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. 2023 Jan 31;870:161889. doi: 10.1016/j.scitotenv.2023.161889

Application of silver-based biocides in face masks intended for general use requires regulatory control

Jan Mast a,⁎, Erik Van Miert b, Lisa Siciliani a, Karlien Cheyns a, Marie-Noëlle Blaude b, Charlotte Wouters a, Nadia Waegeneers b, Ruud Bernsen c, Christiane Vleminckx b, Joris Van Loco a,b, Eveline Verleysen a
PMCID: PMC9886386  PMID: 36731552

Abstract

Silver-based biocides are applied in face masks because of their antimicrobial properties. The added value of biocidal silver treatment of face masks to control SARS-CoV-2 infection needs to be balanced against possible toxicity due to inhalation exposure. Direct measurement of silver (particle) release to estimate exposure is problematic. Therefore, this study optimized methodologies to characterize silver-based biocides directly in the face masks, by measuring their total silver content using ICP-MS and ICP-OES based methods, and by visualizing the type(s) and localization of silver-based biocides using electron microscopy based methods. Thirteen of 20 selected masks intended for general use contained detectable amounts of silver ranging from 3 μg to 235 mg. Four of these masks contained silver nanoparticles, of which one mask was silver coated. Comparison of the silver content with limit values derived from existing inhalation exposure limits for both silver ions and silver nanoparticles allowed to differentiate safe face masks from face masks that require a more extensive safety assessment. These findings urge for in depth characterization of the applications of silver-based biocides and for the implementation of regulatory standards, quality control and product development based on the safe-by-design principle for nanotechnology applications in face masks in general.

Keywords: Face masks, Biocide, Nanoparticle, Silver, Ag, Textile, Physicochemical characterization, electron microscopy, ICPMS, Risk assessment

Graphical abstract

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1. Introduction

Silver (Ag) is known for its bactericidal and antiviral properties. Mechanisms of action of the antimicrobial activity of silver include interaction with bacterial cell membranes, the gradual release of silver ions that interact with proteins and inhibit essential cell functions, the interaction with DNA and the generation of reactive oxygen species (Durán et al., 2016). The antimicrobial activity of silver is proposed and applied as an instrument to fight the COVID-19 pandemic. Ag0 nanoparticles (NPs) have for example been demonstrated to be active against SARS-CoV-2 (Almanza-Reyes et al., 2021; Morozova et al., 2022).

Treatment of textiles with silver-based biocides gives these textiles a broad spectrum of antibacterial and antiviral properties (Memon et al., 2018; Radetić, 2013; Zhang et al., 2009), leading to application of silver-based biocides in various types of medical textiles, including face masks intended for medical use. In addition, silver-based biocides are applied in face masks intended for use by the general public. Ag0 NP treated textiles were reported to have antiviral capabilities against SARS-CoV-2 (Ahmed et al., 2021).

Exposure to silver-based biocides, as Ag+ ions, Ag0 particles and specifically NPs, can induce a health risk, depending on the type of silver-based biocide, its amount, its stability during use and cleaning and the type and duration of exposure of the users (Ferdous and Nemmar, 2020; Theodorou et al., 2014; Weldon et al., 2016). Depending on the extent of exposure, a pro-inflammatory response can occur especially during intensive use and co-occurrence of an infectious inflammatory reaction, for example COVID-19 (Seiffert et al., 2016). In vitro studies have demonstrated size-, dose- and coating-dependent cellular uptake of Ag NPs and in vivo studies demonstrated induction of a pro-inflammatory response in the lungs upon inhalation of Ag NPs as well as their translocation into the bloodstream with effects in different organs (Ferdous and Nemmar, 2020). However, in-depth investigations are limited and gaps still remain in the risk assessment of Ag in the form of NPs both for humans and the environment. Therefore, albeit that the usefulness of face masks in the management of SARS-CoV-2 infections is not questioned (Adenaiye et al., 2021), the added value of biocidal silver treatment of face masks to control SARS-CoV-2 infections remains, to our knowledge, to be further substantiated.

