Environ. Sci. Technol. 2008, 42, 5106–5111
Difference of Toxicity and
Accumulation of Methylated and
Inorganic Arsenic in
Arsenic-Hyperaccumulating and
-Hypertolerant Plants
Z E - C H U N H U A N G , † T O N G - B I N C H E N , * ,†
MEI LEI,† YING-RU LIU,† AND
TIAN-DOU HU‡
Center for Environmental Remediation, Institute of
Geographic and Natural Resources Research,
Chinese Academy of Sciences, A11 Datun Road,
Beijing 100101, P.R. China, and Laboratory of Synchrotron
Radiation, Institute of High Energy Physics, Chinese Academy
of Sciences, Beijing 100039, P.R. China
Received December 25, 2007. Revised manuscript received
April 19, 2008. Accepted May 07, 2008.
The arsenic (As) hyperaccumulators, Pteris vittata and
Pteris cretica and an As-tolerant plant Boehmeria nivea,
were selected to compare the toxicity, uptake, and transportation
of inorganic arsenate (As(V)) and its methylated counterpart
dimethylarsinic acid (DMA). The XANES method was used to
elucidate the effect of As species transformation on As toxicity
and accumulation characteristics. Significantly higher toxicity
and lower accumulation of DMA than inorganic As(V) was shown
in the As hyperaccumulators and the As-tolerant plant.
Reduction of As(V) was commonly found in the plants. Arsenic
complexation with thiols, which have less mobility in plants
and usually occur in As-tolerant plants, was also found in rhizoids
of P. cretica. Plants with greater ability to form As-thiolate
have lower ability for upward transport of As. Demethylation
of DMA occurred in the three plants. The DMA component
decreased from the rhizoids to the fronds in both hyperaccumulators, while this tendency is reverse in B. nivea.
Introduction
Arsenic (As) can be present in the environment as various
chemical forms. Species-specific phytotoxicity and phytoavailability have been investigated in a number of former
studies, and the species of interest include arsenite [As(III)],
arsenate [As(V)], methylarsonic acid (MMA), and dimethylarsinic acid (DMA). In general, it is considered that organic
arsenic species are less toxic than inorganic species to a wide
range of organisms (1–3), whereas studies on Spartina species
(4, 5), tomato (Lycopersicum esculentum) 6, 7), and turnip
(Brassica napus) (8) showed that DMA and MMA were more
toxic than their inorganic counterparts. The degree of
bioavailability of As chemical forms varies according to the
plant species. They can be ordered as follows: DMA < As(V)
< MMA < As(III) in rice (3) and Spartina species (4, 5), MMA
< DMA < As(III) < As(V) in turnip (8), DMA e As(III) e As(V)
* Corresponding author tel: +86-10-64889080; fax: +86-1064889303; e-mail: [email protected].
†
Institute of Geographic and Natural Resources Research.
‡
Institute of High Energy Physics.
5106
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 14, 2008
, MMA in radish (Rhapanus sativus) (9) and DMA < MMA
, As(V) ≈ As(III) in tomato (6). The mobility of As chemical
forms in plants is also species-specific. Upon absorption,
DMA is readily translocated to the shoot compared to
inorganic As and MMA, which are mainly accumulated in
the roots in Spartina species and rice (3, 4), whereas both
MMA and DMA have a greater upward translocation than
inorganic As in tomato (6). The diversity of As uptake and
transportation behaviors in different plants suggests that As
metabolism in plants might be more complex than their
apparent behaviors. Elucidation of the occurrence and
regulation of As chemical form transformation in plant tissues
is important to further our understanding of As behaviors in
plants.
Biotransformation of inorganic As to less toxic organic As
is reported commonly in aquatic organisms and fungi (10).
Recently, it was found that terrestrial plant species could
also reduce arsenate to arsenite (2, 11–14) and synthesize
phytochelatins (PCs) or glutathione (GSH, a precursor of PCs)complexed As. Therefore, As species transformation and
complexation are considered to be involved in the detoxification of As in plants (11, 15–19) and attract great interest
in plant physiological studies.
Currently, As species are measured mostly by sample
extraction ex situ techniques. Although these techniques have
the advantage of low detection limits, their time-consuming
pretreatment may alter the chemical form of the As in
biological samples from the terrestrial environment (20).
Because of the limitations in technology, no publication
reported intact metal-(loid)-PC forms in plant tissues using
traditional chromatographic separation until the first unequivocal As-PC complex was identified using HPLC-(ICPMS)-(ESI-MS) (17, 21). X-ray absorption spectroscopy (XAS)
provides another way to study elemental chemical form.
