Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 978-984  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal web link: http://www.jett.dormaj.com  
Toxicity of Silver Nanoparticles and Their Removal  
Applying Phytoremediation System to Water  
Environment: An Overview  
1
1,2  
1
Zainab Mat Lazim , Salmiati *, Abdul Rahman Samaluddin , Mohd  
3
2
Razman Salim , Nor Zaiha Arman  
1
Department of Water and Environmental Engineering, School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Johor Bahru,  
Malaysia  
2
Institute Centre for Environmental Sustainability and Water Security (IPASA), Universiti Teknologi Malaysia, Johor Bahru, Malaysia  
3
Civil Engineering Department, Faculty of Engineering, Technology and Built Environment, UCSI University, Cheras, Kuala Lumpur, Malaysia  
Received: 13/02/2020  
Accepted: 17/06/2020  
Published: 20/09/2020  
Abstract  
The widespread use of silver nanomaterials potentially harms the health of the whole ecosystem, especially the aquatic environment.  
Silver nanoparticles (AgNPs) are directly released into environment from washing machines, colloidal silver medicines, and other AgNPs-  
containing products. Review of ecotoxicological studies and the prediction of the future environmental concentrations (PEC) shows the  
presence of a toxic level of AgNPs in the surface water and reveals their effect and risks to aquatic organisms. However, the AgNPs transport  
behavior, their transformation in the natural environment, and how this behavior poses a risk to human and ecosystem health are significant  
issues that have not been clearly known; thus, there is a pressing need to investigate them and provide effective solutions. This study reviews  
the potential of macrophytes to remove AgNPs in aqueous solutions. It also discusses the impact of AgNPs on water environments, their  
toxicity to aquatic organisms, and the phytoremediation functions.  
Keywords: Silver nanoparticle; Macrophyte; Phytoremediation; Surface water  
bacteria, plants, fishes, etc. and, thereby indirectly to humans [13,  
1
Introduction1  
1
4, 15, 16]. Thus, there is a crucial need for further research  
In recent years, manufactured nanoparticles (NPs) and  
aiming at understanding the environmental behavior of NPs and  
predicting their environmental implications [4, 10].  
nanotechnology have grown very quickly and have been broadly  
used. Annually, around 500 tons of silver nanoparticles (AgNPs)  
are produced, representing a major class of engineered NPs  
frequently used in manufactured products and also a significant  
potential for environmental impact [1, 2, 3, 4, 5, 6]. AgNPs have  
widely used in different industries, medical imaging, textile,  
house products, etc. because of not only their high antibacterial  
properties, but also high electrical and thermal conductivity [2, 5,  
The AgNPs-contaminated aquatic system is a possible route  
for human exposure when it is used as a source of potable water.  
Different people show different reactions to this exposure such as  
rash, inflammation, swelling, and mild allergic reaction, and in  
some cases, no effect is observed. Living organisms (e.g.,  
microbes involving in nutrient cycle, waste composting, and other  
beneficial and harmful bacteria) in the aquatic environment can  
be also affected directly. Previously-conducted studies on  
toxicology have proved that AgNPs can cause DNA damage,  
chromosomal aberrations, and even a slight effect on the brain as  
revealed by tests on rats, and also their effect on the early  
development of zebrafish embryos has been confirmed. In  
addition, there are some biological concerns due to the fact that  
harmful microbes might become resistant toward AgNPs that are  
used as anti-microbe agents and also for coating some medical  
equipment.  
7
, 8, 9, 10].  
However, these AgNPs containing products mostly end up in  
the environment and aquatic systems due to accidentally leakage  
during the manufacturing, production, distribution and disorderly  
disposal. These concerns have led to several studies investigating  
the detection of the particles in the aquatic environment, the fate  
and transformation of AgNPs in the aquatic environment, and the  
potential environmental toxicology of these AgNPs to aquatic  
organisms [11, 12]. Literature shows the extensive use of AgNPs  
has exerted adverse effects on the aquatic ecosystem, especially  
Corresponding author: Salmiati, (a) Department of Water and Environmental Engineering, School of Civil Engineering, Faculty of  
Engineering, Universiti Teknologi Malaysia, Johor Bahru, Malaysia, and (b) Institute Centre for Environmental Sustainability and Water  
Security (IPASA), Universiti Teknologi Malaysia, Johor Bahru, Malaysia. Email: salmiati@utm.my.  
