Available online at www.sciencedirect.com
Environmental Pollution 154 (2008) 212e218
www.elsevier.com/locate/envpol
Phytoextraction by arsenic hyperaccumulator Pteris vittata L.
from six arsenic-contaminated soils: Repeated harvests
and arsenic redistribution
Maria I.S. Gonzaga a, Jorge A.G. Santos a, Lena Q. Ma b,*
b
a
Department of Soil Chemistry, Universidade Federal da Bahia, Cruz das Almas, 44380000, Brazil
Soil and Water Science Department, University of Florida, 2169 McCarty Hall, Gainesville, FL 32611-0290, USA
Received 23 May 2007; received in revised form 26 September 2007; accepted 7 October 2007
Pteris vittata was effective in continuously removing arsenic from contaminated soils after three repeated harvests.
Abstract
This greenhouse experiment evaluated arsenic removal by Pteris vittata and its effects on arsenic redistribution in soils. P. vittata grew in six
arsenic-contaminated soils and its fronds were harvested and analyzed for arsenic in October, 2003, April, 2004, and October, 2004. The soil arsenic
was separated into five fractions via sequential extraction. The ferns grew well and took up arsenic from all soils. Fern biomass ranged from 24.8 to
33.5 g plant1 after 4 months of growth but was reduced in the subsequent harvests. The frond arsenic concentrations ranged from 66 to 6,151 mg kg1,
110 to 3,056 mg kg1, and 162 to 2,139 mg kg1 from the first, second and third harvest, respectively. P. vittata reduced soil arsenic by 6.4e13%
after three harvests. Arsenic in the soils was primarily associated with amorphous hydrous oxides (40e59%), which contributed the most to arsenic
taken up by P. vittata (45e72%). It is possible to use P. vittata to remediate arsenic-contaminated soils by repeatedly harvesting its fronds.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Continuous phytoextraction; Plant arsenic uptake; Arsenic fractionation
1. Introduction
Arsenic contamination in soils is a serious concern as it affects both human and animal health. It results from the extensive use of arsenic compounds such as pesticides, insecticides,
defoliants, wood preservatives, and soil sterilants in the past.
Agricultural, industrial and commercial activities have resulted in numerous sites in Florida and worldwide with elevated arsenic concentrations in soils (Azcue and Nriagu,
1994). It is important to remediate these contaminated sites
to adequately protect public health.
As soils continually undergo physical, chemical and biological processes, arsenic continuously redistributes and repartitions among solid-phase components (McGrath and Cegarra,
* Corresponding author. Tel.: þ1 352 392 9063x208; fax: þ1 352 392 3902.
E-mail address: [email protected] (L.Q. Ma).
0269-7491/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.envpol.2007.10.011
1992; Han et al., 2001). First they go through an initial fast retention process and then slow reactions take place, depending
on metal species, soil properties, level of input and time (Han
and Banin, 1999; Han et al., 2001). Both processes redistribute
arsenic from labile fractions into more stable forms over time
(Han and Banin, 1999).
Therefore, arsenic availability is expected to be different
among soils with different properties, and different levels and
sources of arsenic contamination. All those factors influence
the ability of a plant to access arsenic from soils, especially
over a long time period. This is the limitation faced by the
new technology phytoextraction, which uses plants to clean up
contaminated soils as an efficient and less costly alternative.
Even though hyperaccumulator plants possess highly efficient mechanisms to acquire and concentrate arsenic in their
tissues, not all contaminated sites are suitable for treatment
by phytoextraction. This is because arsenic concentration
and availability, and depth of arsenic contamination in soil
M.I.S. Gonzaga et al. / Environmental Pollution 154 (2008) 212e218
can be limiting factors. The ideal plant used for this purpose
should take up large amounts of arsenic, be adapted to the local soil and climate characteristics and have the ability to continually accumulate, translocate and tolerate high
concentrations of arsenic over the whole growth cycle (Garbisu and Alkorta, 2001). Therefore several harvests of hyperaccumulator plants are necessary to reduce soil arsenic
concentration to acceptable levels (Raskin et al., 1994).