In the European Union the application of silver-based biocides is strictly regulated. Application of silver for the purpose of protecting the integrity of textiles, including face masks intended for general use, falls within the scope of a treated article. The treated masks can therefore be placed on the market without authorization provided that they meet the requirements of Article 58 of Regulation (EU) No 528/20125 (“Regulation No 528/2012 of the European Parliament and of the Council of 22 May 2012 Concerning the Making Available on the Market and Use of Biocidal Products,” 2012). The use of silver as a disinfectant with the intention of protecting the user against a viral or bacterial infection falls under the definition of a biocidal product and is subject to prior authorization without making it available on the market in accordance with the conditions for granting an authorization as set out in Article 19 of Regulation (EU) No 528/20125. Silver in its nanoparticle form, following a decision by the European Commission, can no longer be used as a biocidal substance (“Commission implementing decision(EU) 2021/1283 of 2 August 2021 on the non-approval of certain active substances in biocidal products pursuant to Regulation (EU) No 528/2012 of the European Parliament and of the Council,” 2021). Nevertheless, the antiviral activity of silver NPs in face masks is advertised as a positive sales argument.

Particularly the question whether the application of silver-based biocides in face masks leads to inhalation exposure is relevant. Publications on the release of silver (nanoparticles) from textiles mainly focus on the development of resistance by bacteria and release of biocidal silver is examined mostly from an ecological point of view, for example considering leaching during washing of the textiles as a source of silver in waste water (Kim et al., 2017; Lorenz et al., 2012; Mitrano et al., 2014; Reed et al., 2016). The study of Pollard et al. examining metal leaching from antimicrobial cloth face masks intended to slow the spread of COVID-19 showed that leaching of silver and copper varied widely across brand, metal, and leaching solution, but in some cases was as high as 100 % of the metals contained in the as-received mask after 1 h of exposure. The authors concluded that “metal-impregnated so-called ‘antimicrobial masks’ are more likely to contaminate wastewater streams with excess silver and copper and/or increase human exposure to these metals than they are to possess any long term beneficial antimicrobial properties”(Pollard et al., 2021).

Direct measurement of silver (particle) release to estimate exposure in a setup mimicking respiration is technically very challenging. No literature data demonstrating silver (nanoparticle) release while wearing silver treated face masks are available, but the absence of release, for example tested as a quality parameter, has not been demonstrated either. The extent of the release of silver in the form of ions and/or nanoparticles from face masks resulting in exposure by inhalation, required for threshold based risk analysis, remains a knowledge gap.

This study aims to evaluate the quality of face masks intended for general use and containing silver based biocides from a safe-by-design perspective. Hereto, it optimizes methodologies that allow characterizing silver-based biocides applied in face masks by measuring their silver content and determining the type(s) and in situ localization of silver-based biocides. This information will be applied in an approach which compares the silver content in the mask with limit values derived from existing occupational inhalation exposure limits for the relevant silver biocides making a minimum of assumptions. In this way, face masks containing silver-based biocides that can be considered intrinsically safe are identified and differentiated from face masks that require a more extensive safety assessment.

2. Materials and methods

Face masks intended for the general public were sampled aiming to include face masks containing different biocides available on the market (Table S1). This selection contains reusable face masks distributed by the Belgian federal government and by Belgian regional governmental instances, reusable face masks from commercial suppliers, and, for comparison, single use face masks from commercial suppliers. These same masks were evaluated earlier regarding the presence of titanium dioxide (TiO2) particles (Verleysen et al., 2022).

In Fig. S1, a general overview of the methodology applied to evaluate silver based biocides in face masks is provided. The silver-based biocides applied in the selected face masks were analyzed by transmission electron microscopy (TEM) using the approach described in detail by Wouters et al. (Wouters et al., 2022). Briefly, ultra-thin sections of individual layers of face masks were prepared by embedding them in an epoxy resin, followed by sectioning using ultramicrotomy. These sections were analyzed by high angle annular dark field (HAADF) – scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDX). (Nano)particles localized in the sections of the face masks were visualized, and their elemental composition was determined. The size of particles identified to be silver by EDX was manually measured. The mass of Ag0 NP at the fiber surface (AgMask-15) was estimated from the total mass of silver and the fraction of the particles at the surface of the fibers using the method described in (Verleysen et al., 2022; Wouters et al., 2022) to estimate the mass of TiO2 particles at the fiber surface. This estimation assumes that the fibers are round and that the silver particles are homogeneously distributed in the matrix of the fibers.

