Genotoxicity of organic pollutants in source of drinking water on microalga Euglena gracilis

Article (PDF Available)inEcotoxicology 18(6):669-76 · July 2009with56 Reads
DOI: 10.1007/s10646-009-0343-0 · Source: PubMed
Abstract
The potential toxicities of organic pollutants in the drinking water source at Meiliang Bay of Lake Taihu were investigated by comet assay and antioxidant enzyme approach on microalgae Euglena gracilis. The organic extracts of the water samples could induce DNA damage on microalgae cells. Statistically significant differences (P < 0.05) were observed at groups of 0.3x, 3x and 10x concentrations compared with the control and a solvent control (DMSO). The organic extracts also affected antioxidant enzyme activity and induced lipid peroxidation in the microalga. In the high dose group, there was an obvious increase in SOD content (P < 0.05). The results suggest that the concentrated organics from water sample extracts have adversary effects on E. gracilis and could possibly damage the ecosystem.
Genotoxicity of organic pollutants in source of drinking water
on microalga Euglena gracilis
Mei Li Æ Changwei Hu Æ Xiangyu Gao Æ
Yue Xu Æ Xin Qian Æ Murray T. Brown Æ
Yibin Cui
Accepted: 18 May 2009 / Published online: 4 June 2009
Ó Springer Science+Business Media, LLC 2009
Abstract The potential toxicities of organic pollutants in
the drinking water source at Meiliang Bay of Lake Taihu
were investigated by comet assay and antioxidant enzyme
approach on microalgae Euglena gracilis. The organic
extracts of the water samples could induce DNA damage
on microalgae cells. Statistically significant differences
(P \ 0.05) were observed at groups of 0.39,39 and 109
concentrations compared with the control and a solvent
control (DMSO). The organic extracts also affected antiox-
idant enzyme activity and induced lipid peroxidation in the
microalga. In the high dose group, there was an obvious
increase in SOD content (P \ 0.05). The results suggest that
the concentrated organics from water sample extracts have
adversary effects on E. gracilis and could possibly damage
the ecosystem.
Keywords Drinking water source Organic pollutant
Euglena gracilis Toxicity Comet assay
Introduction
There are more and more genotoxic pollutants released into
the aquatic environment following the developments of
industry and agriculture (Turgeon et al. 2004; Rajaguru
et al. 2002), which is threatening the safety of drinking
water source and affecting the lives for hundreds of mil-
lions of people. Kusamran et al. (2003) and Sujbert et al.
(2006) reported that the positive mutation of the minim
organic pollutants existed in drinking water. Therefore, it is
important to evaluate the effects of genotoxic agents in
drinking water and in sources of drinking water on human
health and on ecological population through biomonitoring
approaches.
There are many methods used to evaluate the genotox-
icity of drinking water. Alkaline single cell gel electro-
phoresis (SCGE) or comet assay, DNA repair processes
and genetic toxicological tests have been explored broadly
for environmental biomonitoring or clinical applications
(Singh et al. 1988; Tice et al. 2000). The comet assay is a
simple, convenient, rapid, and sensitive technique for the
determination of genotoxicity and the evaluation of DNA
damage. It can be used to detect chemically or physically
induced single-strand breaks in the DNA of an individual
cell of various kinds (Fairbairn et al. 1995; Cotelle and
Ferard 1999). In recent years, the comet assay was widely
used in DNA damage, biological surveillance, and geno-
toxicity evaluation for different kinds of field studies, and it
is becoming one of major tool for pollutant biomonitoring
in the aquatic environment as well (Mitchelmore and
Chipman 1998; Klobuear et al. 2003; Akcha et al. 2008).