Elemental coordination structure obtained from the extended
X-ray absorption fine structure (EXAFS) component of XAS
can be used to identify unknown species, and X-ray absorption near edge structure (XANES) allows identification of the
principal components of mixtures of species if the spectra
of appropriate model compounds are available. Furthermore,
XAS is indifferent to solution or solid-phase samples, so it
might be a unique tool for determining the chemical form
of an element with minimal pretreatment (22). With these
advantages, the biological and environmental applications
of XAS have become increasingly popular in recent years.
In this study, toxicity, uptake, and transportation of
inorganic As(V) and its methylated counterpart (DMA) were
compared in three plant species (Pteris vittata, Pteris cretica,
and Boehmeria nivea) each with a different As accumulation
ability. The XANES method was utilized to elucidate the As
species transformation in each plant. The relationship
between As species transformation and As toxicity and
accumulation characters is also discussed in this paper.
Materials and Methods
Experimental Treatment and Arsenic Analyses. Two hyperaccumulators (P. vittata and P. cretica) found by Chen’s
group (23) and an As-hypertolerant plant (B. nivea) (24) from
similar wild habitats were selected for this study. Propagules
of each species were collected from the same As-contaminated site at the Shimen As Sulphide Mine, Hunan, China.
Spores of P. vittata and P. cretica, and the seeds of B. nivea,
were sown on moist soil in a seedbed covered with a plastic
cling film to retain moisture. After germination, young plants
which were ca. 2 cm in height with true leaves were
transplanted into plastic pots containing 0.7 kg quartz sand
10.1021/es703243h CCC: $40.75
 2008 American Chemical Society
Published on Web 06/18/2008
TABLE 1. Biomass of Pteris vittata, P. cretica, and Boehmeria nivea Plants Grown in Sand Treated with 10 · L-1 As in the
Form of Either Arsenate [As(V)] or Dimethylarsinic Acid (DMA) in Nutrient Solution for 4 Weeks
biomass (g · pot-1, FW)
P. vittata
P. cretic
B. nivea
treatment
rhizoid
frond
rhizoid
frond
root
shoot
control
As(V)
DMA
1.5 ( 0.3 aa
2.6 ( 0.3 a
2.1 ( 0.8 a
2.4 ( 0.8 a
3.9 ( 0.5 b
2.0 ( 0.8 a
0.7 ( 0.4 a
0.5 ( 0.3 a
0.9 ( 0.4 a
1.0 ( 0.4 a
0.8 ( 0.2 a
1.3 ( 0.5 a
5.5 ( 0.2 b
2.9 ( 0.4 a
1.6 ( 1.6 a
20.0 ( 0.4 b
13.4 ( 2.1 ab
6.1 ( 5.1 a
a
Mean ( SD (n ) 3). Values followed by the same letter are not significantly different at P < 0.05
(Student-Newman-Keuls test) within the same column.
pretreated with dilute HCl and washed with deionized water
and a nutrient solution modified from Hoagland’s formula
to reduce the concentrations of most ions to meet the
requirement of ferns. The nutrition solution contained 2.0
mmol · L-1 Ca(NO3)2, 0.75 mmol · L-1 K2SO4, 0.1 mmol · L-1 KCl,
0.25 mmol · L-1 KH2PO4, 0.65 mmol · L-1 SO4, 0.1 mmol · L-1
EDTA-Fe(III), 0.01 mmol · L-1 H3BO3, 0.001 mmol · L-1
MnSO4 · H2O, 0.001 mmol · L-1 ZnSO4 · 7H2O, 0.0001 mmol · L-1
CuSO4 · 5H2O, and 5.0 × 10-6 mmol · L-1 (NH4)Mo7O24 · 4H2O.
The plants were allowed to acclimate for 7 days before the
nutrient solution was replaced with nutrient solution containing 0 or 10 · L-1 of As in the form of either inorganic As(V)
as Na2HAsO4 or methylated As as sodium dimethylarsinic
(DMA). Since the As species in aqueous solution remains
stable for a period of up to 4 days with respect to oxidation/
reduction and methylation/demethylation reactions (8), the
solution was renewed every 3 days to maintain the As
concentration and species during the experimental period.
The plants were placed in a growth chamber with the
following conditions: 16 h of light period with a light intensity
of 300 µmol · m-2 s-1, temperature cycle of 26 °C/15 °C (day/
night), and average relative humidity of 60%. Each of the
treatments was repeated in triplicate.
