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Antimicrobial silver nanoparticles – regulatory situation in the European Union

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Nanosilver is one of the most prominent nanomaterials, resulting from its capability to fight germs like bacteria, fungi and yeasts. Those germs cause nosocomial infections, food poisoning, material deterioration, food and feed spoilage. In the present review, we give insights into antimicrobial silver nanoparticles from a regulatory point of view. Silver nanoparticles release silver ions, which act as the biocidal substance. This mode of action makes it difficult for regulators to judge the risk effects related to silver nanoparticles. In this article the present situation concerning nanosilver (as a silver ion releasing technology) - state of the art, toxicological effects and risk assessment is discussed. Finally, the benefits of using silver nanoparticles in consumer products are compared to regulatory challenges in bringing such products on the market.
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Materials Today: Proceedings 4 (2017) S200S207
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Selection and Peer-review under responsibility of 7th North Rhine-Westphalian Nano-Conference.
NRW 2016
Antimicrobial silver nanoparticles regulatory situation in the
European Union
Gregor Schneidera
*
aRAS AG, An der Irler Hoehe 3a, 93055 Regensburg, GERMANY
Abstract
Nanosilver is one of the most prominent nanomaterials, resulting from its capability to fight germs like bacteria, fungi and yeasts.
Those germs cause nosocomial infections, food poisoning, material deterioration, food and feed spoilage.
In the present review, we give insights into antimicrobial silver nanoparticles from a regulatory point of view. Silver
nanoparticles release silver ions, which act as the biocidal substance. This mode of action makes it difficult for regulators to
judge the risk effects related to silver nanoparticles. In this article the present situation concerning nanosilver (as a silver ion
releasing technology) - state of the art, toxicological effects and risk assessment is discussed. Finally, the benefits of using silver
nanoparticles in consumer products are compared to regulatory challenges in bringing such products on the market.
© 2017 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-
nc-nd/3.0/).
Keywords: Nanosilver, biocide, regulation, safety assessement, nanoparticle, antimicrobial
1. Introduction
Almost ten years ago, several articles published by NGOs raised concerns regarding the safety of nanomaterials.
Consequently researches and authorities all over the world requested more data on nanorisks and specific treatment
of nanomaterials in all related legislations. One of the most prominent materials is nanosilver or silver nanoparticles.
This substance is used in biocidal products for disinfection and microbial inhibition on surfaces. Biocidal products
This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike License, which
permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.
* Corresponding author. Tel.: +49 (0)941/60 717-305; fax: +49 (0)941/60 717-399.
E-mail address: GS@ras-ag.com
G. Schneider/ Materials Today: Proceedings 4 (2017) S200S207 S201
are necessary to control organisms that are harmful to human or animal health and to avoid damage to natural or
manufactured materials caused by microorganisms.
The use of silver was and still is multiple: Silver was used for many different applications throughout history.
Due to its properties it was used in currencies, ornaments, jewellery, electrical contacts and photography. However,
one of the most beneficial uses was the antimicrobial effect silver exerts to fungi, viruses, algae and of course
bacteria. Therefore, silver has been used as disinfectant for a long time, e.g. in treating wounds and burns. [1
For many decades nanosilver, formerly known as colloidal silver, has been used for many different purposes (e.g.
as medical product, for wound care, water treatment, disinfection, etc.) [
]
2
Innovations in surface chemistry and process engineering led to a new linne of nanosilver products in the form of
concentrates or masterbatches that are usable for active surfaces as well as materials like thermoplastic polymers.
].
This article explains the technology behind nanosilver and elucidates the legislative framework for bringing a
nanostructured biocide on the market. The focus here is on European biocidal products legislation, for which most
experience exists.
2. Silver use
2.1 Ancient use of nanosilver
At the end of the 19th century scientists started to produce nanosilver dispersions in a technical way. At that
time, the term “nano” was not used, yet particle suspensions were in a “millimicron” scale or colloidal dispersions.