9
78  
Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 978-984  
2
Toxicity of Silver Nanoparticle  
In the aquatic environment, many factors that affect the fate and  
transformation can be effective on the toxicity and characteristics  
of AgNPs. Many parameters, including time, influence the  
presence of AgNPs in water environment, which might be still in  
The toxicity of AgNPs and the dynamic nature of these  
particles in complex media and living systems have been  
investigated for many years; however, the risk toward human  
health, particularly the mammalian cells is still unclear [17, 18,  
nanoparticle  
shape,  
suspension  
in  
surface  
water,  
1
9].  
aggregate/agglomerate, dissolved, or bound with natural organic  
materials or other substances that present in the aquatic system.  
Dissolution also may occur when oxidation happens, which  
changes Ag0 to Ag+1. This ionic state of Ag is more toxic toward  
aquatic organism; however, this oxidation process is complicated  
because it depends on time and water physicochemical  
characteristics [2, 20, 21, 22, 23, 24]. A number of important  
studies carried out into the toxicity of AgNPs are listed in Table  
Table 1: The Toxicity of AgNPs  
Effects of the AgNPs  
Toxicity  
No  
Studies  
References  
Decreased hatchability  
of embryos and eye  
size  
Fish: Japanese  
medaka  
1
[25]  
Biological systems:  
virus, bacteria,  
fungi, Protist,  
animal cell lines,  
and human cancer  
cell lines  
1
.
Inhibitory effect on all  
biological systems  
tested  
2
3
[26]  
3
Phytoremediation in Aquatic Media  
Phytoremediation is a natural process through which plants  
Inhibited hatchability  
behavioral retardation  
in early-life stages;  
Effects on embryos;  
Neurodevelopmental  
toxicity altered  
are used to remove contaminants from soil, air, and water  
resources. Phytoremediation has a few types: accumulation,  
degradation, stabilization, rhizodegradation, rhizofiltration, and  
volatilization of the contaminant in the environment [38, 39, 40].  
Generally, for water or aquatic environment remediation,  
macrophytes are used as phytofiltration or rhizofiltration, which  
involves the removal of contaminants by adsorption/absorption  
through the plant roots. Macrophytes also do the task of  
phytoaccumulation through accumulating contaminants in their  
biomass such as tissues of the roots, stems, or leaves. This process  
can reduce pollutants in water environments such as wetlands and  
estuary areas. Phytoremediation is a useful technique for  
removing pollutant from the contaminated water. These  
macrophytes can go through phytomining process that refers to  
harvesting back the metals from water environment for recycling  
purposes [41].  
The macrophytes used for rhizolfiltration of AgNPs require an  
extensive root system capable of tolerating the contaminated  
water source and aggressively accumulating and filtrating the  
contaminants. Moreover, macrophytes are better than invasive  
species that quickly reproduce for self-sustaining [42, 43, 44].  
The phytoremediation of contaminated water can be normally  
performed with a low cost since no expensive equipment and  
chemical is needed for this process. The techniques of  
rhizofiltration and phytoaccumulation can improve water and soil  
quality with only a negligible site disruption [38, 40]. However,  
the appropriate use of macrophytes needs more experiments,  
analyses, and observations since AgNPs can negatively affect the  
plants itself. Once the AgNPs enter the aquatic system, the  
unclear fate and transformation of AgNPs will affect the  
mechanism of this phytoremediation. AgNPs can be transformed  
physically and chemically by aggregation or disaggregation,  
bonding with natural organic matter, or dissolution, which affect  
the stability of AgNPs, the uptake and accumulation of AgNPs by  
macrophytes, their bioavailability as well as their toxicology  
effect toward living organisms and phytoremediator [4, 9, 10, 45,  
46, 47]. The toxicity of AgNPs prevents macrophyte from  
effectively remediating the contaminated water. Microorganisms  
and bacteria communities that surround and are attached to  
rhizosphere are supposedly very beneficial for phytoremediation  
potential; however, the toxicity of AgNPs is harmful to these  
microorganism communities and affect their functioning in their  
[
27, 28]  
Fish: Zebrafish  
locomotion  
Reduced ATP content  
of the cell;  
Inactivate enzymes  
from several cellular  
Human glioblastoma pathways depolarizing  
cells (U251)  
human lung  
fibroblast cells  
and mitochondrial  
membrane;  
Damaging lysosomes;  
Increased the  
[29, 30,  
31, 32]  
4
5
(
IMR-90)  
production of reactive  
oxygen species (ROS)  
in a dose-dependent  
manner  
Cross the blood-brain  
barrier and caused  
long-term contextual  
memory impairment  
Development of  
abnormalities  
Mammal: Mice  
[33]  
6
7
Sea urchin  
[4]  
[5]  
Affecting prokaryotes,  
invertebrates, and the  
fish  
Ecotoxicological  
1  
ng L )  
(
Reduced the zucchini  
biomass and  
transpiration rate  
Affecting population  
size of certain types of  
bacteria  
Plant: Zucchini  
seeds  
8
9
[34]  
[35]  
Microbial profile of  
caecum  
Symptom of  
poison with Cd:  
anxiety, color vision,  
increased mucus  
secretion, and death  
with the open  
Roach (Rutilus  
rutilus) and  
Goldfish (Carassius  
auratus)  
1
1
0
1
[36]  
[37]  
mouth  
No bactericidal  
activity in  
concentration of  
AgNPs up to 128μg/ml  
Gram-positive and  
Gram-negative  
bacteria  
9
79  
Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 978-984  
ecosystems [46, 48].  