Fig. S1.

Fig. S1

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Overview of the methodology applied to evaluate silver-based biocides in face masks.

In order to acquire a low magnification view of the fibers, samples were prepared for scanning electron microscopy (SEM). Using stainless steel scissors, a piece of approximately 1 by 1 cm was cut out from the middle of the face mask. The individual layers were separated. Each piece was stuck to a 25.4 mm aluminum pin stub (MicrotoNano) using a carbon double sided sticker (MicrotoNano). For additional adhesion and charge reduction, copper tape (MicrotoNano) was placed over the edges of the mouth mask piece leaving an area of approximately 8 by 8 mm for imaging. SEM images and corresponding EDX analyses were made with the Phenom Pharos G2 field emission gun SEM. Due to the non-conductive nature of face masks, all SEM images were made at a pressure of 60 Pa to avoid potential charging effects. Either 10 kV or 15 kV and the lowest spot size were used to acquire the images. Images were acquired with the backscatter electron detector, at magnifications of 1000, 5000 - and 10,000 times.

To analyze the total Ag content of the face masks, two different microwave digestion methods were used, depending on the material, as described by Verleysen et al. (Verleysen et al., 2022). The digestion methods, based on high temperature (220–260 °C) microwave heating and strong acidic (H2SO4 and HNO3) media are described in detail for nonwoven textiles in face masks (Mercier et al., 2022). The protocols allow the digestion of all types of fabrics of the selected face masks (polyethylene terephthalate (PET)-, polytetrafluoroethylene (PTFE)-, cotton, polypropylene, polyamide- and elastane-containing textiles) resulting in a complete release of metallic contents in order to analyze their elemental contents by ICP techniques. After dilution of the digests, the total Ag concentration was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) for high Ag (>10 mg/kg) concentrations and by inductively coupled plasma mass spectrometry (ICP-MS) for lower concentrations. Quantification of Ag by ICP-OES was performed at a wavelength of 328.068 nm (Varian 720, Agilent technologies) or by ICP-MS (Varian 820) for a m/z of 107, using matrix matched calibrations. All samples were prepared and analyzed in duplicate.

The assessment of potential risks associated with the inhalation exposure of silver-based biocides released from face masks during normal use, is constrained due to the lack of available data on such exposure or on silver release. Therefore, an approach comparing the measured Ag content of the face mask with 2 limit values, defined by the nature of the detected silver-based biocide, was applied to evaluate the safety of the face masks with a minimum of assumptions. Two forms of silver-based biocide were considered, namely a generic one, where silver occurs as metal dust, fume, and soluble compounds, and a specific one, where silver occurs as nanoparticles. The National Institute for Occupational Safety and Health (NIOSH) has defined an occupational exposure limit (OEL) for both forms, i.e. 10 μg/m3 and 0.9 μg/m3 respectively (Current intelligence bulletin 70, 2021). Based on these OELs, limit values were obtained using the following equation:

limit value=OELAdditional Safety factorxVairxDuration

The limit value is an estimate for the maximum amount of silver (μg) that can be released during a mask's use (duration in hours, assuming a constant release rate over the usage period) and inhaled (Vair = inhaled air volume, in m3/h) without generating safety concerns. An additional safety factor of 2 was included because the investigated face masks were intended to be worn by the general public. The general public population is more variable than the professionally active population for which the OELs were originally intended. According to European Chemicals Agency (ECHA) guidance (ECHA, 2017), the assessment factors accounting for intra-species differences in the professional and the general populations differ with a factor of 2. The Vair value was set to 1.25 m3/h as recommended by the BPC Ad Hoc Working Group on Human Exposure for scenarios during which exposed people are considered to remain active as is the case for people wearing face masks (ECHA, 2017). The Belgian Government officially recommended to use a new mask every 8 h. When a mask is dirty or humid, it needs to be replaced. For people who have to talk a lot, e.g. school teachers, it is recommended to use a clean mask every 4 h (Belgian Federal Public Service Public Health, Safety of the Food Chain and Environment, 2022). Therefore we considered a worst case usage of 2 masks a day, each during 4 h, ignoring re-use considerations. Table 1 shows the 2 limit values for silver in face masks obtained using the above-mentioned considerations. Masks for which the ratio “limit value/silver content” is larger than 1 have no safety concerns, while masks for which this ratio is smaller than 1 require a more extensive safety assessment.

Table 1.

Limit values for silver in face masks.

Silver form Limit value
Generic (metal dust, fume, and soluble compounds) 25.0 μg
Nanoparticles 2.25 μg
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3. Results

3.1. Amounts and types of silver-based biocides

Using mass spectroscopy and electron microscopy, varying amounts and different types of silver-based biocides were demonstrated in the selection of face masks (Table 2 ). Significant amounts of silver, indicating the application of a silver-based biocide, were demonstrated in 13 face masks (Table 2). In nine of these, silver, but no Ag0 particles, was demonstrated, indicating that the silver biocide is largely present as Ag+ ions. Four face masks (AgMask-03, AgMask-08, AgMask-15 and AgMask-16) were shown to (also) contain a Ag0 coating and/or Ag0 NP.

Table 2.

Summary of the silver content per layer and per face mask, presence of Ag particles per layer, types of the silver biocide (based on STEM-EDX analysis), and comparison of the silver limit values with the silver content per mask.

Reference Ag/mask (μg) Particle locationb Type of Ag biocide Ratio limit value/Ag contentc
Generic silver Nanosilverd
AgMask-01 <0.7 a
AgMask-02 20 Ag+ ions 1.3
AgMask-03 37 E, C, I Ag+ ions, Ag0 NP, large Ag0 particles 0.7f 0.1
AgMask-04 <0.2a
AgMask-05 <0.6a
AgMask-07 <2.8a
AgMask-08 235,044 E, I Ag0 Coating, Ag0 NP, Ag+ ions 0.0001 0.00001
AgMask-10 <0.6a
AgMask-11 <0.6a
AgMask-12 7.3 Ag+ ions 3.4
AgMask-13 13 Ag+ ions 1.9
AgMask-14 87 Ag+ ions 0.3
AgMask-15 165/1.45e E, I Ag0 NP 0.2/ 17.2 0.01/ 1.6
AgMask-16 9.1 C1, C3 CuO particles, Ag0 NP 2.7 0.2
AgMask-17 2.8 Ag+ ions 8.9
AgMask-18 176 Ag+ ions 0.1
AgMask-20 6.5 Ag+ ions 3.8
AgMask-22 14 Ag+ ions 1.8
AgMask-23 <1.5a
AgMask-24 3.2 Ag+ ions 7.8
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a

The indicated limits of detection were calculated for a limit of quantification of 0.25 mg/kg and considering the weight of each face mask.

b

Ag particles are present in the external (E), central (C) or internal (I) layers as assessed by STEM-EDX analysis. C1: first central layer. C3: third central layer.

c

Based on the limit values derived from the NIOSH OELs for silver and nanosilver.

d

Comparisons with the limit values for Ag0 NP are presented only when Ag0 NP are detected in the face mask.

e

The value before the slash refers to the total silver present in the face mask, the value behind the slash refers to the releasable silver on the polymer fiber's surface only; see section 3.1.

f

Bold numbers highlight that the silver content in the face mask exceeds the corresponding limit value.