Pteris vittata L. (Chinese brake fern) is an efficient arsenichyperaccumulator plant (Ma et al., 2001). Because it hyperaccumulates large amounts of arsenic (up to 2.3%) into its
aboveground biomass (fronds) and it is easy to grow in a variety of soil environments (Ma et al., 2001), this plant has the
potential to be used to clean up arsenic-contaminated sites.
Furthermore, its perennial nature makes the phytoextraction
process even more cost-effective since no replanting after harvest is needed. However, practical issues such as the time required to achieve a given target level, the long term efficiency
of the process, and the arsenic pools depleted by the plant still
need to be addressed. Moreover, it is important to test the
growth of P. vittata in different soils and its efficiency in taking up arsenic from different sources of arsenic contamination.
We hypothesize that plant arsenic removal will differ based
on soil arsenic distribution and content. Moreover, the rate of
plant arsenic removal from the soil will reduce over time, due
to reduction in available arsenic fraction. The aim of this study
was thus to: (1) assess the effects of repeated frond harvests on
the rate of arsenic removal by P. vittata growing in arseniccontaminated soils; and (2) investigate the effects of plant
arsenic uptake on arsenic redistribution in soils.
2. Materials and methods
2.1. Soil collection and characterization
Five arsenic-contaminated soils plus a soil with naturally high arsenic concentration (Marl soil) were used for this study. The soils were contaminated
with arsenical insecticide (Avon soil), arsenical wood preservative (CCA
213
soil), arsenical pesticide (CDV soil), arsenical herbicide (EDS soil), and mining activities (Mining soil). Selected physico-chemical properties of the soils
are shown in Table 1.
The soils were collected from the top 20 cm depth, air-dried, and passed
through a 2 mm sieve. They were analyzed for: soil pH, using a 1:2 soil to water ratio and cation exchange capacity using sodium as the index cation
(Thomas, 1982); organic matter content by the Walkley Black method (Nelson
and Sommers (1982); and soil texture by the pipette method (Day, 1965). Concentrations of P, Ca, Mg, and trace elements were determined using the EPA
Method 3051a (USEPA, 1986).
2.2. Experimental set up
Six soils with different sources of arsenic contamination were used to grow
P. vittata. Each treatment was replicated four times and pots without plants
were included as controls, resulting in a total of 30 treatments. The pots
were arranged in a completely randomized design, under greenhouse
conditions.
Ferns with 5e6 fronds and approximately 12 cm in height were transferred
(one per pot) to 2-gallon-size plastic pots filled with 4.0 kg of arsenic-contaminated soils. Before transplant, the soils were thoroughly mixed with Osmocote, extended time-release base fertilizer (N:P:K ratios of 18:6:12) at a rate
of 2 g kg1 soil. Then the fertilizer was applied annually on the surface. After
transplanting, the ferns were watered to 60% of the field capacity.
The first harvest was performed in October, 2003, 4 months after the transplant. The second (April, 2004) and third (October, 2004) harvests were performed in 6-month intervals, from the first harvest and from each other. The
plant aboveground biomass was analyzed for dry biomass and total arsenic
concentration.
2.3. Sampling, digestion and analysis
The plant samples were dried in a 65 C oven for approximately 48 h,
weighed and then ground into powder through a 1 mm mesh screen using a
Wiley Mill. Soil samples collected together with the plant samples were airdried and analyzed.
The soil samples were digested according to the EPA Method 3051a and
the plant samples a modified EPA Method 3051 (Chen and Ma, 1998). One
blank, one standard reference material from National Institute of Standards
and Technology, one duplicate and one spiked sample were included for every
20 samples. Soil and plant samples were digested with nitric acid using a Hot
Block digestion system (Environmental Express, Mt. Pleasant, SC).