Then, to run the experiment, plants of the same size are chosen  
and washed thoroughly by tap water and distilled de-ionized  
water (DDIW) to clean from any impurities. Some other  
researchers just collect the similar size of plants from the river or  
actual pond and then wash them with deionized water before  
keeping in a nutrient solution. The experiments are normally  
performed with three to five replicates. The media sample is taken  
followed by a scheduled time and the visual changes of the plants  
are checked to see whether there is any toxicity effect of silver on  
the plants.  
At the end of the experiment, all the plants are taken out of the  
media and are examined. The plants are again washed thoroughly,  
then are divided into roots, stem, and leaves before air dry at room  
temperature or by oven dry. All the plants parts are then ground  
to get fine powder for further analyses.  
4
The Uptake of Silver Nanoparticles in Aqueous  
Solution  
Plants are key assets for a successful phytoremediation. The  
suitable plants must be able to clean the contaminants, especially  
metal nanoparticles in water sources. Several phytoremediation  
studies have been done to examine the capabilities of  
macrophytes in filtrating the AgNPs-contaminated water and  
wastewater. Usually, a phytoremediation study is conducted in  
lab to get enough data before running for the pilot scale and real  
pond or river. Different plants and methods have been  
investigated to imitate and understand the natural process of  
phytoremediation. Mostly all the plants used in this study are  
collected from actual ponds or rivers; then, they are quarantined  
in artificial ponds/aquariums before being used for further  
experiments. In addition, some plants are grown in a greenhouse.  
Table 2: Summary of Research Conducted into AgNPs Removal  
Results  
Plants  
Pollutants  
Methodology  
(Recovery/uptake/abso  
rb/ removal)  
Ref.  
1
+
0.02, 0.2, and 2 mg L  
Recovery of 96% , 54%  
and 20% for 0.02, 0.2, 2  
mgL-1 of AgNPs  
AgNPs, Ag  
Pistia stratiotes (water lettuce)  
[52]  
(
reduction of silver nitrate by  
sodium borohydride)  
48 hours with a light-dark cycle  
of 14-10 h  
respectively  
Metal level in plants is  
below the LOQ (2 μg  
gdry plant  
AgNPs  
Phragmites australis (salt marsh  
plant)  
1
1
0mg L , natural at 7 days  
[49]  
+
Ag  
1).  
Uptake of Ag :  
1
Mn : 0.75 mg L  
Pleuston-Limnobium  
P. stratiotes and S.  
natans (76%) and L.  
laevigatum and E.  
1  
Cu : 0.37 mg L  
laevigatum, Pistia stratiotes L.,  
and Salvinia natans (L.) All,  
Elodea canadensis Michx.,  
Najas guadelupensis (Spreng.)  
Magnus, Vallisneria spiralis L.,  
and Riccia fluitans L.  
The mixture of colloidal  
solutions of metal nanoparticles  
1
Zn : 0.44 mg L  
Ag + Ag2O : 0.75 mg L  
At 7 days for each pollutant  
[50]  
(Mn, Cu, Zn, Ag + Ag  
2
O)  
canadensis (71%).  
R. fluitans (65%)  
V. spiralis (59%).  
1
5
, 10, 20, 30, 50, and 100 ppm  
Ag+ in MHRFW (used Silver  
nitrate).  
Total silver absorbed  
increases by increasing  
concentration of AgNPs  
Egeria densa / Elodea densa  
Ag+ and AgNps (reduction of  
AgNO by humic acids)  
[51]  
(waterweed)  
3
5
, 10, 20, and 30 ppm AgNps.  