In face mask AgMask-03, the so-called Silvadur™ technology aims at a slow release of silver ions (Carmona-Ribeiro and de Melo Carrasco, 2013). This silver-based biocide consists of polycationic polymers that bind silver anions. In situ EM analysis showed that at least a fraction of the total amount of silver (total Ag = 37 μg per mask) is present as Ag (nano)particles (Fig. 1). Near-spherical Ag NPs with sizes ranging from 13 to 27 nm and larger near-spherical silver nanoparticles with sizes ranging from 55 to 115 nm (Fig. 1) were observed at the surface or close to the cotton fibers. In addition, larger irregularly shaped silver particles ranging from 500 nm to 1 μm were detected outside of the textile fibers, close to the surface of polyester and cotton fibers (Fig. S2).

Fig. 1.

Fig. 1

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Representative STEM-EDX analysis of nanoparticles at the surface of cotton fibers in AgMask-03. (a) shows HAADF-STEM image of a section of cotton fibers showing particles indicated by pink arrows, (b-d) shows the STEM-EDX results of the particle indicated by the yellow box in (a). (b) is a higher magnification STEM image of the particle. (c) shows the corresponding spectral images of Ag obtained by EDX and (d) the EDX spectra of the area indicated by the yellow box in (b). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. S2.

Fig. S2

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Representative STEM-EDX analyses of particles at the surface of a cotton fiber (a-h) and a polyester fiber (i-l) in AgMask-03. (a) and (e), and (i) show, respectively, HAADF-STEM images of sections of cotton and polyester fibers with particles at their surface, (b-d, f-h, j-l) represent STEM-EDX analyses of the particles indicated by pink arrows in (a), (e) and (i). (b), (f) and (j) show higher magnification STEM images of the particles; (c), (g) and (k) the corresponding spectral images of Ag obtained by EDX, and (d), (h) and (l) the EDX spectrum of the area indicated by the yellow box in (b), (f) and (j).

In face mask AgMask-08, the total amount of silver is very high (>110 mg/outer layer). This is explained by the coating of the woven fibers of the external and internal layer with metallic silver (Fig. 2 and Fig. S3), with an approximate average thickness of 650 nm. Parts of this coating, ranging from 500 nm to 3.5 μm in size, were observed outside of the fibers, probably because they detached (Fig. 2E and Fig. S3). A high amount of Ag0 NP was observed on the coating (Fig. S3). The representative SEM images of AgMask-08 (Fig. S3), combined with EDX, confirm that the fibers of the external layers of this mask are nearly completely coated with a silver coating. This coating was damaged or incomplete in many areas: Fig. S3A and Fig. S3B show that the Ag0 coating is released from the fiber surface at the pressure points of the woven fabric. Where the coating is detached, many Ag0 NP are observed. Their size ranges from approximately 16 nm, the minimal size that readily can be detected with this SEM configuration, to 100 nm. The coating appears to be made up of Ag0 NP: zooming in on the coating revealed that the coating consists of numerous finely packed or compressed nanoparticles (Fig. S3C and Fig. S3D). In addition, Ag nanoparticles were observed inside the fibers. These silver nanoparticles have medium sphericity (near-spherical) and their size ranged from 10 to 20 nm. It can be assumed that these metallic (Ag0) particles are formed de novo by reduction of Ag+ ions, migrating into the fiber from the external silver coating. AgMask-08 contains four central layers similar to those observed in the control masks such as AgMask-01. These layers are expected not to contain silver particles. The relatively high amount of silver detected in these central layers (208 μg) is assumed to originate from contamination from the surrounding layers with very high silver content. STEM-EDX analyses detected only two particles in the four inner layers of AgMask-08.

Fig. 2.

Fig. 2

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Representative STEM-EDX analyses of particles in the woven fabric of AgMask-08. (a), (e) and (i) show HAADF-STEM images of sections of fibers. (b), (f) and (j) show higher magnification STEM images of the particles indicated by pink arrows in (a), (e) an (i), respectively. (c), (g) and (k) show the corresponding spectral images of Ag obtained by EDX. (d), (h) and (l) show the EDX spectra of the area indicated boxes in, respectively, (b), (f) and (j). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. S3.