Table 1
Selected physico-chemical properties of six arsenic-contaminated soils
Soil characteristic
Marl
Avon
CCA
CDV
Mining
EDS
pH
CEC (cmolþ kg1)a
OM (g kg1)
Total As (mg kg1)
Extractable As (mg kg1)b
Extractable P (mg kg1)b
Extractable Ca (g kg1)
Extractable Mg (mg kg1)
Amorphous Fe (mg kg1)c
Amorphous Al (mg kg1)c
Sand (%)
Silt (%)
Clay (%)
Soil textural class
7.85
26.6
1.80
22.7
22.2
0.36
21.0
120
3.96
5.23
40.1
41.0
18.9
Loam
6.70
4.50
19.6
26.5
14.8
31.9
1.89
28.8
509
632
86.6
8.90
4.50
Loamy sand
7.00
4.40
11.0
110
58.8
24.8
2.96
130
1322
884
88.2
9.10
2.70
Loamy sand
6.76
16.8
26.5
211
45.9
19.2
2.04
64.8
5577
1163
84.0
14.0
2.00
Loamy sand
6.75
12.0
4.20
214
22.5
8.07
4.92
63.6
1626
179
80.7
15.2
4.10
Loamy sand
6.70
22.8
28.0
640
499
96.0
1.60
336
1117
1056
85.1
11.7
3.20
Loamy sand
a
b
c
CEC, cation exchange capacity.
Mehlich III solution.
Extracted using 0.2 M oxalic acid þ ammonium oxalate solution.
214
M.I.S. Gonzaga et al. / Environmental Pollution 154 (2008) 212e218
Approximately 0.5e1.0 g of air-dried soil or 0.1e0.5 g of dry plant samples were mixed with 1:1 HNO3:water and allowed to set for approximately
24 h. They were heated at 105 C for 2 h and then cooled for 3 min. The samples were mixed with 1 ml of 30% H2O2 and placed on the block digester for
additional 15 min. After the second heating, the samples were cooled completely and diluted to a 50 ml volume with distilled water. A filter cartridge
was placed at the bottom of the digestion tube. The digested samples were analyzed for As concentration with a SIMMA 6000 graphite furnace atomic absorption spectrophotometer (GFAAS, Perkin-Elmer, Norwalk, CT) using the
EPA SW 846 method 7060A.
2.4. Arsenic fractionation
It is important to determine how plant arsenic uptake affects soil arsenic
redistribution since plant arsenic uptake reduces soil arsenic availability. A sequential extraction procedure was used to account for the changes in different
soil arsenic-pools as a function of plant uptake. According to Wenzel et al.
(2001), soil arsenic was separated into five fractions with decreasing availability: non-specifically bound (N)dextracted with 0.05 M (NH4)2SO4; specifically bound (S)dextracted with 0.05 M (NH4) H2PO4; amorphous hydrous
oxide-bound (A)dextracted with 0.2 M ammonium oxalate, buffered at pH
3.25; crystalline hydrous oxide-bound (C)dextracted with 0.2 M ammonium
oxalate and 0.1 M ascorbic acid buffered at pH 3.25. The residual fraction
(R) was determined using the EPA 3051a method. Samples from each fraction,
with the exception of the residual fraction, were centrifuged at 3500 rpm for
15 min at 20 C. The supernatants were collected and filtered through Whatman 42 filter paper and analyzed for arsenic concentration using GFAAS.
2.5. Statistical analyses
All results were expressed as an average of four replicates. Treatments effects were determined by analysis of variance according to the General Linear
Model procedure of the Statistical Analysis System (SAS, 1987). Duncan test
at a 5% probability was used for post-hoc comparisons to separate treatment
differences.
Fig. 1. Frond biomass from each harvest (a) and three harvests (b) of Pteris
vittata after growing in six contaminated soils for 4e6 months. Means followed by the same letter for a given soil (a) and for all soils (b) are not different by the Duncan test at p < 0.05. Values are expressed as mean SD with
n ¼ 4.
3. Results and discussion
To evaluate the effects of repeated harvests on arsenic removal by P. vittata from six contaminated soils, we determined both frond biomass (d.w.) and arsenic concentrations
from three harvests. The effects of plant arsenic uptake on
soil arsenic distribution were evaluated by fractionating soil
arsenic into five fractions of different availability via sequential extraction at the end of the experiment.
