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Accumulation of arsenic in Lemna gibba L. (duckweed) in tailing
waters of two abandoned uranium mining sites in Saxony, Germany
Martin Mkandawire*, E. Gert Dudel
Institute of General Ecology and Environmental Protection, Dresden University of Technology, Pienner Strae 8, D-01737 Tharandt, Germany
Received in revised form 1 June 2004; accepted 2 June 2004
Abstract
Accumulation of arsenic in Lemna gibba L. was investigated in tailing waters of abandoned uranium mine sites, following
the hypothesis that arsenic poses contamination risks in post uranium mining in Saxony, Germany. Consequently, macrophytes
growing in mine tailing waters accumulate high amounts of arsenic, which might be advantageous for biomonitoring arsenic
transfer to higher trophic levels, and for phytoremediation. Water and L. gibba sample collected from pond on tailing dumps of
abandoned mine sites at Lengenfeld and Neuensalz-Mechelgrun were analysed for arsenic. Laboratory cultures in nutrient
solutions modified with six arsenic and three PO43 concentrations were conducted to gain insight into the arsenicL. gibba
interaction. Arsenic accumulation coefficients in L. gibba were 10 times as much as the background concentrations in both
tailing waters and nutrient solutions. Arsenic accumulations in L. gibba increased with arsenic concentration in the milieu but
they decreased with phosphorus concentration. Significant reductions in arsenic accumulation in L. gibba were observed withthe addition of PO4
3 at all six arsenic test concentrations in laboratory experiments. Plant samples from laboratory trials had on
average twofold higher bioaccumulation coefficients than tailing water at similar arsenic concentrations. This would be
attributed to strong interaction among chemical components, and competition among ions in natural aquatic environment. The
results of the study indicate that L. gibba can be a preliminary bioindicator for arsenic transfer from substrate to plants and
might be used to monitor the transfer of arsenic from lower to higher trophic levels in the abandoned mine sites. There is also
the potential of using L. gibba L. for arsenic phytoremediation of mine tailing waters because of its high accumulation capacity
as demonstrated in this study. Transfer of arsenic contamination transported by accumulations in L. gibba carried with flowing
waters, remobilisation through decay, possible methylisation and volatilisation by L. gibba need to be considered.
D 2004 Elsevier B.V. All rights reserved.
Keywords: Tailing waters; Arsenic accumulation; Bioaccumulation; Phytoremediation; Bioindication; Phosphates
1. Introduction
The states of Saxony and Thuringia in southeastern
Germany were the third largest uranium producers in
the world during the Cold War era (Meinrath et al.,
2003). Unfortunately, uranium mining and processing
were done with little consideration for the environ-
ment. Inherent to this, the contamination impact of
abandoned uranium mine sites has come beyond
active mining operations, remaining an issue despite
decades of remediation initiatives (Enderle and Frie-
drich, 1995; Diehl, 1998; Diehl, 2003). During ura-
0048-9697/$ - see front matterD 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.scitotenv.2004.06.002
* Corresponding author. Tel.: +49-351-463-31393; fax: +49-
351-463-31399.
E-mail address: [email protected] (M. Mkandawire).
www.elsevier.com/locate/scitotenv
Science of the Total Environment 336 (2005) 8189
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nium mining and extraction, large amounts of ore
were excavated because the ores often contain only
between 0.1% and 0.2% uranium (Diehl, 1995; Diehl,
2003). In the process, nontarget elements were ex-posed. Consequently, abandoned uranium mine waste
dumps and tailings may be sources of not only
radioactive pollutants (i.e. uranium and daughter ele-
ments) but also heavy metals (e.g. iron, copper, zinc,
cadmium, nickel, cobalt), arsenic and sulphates,
which are potentially toxic (Diehl, 2003).
Arsenic requires equal attention in post-uranium
mining remediation because of its high toxicity (Mole-
nat et al., 2000; Dieter, 2003), and its high mobility in
the environment (Roussel et al., 2000; Farquhar et al.,
2002). Arsenic shows toxicity even at low-level
exposures. Because of this, the World Health Organi-
sation (WHO) has set concentration limits for drinking
water at 10 Ag l 1 and for foodstuffs at 2 mg l 1
(Dikshit et al., 2000; Robinson et al., 2003a). The
predominant form of arsenic in the environment is As
(V) because As (III) is oxidised by atmospheric
oxygen (Bissen and Frimmel, 2000; Molenat et al.,
2000). Under prolonged reducing conditions, almost
all of the adsorbed arsenic is reduced to As3 + (Chak-
ravarty et al., 2002; Giusti and Zhang, 2002). Arsenic
occurs in various mineral forms, of which 60% are
arsenates, 20% are sulphides and sulphosalts, 10% areoxides and the remainder are arsenides, native ele-
ments and metal alloys. Aqueous arsenic concentra-
tions are controlled by anion exchange and by co-
precipitation with iron and manganese oxyhydroxides.