After 4 weeks growth, the plants were harvested and
washed with tap water followed by three rinses with deionized
water. Each plant was divided into leaves/pinnae, stems/
petioles, and roots/rhizoids and freeze-dried under vacuum
at -50 °C for 48 h. The samples were stored in a -30 °C
freezer prior to XAS measurement. After XAS measurement,
all plant samples were digested with a mixture of
HNO3-HClO4-H2SO4, and the As concentration was analyzed
using an atomic fluorescence spectrometer (AFS-2202,
Haiguang Instrumental Co., China).
Statistical comparisons of means were performed using
the one-way ANOVA as implemented in the SPSS 10.0
software.
XAS Measurement and XANES Fitting. Immediately prior
to analysis, the freeze-dried samples were carefully ground
into powder and packed in a 3 cm × 0.7 cm sample holder
for XAS measurement. Aqueous solutions of the analytically
pure reagents, sodium arsenite, sodium arsenate dibasic,
and dimethylarsinate (DMA) were used as reference compounds for the inorganic As(III), As(V), and DMA, respectively.
As (III)-tris-glutathione (As-GSH), synthesized by adding a
10-fold molar excess of glutathione to a solution of sodium
arsenite, was used to model As coordinated to three thiols
(11). All of the As reference compounds contained 1000
As · kg-1 and were pipetted into a lucite liquid holder of the
same size for XAS measurement.
Arsenic K-edge (11867 eV) X-ray absorption spectrum
collection was performed using a double crystal monochromator (Si 111) in fluorescence mode at room temperature
at the XAFS station on Beamline 4W1B of the Beijing
Synchrotron Radiation Facility (BSRF). The electron storage
ring was operated at 2.2 GeV. Then the pre-edge background
was removed followed by normalization. Near-edge spectra
with 11840-11940 eV were selected and quantitatively
analyzed using LSfitXAFS software (25) in which the nearedge spectra of plant samples were fit to those of As reference
compounds to determine the component As species in the
plant tissues. All small components (<1%) were excluded
from the final fits.
Results and Discussion
Effect of As Species on Plant Growth. Phytotoxicity of both
As species was found in B. nivea. The growth of B. nivea was
significantly inhibited by both As species exposure (Table 1).
The growth inhibition was significantly greater in the DMA
treatment than that in the inorganic As(V) treatment. This
finding is consistent with other studies on terrestrial plants
(3–7) and confirms the view that DMA is more toxic than
inorganic As to terrestrial plants.
The biomass of P. vittata and P. cretica were not
significantly reduced by exposure to either As species (Table
1); on the contrary, inorganic As(V) treatment even significantly increased the shoot biomass of P. vittata compared
to that of control. It might be because both As-hyperaccumulating plants have a high hypertolerance to As.
As Accumulation and Transportation in Plants. Total As
uptake by each of the three plants was relatively lower in the
DMA treatment than that in the inorganic As(V) treatment.
Similar results have been reported for rice (3, 26), Spartina
species (4, 5), radish (9), turnip (8), tomato (6, 7), Silene
vulgaris, and Plantago major (27). Thus the uptake of DMA
may be generally lower than that of inorganic As(V), regardless
of whether the plant is an As-hyperaccumulator or As-tolerant
plant.
Typical As hyperaccumulation were shown in both
hyperaccumulators in the inorganic As(V) treatment. The As
concentration are highest in pinnae, followed by petioles
and rhizoids (Table 2) whereas, for B. nivea, As taken up was
predominantly remained in the roots with a small proportion
translocated to the shoots. Overall, when exposed to inorganic
As(V), the abilities of the three plants to transport As from
underground tissues to above-ground tissues followed the
order: P. vittata > P. cretica > B. nivea.
Although most of As taken up by B. nivea was also stored
in its root, the As concentration in its leaves and stems and
the TF were all higher in the DMA treatment than those in
the inorganic As(V) treatment (Table 2). It suggested that the
potential for B. nivea to transport As from its roots to shoots
is greater when exposed to DMA. This phenomenon is
consistent with that found in the rice plant (3). For P. vittata
and P. cretica in the DMA treatment, the As concentration
in above-ground tissues was lower than that in underground
tissues (Table 2). It suggested that the abilities for both
hyperaccumulating species to accumulate As and to transport
As to their fronds were reduced tremendously in DMA
treatment. By comparing TFs within the DMA treatment, P.
cretica showed the highest ability to transport As to aboveground tissues.