As primary producers, phytoplankton constitutes the
first level of trophic chains which is crucial to the eco-
system. Because of their short generation times, unicellular
algae are an ideal group to study responses to different
environmental factors and are free of complications
inherent in research on more complex higher plants. Fur-
thermore, assays using microalgae are generally highly
sensitive, rapid and a cost-effective means to evaluate
M. Li X. Gao Y. Xu X. Qian Y. Cui (&)
State Key Laboratory of Pollution Control and Resource Reuse
and School of the Environment, Nanjing University,
22 Hankou Road, 210093 Nanjing, China
e-mail: cuiyb@nju.edu.cn
C. Hu
School of Life Science, Linyi Normal University,
276005 Linyi, China
M. T. Brown
School of Biological Sciences, University of Plymouth,
Plymouth, Devon PL4 8AA, UK
123
Ecotoxicology (2009) 18:669–676
DOI 10.1007/s10646-009-0343-0
changes in environmental conditions, especially with
respect to water pollution (Sosak-Swiderska et al. 1998).
Microalgae respond rapidly and predictably to a wide range
of pollutants and provide a potentially useful early warning
signal of deteriorating conditions and their possible causes.
For these reasons, algae are being widely used as ecolog-
ical indicators and phytoremediation organisms in polluted
aquatic environments (Kelly et al. 1998). In this study,
E. gracilis was selected as the test organism due to its ease
of culturing, standardization of inoculum, availability in
microalgal culture collections and its wide distribution in
aquatic ecosystems.
This study was undertaken with the objective of devel-
oping biochemical assays to monitor stress and tolerance
responses in microalgae used as pollutant indicator organ-
isms in aquatic ecosystems for drinking water sources.
Methods
Microalgal culture
A culture of the microalga E. gracilis was obtained from
Mid-Sweden University, Sundsvall, Sweden. Cultures were
grown and maintained in 250 ml Erlenmeyer flasks con-
taining a culture medium (Checcucci et al. 1976)at
23 ± 1°C under 12 h light/12 h dark cycle provided by
cool white fluorescence lights at 85–90 lmol photon/(m
2
s)
irradiance for a period of 8 days.
Sample preparation
Twenty liters samples of a drinking water source were
collected at 0.5 m beneath the water-surface during March
2008 from Meiliang Bay, Lake Taihu, in Wuxi. After being
stored for about 24 h, the water sample (20 l) was filtered
through gauze and filter paper to remove suspended
materials or sediments, and then passed through a column
with non-polar neutral resin (XAD-2) to adsorb organic
compounds at a flow rate of 30–40 ml/min. The column
was eluted with carbinol, acetone and dichloromethane
successively. The elution was dried by blowing with
nitrogen at 50°C and re-dissolved in 2.0 ml dimethysulph-
oxide (DMSO) (Greenberg et al. 1992; Bian and Kang
1994). The samples were preserved at -20°C in the dark.
Microalgal treatment
Experiments were conducted in 250 ml flasks, which had
been autoclaved at 121°C for 20 min. The inoculums were
mixed in media with or without organics extracts. A gra-
dient of four concentrations of the organic extracts from the
drinking water source samples were used. Each dosage
equals 0, 0.3, 3, and 10 times the concentration in the
source water. DMSO was used as solvent control. The
initial cellular concentration was about 1 9 10
5
cells/ml of
the microalga.
Growth and pigment bioassay
The algal growth as cell density was measured spectro-
photometrically (VIS-7220 spectrophotometer, Rayleigh
Analytical Instrument Corp., Beijing) at a wavelength of
680 nm in a cuvette with a 1-cm light path. OD
680
values
were converted to cell counts using the liner regressions
between optical density (OD
680
) and cell counts (y), which
had been determined in the preliminary experiments
(y = (94.309 9 OD
680
? 0.91) 9 10
4
, R
2
= 0.999). Pig-
ments were extracted with 90% acetone and determined in
accordance with Jeffrey and Humphrey (1975) for chlo-
rophyll content and Strickland and Parsons (1972) for
carotenoid content. The levels were expressed in lg/ml.