Fig. S3

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Representative SEM images of AgMask-08 at magnifications of 1000× (a), 10,000× (b), 250,000× (c) and 200,000× (d).

In face mask AgMask-15, silver is present in both the external (83 μg) and the internal (82 μg) layer. STEM-EDX analyses (Fig. 3 and Fig. S3) allowed to differentiate the silver nanoparticles, which are mostly isolated, from the often agglomerated TiO2 particles, which are also present in the fibers (Mast et al., 2021). The applied Ag-based biocide consists of metallic Ag NP distributed in the polyamide matrix of the fibers (Fig. 3 and Fig. S4). These Ag NP are near-spherical (medium sphericity) and their size ranges from 11 nm to 58 nm, which is in agreement with Egger et al. (Egger et al., 2009), and with the Environmental Protection Agecy (EPA) authorization for the applied biocide (EPA, 2011). The latter document distinguishes small silver particles that are sintered on amorphous silicon dioxide forming a silver-silica composite and silver particles that are “broken away from the composite”. High resolution STEM-EDX analyses (data not shown) indicated that the observed Ag0 NP are present in the fibers of the AgMask-15 face mask as particles separated from the silica composite. There were no indications that a silver-silica composite containing nanosilver sintered onto amorphous silicon dioxide, is present (Egger et al., 2009; EPA, 2011). The observed relatively low Si signal can be attributed to the background signal of the detector. Assuming that all silver is present as Ag0 NP, 0.91 % (0.76 μg) and 0.54 % (0.69 μg) of the Ag0 NP are estimated to be present at the fiber surface of the external and the internal layers of AgMask-15, respectively.

Fig. 3.

Fig. 3

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Representative STEM-EDX analysis of particles in a section of a polyamide fiber in AgMask-15. (a) is a HAADF-STEM image showing titanium dioxide (green arrow) and silver (pink arrow) particles. (b) and (e) are, respectively, higher magnification STEM images of the titanium dioxide and silver particles indicated in (a). (c) and (f) show the corresponding spectral images of Ti and Ag obtained by EDX. (d) and (h) show the matching EDX spectra. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. S4.

Fig. S4

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Representative STEM-EDX analyses of particles in a polyamide fiber in AgMask-15. (a) and (e) are HAADF-STEM images of a section of polyamide fibers. (b) and (f) are higher magnification STEM images of the particles indicated by the pink arrows in (a) and (e). (c) and (g) are the corresponding spectral images of Ag obtained by EDX. (d) and (h) are the respective EDX spectra of the area indicated by the yellow box in (b) and (f).

AgMask-16 contains the Argo9825 preservative and antimicrobial agent for use in the manufacture of cellulose, polymer, plastic, and textile products (EPA, 2016). According to its EPA registration file, this biocide is based on CuO (93.337 %), and further also contains zinc (0.313 %), silver (0.007 %) and other ingredients (6.343 %) (EPA, 2016). This mask was originally selected as a control of the specificity of EDX element detection. STEM-EDX analysis confirmed that this mask contains many CuO NP. It also showed that the minor amount of contaminating silver (0.007 %) is, at least partly, present as Ag0 NP (Fig. 4 ), which can be clearly differentiated from the CuO particles using STEM-EDX analysis.

Fig. 4.

Fig. 4

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Representative STEM-EDX analyses of particles in the non-woven fibers of AgMask-16. (a), (e) and (h) show HAADF-STEM images of sections of non-woven fibers. (b), (f) and (i) show high magnification STEM images of copper (orange arrow) and silver (pink arrow) particles in (a), (e) and (h). (c-d), (g) and (j) show the corresponding spectral images obtained by EDX. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3.2. Evaluation of the silver levels in face masks

To evaluate the safety of the silver present in the face masks, Table 2 compares the total amount of silver per face mask with the limit value(s). Out of the 13 face masks which contain detectable amounts of silver, 7 contain levels that are well below the relevant limit values (AgMask-02, AgMask-12, AgMask-13, AgMask-17, AgMask-20, AgMask-22, and AgMask-24). Their silver levels were compared with the limit value for the generic form of silver only, because these face masks do not contain Ag particles as assessed by electron microscopy. The silver biocide, quantified by ICP-OES, is hence assumed to be (largely) present in its ionic form. The levels are so low that even if all silver would be released during a single use, these face masks are not expected to generate safety concerns. Hence, these masks can be considered intrinsically safe.

