3AsO3 and HAs0d2-,respectively, according to the known thermodynamic data (13).
The organoarsenicals found in the environment are
primarily derived from biomethylation, i.e., the synthesis
Table 2. Size Distribution of Soluble Arsenic Species in
Well Waters of Putai, Taiwan
molecular mass range (kDa)
concn (pg/L)
range (Wg/L)
% soluble As
>300
300-10
86 f 14
(76-102)
10.8
5f4
(1-10)
0.6
10-5
5-1
<1
*
15 f 11 43 f 18 645 147
(4-27)
(13-69) (485-775)
5.4
81.2
1.9
of organoarsenic compounds requires the involvement of
a living organism and, presumably the intervention of
arsenic within the metabolic pathways of the cell (14).
Besides MMA and DMA, other biologically produced
organoarsenicals with more complex organic moieties are
also known, these also possess methyl groups. According
to Cullen and Reimer, MMA and DMA are the only
organoarsenicalsthat have been found as dissolved species
in natural waters (14). The low MMA and DMA concentrations found in the well waters of the Putai area
suggest that other more complicated organoarsenicals are
probably not present in significant amounts in the well
water. It is possible that some of the dissolved arsenic
species may be associated with high molecular weight
organic materials such as humic substances in the well
water. Humic substances have been detected in the well
water of the BFD area (15).
The molecular weight distribution of soluble arsenic
species in the well waters of the BFD area determined by
the ultrafiltration technique is given in Table 2. The
predominant molecular mass of the dissolved arsenic in
the well waters is less than lOOODa (about 81% ), suggesting
that the major forms of the arsenic species in the well
water are probably individual ions or molecular species.
A significant fraction of the dissolved arsenic in the well
waters is probably associated with the humic substances
based on the data given in Table 2. The molecular mass
of humic substances is roughly in the range of 104-106 Da.
The fraction with molecular mass >300 000 Da accounts
for about 11% of the total dissolved arsenic. The average
concentration of arsenic in this fraction is about 86 f 14
pg/L, significantly greater than the CFR’s MCL of arsenic
in drinking water. According to the ultrafiltration data,
the distribution of dissolved arsenic in the well waters can
be roughly divided into two main groups, one with
molecular mass <lo00 Da and the other with molecular
mass >300 000 Da. When a >300 000 Da fraction sample
was injected into the PIC-HPLC, two peaks were observed
corresponding to the elution times of As3+and As5+. The
ratio of As3+/As5+concentrations is 9:l. The rest of the
arsenic in the high molecular weight fraction could not be
eluted from the column. The majority of the arsenic in
the elutable fraction appears to be As3+. The chemical
nature of these high molecular weight arsenic containing
species is unknown. Isolation and characterization of the
dissolved arsenic species in the well water may provide
very useful information for understanding the toxicity of
arsenic and the cause of BFD.