Comet assay
The comet assay with E. gracilis was performed following
Aoyama et al. (2003) with some modifications. Treated
cells cultured for 8 days were centrifuged at 4,000 rpm for
5 min and 2 9 10
5
cells/ml were embedded in 75 llof
0.7% low-melting agarose (LMA) sandwiched between a
bottom layer of 1% normal-melting agarose (NMA) and a
top layer of 1% low-melting agarose (LMA) on chilled
microscope slides. The slides were dipped into a lysis
solution containing 2.5 M NaOH, 1.0 mM Na
2
EDTA,
0.01% sodiumdodecylsulphate (SDS), 1% TritonX-100,
10% DMSO for 20 min and then in a horizontal electro-
phoresis unit filled with fresh alkaline electrophoresis
buffer (300 mM NaOH and 1 mM Na
2
EDTA, pH 13.0) to
a level approximately 0.2 cm above the sides at 4°C for
20 min to allow DNA unwinding before electrophoresis.
Electrophoresis was conducted at 4°C using 20 V and
200 mA for 20 min. The above steps were conducted in red
light to avoid DNA damage. After electrophoresis, slides
were washed three times with a neutralizing buffer
(400 mM Tris–HCl, pH 7.5), the DNA were stained with
ethidium bromide (EB; 2 lg/ml), and the slides were
examined with a fluorescent microscope (BX41, Olympus,
Japan). Three slides for each treatment were prepared and
at least 50 cells were analyzed from each slide. Photos
were taken with a digital camera (C-5050ZOOM, Olym-
pus). Images were analyzed according to the method of
Collins et al. (1995) using the comet assay software project
(CASP 1.2.2). Although the software reports several
parameters, data for percentage tail DNA are presented
here as a measure of single-strand DNA breaks/alkali-
670 M. Li et al.
123
labile sites to evaluate DNA damage of microalgae
E. gracilis treated with different concentrations of water
extracts, since this is considered to be the most reliable
parameter (Collins 2004). Furthermore, the results
expressed as percentage tail DNA were similar to other
commonly used comet parameters, such as the olive tail
moment.
Antioxidative enzymes assay
For enzyme assays, E. gracili samples cultured for 8 days
were centrifuged at 3,000 rpm for 10 min and resuspended
in 1/15 mmol/l of pre-cooled sodium phosphate buffer
(pH 7.0). After sonication for 5 min in an ice bath, the cell
debris was removed by centrifugation at 12,000 rpm for
20 min at 4°C. The content of lipid peroxidation products,
malondialdehyde (MDA), was determined according to the
methods provided by Heath and Parker (1968). The results
were expressed as nmol/10
6
cells.
Total superoxide dismutase activity (SOD, EC 1.15.1.1)
was determined by the ferric cytochrome c method using
xanthine/xanthine oxidase as the source of superoxide
radicals, and a unit of activity was defined as that described
in McCord and Fridovich (1969), which was expressed as
U/10
6
cells. The concentration of reduced glutathione
(GSH) was determined spectrophotometrically with dithio-
nitrobenzoic acid (DTNB) at 412 nm (Rijstenbil et al. 1994).
Protein content of homogenates was determined by the
reaction with Coomassie Blue dye, using bovine serum
albumin as the standard, in a VIS-7220 spectrophotometer
(Bradford 1976).
Statistical analysis
The differences between the control and treated samples
were analyzed by one-way ANOVA using Origin 8.0 sta-
tistical software, taking P \ 0.05 as significant according
to Tukey’s multiple comparisons tests. Each experiment
had three replicates. The mean values ± SD are reported in
the figures.
Results
Effect on growth
It can be seen in Fig. 1 that microalgae E. gracilis could
grow under experimental conditions. Growth inhibition
was not observed in group of 0.39 and DMSO group. But
growth was inhibited by 7.85% and 10.22% in groups of
39 and 109 , respectively when compared to the control.
At the end of the experiment, the number of cell in the
control was in the range of 5.6 9 10
5
cells/ml, whereas, at
group 109 it was 5.0 9 10
5
cells/ml. There was no sta-
tistically significant difference between the control and the
solvent control (DMSO group).