The amount of Ag+ ions in the face masks AgMask-14 and AgMask-18 exceeds the corresponding limit value, indicating that only a fraction (30 % and 10 % respectively) of the available Ag+ ions can be released under single use conditions without safety concerns.

In AgMask-16, the CuO based, EPA-registered Argo9825 preservative and antimicrobial agent is applied. This mask was shown to contain a small number of Ag0 NP. Although the mass fraction of silver in the Argo9825 biocide is minute (0.007 %), the amount of silver exceeds the limit value for nanosilver.

The amount of silver in AgMask-15 exceeds both the limit values for generic and nanoparticulate silver. However, STEM-EDX analysis shows that the silver nanoparticles are encapsulated in the face mask's polymer fibers and most of these particles can be considered unavailable for release. When considering only the fraction of the particles present at the fiber's surface, i.e. in total 1.45 μg, the amount of silver which potentially can be released is below the limit values and the mask can thus be considered safe.

The total amount of silver, including silver nanoparticles, in AgMask-03 is relatively high, exceeding both limit values. When >70 % of the silver present in the face mask is released during a single use as Ag+, or 10 % as Ag0 NP, the limit values for intrinsic safety are exceeded.

The total amount of silver in AgMask-08 is markedly higher than that of the other evaluated face masks and exceeds the limit values with several orders of magnitude indicating that even very small silver releases, down to 0.1–0.01 ‰, results in exceeding the limit values for intrinsic safety. This mask contains a coating of non-nanoparticulate metallic silver at the particle surface, and Ag0 NP at the surface of the coating and of the agglomerated TiO2 particles in the fiber matrix.

4. Discussion

Wearing face masks is an important and widely applied public health measure to control infectious agents. Textile companies propose new solutions to the challenges associated with, for example, the COVID-19 pandemic, incorporating specific nanofiber, nanocomposite and nanoparticle technology into face masks (Palmieri et al., 2021) including the application of silver-based biocides (Ahmed et al., 2021). Albeit that the usefulness of face masks in the management of SARS-CoV-2 infections is unquestionable (Adenaiye et al., 2021), in depth research of (nano)technology applications in textiles, and specifically the added value of biocidal silver treatment of face masks, is important to avoid possible future consequences caused by a poorly regulated use.

To evaluate the amounts and presence of silver-based biocides in face masks, an approach was set up that combines total silver measurement using ICP-MS or ICP-OES with in situ analysis of silver-based biocides in ultra-thin sections of face masks using STEM and EDX. Digestion of the specific materials used for face masks requires very acidic conditions and the use of hydrofluoric acid (Rujido-Santos et al., 2022). To avoid this very hazardous acid, a digestion method at high temperature was validated previously (Mercier et al., 2022; Verleysen et al., 2022). The combination of this digestion method with ICP-MS and ICP-OES techniques allowed precise quantification of Ag in a wide concentration range (0.25–100,000 mg/kg) which covers the measured amount of silver in the examined face masks.

In situ analysis of silver-based biocides in ultra-thin sections of face masks using STEM and EDX combines spatially resolved structural and chemical information to identify, localize and characterize properties of (nano)particles in textile fibers, a method already successfully applied for the characterization of TiO2 in face masks (Verleysen et al., 2022). A detailed description of the developed sample preparation, imaging and image analysis procedure is made publicly available (Wouters et al., 2022). This approach allowed us to differentiate between the type and appearance of silver biocide applied (ionic/NP form, coating). The high resolution imaging capability of the STEM-EDX technique has proven to successfully identify silver particles of sizes down to 13 nm. Due to limited sampling, however, only a small part of the specimen can be examined, such that low numbers of Ag0 NP (or non-homogeneities) might remain undetected in this type of analysis.