VOL. 42, NO. 14, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
5107
TABLE 2. Arsenic Accumulation and Translocation Factor (TF) in Plants Grown in Sand Treated with 10 · L-1 As in the Form of
Either Arsenate [As(V)] or Dimethylarsinic Acid (DMA) in Nutrient Solution for 4 Weeks
As concentration ( · kg-1, DW)
As added
As(V)
DMA
plant
species
root or
rhizoid
stem or
petiole
leaf or
pinna
translocation
factor (TF)
total As uptake
by plant
(µg · pot-1)
P. vittata
P. cretica
B. nivea
P. vittata
P. cretica
B. nivea
416.6 ( 166.5 Aaa
750.5 ( 132.9 Bb
421.7 ( 18.9 Aa
324.6 ( 50.2 Ab
131.6 ( 24.8 Aa
290.2 ( 101.6 Ab
723.4 ( 372.1 Bb
447.6 ( 169.9 Bab
42.1 ( 6.3 Aa
42.3 ( 30.6 Aa
35.2 ( 17.2 Aa
70.9 ( 15.2 Ba
4243 ( 1631 Bb
2805 ( 994 Bb
31.7 ( 14.8 Aa
27.9 ( 9.7 Aa
70.8 ( 38.2 Aa
53.8 ( 6.2 Ba
10.0 ( 2.3 Bc
3.7 ( 0.8 Bb
0.07 ( 0.03 Aa
0.10 ( 0.04 Aa
0.54 ( 0.3 Ab
0.24 ( 0.12 Bab
2462 ( 200 Bc
872.9 ( 59.2 Bb
288.3 ( 26.0 Ba
38.0 ( 1.0 Aa
56.5 ( 1.1 Ac
45.0 ( 0.3 Ab
a
Mean ( SD (P < 0.05, n ) 3). Total As uptake by plant ) ∑biomass of tissue × As concentration in corresponding
tissue. Values followed by the same letter are not significantly different at P < 0.05 (Student-Newman-Keuls test) within
the same column. Capital letters indicate the significance between As species treatments, and small letters indicate the
significance between plant species (P < 0.05, n ) 3).
FIGURE 1. Edge fitting of arsenic K near-edge spectra from tissues of plants exposed to inorganic As(V) (A) and DMA (B). Sample
spectra were fitted with combinations of spectra from various arsenic reference compounds. In both panels the dots show the
experimental data and the solid lines represent the best fit. Dashed lines a, b, c, d, and e indicate the white line position of As K
near-edge spectra from As(III)-glutathione (GSH), As(III), dimethylarsinate (DMA), methylarsonate (MMA), and As(V), respectively. The
arrow indicates the peak in the experimental data that could not be perfectly simulated
Reduction and Complexation of As in Plants Exposed
to Inorganic As(V). Best fittings of As K-edge XANES spectra
show that As components in the plants tissues are appropriately simulated by the As reference compounds used
in present study (Figure 1), except that a peak in the spectrum
5108
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 14, 2008
of rhizoids of P. vittata in the DMA treatment (indicated by
the arrow in Figure 1B) could not be simulated satisfactorily.
In the inorganic As(V) treatment, a large amount of As(III)
was present in tissues of P. vittata (Figure 1A and 2), indicating
that P. vittata could reduce As(V) to As(III). Moreover, the
FIGURE 2. Arsenic species (percentage of total As) determined
by X-ray absorption near-edge fitting in plants grown in sand
treated with 10 As · L-1 inorganic As(V) in nutrient solution for 4
weeks. DMA and MMA were also examined but rejected from
all fits.
As(III) percentage increased sequentially from the rhizoid to
the petiole and pinna. Percentages of As(V) and As(III) in
rhizoid of P. vittata were 47% and,53%, respectively, and
As(III) increased to 88% in the pinna. Significantly less
inorganic As(V) component in P. cretica and B. nivea than
that in the corresponding tissues of P. vittata suggests that
P. cretica and B. nivea have greater potential to reduce As(V).
Besides inorganic As(V) and As(III), arsenic modeled as
As(III)-GSH was also found in P. cretica and B. nivea. Overall,
the order based on As(III)-GSH percentages is B. nivea > P.
cretica > P. vittata. Different to that As were mainly present
as inorganic As(V) or As(III) in P. vittata and P. cretica, the
vast majority of As in B. nivea was mainly presented as organic
As(III)-GSH, and the As(III)-GSH percentages were 86%,
100%, and 72% for roots, stems and leaves, respectively.