Most of the nanosilver dispersions during this time were already used as medical products: “Under the name
“Collargol” such a kind of nanosilver has been manufactured commercially since 1897 and has been used for
medical applications.” [2]
Those medical products mainly used the antimicrobial effect of nanosilver. Infections have been treated with
colloidal silver until the 1930s. After antibiotics had been invented and became widespread, the use of nanosilver
declined for decades, but found a renewal when nanotechnology became a scientific discipline.
2.2 Mode of action
The biocidal activity of silver itself has been investigated extensively and is well described: The antimicrobial
activity of silver primarily was identified as an oligodynamic effect by Ravelin and Nägeli and described by Russel
et al. [3]. In substances showing this oligodynamic effect, only very small portions of the active substance are
needed for significant antimicrobial activity [3]. Scientists define nanosilver as particles in a size range between 1
and 100 nm [4]. It is state of the art to incorporate these nanoparticles e.g. into polymers to avoid microbial growth
on their surface [5], [6
]. The principal mode of action is described in Figure 1.
Figure 1: Schematic overview of the nanosilver effect on surfaces (© RAS AG)
S202 G. Schneider / Materials Today: Proceedings 4 (2017) S200S207
Water molecules are penetrating the upper layers of almost every surface that is based on polymers, lacquers or
resins [7
Only silver ions are released, silver nanoparticles remain in the material even when acids are used for migration
tests. This was described by Bott [
]. Nanosilver particles, incorporated in those surfaces, release silver ions (Ag+) by specific corrosion
processes [3].
8
Driven by concentration gradients, the silver ions are „pulled“ to the upper layer of the surface, were most of the
moisture with less silver ions is present [
] when checking silver migration out of LDPE films for food contact. For his
research, he used a LDPE film that contains silver nanoparticles. After migration in 3% acetic acid investigated a
high silver concentration and concluded, that this only could be explained by migration of silver ions. “The small
silver ions (effective ion radius Ag 0.115 nm diffuse in the polymer much faster than the SNP particles of at least 10
nm. Mechanistically this Ag migration is enhanced by the penetration of the small acetic acid molecules into the
LDPE film. This leads already in the polymer to Ag formation from the silver particles followed by acetic acid
mediated diffusion of the silver ions.” [8] His findings shew that the silver nanoparticles themselves remained in the
film and the surface. This was supported by other studies with other nanoparticles (e.g. TiN). He concluded that “not
the silver particles themselves but dissolved silver ions only are released from the polymer which is the reason for
the intended antimicrobial effect of polymers with incorporated silver nanoparticles.” [8]
9
4
]. This liquid layer contains the microbes as well, so the silver ions have
reached their target sites [ ] where they have different mechanisms to influence microbial vitality.
Silver ions exhibit a broad antimicrobial profile against bacteria, fungi and virus as well. Even bacteria strains,
which are resistant against antibiotics, e.g. MRSA can be fought with silver [10]. This makes silver and nanosilver
an excellent biocidal substance for applications in medical devices and the food sector. Examples are coated surgical
instruments, polymer implants (catheters) or nanosilver incorporated into textiles [11
].
3. Nanosilver as a new technology
It is obvious that almost every silver ion releasing substance is principally capable of fighting germs. The use of
nanosilver has some benefits, which are a consequence of its unique properties.
The most important reason is the enormous increase of active surface when reaching the scale of nanometers.
Nanosilver particles release magnitudes of more silver ions compared to microsilver particle of the same weight
[12
The second advantage is the depot effect of nanosilver particles. Other technologies like silver salts release
almost all silver ions during the early stage of immersion. The elemental silver in the core of the nanosilver particle
and its outer layer of silver oxide serve as a depot which releases just small amounts of silver ions, sufficient for
high activity and an antimicrobial effect lasting for years.