3.1. Plant biomass
Plant aboveground biomass and regrowth capacity are important factors in the phytoextraction of arsenic from contaminated soils using perennial plants since multiple harvests are
necessary to reduce soil arsenic to acceptable levels (Fayiga
and Ma, 2005). Despite the differences in properties and arsenic concentrations among the six soils, the ferns grew well in
all soils during the first 4 months of the experiment (June to
October, 2003), showing no toxicity symptom. The plant biomass ranged from 24.8 to 33.5 g plant1 (Fig. 1a).
However, there was a significant reduction in the frond biomass from the second harvest, which reduced by 40e84%
compared to that from the first harvest (Fig. 1a). This was primarily due to the drastic method used in the first harvest. All
fronds were removed during the first harvest, which made it
difficult for plants to regenerate. Therefore, in the subsequent
harvests, the plants were removed at 15 cm height in addition
to leaving fiddleheads to help with regrowth. The fact that the
plant biomass in the third harvest was generally better than
that from the second harvest supports this hypothesis.
Even though P. vittata is tolerant to arsenic, high concentration in the medium is detrimental especially for young plants
(Srivastava, 2005) and plants under regeneration conditions.
Tu and Ma (2002) reported that addition of 500 mg kg1 As
to a sandy soil (high arsenic availability) reduced the biomass
of P. vittata by 64%, but at 200 mg kg1 As, it did not affect
biomass production. This is consistent with our results.
Among the six soils, the Marl soil produced the highest fern
biomass (Fig. 1b). Jones (1987) reported that P. vittata thrives
preferentially in calcareous soils. The Marl soil had the highest
pH (7.85) and calcium concentration (2.1%), yet the lowest
arsenic concentration (22.7 mg kg1) among the six soils
(Table 1), which helped regrowth of the fern after the drastic
first harvest. Contrary to the Marl soil, EDS soil produced
the lowest biomass (Fig. 1b), showing the lowest regrowth
capacity. The soil with the highest total (638 mg kg1) and
extractable (499 mg kg1) arsenic concentrations (Table 1)
adversely impacted on plant regrowth after the first harvest.
The effects of successive fern harvest on plant biomass and
arsenic removal by P. vittata is relatively scarce and
M.I.S. Gonzaga et al. / Environmental Pollution 154 (2008) 212e218
215
Table 2
Arsenic concentrations and bioconcentration factors in the fronds of Pteris vittata after growing in contaminated soils for 4e6 months
Soil
Marl
Avon
CCA
CDV
Mining
EDS
a
b
Frond arsenic (mg kg1)
Bioconcentration factora
Harvest 1
Harvest 2
Harvest 3
Harvest 1
166 11.0 ab
336 32.0 a
659 70.0 a
1872 200 a
1079 187 a
6151 493 a
110 17.0 b
181 43.0 b
325 43.0 b
477 85.0 b
423 59.0 b
3056 428 b
162 17.0 a
280 52.0 a
747 211 a
715 146 b
962 273 a
2139 466 b
7.67 0.51
22.2 2.15
11.2 1.12
40.9 4.14
47.8 8.60
12.3 1.02
Harvest 2
a
a
a
a
a
a
4.70 0.82
12.0 1.07
5.61 0.75
10.6 1.84
19.1 2.87
6.14 0.89
Harvest 3
b
b
b
b
b
b
7.57 0.82
18.6 3.40
12.7 3.55
15.6 3.22
43.0 12.4
4.35 0.89
a
a
a
b
a
b
Concentration ratio of arsenic in fronds to extractable arsenic in soil.
Means followed by the same letter in a row for a given soil are not different by the Duncan test at p < 0:05. Values are expressed as mean SD with n ¼ 4.
inconsistent. For instance, pot experiments using P. vittata
showed that the amount of biomass harvested decreased after
two or three successive cuttings as well as the amount of arsenic extracted from a soil (McGrath et al., 2002). However,
Kertulis-Tartar et al. (2006) found positive results when growing P. vittata under field conditions. It is likely that the exploitation of a greater soil volume under field conditions compared
to a pot study may account for some of the differences between the two studies (McGrath et al., 2002; Kertulis-Tartar
et al., 2006).