Arsenate anion exchange dynamics are analogous to
those of phosphate, with competition for exchange
sites favouring phosphate over arsenate (Mkandawire
et al., in press, 2004). Arsenic uptake by plants has
also been shown to be associated with phosphate,
where presumably arsenate is taken up as a phosphate
analogue (Meharg and Macnair, 1991). Under reduc-ing conditions, the ferric iron is reduced to ferrous
iron, resulting in mobilisation of some of the adsorbed
arsenic, particularly from sediments and the plant root
zone (Khattak et al., 1991; Giusti and Zhang, 2002;
Kneebone et al., 2002).
In view of this, it was hypothesised that arsenic
poses equal contamination risks in waters from
abandoned uranium mines and that it transfers easily
to higher trophic levels through accumulation in
macrophytes. The accumulation of arsenic in floating
macrophytes is further influenced by physicochemi-
cal properties of the aquatic system like the arsenic
phosphate ratio, which affect the macrophyte growth,
and the bioavailability of arsenic and growth limitingnutrients. Hence, the accumulation in some macro-
phytes may open opportunities for contamination
monitoring and phytoremediation. Lemna gibba L.
(duckweed) was chosen for the current investigations
because it was found growing naturally in wetland
tailing ponds of former uranium mining sites at
Lengenfeld and Neuensalz-Mechelgrun in southwest-
ern Saxony in an earlier study (Mkandawire and
Dudel, 2002). In this earlier study, Mkandawire and
Dudel (2002) showed that this floating macrophyte is
capable of accumulating relatively large uranium
quantities. Most members of the Lemna genus are
used as model plants for phytoremediation, nutrient
and metal uptake studies, and bioassays (Ensley et
al., 1996). The aim was to determine the capacity of
arsenic accumulation in L. gibba under the influence
of arsenic and phosphorus concentration in the
milieu. The ultimate goal was to assess the possibil-
ity to use L. gibba L. for bioindication and phytor-
emediation of arsenic contamination in the tailing
waters.
2. Methods
2.1. Field sampling
Plants and water were sampled several times from
wetland ponds of a tailing dam at three sampling
points on the Lengenfeld uranium mine site between
August and December 2001 and at five sampling
points in the Neuensalz-Mechelgrun mine from Feb-
ruary to December 2002 (Fig. 1). The sampling for
both plants and water was repeated four times at eachsampling point during each sampling time. Reference
samples were collected in a stream above the mine
tailing dumps at Lengenfeld. Water samples were
filtered right in the field through cellulose acetate
filter membranes (0.45-Am pore size), and each sam-
ple was divided into two portions. One portion was
adjusted to pH 2 with 2% HNO3 for arsenic determi-
nation, and the other was without pH adjustment for P
analysis. All water samples were handled according to
German standards (DIN 38 405-30; 38 404; 38 402
M. Mkandawire, E.G. Dudel / Science of the Total Environment 336 (2005) 818982
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and 38 412 specification). All plant samples were
freeze-dried until constant weight was achieved and
were digested using HNO3 H2O2 mixture in a mi-
crowave digester (MW-Digestion, CEM MARS 5,
Matthews, NC, USA). Total arsenic in water and plantsamples was determined by ICP-MS (PQ2+, VG
Elemental, Winsford, UK), and P was determined
using ICP-OES (Perkin Elmer Plasma 2, Wellesley,
USA). The samples were diluted 10 times with 2%
HNO3 for ICP-MS determination. Drift correction
was done with addition of 10 ppb rhodium and 10
ppb lutetium as internal standards. Certified reference
materials NIST1575 and GBW7604, which were
digested and diluted in the same manner as the
samples, were used. All sample set contained at least
four blanks, and all measurements were repeated four
times.