Effects on content of chlorophyll a, b and carotenoids
Figure 2a and b show the chlorophyll a, b and carotenoids
content in E. gracilis, calculated from the spectrophoto-
metric data. Photosynthetic pigment (chl a, chl b and
carotenoid) exhibited similar response upon water extracts
exposure. Exposure to the higher concentration of group
109 chl a and chl b resulted in a significant decrease
(11.15% and 14.98%, respectively, P \ 0.05), but there was
no statistically significant difference in groups of 0.39,39,
and DMSO when compared to the control. Similar to
chlorophylls, carotenoids were also not affected signifi-
cantly up to 109 where carotenoid content decreased
23.58% compared to the control.
Effects on content of soluble protein and lipid
peroxidation products
There was no significant difference in soluble protein
among treatments with or without water extracts and sol-
vent control (Fig. 3). Figure 4 show that the lipid peroxi-
dation measured as total MDA content in E. gracilis in all
treatment increased gradually compared to the control. But
only in groups of 0.39 and 39 was there a statistically
significant difference (P \ 0.05). The maximum increase
of MDA content in 39 was 45.28% higher than that in the
control.
12345678
0.1
0.2
0.3
0.4
0.5
0.6
Cell number (× 10
6
)
Time (da
y
)
0
0.3
3
10
DMSO
Fig. 1 Growth curves of E. gracilis exposed to different concentra-
tions of water extract. Algae were cultured at 23 ± 1°C, 85–90 lmol
photon/(m
2
s) irradiance and 12:12 h light/dark cycle. The results are
the mean of three replicates for each treatment. (Error bars not
shown)
Genotoxicity of organic pollutants in source of drinking water 671
123
Effects on SOD activity and glutathione content
The activity of SOD (Fig. 5a) shows that there was no sig-
nificant difference among the groups of 39,109 and DMSO.
In group of 0.39, SOD activity was increased by 16.5%
(P \ 0.05) compared to the control. As for glutathione
(GSH) content there was no significant difference among all
the groups when compared to the control (Fig. 5b).
Effects on DNA integrity
Data for tail DNA (%), presented as a measure of single-
strand DNA breaks/alkali-labile sites, were similar to other
commonly used comet parameters, such as the Olive tail
moment. There were significant differences (P \ 0.05,
P \ 0.01) between the control and all three concentrations
(71.5%, 78.6%, and 113.5%) and a dose-dependent increase
for the induction of DNA damage was observed. The highest
amount of DNA damage (expressed as percentage tail DNA)
was observed in the microalgae exposed to the highest
concentration of extract water (group 109; Fig. 6). But there
was no significant difference between the control and the
solvent control. Photos of control assays show that no
damage (Fig. 7a) was caused by the exposures (Fig. 7b).
Discussion
Jiangsu province in China has a developed chemical
industry, and the chemical composition of organic extracts
from the river and lake were mostly anthropogenic. There
0 0.3 3 10 DMSO
0
2
4
6
8
10
12
Content (µg/ml)
Chl a
Chl b
Groups
Grou
p
s
*
*
(a)
(b)
0 0.3 3 10 DMSO
0
1
2
3
4
5
6
CAR Content (µg/ml)
*
Fig. 2 Chlorophyll a, b (a) and cartotenoid (b) contents of E. gracilis
treated with different concentrations of water extract. Data are the
means ± SD of three replicates. * P \ 0.05
0 0.3 3 10 DMSO
0.00
0.02
0.04
0.06
0.08
0.10
0.12
Protein (mg/10
6
cells)
Grou
p
s
Fig. 3 Soluble protein contents of E. gracilis supplemented with
different concentrations of water extract. Protein content of homog-
enates was determined by reaction with Coomassie Blue dye using
bovine serum albumin as the standard. Data are the means ± SD of
three replicates. * P \ 0.05
0 0.3 3 10 DMSO
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
MDA (U/10
6
cells)
Groups
*
*
Fig. 4 Level of lipid peroxidation products (MDA) measured as
thiobarbituric acid reactive substances in E. gracilis exposed to
different concentrations of water extracts. Data are the means ± SD
of three replicates. * P \ 0.05
672 M. Li et al.
123
were more than 40 priority pollutants (e.g., pesticides,
hydroxybenzenes and heterocyclics) found in the extracts
(Chen et al. 2007). An increasing number of industrial,
agricultural, and commercial organic pollutants in the
aquatic environment lead to various deleterious effects on
organisms, and in lower concentrations, the organic pol-
lutants may have no detectable acute effects on organisms,
but may reduce their survival via long-term chronic effects.