Arsenic complexed in nontoxic forms, such as PCs or GSH,
and stored away from metabolic activity in the vacuole are
widely found in As nonhyperaccumulating plants and are
considered to be involved in the detoxification of As
(2, 11, 15, 16). For P. cretica, As(III)-GSH occupies about 27%
of the total As in its rhizoids but was undetected in its petioles
and pinnae. Using HPLC-(ICP-MS)-(ESI-MS), only about 1%
of As present in PC complexes (GS-As(III)-PC2) was found
in the frond of P. cretica (21). Significant As-S coordination
in the rhizoids of P. cretica was reported first in our previous
EXAFS analyses (18). The proportion (27%) of As complexed
with thiols quantitatively calculated in this study is the largest
ever reported in As-hyperaccumulators.
Although no As(III)-GSH was found in P. vittata in present
XANES examination, As coordinated with S was recorded in
the rhizoid and petiole of P. vittata in our previous EXAFS
measurement (14). Whereas, small coordination numbers
shown in that EXAFS measurement indicated that the S
coordinated As component was low in percentage. A recent
study using XAS imaging also found that S coordinated As
was restricted to a narrow region surrounding the veins of
pinna (28). Since a small amount of S-coordinated As form
in plant tissues might be concealed from detectable in mixed
bulk sample, it might interpret the phenomenon that none
of them has be detected in present and previous studies
(29, 30). Although As apparently induced the formation of
bothGSHandSHatelevatedconcentrationsinP.vittata(30,31),
the concentrations of PCs (32) are considerably lower in
comparison to those reported for S. vulgaris (33), Holcus
lanatus (34) and Rauwolfia serpentina in cell cultures (15).
Thus, the lower thiol-complexed As levels in P. vittata may
be due to its inability to synthesize sufficient thiols to complex
with all accumulated As. Nevertheless, minimal As complexed
with thiols in hyperaccumulators, especially in the frond,
could demonstrate that the complexation may not play a
dominant role in the detoxification of As in hyperaccumulators. It was also suggested that lack of thiol coordination
FIGURE 3. Arsenic species (percentage of total As) determined
by X-ray absorption near-edge fitting in plants grown in sand
treated with 10 As · L-1 DMA in nutrient solution for 4 weeks.
MMA was also examined but was rejected from all fits.
may be a common theme in plants that have evolved to
hyperaccumulate metals (28).
In this study, the order of As accumulation and transportation from underground tissue to above-ground tissue
in inorganic As(V) treatment is P. vittata > P. cretica > B.
nivea. This order is the reverse of their ability to form thiolcomplexed As in roots or rhizoids. Thus, As complexed with
thiol in roots/rhizoids seems to have a negative effect on
their translocation. Although arsenic in As-tolerant plants is
mainly present as As-thiolate species, its form in the xylem
sap was found to be present as the oxyanions As(V) or As(III)
(11, 35). In P. vittata, inorganic As(V) was found to be the
predominant form transported in the sap (28, 36). Therefore
it could be concluded that As might translocate in plant tissue
as the form of anion As(V) or As(III) rather than thiols
complexed forms in any As-hyperaccumulating or -nonhyperaccumulating plants. As-tolerant plants containing a
larger amount of As-thiolate species stored in the root with
less potential to be transported might account for their lower
TF than that of hyperaccumulators. In this study, the
significantly higher TF in P. vittata than that in P. cretica
may be due to an analogous reason.
Demethylation in Plants Exposed to DMA and Its Effects
on As Accumulation. XANES fittings showed that in the DMA
treatment all three plant species contained inorganic As(V),
As(III), and As-GSH, other than the supplied form, DMA
(Figure 3). This might indicate that supplied DMA is
demethylated by plants. Demethylation of DMA has also been
found in As-tolerant plants, S. vulgaris and P. major, and the
demethylation ability of S. vulgaris was significantly greater
than that of P. major (27). It is still unclear how the
demethylation occurred. Since demethylation from DMA to
MMA was not observed whenever in the present or previous
studies (27, 36, 37), it was hypothesized that DMA might be
directly demethylated to inorganic As(V) rather than via MMA
as an intermediate (38).
XANES fitting showed that in DMA treatment As in rhizoids
of P. vittata is present almost as it was supplied (Figure 1B
and 3). This might indicate that the rhizoids of P. vittata
have less ability to demethylate DMA. The DMA component
decreased from the rhizoids to the pinnae, and only 54% of
the residue remained in the pinnae of P. vittata (Figure 3).