]. The amount of released silver ions is directly linked to antimicrobial efficacy. This means that nanosilver
particles show a much higher biocidal activity while requiring less material compared to microsilver or full silver
coating.
Nanosilver particles continuously release silver ions. Nanosilver particles establish a steady state of silver ion
concentration that remains constant for a long time without a decrease in antimicrobial activity over time even when
the treated product is exposed to UV-light or subjected to harsh cleaning procedures. For technical applications used
in the food sector, e.g. for paints, in consumer products or hygienic surfaces for storage of food, nanosilver is
incorporated into the substrate material (e.g. polymer or coating) and is therefore irreversibly immobilized.
In polymer fibers, the nanosilver particles protect the textiles (e.g. soaker pads for fresh meat) against the
uncontrolled growth of germs. Even food related germs like Salmonella don’t have any chance to survive in these
textiles. The infection chain is interrupted and food related infectious diseases are avoided.
The major advantage of using such textiles is due to their durability, compared to other textiles, which lose
antimicrobial activity after a few washing cycles. By incorporating the nanosilver particles (no textile coating is
used) into the polymers, the particles cannot be washed out. They continuously release silver ions for a high
antimicrobial activity. Studies show, that even after 200 laundries at 60°C the textiles still remain antimicrobial [13].
The nanosilver avoids the growth of germs in the textile. This means it is not necessary to dry the textiles after
washing. Wet storage becomes feasible: Nanosilver in textiles therefore minimizes energy costs and CO2-exhaust by
making laundry more efficient. Current studies have shown that the major contribution to the energy savings during
G. Schneider/ Materials Today: Proceedings 4 (2017) S200S207 S203
a textiles lifetime is caused by washing and drying. Figure 2 shows the numbers of the improved environmental
impact: Compared to normal textiles, it is possible to save 50% of electrical energy and have 30% less
environmental impact [14
]. This is due to a lower consumption of detergents and a reduction of electric energy
consumption resulting from fewer washing and drying cycles.
Figure 2: Improved Environmental impact of nanosilver textiles: (Research Project LICARA, funded by European Union Seventh
Framework Programme (FP7/2007-2013) under grant agreement n° 315494) [14])
4. Nanospecific regulation and safety assessment
4.1. History
In the last ten years, lots of papers have been published, that talked about a wide availability and distribution of
consumer produtcs that contain nanosilver. [15 1], [ ].
Such publications and the apparently abundant availability of so-called nanoproducts in the web gave regulators
the impression that thousands of articles treated with nanosilver would already be on the market. Consequently
voices for requesting special registration procedures of nano-biocides have been raised. One of the first legislative
acts implementing nano-specific regulation was the European Biocidal product regulation (EU-BPR, [16
])
4.2. Biocidal product regulation (BPR) and Nanosilver
Depending on the application, the usage of a biocidal substance or product in the EU is subject to several
regulatory frameworks, for example the Biocidal Products Regulation (BPR). This regulation (528/2012 EU),
applies as of September 1st, 2013 and replaces Directive 98/8/EC.
If materials are treated with silver to avoid the growth of germs (bacteria, fungi, yeast, virus, etc.), this
application is in principle inside the scope of the BPR.
Within the authorization process substances owning similar physico-chemical, toxicological and ecotoxicological
properties can be grouped together as one “category”. As a result nanosilver is classified as active substance
S204 G. Schneider / Materials Today: Proceedings 4 (2017) S200S207
„silver“(CAS Nr. 7440-22-4). Because the bulk form of silver is a known biocide for a long time, nanosilver is
authorized according to the guidelines for “existing substances”, where transitional measures apply.
The EU-Regulation for biocides, who mentions explicitly in § 19: “Where nanomaterials are used in that product,
the risk to human health, animal health and the environment has to be assessed separately.” [16], therefore an
additional set of tests with nanosilver were necessary. Also other regulatory authorities were struggling with the
evaluation of nano-specific risks, to ensure the highest possible level of safety for their citizens.