According to Jones (1998), P. vittata grows better in
a warmer climate. So, it is likely that the cooler climate
from November to April in Florida (i.e., 6e23 C) was also
a limiting factor for the low plant biomass production in the
second harvest. For all soils, the first and third harvests
(growth period from June to October) yielded larger plant biomass than the second harvest (growth period from October to
April). In a field experiment, Kertulis-Tartar et al. (2006) also
reported a greater biomass production when P. vittata plants
were harvested in October.
used during the first harvest, which hurt both plant growth
and plant arsenic uptake.
In addition to plant biomass and arsenic concentrations, bioconcentration factor (BF), defined as the ratio of arsenic concentration in the plant tissue to that in the soil, has been used
to characterize the effectiveness of plant arsenic accumulation
(Ma et al., 2001). In this study, extractable soil arsenic instead
of total soil arsenic was used since the former is a better indicator of plant available arsenic in soils. However, in this study
it was not the case. The correlation coefficient between frond
arsenic concentrations from the first harvest and total arsenic
concentrations was 0.98 compared to 0.97 for extractable
soil arsenic (data not shown).
Typical of hyperaccumulators, the BFs in P. vittata fronds
from all soils were significantly greater than one, ranging
from 4.7 to 48 (Table 2), indicating the ability of P. vittata to
bioconcentration of arsenic from all soils. Similar to arsenic
3.2. Arsenic concentration and bioconcentration factor
The frond arsenic concentrations ranged from 166 to
6151 mg kg1 in the first harvest, from 110 to 3056 mg
kg1 in the second harvest, and from 162 to 2139 mg kg1
in the third harvest (Table 2). The total arsenic concentrations
in the six soils used in this study varied from 22.7 mg kg1 in
the Marl soil to 638 mg kg1 in the EDS soil (Table 1). Higher
soil arsenic concentrations led to higher plant arsenic concentration, which was the highest in the EDS (2139e6151 mg
kg1) and the lowest in the Marl soil (110e166 mg kg1)
(Table 2).
Similar to plant biomass (Fig. 1a), the frond arsenic concentrations in the second harvest were 34e75% lower than
those in the first harvest, whereas those from the third harvest
were 47e130% greater than those from the second harvest excluding the EDS soil (Table 2). There was no significant difference in the frond arsenic concentrations between the first and
third harvest for all soils, except for the CDV and EDS soils.
Apparently, better growth (greater biomass) resulted in greater
arsenic uptake by P. vittata. The lower frond arsenic concentrations from the second and third harvest compared with
the first harvest were again the result of the drastic method
Fig. 2. Arsenic removal from each harvest (a) and three harvests (b) by P. vittata after growing in six contaminated soils for 4e6 months. Means followed
by the same letter for a given soil (a) and for all soils (b) are not different by
the Duncan test at p < 0.05. Values represent mean SD (n ¼ 4).
216
M.I.S. Gonzaga et al. / Environmental Pollution 154 (2008) 212e218
concentrations in the fronds, BFs in the fronds from the first harvest were the greatest, followed by those from the third, with
those from the second being the lowest. Among the six contaminated soils tested, BF was the highest in the CDV soil and lowest in the Marl soil though they had similar extractable soil
arsenic (Table 1). The data indicates that other factors, such as
OM content, were also important in controlling plant arsenic
uptake. Whereas the CDV had almost the highest OM content,
the Marl soil had the lowest among the six soils (Table 1).
Although the interactions between soil organic matter, soil
minerals, and arsenic are complex, studies on dissolved organic matter indicate that organic compounds tend to displace
arsenic that is bound to iron oxides/hydroxides, resulting in the
release of dissolved arsenic into the soil, increasing its availability (Redman et al., 2002; Saada et al., 2003). This is a result
of the anionic nature of many organic compounds in soils.