Studies on As species in xylem sap showed that As was
presented mainly as its original form, with only a low
concentration of demethylated inorganic As in xylem sap,
when P. vittata was treated with DMA (36, 37). Thus, the
lower DMA residue in the fronds suggests that the demethylation mainly takes place in shoot tissues. In P. cretica,
the DMA percentages were 32% and 17% for rhizoids and
petioles, respectively, and no DMA was found in pinnae
(Figure 3). Overall, the DMA component in P. cretica was
significantly lower than that in corresponding tissues of P.
vittata. It suggests that P. cretica has a greater ability for
VOL. 42, NO. 14, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
5109
DMA demethylation than P. vittata. The inorganic As(III)
component increased from the rhizoids to the pinnae, with
a proportion of 94% in the pinnae, indicating that P. cretica
also reduced As(V) after DMA was demethylated. In B. nivea
only 21% of the total As was present as DMA in its roots in
the DMA treatment, and the DMA percentages increased
sequentially from its root to the stems and leaves. The most
abundant As species accounted for about 49% of total As in
the roots of B. nivea is As(III)-GSH, indicating that a portion
of the DMA taken up by B. nivea was demethylated and
reduced to As(III) and some As(III) was complexed with thiols.
Comparing the methylated As residue in the plants, the
demethylation ability in the plant was greatest in P. cretica.
As DMA is more phytotoxic than inorganic As(V), the lower
amount of DMA residue in P. cretica might correlate to the
lowest growth inhibition by DMA on P. cretica (Table 1). A
previous finding that DMA and MMA were more phytotoxic
to Phaseolus vulgaris in foliar application than in root
application (39) might also be due to greater demethylation
following root applications than for foliar applications.
In P. vittata and P. cretica, the DMA component decreased
in proportion from the rhizoids to the fronds. The present
finding for P. vittata infers that a stronger demethylation
ability in the fronds might, at least partly, contribute to the
lower DMA residue amount in the fronds. Another hypothesis
to explain the decrease of DMA proportion from the rhizoids
to the fronds is that DMA may have less mobility in plants
than inorganic As. The greater TF in the inorganic As(V)
treatment than that in the DMA treatment found in both
hyperaccumulators is consistent with this hypothesis. Moreover, P. cretica with the highest potential to demethylate
DMA had the higher TF in the DMA treatment than P. vittata
and B. nivea also agrees with this hypothesis. This hypothesis
seems inconsistent in that TFs in methylated As treatments
are greater than that in inorganic As treatment in As-tolerant
plants shown in present and previous studies (4, 6, 8).
However, when the fact that inorganic As tends to complex
with thiols in roots of As-tolerant plants is considered, it can
be inferred that the higher TF in the DMA treatment is the
result of less As being complexed with thiol in the DMA
treatment, rather than DMA having higher mobility than
inorganic As in plants.
Acknowledgments
The study was sponsored by the National Foundation for
Distinguished Youth of China (Grant No. 40325003) and the
National High-Tech R & D Program (Grant No. 2007AA
061001).
Supporting Information Available
Arsenic K near-edge spectra of five selected reference
compounds in aqueous solution containing 1000 As · L-1 show
that they vary greatly and could be easily distinguished (Figure
S1). This material is available free of charge via the Internet
at http://pubs.acs.org.
Literature Cited
(1) Quaghebeur, M.; Rengel, Z. Arsenic speciation governs arsenic
uptake and transport in terrestrial plants. Microchim. Acta 2005,
151, 141–152.
(2) Meharg, A. A.; Hartley-Whitaker, J. Arsenic uptake and metabolism in arsenic resistant and nonresistant plant species. N.
Phytol. 2002, 154, 29–43.
(3) Marin, A. R.; Masscheleyn, P. H.; Patrick, W. H. The influence
of chemical form and concentration of arsenic on rice growth
and tissue arsenic concentration. Plant Soil 1992, 139, 175–
183.
(4) Carbonell-Barrachina, A. A.; Aarabi, M. A.; DeLaune, R. D.;
Gambrell, R. P.; Patrick, W. H. The influence of arsenic chemical
form and concentration on Spartina patens and Spartina
alterniflora growth and tissue arsenic concentration. Plant Soil
1998, 198, 33–43.
5110
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 14, 2008
(5) Carbonell-Barrachina, A. A.; Aarabi, M. A.; DeLaune, R. D.;
Gambrell, R. P.; Patrick, W. H., Jr. Arsenic in wetland vegetation:
Availability, phytotoxicity, uptake and effects on plant growth
and nutrition. Sci. Total Environ. 1998, 217, 189–199.