As a result of this high demand the international “ Organisation for Economic Co-operation and Development’s
(OECD) Working Party on Manufactured Nanomaterials (WPMN) is carrying out one of the most comprehensive
nanomaterial research programs: the OECD WPMN Sponsorship Program for the Testing of Manufactured
Nanomaterials.” [17
Consequently the only nanosilver product in Europe, which can provide an additional nano-specific dataset and
nano-risk assessments, is the reference material NM 300 K. The results of this extensive research guarantee the safe
use of agpureW10 nanosilver and agpureW10 treated articles.
]. Herein the silver reference nanomaterial in the OECD WPMN international testing program,
is the nanosilver product “agpure W10” which is characterized as NM 300K. (agpure W10 is produced by RAS AG)
For food applications, the used biocidal product had to be authorized or had to be notified as existing active
substance for product type 4. Being an existing substance, the deadline for authorization respectively the inclusion
of silver (nano) into Annex I of the BPR can't be scheduled at the moment. But everybody who is using NM 300 K
can therefore benefit from the transitional measures meant before. Examples of the safety assessment, based on
public available studies elucidate the quality of existing data for nanosilver.
4.3. Technology and physical-chemical properties
EU Joint Research Centre (JRC) published a report [18] and material information sheet [18
] for NM 300 K,
which summarizes the physical and chemical properties of the material. Figure 3 shows a TEM image of this
nanosilver suspension, which demonstrates the homogenous particle size distribution.
Figure 3: TEM-image of NM 300K (= agpure W10, a product of RAS AG) nanosilver particles. (Klein et al. 2011 [17]).
4.4. Toxicology of Silver nanoparticles and Food contact migration. .
When talking about nanotoxicology it has to be considered, that the increasing number of studies on the safety of
nanomaterials was not followed by an increase in quality and reliability of such studies. Because of that Krug and
Wick [19] in their review were even forced to describe inadequate methods “together with recommendations how to
avoid this in the future, thereby contributing to a sustainable improvement of the available data.”
G. Schneider/ Materials Today: Proceedings 4 (2017) S200S207 S205
This means any results of studies on nano-risks have to be used very carefully. As a summary of data on
mammalian or ecotoxicity the use of nanosilver can be considered to be safe for humans and the environment, when
certain rules are followed. Even the use in food contact materials is feasible.
When talking about migration of silver from silver nanoparticle containing substances it could be shown, that
only the silver ion is the relevant species that is released from materials containing nanosilver: “In conclusion, not
the silver particles themselves but dissolved silver ions only are released from the polymer which is the reason for
the intended antimicrobial effect of polymers with incorporated silver nanoparticles.” [8].
Studies show, when using NM 300K incorporated in polymers this release is below the EFSA Substance
migration limit of 0.05 mg/kg of food: “The AFC panel also took note of the WHO "Guidelines for drinking-water
quality" [20]. According to these Guidelines a total lifetime oral intake of about 10 g of silver (equal to 0.39
mg/person/day) can be considered on the basis of epidemiological and pharmacokinetic knowledge as the human
NOAEL. To maintain the bacteriological quality of drinking water, levels of silver up to 0.1 mg/l, could be tolerated
without risk to health. On the basis of a daily intake of 2 l of drinking water this concentration is equal to a daily
silver intake of 0.2 mg/person and gives a total dose over 70 years of half the human NOAEL. Based on the data
above, a Restriction of 0.05 mg/kg of food (as silver) for the substance would limit intake to less than 12.5 % of the
human NOAEL” [21
The highest silver migration rates (6.8 μg/dm²) were found with 3% acetic acid as a food simulant and the plastic
film with the highest silver content (11.000 ppm). [
]
22
Even under food contact related migration conditions that can be found in normative literature like Directive
97/48/EC.: „…silver was neither found in 95% ethanol although the solubility or ability to disperse would have been
sufficient nor in isooctane which is known to be very aggressive to LDPE by swelling the polymer. From a
migration theoretical view the SNP of at least 10 nm size cannot move anymore at the applied severe test
temperatures at a measurable speed in a polymer and therefore are not expected to migrate out of the film. This is
supported by other studies with other nanoparticles (e.g. TiN).” [
]
8]
The review of Cushen et al. [23
Echegoyen and Nerin [
] collected available data on silver migration from nano and non-nanosilver
containing products. The migration from the nanosilver containing product was the lowest, not exceeding 0.35
µg/dm².