3.3. Plant arsenic removal from soils
P. vittata had a significantly higher arsenic accumulation
(arsenic concentration plant biomass) in the first harvest as
compared to the second and third harvests, in the Avon,
CDV and EDS soils (Fig. 2a). Therefore, the first harvest accounted for most of the arsenic removed from these soils. In
the Marl, CCA and Mining soils, arsenic accumulation in
the first harvest was similar to that of the third harvest.
Excluding the Mining soil, arsenic accumulation in the first
harvest followed the trend of soil arsenic concentrations
(Fig. 3). The total arsenic removed by the plants varied from
1.71 to 4.54 mg pot1 in the Marl soil, and from 17.0 to
175 mg pot1 in the EDS soil. More specifically, the plants removed 10.0, 13.5, 42.7, 70.9, 53.3, and 210 mg arsenic per pot
from the Marl, Avon, CCA, CDV, Mining and EDS soils, respectively (Fig. 2a). In other words, the amount of arsenic removed
from the EDS soil was 21 times more than that from the Marl,
which had the lowest soil arsenic among the six soils (Table 1).
The percentage of arsenic removed from each soil by the
fern was used to compare soils with different arsenic concentrations (Fig. 2b). In general, arsenic accumulation by P. vittata translated to soil arsenic reduction of 5.8e13%. After
three harvests, the ferns removed 8.2% of arsenic from the
EDS soil (with the highest soil arsenic), and 12% from the
Marl and Avon soils (with the lowest arsenic). This is lower
than the 26% removal rate reported by Tu et al. (2002). However, the larger quantity of soil used in this experiment (4.0 vs.
1.5 kg) may have contributed to the difference.
Though the arsenic concentrations in fern biomass were
greater in Avon soil than in Marl soil, the plants removed
Fig. 3. Arsenic concentrations (mg kg1) in different fractions in six contaminated soils before and after plant growth. Values represent mean SD (n ¼ 4). N, nonspecifically bound; S, specifically bound; A, amorphous hydrous oxide-bound; C, crystalline hydrous oxide-bound; and R, residual fraction.
M.I.S. Gonzaga et al. / Environmental Pollution 154 (2008) 212e218
the same amount of arsenic from both soils. This was because
the biomass yield in all three harvests was greater in the Marl
soil than in the Avon soil, which compensated for the lower
plant arsenic concentration in the former. Greater plant arsenic
concentration in Avon soil as compared to Marl soil was
mostly a result of the higher arsenic association with the first
three arsenic fractions in Avon soil (Fig. 3).
3.4. Soil arsenic distribution
Despite the criticisms associated with the fractionation procedure, it provides useful information on arsenic mobility and
availability in soils (Wenzel et al., 2001). Arsenic distributions
in the five fractions based on sequential extraction before and
after plant growth are shown in Fig. 3. Among the five fractions, the N (non-specifically bound) and S (specifically
bound) fractions are considered to be the most plant-available,
whereas R is the least plant-available. The sum of the N and S
fractions constituted 17.5, 22.0, 32.1, 21.7, 4.33 and 46.3% of
the total arsenic and 17.9, 39.4, 60.0, 99.8, 41.2 and 59.3% of
extractable arsenic in the Marl, Avon, CCA, CDV, mining and
EDS soils, respectively (Table 1, Fig. 3). The sum of the N and
S fractions was highly correlated with extractable soil arsenic
(r ¼ 0.99), which was highly correlated with plant arsenic uptake from the first harvest (r ¼ 0.97).
As expected, arsenic in these soils was primarily associated
with the A (amorphous hydrous oxide-bound) fraction, ranging from 40 to 59%, except for the Marl soil, which had a substantial amount in the C (crystalline hydrous oxide-bound)
fraction (59.1%) with only 9.28% in the N þ S fraction
(Fig. 3). In the Mining soil, the A and C fractions constituted
84.3% of the total arsenic. In the EDS soil, the majority of the
arsenic was distributed among the first three fractions in the
order A > S > N, consistent with the high arsenic availability
in this soil (78% total arsenic was extractable).