(6) Burló, F.; Guijarro, I.; Carbonell-Barrachina, A. A.; Valero, D.;
Martı́nez-Sánchez, F. Arsenic species: Effects on and accumulation by tomato plants. J. Agric. Food Chem. 1999, 47,
1247–1253.
(7) Tlustoš, P.; Száková, J.; Pavlı́ková, D.; Balı́k, J. The response of
tomato (Lycopersicon esculentum) to different concentrations
of inorganic and organic compounds of arsenic. Biologia 2006,
61, 91–96.
(8) Carbonell-Barrachina, A. A.; Burló, F.; Valero, D.; López, E.;
Martı́nez-Romero, D.; Martı́nez-Sánchez, F. Arsenic toxicity and
accumulation in turnip as affected by arsenic chemical speciation. J. Agric. Food Chem. 1999, 47, 2288–2294.
(9) Carbonell-Barrachina, A. A.; Burló, F.; Lopez, E.; Martı́nezSánchez, F. Arsenic toxicity and accumulation in radish as
affected by arsenic chemical speciation. J. Environ. Sci. Health
B 1999, 34, 661–679.
(10) Cullen, W. R.; Reimer, K. J. Arsenic speciation in the environment.
Chem. Rev. 1989, 89, 713–764.
(11) Pickering, I. J.; Prince, R. C.; George, M. J.; Smith, R. D.; George,
G. N.; Salt, D. E. Reduction and coordination of arsenic in Indian
mustard. Plant Physiol. 2000, 122, 1171–1177.
(12) Quaghebeur, M.; Rengel, Z. The distribution of arsenate and
arsenite in shoots and roots of Holcus lanatus is influenced by
arsenic tolerance and arsenate and phosphate supply. Plant
Physiol. 2003, 132, 1600–1609.
(13) Salt, D. E.; Prince, R. C.; Pickering, I. J. Chemical speciation of
accumulated metals in plants: evidence from X-ray absorption
spectroscopy. Microchem. J. 2002, 71, 255–259.
(14) Huang, Z. C.; Chen, T. B.; Lei, M.; Hu, T. D. Direct determination
of arsenic species in arsenic hyperaccumulator Pteris vittata by
EXAFS. Acta Bot. Sin. 2004, 46, 46–50.
(15) Schmöger, M. E. V.; Oven, M.; Grill, E. Detoxification of arsenic
by phytochelatins in plants. Plant Physiol. 2000, 122, 793–801.
(16) Hartley-Whitaker, J.; Ainsworth, G.; Vooijs, R.; Ten Bookum,
W.; Schat, H.; Meharg, A. A. Phytochelatins are involved in
differential arsenate tolerance in Holcus lanatus. Plant Physiol.
2001, 126, 299–306.
(17) Raab, A.; Schat, H.; Meharg, A. A.; Feldmann, J. Uptake,
translocation and transformation of arsenate and arsenite in
sunflower (Helianthus annuus): Formation of arsenic-phytochelatin complexes during exposure to high arsenic concentrations. N. Phytol. 2005, 168, 551–558.
(18) Huang, Z. C.; Chen, T. B.; Lei, M.; Hu, T. D.; Huang, Q. F. EXAFS
study on arsenic species and transformation in arsenic hyperaccumulator. Sci. China, Ser. C: Life Sci. 2004, 47, 124–129.
(19) Sneller, F. E. C.; Van Heerwaarden, L. M.; Kraaijeveld-Smit, F. J. L.;
Ten Bookum, W. M.; Koevoets, P. L. M.; Schat, H.; Verkleij, J. A. C.
Toxicity of arsenate in Silene vulgaris, accumulation and
degradation of arsenate-induced phytochelatins. N. Phytol.
1999, 144, 223–232.
(20) Koch, I.; Hough, C.; Mousseau, S.; Mir, K.; Rutter, A.; Ollson, C.;
Lee, E.; Andrewes, P.; Granhchino, S.; Cullen, B.; Reimer, K.
Sample extraction for arsenic speciation. Can. J. Anal. Sci.
Spectrosc. 2002, 47, 109–118.
(21) Raab, A.; Feldmann, J.; Meharg, A. A. The nature of arsenicphytochelatin complexes in Holcus lanatus and Pteris cretica.
Plant Physiol. 2004, 134, 1113–1122.
(22) Yan, X. L; Chen, T. B.; Liao, X. Y.; Huang, Z. C.; Pan, J. R.; Hu,
T. D.; Nie, C. J.; Xie, H. Arsenic transformation and volatilization
during incineration of the hyperaccumulator Pteris vittata L.