Such effects could be manifested by minor or major genetic
damage to somatic and germ cells and by the development
of disorders, e.g., cancer, that requires long, latent periods
before becoming clinically visible (White and Rasmussen
1998). But the methods of chemical tests and the short-
term bioassays used by now can not reflect the potential
danger to the aquatic organisms and human health in time.
It is very important to develop a rapid, sensitive, and
reliable screening methodology for the evaluation of
genotoxic impacts at low levels and in early exposure
stages.
0
2
4
6
8
10
12
14
16
SOD (U /10
6
cells)
Groups
*
(a)
(b)
0 0.3 3 10 DMSO
0 0.3 3 10 DMSO
0.0000
0.0001
0.0002
0.0003
0.0004
0.0005
GSH (mg/10
6
cells)
Groups
Fig. 5 Total SOD activity (a) and GSH content (b)ofE. gracilis
supplemented with different concentrations of water extracts. Data are
the means ± SD of three replicates. * P \ 0.05
0 0.3 3 10 DMSO
0
2
4
6
8
10
12
14
Tail DNA (%)
Grou
p
s
**
*
*
Fig. 6 Induction of DNA damage (represented as tail DNA, %) in
E. gracilis following exposure to different concentrations of water
extracts in vivo. Date are the means ± SD of the three replicates
(* P \ 0.05)
Fig. 7 Typical comet image of microalgae E. gracilis cells in control
(no obvious damage) (a) and exposed to 109 water extracts
(significant damage) (b)
Genotoxicity of organic pollutants in source of drinking water 673
123
Due to their pivotal importance as primary producers
algae are being increasingly used as ecological indicators
and phytoremediation organisms in polluted, urban aquatic
environments (Kelly et al. 1998). Eukaryotic cells are
basically used in the comet assay. However, few reports
describe the applicability of microorganisms. Erbes et al.
(1997) detected DNA damage in the green alga Chla-
mydomonas reinhadtii exposed to 4-nitroquinoline-1-oxide,
N-nitrosodimethylamine and H
2
O
2
. Watanabe and Suzuki
(2002) used comet assay to examine DNA damage in
E. gracilis caused by Cd
2?
-induced active oxygen stress.
Aoyama et al. (2003) performed a comet assay of unicel-
lular green alga E. gracilis that was exposed to genotoxic
chemiscals. In this study we used E. gracilis as an eco-
logical indicator to detect the drinking water source.
Some studies demonstrated that high dose exposure
could severely damage DNA, which would result in the
decline of visual DNA damage for massive dissociative
fraction of DNA missed in electrophoresis, and very low
dosages would lead to the difference among groups being
inconspicuous (Devaux et al. 1997). The results of the
present comet assay showed that the organic extracts from
the water samples could induce DNA damages to micro-
algae E. gracilis which might affect its survival in the long-
term. This indicates that the water body of Meiliang Bay,
Lake Taihu may have chronic adverse effect on E. gracilis
and due to its importance in the ecosystem, the whole
system may be in danger. Compared with other kind of
assay materials, the microalgae E. gracilis is more sensitive
than results with human peripheral blood (Wu et al. 2008),
mouse spermatid cells (Chen et al. 2007) and zebra fish
embryos (Chen et al. 2007).
Membrane destabilization is generally attributed to lipid
peroxidation resulting from an increased production of
reactive oxygen species (ROS) (Mead et al. 1982), and
lipid peroxidation can be initiated by redox activating
metal ions themselves (Chaoui et al. 1997). The increase in
lipid peroxidation observed in this study is considered as an
indicator of increased oxidative damage caused by organic
pollutants to cells. Antioxidant status generally increases
with pollutant concentration, indicating that the organism
is capable of inducing a protective strategy. Accumulation
of MDA reflects the extent of oxygen-derived free radical
induced cell damage, as we observed that the level of DNA
damage increased parallel to the MDA level (group 109).