Based on arsenic fractionation in 20 arsenic-contaminated
soils, Wenzel et al. (2001) also showed that most of the arsenic
was associated with the A fraction. This study suggests that, regardless of the sources of arsenic contamination, arsenic was
sorbed by hydrous Fe and Al oxides, making the A fraction
the most dominant arsenic sink in soils (Smith et al., 1998).
Plant arsenic uptake influenced arsenic distribution among
the five fractions in the soils. Among the fractions, the A fraction contributed the most to arsenic reduction (45.3, 48.0, 72.0
and 59.0%) for the Avon, CCA, CDV and mining soils, respectively (Table 3). The A fraction had the highest arsenic concentrations in these soils too (Fig. 3). This was not observed
for the Marl and EDS soils where the highest reduction was
from the C and S fraction, respectively (Fig. 3, Table 3).
Even though the greatest arsenic mobilization in the EDS
soil occurred in the S fraction (46.4%), both the N and A fractions also contributed to a great extent (49.2%).
Total arsenic concentration is not a good predictor of arsenic
bioavailability, because only arsenic dissolved in water can be
transported to the roots and taken up by plants. Plants tend to
first take up the most available fraction of arsenic from the soils
and as this pool becomes smaller, some of the arsenic from
217
Table 3
Arsenic reduction by P. vittata from each fraction in six contaminated soils after three harvests
Soil
As removed
(mg pot1)
N
(% As)a
S
(% As)
A
(% As)
C
(% As)
R
(% As)
Marl
Avon
CCA
CDV
Mining
EDS
9.93
13.5
41.9
72.1
50.0
210
13.9
20.9
15.0
5.60
1.17
28.0
9.65
27.8
16.3
18.9
7.18
46.4
3.47
45.3
47.9
71.6
58.7
21.2
62.3b
4.71
16.2
1.85
26.9
3.26
10.6
1.28
4.60
2.03
5.98
1.56
a
N, non-specifically bound; S, specifically bound; A, amorphous hydrous
oxide-bound; C, crystalline hydrous oxide-bound; and R, residual fraction.
b
The fraction with the highest arsenic reduction for a given soil is in bold.
other fractions will be slowly transformed to a water-soluble
fraction to reestablish the equilibrium (McGrath et al., 2000).
Among the five arsenic fractions, the N fraction is the most
available to plants. Therefore, it is reasonable to assume that,
only arsenic in the N fraction can be readily taken up by the
plant and arsenic in other fractions has to convert to the N fraction before being taken up by the plant. In other words, the N
fraction acts as both a source of arsenic for the plant and
a sink for arsenic in the soil, thus linking arsenic in the soil
with the arsenic taken up by a plant. The fact that large amounts
of arsenic taken up by P. vittata were from other fractions demonstrates the ability of P. vittata in solubilizing arsenic of low
availability from soils, making it available for uptake.
4. Conclusions
Good biomass production of P. vittata was obtained during
the first growth period in all six contaminated soils, regardless
of the differences in soil properties and arsenic concentrations.
However, the plants had a reduced biomass production during
the second growth period, which was improved in the third period. The reduced plant biomass from the second harvest was
attributed to both the drastic harvest method used and a cooler
climate. Arsenic removal by P. vittata from the soils followed
the same trend as biomass production and arsenic concentration. Arsenic uptake by P. vittata affected the distribution of
arsenic in the soils, with all fractions being mobilized, reaffirming the ability of P. vittata in solubilizing arsenic from
all fractions in the soil. However, the first three arsenic fractions contributed the most to plant arsenic uptake, except in
Marl soil. In order to achieve an effective phytoextraction of
arsenic, it is crucial that proper agronomic techniques and
fern management be applied. Additional research is needed
to evaluate the capacity of continual phytoextraction in contaminated soils on a long-term basis.
Acknowledgment
This research was supported in part by the National Science
Foundation (Grant BES-0132114). The senior author would
like to acknowledge the CAPES Fellowship provided by Institute of International Education.
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M.I.S. Gonzaga et al. / Environmental Pollution 154 (2008) 212e218
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