24
These results demonstrate that the even for food contact applications a daily use of nanosilver containing
products is safe for humans and the environment. Because these products with integrated nanosilver particles wound
not lead to a considerable silver migration into the foodstuff.
] concluded, that “in all cases the total silver migration is far below the maximum
migration limits stated by the European legislation…”.
5. Conclusion
Silver is known to be used since the 4th millennium BC. Nanosilver dispersions were used as medical products
already in the 19th century without showing adverse effects on patients. Additionally, silver has been authorized by
EU EFSA as E174 for coloring food.
The antimicrobial effect of silver is well understood. Silver ions exhibit a broad antimicrobial profile against
bacteria, fungi and virus as well. Even bacteria strains that are resistant against antibiotics, e.g. MRSA, can be
fought with silver [10]. This makes silver and nanosilver an excellent biocidal substance for applications in medical
devices and in the food sector.
Increased surface area and silver ion release combined with a silver depot effect makes nanosilver the ideal
additive to be used as a biocidal substance for any type of surfaces.
For technical applications used in the food sector, e.g. for paints, in consumer products or hygienic surfaces for
storage of food, nanosilver is incorporated into the substrate material (e.g. polymer or coating) and is therefore
irreversibly immobilized.
S206 G. Schneider / Materials Today: Proceedings 4 (2017) S200S207
Compared to normal textiles, nanosilver textiles save 50% of electrical energy and result in a 30% lower
environmental impact. This is due to a reduced consumption of detergents and a benefit of electric energy resulting
from fewer washing and drying cycles.
Silver is used in the food area to fight microorganisms that cause food spoilage or even diseases like food
poisoning. Especially animal stalls are a major source of multidrug-resistant organisms such as the dreaded MRSA
wound and pus germ or dangerous intestinal bacteria like 3,4MRGN (Multi Resistant Gram Negatives). All relevant
bacterial strains are sensitive against silver, even the multiresistant strains that will increasingly cause hygienic
problems.
The regulation of nanosilver for food contact materials is a complex issue. One topic, which is discussed at the
moment within European authorities, is the approach on how to deal with applications for BPR product type 4 to
avoid legal uncertainty and dual approval processes (EU-BPR 528/2012 vs. (EU) No 10/2011 positive list). But it
seems obvious that nanosilver products that wanted to be placed on the EU-market have to be authorized compliant
to existing law and their nano-specific risk has to be assessed additionally.
Becoming the silver reference nanomaterial within the OECD WPMN international testing program, the
nanosilver product “agpure W10” (produced by RAS AG) was characterised as NM 300K. It is the only nanosilver
in Europe which provides extensive research data on nanosafety. Summarizing the data on mammalian and
ecotoxicit, using nanosilver can be considered to be safe for humans and the environment, as long as certain rules
are followed.
The results of the nanorisk assessment and silver migration studies show that the use of a product for food contact
applications which contains NM 300K nanosilver as antimicrobial additive is safe for humans and the environment.
It will not lead to a considerable silver migration into the food.
Overall, nanosilver for food contact materials is a safe material that can be used to face new challenges in our
society. Besides the conservation of resources, more hygiene will be demanded, to guarantee safe food in a growing
population. Even new threads like multiresistant bacteria, as a consequence of factory farming, can be stopped by
using nanosilver [25
].