2.2. Laboratory experiments
Stock-cultured L. gibba L., a strain collected from
the arboretum of Humboldt University, Berlin-Baum-
schulweg, was used in two-factor diluted modified
Hutner nutrient solution. The experiments were set in
semicontinuous culture mode on Lemna culture equip-
ment (Mkandawire and Dudel, 2002) placed in the
ecotron (plant growth chamber, NEMA, Netzchkau,
Germany). The ecotrons environmental conditions
were set as described elsewhere (Mkandawire and
Dudel, 2002, Mkandawire et al., in press, 2004). Six
Fig. 1. Location of the study sitesabandoned uranium mines at Lengenfeld and Neuensalz-Mechelgrun; and, sketch map detailing sampling
plans in the study sites.
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arsenic test concentrations (10, 50, 100, 250, 500, and
1000 Ag l 1) prepared from NaHAsO47H2O and
three phosphate concentrations (0.013, 13.61, 20.0,
and 40.0 mg l 1
) prepared from K2HPO4 were used.All reagents in the study were of analytical grade. One
hundred and fifty fronds (two or three leaves per
frond) of similar size from a 7-day-old preculture
were inoculated systematically into each vessel con-
taining 700 ml of test solutions. Aliquots were sam-
pled at the start and then every second day. The
experiments lasted 21 days. At the end of the exper-
iment, Lemna biomass was harvested and an aliquot
was sampled. All experiments were replicated four
times in a factorial random design, and parallel control
experiments were run.
2.3. Data analysis
The bioaccumulation coefficient (u) represented
the frond/solution element concentration quotient. It
was estimated by: u=[Cfrond]/[CH2
O], where [Cfrond] is
the element concentration (mg l 1) accumulated in
the frond and [CH2O] is the soluble metal concentra-
tion (mg l 1) in the solution. Statistical analysis was
performed with natural logarithmic (ln)-transformed
values, using ANOVA, and correlations using Spear-
man. All statistical analyses were performed usingprogram SPSS 10.1.0 for Windows.
3. Results and discussion
3.1. Arsenic and its speciation in mine tailing waters
Arsenic concentration in tailing waters and that
accumulated in L. gibba L. at different sampling
points are summa rised in Table 1. The results
revealed that on average the tailing waters in samplesfrom both Lengenfeld and Neuensalz-Mechelgrun
had significantly higher arsenic content than did
waters from the reference site. Large standard devia-
tions are due to temporal variations in Neuensalz-
Mechelgrun speciation calculation with geochemical
modelling software, PhreeqC+ 2.8.0.0 Alpha version
(Parkhurst and Appelo, 1999), which indicate that in
ambient systems, arsenic occurred as arsenate
(Hn
AsO43 n) or arsenite (H
nAsO3
3 n) complexes.
Over the pH value range of 6.08.1 found in tailing
waters, the predominant species of As (V) was
H2AsO4 and that of As (III) was H3AsO3, of which
the reduced form is the more mobile. The content of
arsenic at the Lengenfeld sampling points differedsignificantly (data not shown). Due to the short
sampling period, the temporal variation was not
significant. Differences in arsenic water content from
sampling points in Neuensalz-Mechelgrun were both
temporally and spatially significant. The content of
arsenic was the lowest in water between July and
August 2002. The following factors might have
contributed to this: the year 2002 had the highest
rainfall recorded in the area for a decade, and dilution
took place; high temperatures were also recorded
during the period. This was also the productive periodfor macrophytes in the tailing ponds (data not
shown). Aquatic plants play a key role in remobilis-
ing arsenic (Hallberg and Johnson, 2003). Ferrous
iron oxidised to ferric form, which leads to precipi-
tation of iron oxyhydroxides in the rhizosphere (iron
plaque) (Godowski et al., 1995; Arienzo et al., 2002).
As a result, there is a decreasing concentration
gradient of dissolved iron towards the plant roots.
The iron oxyhydroxides consequently bind arsenic
(Robinson et al., 2003b).