Furthermore, the decrease of MDA detected in group
(109) may be explained by the destruction of MDA after it
damaged the cell (Farmer and Davoine 2007). This may
also be partially responsible for the further increase of
DNA damage in group (109) as MDA has potential
genotoxic activities (Del Rio et al. 2005).
It is well known that ROS are produced in cells when
exposed to environmental stresses, e.g., exposure to high
light intensities, UV radiation, metals. Increasing the levels
of ROS can lead to severe cellular injury or death. Therefore,
induction of antioxidant enzymes is an important protective
mechanism to minimize cell oxidative damage in polluted
environments. The antioxidant enzymes are important
components in preventing oxidative stress in plants, because
the activity of one or more of these enzymes is generally
increased when exposed to stressful conditions and these
elevated activities correlate to increased stress tolerance
(Allen 1995; Mazhoudi et al. 1997).
The level of SOD activity exhibited varied responses to
the water extract treatments, which was dependent on the
concentration. Apart from these enzymes, some antioxi-
dants like GSH may play a role in inducing resistance to
environmental stress by protecting labile macromolecules
against the attack by free radicals that are formed during
various metabolic reactions and lead to oxidative stress
(Alscher 1988), but not in our results. Similarly, little
variations of the contents of protein, chlorophyll a, b and
carotenoids were detected in this study, which is consistent
with the growth curves. These observed phenomena alone
may lead to a conclusion that the water extracts are not
harmful. However, this conclusion may not be accepted
when taking the results of SOD, MDA and especially
comet assay into consideration.
Conclusion
In conclusion, our study revealed that drinking water pro-
duced from Meiliang Bay, Taihu Lake could cause cyto-
toxicity, oxidative stress and DNA damage in microalgae
E. gracilis. Our data indicated that the source water was
contaminated with substances capable of inducing DNA
damage in the microalgae E. gracilis. The potential geno-
toxcity of the source water is a warning of possible adverse
effects it may possess on human health, therefore we rec-
ommend further investigations be conducted to evaluate
the safety of the source water and ensure human health will
not be compromised. The study also demonstrated that the
comet assay could be applied to the detection and assess-
ment of geotaxis materials in the drinking water sources.
Compared with other biomarkers, the comet assay of
microalgae is a more sensitive tool for environmental
monitoring, especially for evaluating mutagenic/carcino-
genic changes in exposed individuals.
Acknowledgments This work was supported by the National Basic
Research Program of China (973 Program, No. 2008CB418003),
National Nature Science Foundation of China-Guangdong Govern-
mental Funding (U0733007) and the Social Development Foundation
of Jiangsu Province (No. BS2007049). Great thanks go to Professor
Nils Ekelund, Mid Sweden University, Sundsvall, Sweden for the gift
of microalgae.
674 M. Li et al.
123
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    • "As previously mentioned , this protist is able to accumulate high amounts of Cd 2+ . However, clear alterations in cell growth, cellular structure, flagellar motility, photosynthesis function, and protein and nucleic acid contents under stress conditions (Cd 2+ , Cr 6+ , Cu 2+ , Ni 2+ ; Zn 2+ , laundry detergents , pesticides, hydroxybenzenes and heterocyclic organic compounds ) can also be used as sensitive toxicity reporters (Azizullah et al., 2011; Einicker-Lamas et al., 2002; Li et al., 2009; Rocchetta et al., 2012). For heavy metal pollution sensed by E. gracilis cells, routine microscopy inspection could be implemented, detecting multinucleation and giant cells (rounded cells with approximately 2 times larger size), decreased motility, chloroplast disorganization, and accumulation of paramylum grains. "
    [Show abstract] [Hide abstract] ABSTRACT: Free-living microorganisms may become suitable models for recovery of non-essential and essential heavy metals from wastewater bodies and soils by using and enhancing their accumulating and/or leaching abilities. This review analyzes the variety of different mechanisms developed mainly in bacteria, protists and microalgae to accumulate heavy metals, being the most relevant those involving phytochelatin and metallothionein biosyntheses; phosphate/polyphosphate metabolism; compartmentalization of heavy metal-complexes into vacuoles, chloroplasts and mitochondria; and secretion of malate and other organic acids. Cyanide biosynthesis for extra-cellular heavy metal bioleaching is also examined. These metabolic/cellular processes are herein analyzed at the transcriptional, kinetic and metabolic levels to provide mechanistic basis for developing genetically engineered microorganisms with greater capacities and efficiencies for heavy metal recovery, recycling of heavy metals, biosensing of metal ions, and engineering of metalloenzymes.