Environ. Sci. Technol. 2008, 42, 1479–1484.
(23) Chen, T. B; Wei, C. Y.; Huang, Z. C.; Huang, Q. F.; Lu, Q. G.; Fan,
Z. L. Arsenic hyperaccumulator Pteris vittata L. and its arsenic
accumulation. Chin. Sci. Bull. 2002, 47, 902–905.
(24) Wei, C. Y.; Chen, T. B. The ecological and chemical characteristics
of plants in the areas of high arsenic levels. Acta Phytoecol. Sin.
2002, 26, 695–700. (in Chinese with English abstract).
(25) Dogan, P. A computer program for analyzing complex bulk XAFS
spectra and for performing significance tests. J. Synchrotron
Radiat. 2004, 11, 295-198.
(26) Abedin, M. J.; Feldmann, J.; Meharg, A. A. Uptake kinetics of
arsenic species in rice plants. Plant Physiol. 2002, 128, 1120–
1128.
(27) Schmidt, A. C.; Mattusch, J.; Reisser, W.; Wennrich, R. Uptake
and accumulation behaviour of angiosperms irrigated with
solutions of different arsenic species. Chemosphere 2004, 56,
305–313.
(28) Pickering, I. J.; Gumaelius, L.; Harris, H. H.; Prince, R. C.; Hirsch,
G.; Banks, J. A.; Salt, D. E.; George, G. N. Localizing the
biochemical transformations of arsenate in a hyperaccumulating
fern. Environ. Sci. Technol. 2006, 40, 5010–5014.
(29) Lombi, E.; Zhao, F. J.; Fuhrmann, M.; Ma, L. Q.; McGrath, S. P.
Arsenic distribution and speciation in the fronds of the
hyperaccumulator Pteris vittata. New Phytol. 2002, 156, 195–
203.
(30) Webb, S. M.; Gaillard, J. F.; Ma, L. Q.; Tu, C. XAS speciation of
arsenic in a hyper-accumulating fern. Environ. Sci. Technol.
2003, 37, 754–760.
(31) Cao, X. D.; Ma, L. Q.; Tu, C. Antioxidative responses to arsenic
in the arsenic-hyperaccumulator Chinese brake fern (Pteris
vittata L.). Environ. Pollut. 2004, 128, 317–325.
(32) Zhao, F. J.; Wang, J. R.; Barker, J. H. A.; Schat, H.; Bleeker, P. M.;
McGrath, S. P. The role of phytochelatins in arsenic tolerance
in the hyperaccumulator Pteris vittata. New Phytol. 2003, 159,
403–410.
(33) Schat, H.; Llugany, M.; Vooijs, R.; Hartley-Whitaker, J.; Bleeker,
P. M. The role of phytochelatins in constitutive and adaptive
heavy metal tolerances in hyperaccumulator and non-hyperaccumulator metallophytes. J. Exp. Bot. 2002, 53, 2381–2392.
(34) Hartley-Whitaker, J.; Ainsworth, G.; Meharg, A. A. Copper- and
arsenate-induced oxidative stress in Holcus lanatus L. clones
with differential sensitivity. Plant Cell Environ. 2001, 24, 713–
722.
(35) Mihucz, V. G.; Tatár, E.; Virág, I.; Cseh, E.; Fodor, F.; Záray, G.
Arsenic speciation in xylem sap of cucumber (Cucumis sativus
L.). Anal. Bioanal. Chem. 2005, 383, 461.
(36) Kertulis, G. M.; Ma, L. Q.; MacDonald, G. E.; Chen, R.;
Winefordner, J. D.; Cai, Y. Arsenic speciation and transport in
Pteris vittata L. and the effects on phosphorus in the xylem sap.
Environ. Exp. Bot. 2005, 54, 239.
(37) Chen, R. X.; Smith, B. W.; Winefordner, J. D.; Tu, M. S.; Kertulis,
G.; Ma, L. Q. Arsenic speciation in Chinese brake fern by ionpair high-performance liquid chromatography-inductively
coupled plasma mass spectroscopy. Anal. Chim. Acta 2004, 504,
199–207.
(38) Bowell, R. J. Sulfide Oxidation and arsenic speciation in tropical
soils. Environ. Geochem. Health 1994, 16, 84–84.
(39) Sachs, R. M.; Michael, J. L. Comparative phytotoxicity among
four arsenical herbicides. Weed Sci. 1971, 19, 558–564.
ES703243H
VOL. 42, NO. 14, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
5111