Table 1
Arsenic concentrations in water and L. gibba samples from
reference sites, Lengenfeld and Neuensalz-Mechelgrun
Site Sample
point
[As] in surface
mine water
(Ag l 1)
As accumulation
(mg kg 1
dry biomass)
Reference RW1 7.55F 3.40*** 77.83F 35.05***
RW2 3.04F 2.13*** 29.71F 21.54***
RW3 5.61F 3.11*** 44.98F 28.91***
Lengenfeld LTW1 47.01F11.2** 519.61F 64.75***
LTW2 62.96F 20.77** 937.62F 253.03*
LTW3 265.42F 228.31 1543.22F 238.29
Neuensalz- MTW1 106.71F 30.46 1296.90F 241.17
Mechelgrun MTW2 109.84F 72.31 1107.78F 312.87
MTW3 167.92F 90.97 1447.96F 522.03
MTW4 64.03F 21.11** 1035.74F 381.43
MTW5 57.50F 21.71** 707.26F 310.09
MTW6 53.48F 22.98** 687.43F 395.75
Sampling periods: reference site and Lengenfeld between August
and October 2001, n = 31; Neuensalz-Mechelgrun between February
and December 2002, and n = 108. Values are means of four repeated
measuresF standard deviation.
*p = 0.05.
**p = 0.01.
***p = 0.001.
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3.2. Arsenic accumulation in L. gibba samples from
the field
3.2.1. Influence of the milieu arsenic concentrationArsenic accumulation in L. gibba L. from the tailing
water ranged from 0.54 to 110.8 mg kg 1 in fresh
mass, and 61.7 to 1966.48 mg kg 1 in dry biomass.
Mean accumulations are presented in Table 1. Effect of
arsenic on L. gibba growth and yield has been studied
(Mkandawire et al.,in press, 2004) Uptake and accu-
mulation of arsenic in L. gibba in both Lengenfeld and
Neuensalz-Mechelgrun increased with arsenic concen-
tration in the milieu tailing waters fitting in a sigmoid
regression (r2 = 0.93 in Lengenfeld, r2 = 0.89 in Neu-
ensalz-Mechelgrun; p < 0.05 at 95% confidence inter-
val; Fig. 2). The accumulation pattern in the fronds
suggests that the water uptake by L. gibba induced
arsenic migration via mass flow into the frond until the
fronds were saturated with arsenic. Thus, arsenic might
have entered the fronds, either via the symplastic or via
the apoplastic pathways where some active or passive
filtering might occur (Blinda et al., 1997; Parker and
Pedler, 1997; Samardakiewicz and Wozny, 2000).
Mkandawire et al., in press, 2004 found that under
laboratory condition L. gibba tolerated arsenic toxicity
in the range of 10500 Ag l 1 and suddenly shows
toxicity. Robinson et al. (2003b) showed that plantsthat tolerate high concentrations of toxic elements have
an active uptake mechanism for the nonessential
elements. Such plants have constantu over a narrow
concentration range (Robinson et al., 2003b) similar to
the behaviour demonstrated by L. gibba in the labora-
tory investigation (see below). As the element concen-
tration increases in the milieu, a sudden increase in the
plant element concentration occurs. This happens
when the uptake control mechanisms break down,due to overload of the regulatory mechanism (Zhao
et al., 2002). When this phenomenon occurs, the plants
show toxicity symptoms and biomass production is
reduced (Wenzl et al., 2001). The current result and
results from the previous studies on arsenic toxicity to
L. gibba(Mkandawire et al., in press, 2004) attest to the
general phenomenon.
3.2.2. Influence of milieu phosphorus concentration
Fig. 3 shows that accumulation of arsenic in L.
gibba at both sites correlated negatively to the P
content of the tailing waters (r2 = 0.916; at p = 0.05
and 95% confidence interval). This phenomenon has
been observed in other plant species too (Creger and
Peryea, 1994; Carbonell-Barrachina et al., 1998;
Peryea, 1998; Cao et al., 2003). Phosphates have
long been reported to suppress plant uptake of
arsenate (Pickering et al., 2000). For instance, phos-
phorus addition resulted in a reduction of arsenic
uptake by 5572% over the control in Indian mus-
tard (Brassica juncea) (Pickering et al., 2000). Most
of the studies which reported this relationship were
conducted in either amended soil or hydroponicculture experiments in laboratory (e.g. Bissen and
Frimmel, 2000; Jackson and Bertsch, 2001; Cao et
al., 2003). This study reports results that demonstrate
the behaviour in the natural aquatic system. Howev-
er, the effect of phosphates on arsenate uptake seems
Fig. 2. Accumulation of arsenic in L. gibba in relation to arsenic concentration in milieu tailing waters.