Nomenclature
BPR Biocidal Products Regulation
CAS Chemical Abstracts Service
DNA/RNA Deoxyribonucleic acid/Ribonucleic acid
EC European Commission or European Community
EFSA European Food Safety Authority
ESBL Extended-spectrum beta-lactamase
EU European Union
FCM Food contact material
JRC Joint Research Centre
MRGN Multi Resistant Gram Negatives
MRSA Methicillin-resistant Staphylococcus aureus
NOAEL no observed adverse effect level
OECD Organisation for Economic Co-operation and Development
PIM Plastics Implementation Measure
TEM Transmission electron microscopy
UV-VIS Ultraviolet- visible
WHO World Health Organization
WPMN Working Party on Manufactured Nanomaterials
G. Schneider/ Materials Today: Proceedings 4 (2017) S200S207 S207
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... The hetero-aggregation between nanoparticles and biogenic particles can increase the bioavailability of nanomaterials, and these biomacromolecule-nanoparticle aggregates may offer a way of entry for nanomaterials into cells and subsequently determine the fate of the material in the organism (Lowry et al. 2012). An important consideration for several nanoparticles employed in the food, cosmetic, and medical industries (such as silver nanoparticles) is that these particles may display biocidal properties, making them less attractive to microbial colonization (Schneider 2017). This difference, combined with the polydisperse nature of plastic nanoparticles and varying surface charges, may make nanoplastics more likely to be incorporated into extracellular polymeric substances (EPSs), as the binding of biomacromolecules can coat the nanoplastic and reduce its surface energy, rendering it more stable. ...
Chapter
Nanoplastics can be classified into primary and secondary nanoplastics, where primary nanoplastics are industrially produced for specific purposes and secondary nanoplastics result from plastic waste via degradation processes. The origin of nanoplastic particles is an important consideration in nanotoxicological assays. Since nanoplastics are generally thought to be produced unintentionally from microscale plastic debris, it is likely that they form aggregates with other natural and/or anthropogenic materials. Nanoplastics can take on a new biological identity in the marine environment, often dictated by the biomolecular species on their surface. Freshwater nanoplastics may display differing surface functionalities and exist in different concentrations than marine nanoplastics. Phototrophs use light as their energy source to synthesize organic compounds and are widely distributed in marine environments. Though phototrophic microorganisms are vitally important to primary production in the marine environment, heterotrophs may also associate with nanoplastics in the marine environment, and trophic transfer is thus also possible.
... The wide use of Ag NPs in many applications that involve human occupational and consumer exposure is justified by their known antibacterial, antiviral and antifungal properties to prevent infections. Despite its previous use (for instance colloidal silver 'Collargol' has been used for medical applications and has been manufactured commercially since 1897), Ag NPs gained renewed interest when its use as antibacterial and antiviral nanotechnology became more widespread and better supported by scientific evidence (Dung et al. 2020;Schneider 2017). In addition to their benefits, there are concerns about potential human and environmental hazard (Bouwmeester et al. 2009;Epstein et al. 2014;Lead et al. 2018 This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/bync-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way. ...
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In this work, colloidal silver has been added into an acrylic clear cataphoretic bath, evaluating the effect of two different filler amounts on the durability of the composite coatings. The three series of samples were characterized by electron microscopy to assess the possible change in morphology introduced by the silver-based additive. The protective properties of the coatings were evaluated by a salt spray chamber exposure and electrochemical impedance spectroscopy measurements, evidencing the negative effect provided by high amount of silver, which introduced discontinuities in the acrylic matrix. Finally, the durability of composite coatings was studied by exposing them to UV-B radiation, observing a strong phenomenon of silver degradation. Although the coating containing high concentrations of silver demonstrated poor durability, this study revealed that small amounts of silver can be used to provide particular aesthetic features, but also to improve the protective performance of cataphoretic coatings.
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