The concentrations of 19other trace and minor elements
in the well waters of the BFD and the Hsinchu area are
given in Table 3. The available CFR’s MCL in drinking
water for some of the listed elements are also given in the
table (3,4).Except manganese, none of the elements listed
in Table 3 exceeds the CFR’s MCL. The average concentration of Mn is only slightly above the CFR’s MCL
for bottled water. The ratios of the trace element
Environ. Scl. Technol., Vol. 28, No. 5, 1994
878
Table 3. Average Concentrations and Ranges of Minor and
Trace Elements in Well Waters of Putai and Hsinchu,
Taiwan
element
Cd
co
Cr
cu
Fe
Hg
Mn
Ni
P
Pb
Sb
Se
Zn
Na
K
Mg
Ca
Sr
Ba
Putai (pglL)
0.09 f 0.02
(0.07-0.11)
37.2 f 27.2
(6.7-111.0)
10.3 f 3.6
(7.5-14.3)
1.82 f 1.13
(0.92-3.88)
176.2 f 98.4
(33.9-386.0)
0.41 & 0.34
(0.06-1.04)
54.7 f 16.5
(28.7-90.7)
<9
85.8 f 63.6
(15.0-225.7)
4.99 f 5.35
(0.71-14.10)
0.8 f 0.3
<0.08
18.3 f 10.9
(11.0-56.5)
(26.3 f 8.67) X lo4
(16.6-48.7) X lo4
(8.04 f 2.52) X lo3
(4.99-14.2) X lo3
(9.91 i 5.54) x 103
(3.70-22.1) X lo3
(25.2 f 8.25) X lo3
(13.4-43.9) X lo3
216 f 62
(129-336)
146 f 116
(36-399)
Hsinchu (pg/L)
ratio of
Putail
Hsinchu
0.10 f 0.04
(0.06-0.14)
25.0 f 19.5
(5.7-60.2)
C1.4
0.9
2.45 f 1.22
(0.75-5.33)
78.3 f 65.7
(1.6-190.0)
0.34 f 0.20
(0.08-0.68)
135 f 42
(99-183)
e9
24.9 f 17.5
(7.2-63.0)
1.16 f 0.50
(0.68-1.86)
<0.2
C0.08
15.9 f 9.6
(4.5-37.6)
(3.07 f 1.86) X 104
(0.98-5.76) X 104
(7.90 f 8.25) X lo3
(1.69-22.8) X 103
(22.5 f 16.9) x 103
(8.85-54.7) X lo3
(55.2 f 8.76) X lo3
(38.6-74.7) X lo3
323 dz 88
(230-530)
47 f 30
(16-111)
0.7
1.5
7.4
2.3
1.2
0.4
3.4
4.3
4.0
1.2
8.6
1.0
0.4
0.5
0.7
3.1
a 40 CFR 8 141.11, for community water systems, revised in July
1992. 21 CFR § 103.35 for bottled water, revised in April 1992.
concentrations in the well waters of Putai over those of
Hsinchu are also given. Of the 19 elements listed, Cd, Cu,
Mg, Mn, Ca, and Sr are actually lower in the well waters
of the BFD area relative to the Hsinchu area. The
concentrations of Co, Cr, Fe, Hg, P, Pb, Sb, Zn, Na, K, and
Ba are all higher in the BFD well waters relative to the
Hsinchu waters. The chemical properties of Sb are similar
to As (16). For this reason, we also measured the
distribution of Sb species in the water. The average total
Sb concentration in the well waters of the BFD area is
about 0.8 pg/L, within the range of its concentrations
reported for natural waters (16). The predominant Sb
species in the water is Sb5+, with a ratio of Sb3+/Sb5+
around 0.3. The average concentrations of the following
anions in the well waters were obtained from HPIC
analysis: C1- (322 f 3 mg/L), B r (0.97 f 0.01 mg/L), NO3
(0.22 f 0.01 mg/L), HP042- (5.1 f 0.1 mg/L), and Sod2(8.1 f 0.1 mg/L). Fluoride and nitrite ions were not
detectable (<0.1mg/L) under our HPIC conditions. Based
on the data obtained from this study, there is no compelling
reason to suspect that any one of the elements listed in
Table 3 is related to the cause of BFD. However, the
synergistic effects of arsenic and other trace and minor
elements in the well waters with respect to biological
toxicity are unknown. It is possible that high arsenic
contents combined with other trace or minor elements
may enhance their toxicities for biological systems.
880
Environ. Sci. Technoi., Vol. 28, No. 5. 1994
In 1981, the Safe Drinking Water Committee, after
reviewing the epidemiologicalstudies in the United States,
found no positive relationship between high levels of
arsenic in drinking water and adverse health effects (17).
The US. epidemiological studies were conducted in Alaska,
Oregon, and Utah. According to the literature, arsenic
exposure is associated primarily with skin cancer. Associations with other cancersand cardiovasculardysfunctions
have also been found (17). This relationship is consistent
with the observations made in the BFD area in Taiwan.