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to differ from one plant species to another, and the
medium used. A few variations have been reported
in the literature where phosphorus increases arsenic
uptake by plant in soils (e.g. Marin et al., 1993;
Elvira et al., 2003). Much as L. gibba has demon-
strated the relationship between arsenic uptake and
phosphorus, it should not be taken for granted that
most macrophytes in the tailing ponds in the sites
behave in the same way. Hence, investigations of
other macrophyte species in the tailing waters are
necessary.
3.3. Accumulation of arsenic in controlled phosphate
supply
At the completion of the laboratory trials, the
arsenic concentrations in all the plants had reached
equilibrium, indicated by a negligible decrease in the
solution arsenic concentrations. Fig. 4 shows that the
levels for arsenic in the fronds ofL. gibba at the end of
the laboratory experiments ranged from 0.02 (in 40
mg l 1 PO43 ) to 106 mg kg 1 dry biomass (in
0.0136 mg l 1
PO43
) and 0.00187.79 mg kg 1
Fig. 4. Accumulation of arsenic in L. gibba under variable initial PO43 and AsO4
3 concentrations in nutrient solution. The values are means of
four replications and the error bars are standard deviations.
Fig. 3. Relationship between arsenic accumulation in L. gibba to concentration in tailing water.
M. Mkandawire, E.G. Dudel / Science of the Total Environment 336 (2005) 818986
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fresh weight. Toxicity behaviour of arsenic in the
concentration range in nutrient solution has been
reported in Mkandawire et al. (2004, in press). Arsenic
concentrations in L. gibba L. dry biomass have astrong positive correlation with the arsenic concen-
trations of the milieu water (r2 = 0.96; p < 0.05 at 95%
confidence interval), as demonstrated in the field
samples (see above). The arsenic concentration ratio
of plant/solution increased exponentially as the arsenic
concentration in the solution increased. These results
resemble the work of Robinson et al. (2003a) who
described this type of increase to be associated with
active exclusion; viz. at low concentrations, plants are
able to exclude the toxic element, and the barrier
breaks down at higher concentrations. The accumula-
tion of arsenic in L. gibba decreased significantly with
increasing phosphate concentration at all six levels of
test arsenic concentration in the nutrient solution.
These results agree with earlier results by Mkandawire
et al. (2004), Meharg and Macnair (1990), and Rob-
inson et al. (2003a). Speciation modelling with
PhreeqC predicted increasing desorption due to sim-
ilarities in thermodynamic and kinetic properties be-
tween AsO43 and PO4
3 . AsO43 is a sorption
analogy of PO43 and, PO4
3 competes with AsO43
for sorption sites (Mkandawire et al., 2004). There-
fore, it should be expected that more arsenic should bedesorbed in the solution with increasing phosphate. In
spite of this, the uptake of arsenic by L. gibba was
affected. Because arsenate is the dominant form of
arsenic under aerobic conditions and is an analogue of
phosphate, they compete for the same uptake carriers
in the plasmalemma (Smith and Read, 1997). Thus,
arsenate uptake in L. gibba is obviously suppressed by
phosphate, as shown by the much lower arsenic
uptake rates in both laboratory and mine tailing plants
at high P supply, supporting the view that arsenate
uptake is mediated by phosphate transporters.
3.4. Arsenic interaction with L. gibba
The results of arsenic accumulation by L. gibba in
the field samples and in laboratory experiments
showed an increase in the arsenic accumulation with
increasing arsenic concentration in the milieu. This
indicates that the uptake of arsenic by L. gibba occurs
through active exclusion mechanisms. The results also
showed that in the field, arsenic accumulation corre-
lated negatively to increasing P concentration in the
milieu and reduced arsenic accumulation in the labo-
ratory with PO43 concentration. This has been related
to As (V) uptake through PO43
uptake pathway. Afew works argued that active exclusion is not consis-
tent with arsenic uptake via the phosphate uptake
pathway (Smith and Read, 1997; Robinson et al.,
2003a). Our laboratory results show that L. gibba
exhibited arsenic uptake through active exclusion and
at the same time phosphate uptake. This suggests that
it is important to consider arsenic concentrations
together with phosphorus or, indeed, with other ele-
ments like sulphur, manganese, iron, etc., that may
affect speciation in the milieu when investigating
arsenic uptake by L. gibba.