At 7 days  
Pistia stratiotes (water lettuce)  
AgNPs (natural reducing agent,  
Muntingia calabura sp. Leaves)  
Removal of AgNPs for  
both plants were 61%  
7
10 ppb for 96 hours  
This study  
Eichornia crassipes (water  
hyacinth)  
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80  
Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 978-984  
The control plants are also subjected to the same procedure to  
assess Ag initial levels in the selected plants. For determination  
of the levels of Ag and the changes of total AgNps in plants and  
media, samples are subjected first to microwave digestion before  
being analyzed by atomic absorption spectrophotometry (AAS)  
or ICPMS (depending on the given experiment), and FEG ESEM  
experiment. However, the result might be different in a higher  
concentration of AgNPs.  
The results of the previous study showed that P. stratiotes can  
reduce the concentration of AgNPs and ions in aqueous solution.  
The plants also could survive under 0.02 ppm of AgNPs;  
however, the increase of the AgNPs concentration to 2 ppm  
caused the plant's physical shape to be degraded over time; the  
leaves were wilting, discolored, and browned as the root detached  
from the aerial part of the plants [49]. While, the results of a study  
conducted by Leonard Bernas [51] on phytoremediation of silver  
using waterweed showed that the toxicity of silver can be seen by  
a deterioration in the health of plants when exposed to silver in  
concentrations as low as 5 ppm. Plant health is generally  
(FEI) is also used to examine the plants [45, 49, 50, 51, 52, 53,  
5
4]. Many types of methods have been proposed in literature to  
identify the plants that can be better used for phytoremediation of  
AgNps and silver ion. Each method is designed in a way to  
accomplish the objective defined for that specific study. Table 2  
summarizes the studies carried out to remove AgNps from water.  
+
interrupted at concentrations of 20 ppm Ag and AgNPs, as  
5
Plants Mechanism  
The results of some studies have shown that aquatic plants  
revealed by the significant browning of the leaves. Higher  
concentrations of silver had a more pronounced effect on the  
plants for all measurements. The E. densa tests with Ag+ at 50  
and 100 ppm caused the leaves to turn brown and undergo  
chlorosis (insufficient chlorophyll production by leaves) and  
necrosis (cell death from toxic environments and extracellular  
factors).  
Therefore, the presence of Ag+ or AgNPs causes an obvious  
decline in plant health over the exposure period. The obtained  
results of present study show that water lettuce and water hyacinth  
have almost the same percentage removal rate of 61%. This  
means that the plants have almost equal ability in removing  
AgNPs at low concentrations. While, Olkhovych [50] showed  
that the P. stratiotes and S. natans can remove all studied metal  
nanoparticles from water; however, N. guadelupensis was found  
more preferable for phytoremediation of AgNPs with the removal  
rate of 82%.  
have the capability of removing AgNPs at a rate of around 30-  
00%. This proves that aquatic plants or macrophytes are useful  
1
in green cleaning technology.  
In [42, 43, 49], macrophytes of Eichornia crassipes (water  
hyacinth) and Pistia stratiotes (water lettuce) were used for  
phytoremediation of AgNPs in aqueous solution. The studies  
were aimed to investigate the uptake of AgNPs by water hyacinth  
and water lettuce in controlled conditions and evaluate the effect  
of AgNPs on plants health. These macrophytes were selected and  
investigated as these two plants are known to be highly capable  
of tolerating metals and aggressively accumulating contaminants  
and nutrients. Moreover, they have extensive root systems, are  
known as invasive species of floating macrophytes, and have  
already shown promising results for heavy metal water  
purification purposes.  
Green technology is used to utilize plants for the extraction of  
All these plants can be used for phytoremediation and have  
the capability to accumulate Ag of water resources. Results  
obtained from the present study investigating the accumulation or  
uptake of silver by water lettuce and water hyacinth are presented  
in Figure 2.  
certain elements depending on their properties and capabilities. In  
this regard, different plants show different results. The present  
study was conducted on the removal of AgNPs using water lettuce  
and water hyacinth. The obtained results are shown in Figures 1  
and 2.  