    Full-text · Article · May 2016
    • "As a unicellular flagellated protist, Euglena gracilis is an excellent model for research in eukaryotic cell biology (Foltí nová and Grones, 1997). In addition, E. gracilis has been used as a model organism to study the ecotoxicity or genotoxicity of various environmental stressors, such as organic pollutants (Li et al., 2009) and nanoparticles (Brayner et al., 2011). The objectives of this study are as follows: (1) to evaluate the ecotoxicological effects of GO on protozoa E. gracilis by using a growth inhibition test and (2) to investigate the underlying mechanisms of GO toxicity. "
    [Show abstract] [Hide abstract] ABSTRACT: Potential environmental risks posed by nanomaterials increase with their extensive production and application. As a newly emerging carbon material, graphene oxide (GO) exhibits excellent electrochemical properties and has promising applications in many areas. However, the ecotoxicity of GO to organisms, especially aquatic organisms, remains poorly understood. Accordingly, this study examined the toxicity of GO with protozoa Euglena gracilis as test organism. Growth inhibition test was initially performed to investigate acute toxic effects. Protozoa were subsequently exposed to GO ranging from 0.5mgL(-1) to 5mgL(-1) for 10d. The growth, photosynthetic pigment content, activities of antioxidant enzymes, ultrastructure of the protozoa, as well as the shading effect of GO, were analyzed to determine the mechanism of the toxicity effect. Results showed that the 96h EC50 value of GO in E. gracilis was 3.76±0.74mgL(-1). GO at a concentration of 2.5mgL(-1) exerted significant (P<0.01) adverse effects on the organism. These effects were evidenced by the inhibition of growth and the enhancement of malondialdehyde content and antioxidant enzyme activities. Shading effect and oxidative stress may be responsible for GO toxicity. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Full-text · Article · Jun 2015
    • "E. gracilis has been used as a model for studying the biological effects of environmental stressors especially heavy metals [13] [14]. Very recent studies used E. gracilis to monitor the genotoxicity of water contaminants [15] and evaluate the ecotoxicological effects of industrial wastewater [16] [17]. "
    [Show abstract] [Hide abstract] ABSTRACT: Abstract BTEX is a group of volatile organic compounds consisting of benzene, toluene, ethylbenzene and xylenes. Environmental contamination of BTEX can occur in the groundwater with their effects on the aquatic organisms and ecosystem being sparsely studied. The aim of this study was to evaluate the toxic effects of individual and mixed BTEX on Euglena gracilis (E. gracilis). We examined the growth rate, morphological changes and chlorophyll contents in E. gracilis Z and its mutant SMZ cells treated with single and mixture of BTEX. BTEX induced morphological change, formation of lipofuscin, and decreased chlorophyll content of E. gracilis Z in a dose response manner. The toxicity of individual BTEX on cell growth and chlorophyll inhibition is in the order of xylenes > ethylbenzene > toluene > benzene. SMZ was found more sensitive to BTEX than Z at much lower concentrations between 0.005 and 5 μM. The combined effect of mixed BTEX on chlorophyll contents was shown to be concentration addition (CA). Results from this study suggested that E. gracilis could be a suitable model for monitoring BTEX in the groundwater and predicting the combined effects on aqueous ecosystem. Keywords: Volatile organic compounds (VOCs); Cell toxicology; Chlorophyll; Mixed contaminants; Combined effects
    Article · Oct 2014
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