3.5. Comparison of accumulation in laboratory and
field samples
Generally, the arsenic concentrations in L. gibba
samples from tailing waters were approximately two-
fold less than similar arsenic concentrations in solu-
tions. This is because L. gibba in the surface mine
waters was exposed to arsenic for an undefined
period, whereas samples used in laboratory trials were
certified to contain a below-detection amount of
arsenic and were exposed to arsenic only for 21 days.However, the mean bioaccumulation coefficients for
the field L. gibba samples were twofold higher in the
laboratory than in the field. This might be attributed to
the fact that nutrient solutions had limited and defined
amount of ions, whereas tailing waters had an unde-
fined and unlimited amount of ions that definitely
competed with arsenic for uptake sites. The ease with
which elements enter the plants symplast is affected
by the amount of ions present in water (Keltjens and
Van Beusichem, 1998; Samardakiewicz and Wozny,
2000), as well as by other factors such as pH, Eh, andtemperature (Del Castilho and Chardon, 1995). These
factors determine chemical speciation in the milieu.
3.6. Arsenic and uranium accumulation in L. gibba
The mean background concentrations of uranium
in tailing waters found in our earlier studies were
186.0F 56.31 and 277.01F10.18 Ag l 1 in Lengen-
feld and Neuensalz-Mechelgrun, respectively (unpub-
lished data). The mean uranium concentrations were
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significantly higher than the arsenic background con-
centrations at both sites. Uranium accumulations in L.
gibba were within the ranges of 514.47F 83.71 and
612.36F 143.6 mg kg 1
U dry biomass in Lengen-feld and Neuensalz-Mechelgrun, respectively (unpub-
lished data). Comparison of the bioaccumulation
coefficients for uranium found in an earlier study
(Mkandawire et al., in press) with those for arsenic
revealed that the values for uranium were significantly
lower than the values for arsenic. Accumulation of
arsenic and uranium in L. gibba increased with an
increase in the milieu concentration but differed in
relation to PO43. Previous studies showed that ura-
nium accumulation increased within a short range
with PO43 concentration before levelling off. Speci-
ation calculation predicted precipitation of uranyl
phosphates at higher concentrations of both UO22 +
and PO43 in the aquatic system. Hence, much as
phosphate increases U uptake, U bioavailability is
generally reduced (Mkandawire and Dudel, 2002).
4. Conclusions
The results reveal that arsenic accumulates con-
siderably in L. gibba growing in tailing ponds of
abandoned uranium mines at Lengenfeld and Neu-ensalz-Mechelgrun. This indirectly proves that arse-
nic contamination exists in abandoned uranium mine
sites. The accumulation is directly influenced by the
milieu concentration of arsenic and phosphorus. If the
accumulation in other macrophytes is similar to that
observed in L. gibba, arsenic could transfer more
easily from contaminated waters to higher trophic
levels than uranium. Thus, arsenic may pose more
risk than uranium. The results also suggest that L.
gibba should be used as an indicator for arsenic and
for arsenic transfer from contaminated waters toplants. The high arsenic bioaccumulation coefficients
and the ability of L. gibba to reduce arsenic on
average by 40.3% in the solutions show that the
species has potential for arsenic phytoextraction from
contaminated waters. Unfortunately, L. gibba is a
small floating macrophyte that can be transported to
uncontaminated areas with flowing water. Hence,
investigations on the remobilisation and biominerali-
sation mechanisms of arsenic in L. gibba are required.
Further investigations are also required on L. gibbas
defence mechanism against arsenic toxicity, e.g. bio-
methylisation, assimilation, or compartmentalisation.
The influence of fungi and other microorganisms that
enhance phosphate acquisition by the host plant on L.gibba accumulation of arsenic is worth investigating
because of the interaction between phosphate and
arsenate. The study has also opened an area that
requires further investigation to clarify whether active
exclusion and the phosphate pathway uptake mecha-
nism are simultaneously employed in Lemna species
and in other organisms.
Acknowledgements
The German Federal Ministry of Education and
Research (BMBF) supported the study under Project
Grant No. 02WB0222. Arndt Weiske did ICP-MS
analyses, with laboratory assistance from Karin
Klinzmann and Annet Jost. Phosphate analysis with
ICP-OES was done at the Landesforstprasidium of the
State of Saxony, Graupa. Dmitry Tychinin (IPBBM of
the Russian Academy of Sciences) read the manuscript
and made valuable contributions to the language.
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