The standardized mortality ratio was found to be significantly higher in the BFD area relative to other areas in
Taiwan for cancers of the skin, bladder, kidney, lung, liver,
and colon for both sexes (18). In addition to the high
cancer rates, there is BFD which is found only in this area
of Taiwan according to the official record. There is also
a strong correlation between skin cancer, BFD, and the
content of arsenic in the drinking water of the BFD area
according to Tseng ( I , 18). The difference between the
U.S. epidemiologic studies and the BFD case in Taiwan
may be caused by several factors. For example, the arsenic
concentrations in the drinking waters of the U.S. epidemiological studies are significantly lower than those found
in the BFD area. The Fairbanks, AK, study examined
over 200 residents exposed to drinking water containing
a mean arsenic level of 224 pg/L with the longest exposure
in the study population about 10 years. The average
arsenic concentrations in drinking water of the other two
studies are lower than the Alaska study. Perhaps, more
importantly, the prevailing arsenic species in the waters
of the U.S. studies is the pentavalent state As5+ (19),
which is known to be less toxic than the trivalent state
As3+found predominantly in the waters of the BFD area.
In addition, the durations of exposure to arsenic for the
study population in the U.S. epidemiological studies are
short compared with the BFD area in Taiwan, where BFD
records have been kept over half of a century. The mobility
of population in the BFD area is generally small. Most
of the local inhabitants have been living in the same area
for generations and some began using artesian wells with
high arsenic levels in the early 1920s of this century.
Perhaps these factors are responsible for this arsenicassociated chronic disease in Taiwan. The difference in
other environmental factors between the U S . study areas
and the BFD area in Taiwan should also be considered.
Most of the people in the BFD area were engaged in
farming, fishing, and salt production, and their socioeconomic status was considered poor. Lack of nutrition during
and after the war might have exacerbated the effects of
arsenic exposure in the BFD area.
There are other data existing in the literature concerning
high arsenic in drinking water. For example, in the
community of Fallon, NV, arsenic in the level of 100 pg/L
was found in an aquifer reported to be used by local people
since 1941. No adverse health effect has been reported
from this city either. According to the tests, the arsenic
in Fallon's water is all in the pentavalent state As5+ (20).
These documented cases in the United States indicate
that the presence of the pentavalent arsenic species in
drinking water at the specified levels probably would not
create a health hazard. The adverse health effects of the
trivalent arsenic species and other arsenic species in
drinking water cannot be evaluated in the U.S. studies.
The World Health Organization estimated that a lifetime
exposure to arsenic in drinking water at a concentration
of 200 pg/L might give a 5% risk of getting skin cancer
(21). The chemical form of the arsenic was not specified.
According t o a recent report, the U.S.EPA is reviewing
the carcinogenicity of arsenic and the anticipated MCLG
(maximum contaminant level goal) for noncancer effects
would probably be around 2 pg/L (5). We recommend
that the chemical species of arsenic should be included in
this and other future evaluations.
Based on the extensive chemical and arsenic speciation
data of the groundwaters obtained from the BFD area by
this study, we tend to conclude that arsenic is still the
primary suspect for the cause of BFD. Because of its
unique occurrence in Taiwan, BFD may provide an
important case study for understanding the environmental
hazard of long-term exposure to arsenic and the cause of
this painful chronic disease. Further study in identifying
and characterizing the chemical forms of the dissolved
arsenic in the well waters of the BFD area is highly desirable
for the BFD research.
Acknowledgments
This work was supported by a grant from the National
Science Council of Taiwan. Neutron irradiations performed at the Washington State University Nuclear
Radiation Center were supported by a Reactor Sharing
Program funded by the U.S. Department of Energy.
Literature Cited
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Received for review July 14,1993.Revised manuscript received
January 10, 1994. Accepted January 13,1994.'
* Abstract published in Advance ACS Abstracts, February 15,
1994.
Environ. Scl. technol., Vol. 28, No. 5, 1994 881