Figure 2: The accumulation of silver nanoparticle in leaves and roots of  
water hyacinth and water lettuce  
Figure 1: Removal of silver nanoparticle in aqueous solution for 96 hours  
and the removal rate of the silver nanoparticle  
The analysis showed that the root parts of both plants play a  
significant role in the accumulation of AgNPs compared to their  
aerial parts. Another study [49] used salt marsh plant as  
phytoremediator, and the result showed that the accumulation was  
only detected in roots and rhizomes. Any Ag was not detected in  
the aerial part of the plant. However, this plant can accumulate  
AgNPs only in the absence of rhizosediment. Kadukova [55]  
Findings showed that both the above-mentioned plants can  
-
1
survive in lower concentrations (7.0-10.0 µgL ) of AgNPs. In this  
condition, contaminants are retained within the plant. This low  
concentration does not exert any physical effect on the plants. The  
physical form of the plants remained the same until the end of the  
9
81  
Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 978-984  
claimed that metal in water can enter the plants by the intracellular  
Competing interests  
(symplastic) and extracellular (apoplastic) pathways. However,  
The authors declare that there is no conflict of interest that  
would prejudice the impartiality of this scientific work.  
the cell wall of plants limits the extracellular transport in the root  
and lead to lower detection of Ag in the aerial part of plants. For  
this experiment, only the root parts of the plant had to submerge  
in the media; thus, the majority of the accumulated metal  
nanoparticles are more likely to be attached and move in through  
the plant roots. Therefore, these particles have low interaction  
with the aerial part of the plant since the cell wall has a high cation  
exchange capacity. However, silver is known to be toxic to some  
plants, inhibiting enzymes and altering the permeability of the cell  
membrane wall. Thus, a number of silver species are still able to  
make their way into the leaves of plants. This indicates that silver  
is not necessarily bound only to the root tissue of plants. The  
silver species can be transported through damaged cells or these  
species can utilize transport proteins to translocate from roots to  
leaves [56, 57, 58].  
Authors’ contribution  
All authors of this study have a complete contribution for data  
collection, data analyses and manuscript writing.  
References  
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5
Conclusion  
AgNPs rapidly change in particle size and surface chemistry  
upon exposure to media and interaction with their chemical  
environments such as salinity and pH. These exposures need to  
be considered in evaluating the hazard and risks of AgNPs toward  
the aquatic ecosystem since they affect the speciation of AgNPs  
and their toxicity. Toxic effects can be enhanced or decreased due  
to the transformations of AgNPs in the water environment by  
bioaccumulation and the dissolution of AgNPs to the formation  
of Ag+ ions. On the other hand, phytoremediation is a natural  
method that utilizes the plant's metabolic system to remove,  
reduce, degrade, assimilate, and metabolize AgNPs in water  
sources and store them in the biomass of the plants. The  
appropriate selection of aquatic plants can remediate AgNPs-  
contaminated water. Heavy metal contamination is a growing  
environmental concern; thus, successful removal using  
phytoremediation approaches with duckweeds, waterweeds,  
floating, and submerge macrophytes should be studied further to  
provide an environmentally benign solution to the problem.  
Additional studies need to be performed using macrophytes and  
similar organisms to determine the most effective way for silver  
species phytoremediation.  
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Aknowledgment  
The authors would like to acknowledge the Universiti  
Teknologi Malaysia and Ministry of Education of Malaysia for  
1
1
1
providing  
Grants  
Q.J130000.2422.04G06  
and  
Q.J130000.2522.19H06. The authors also appreciate UTM  
Zamalah for providing a scholarship in favor of the undertaken  
project.  
2
46.  
2. Ma, Y., Metch, J.W., Vejerano, E.P., Miller, I.J., Leon, E.C., Marr,  
L.C., Vikesland, P.J., Pruden, A. Microbial community response of  
nitrifying sequencing batch reactors to silver, zero-valent iron,  
titanium dioxide, and cerium dioxide nanomaterials. Water  
Research. 2015. 68, 87-97.  
3. Cui, B., Ren, L., Xu, Q.H. Silver_ nanoparticles inhibited  
erythrogenesis during zebrafish embryogenesis Aquatic  
Toxicology. 2016. 177, 295-305.  
Ethical issue  
Authors are aware of, and comply with, best practice in  
publication ethics specifically with regard to authorship  
(avoidance of guest authorship), dual submission, manipulation  
of figures, competing interests and compliance with policies on  
research ethics. Authors adhere to publication requirements that  
submitted work is original and has not been published elsewhere  
in any language.  
14. Begum, A.N., Aguilar, J.S., Elias, L., Hong, Y. Silver nanoparticles  
exhibit coating and dose-dependent neurotoxicity in glutamatergic  
neurons derived from human embryonic stem cells.  
Neurotoxicology. 2016. 57, 45-53.  
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