The proposed approach demonstrated varying amounts and different types of silver-based biocides in a selection of face masks offered on the Belgian market and intended to be worn by the general public. Following types of silver-based biocides were demonstrated: (i) Ag+ ions, (ii) metallic Ag0 NP distributed in the matrix of the fibers, (iii) Ag NP and large silver particles at the surface of, or close to cotton fibers in face masks containing polycationic polymers binding Ag+ ions (Silvadur™ technology), (iv) as a coating consisting of metallic silver releasing Ag+ ions, Ag0 NP and large silver particles.

For most face masks, the findings agree with the information accompanying the masks. In AgMask-17, advertised to contain silver nanoparticles bound to cotton, the amount of silver was however so low (2.8 μg/mask) that this claim could not be confirmed or refuted. It cannot be excluded that when the amount of silver is relatively low, Ag0 NP remain undetected because their number is below the detection limit of the applied TEM analysis method. In the face masks AgMask-13, AgMask-14, AgMask-18 and AgMask-20, silver ions are claimed by the producer to be released from fibers or filters. In these masks, STEM-EDX analyses showed no silver (nano)particles, nor local concentrations of the Ag signal coinciding with fiber-like structures, confirming the claims that the silver biocide is largely present as Ag+ ions. This finding also implies that the applied approach does not allow to differentiate application of Ag+ ions from the newer generation of silver-based biocides based on (polymeric) fibers that bind and slowly release Ag+ ions (Swamy, 2018).

Several occupational exposure limits, ranging from 100 μg/m3 to 10 μg/m3, have been proposed by regulatory agencies for non-nano silver. Occupational exposure limits were also proposed for nano‑silver. Weldon et al. proposed 0.19 μg/m3 for Ag NPs based on the silver tissue dose and liver bile duct hyperplasia response in female rats observed in a subchronic rat inhalation toxicity study and by taking the human equivalent concentration with kinetics into consideration. Christensen et al. derived OELs of 0.1–0.67 μg/m3 as an 8-h time weighted average (TWA) for Ag NPs, based on rat subchronic inhalation data (Christensen et al., 2011). In 2021 NIOSH proposed an OEL of 0.9 μg/m3 for nanosilver using largely the same dataset as for the other OELs. We chose to use the NIOSH OELs for nanosilver as the basis for our approach as it is most recent and considered the other proposed values. The NIOSH OEL for silver as metal dust, fume, and soluble compounds of 10 μg/m3 was used as it allowed to cover the different forms of silver, using an OELs proposed by a world-wide recognized organization, ensuring consistency, and because the value was also proposed by other institutes. When the silver content of a face mask exceeds a limit value in the presented approach, this does not imply a risk as such, but rather indicates a need for more detailed assessment enabling to make a conclusion of the face mask's safety. On the other hand, if the silver content is lower than the limit values, it indicates that the mask can be considered intrinsically safe, independent of more detailed information on actual exposure. Hence, our approach is an efficient and transparent screening approach identifying safe face mask despite the scarcity of actual exposure information.

More than half of the analyzed face masks that contain detectable amounts of silver, contain levels well below the relevant limit values and can be considered intrinsically safe, independent of more detailed information on actual exposure, i.e. AgMask-02, AgMask-12, AgMask-13, AgMask-17, AgMask-20, AgMask-22, and AgMask-24. Several face masks contain, however, levels of silver which exceeded one or both of the limit values used in this study, i.e. AgMask-3, AgMask-8, AgMask-14, AgMask-15, AgMask-16 and AgMask-18. Apart from AgMask-15 for which electron microscopy data demonstrated that only a part of the silver is available for release, a definitive conclusion (intrinsically safe) regarding the safety of these could not be made. The main reason for this is the absolute scarcity of specific or generic information about the silver release during the use of silver-containing face masks. On the other hand, it is clear that the approach chosen is conservative because several factors were not considered (due to lack of information) but which are key drivers determining the total silver exposure during use. The total amount of silver in the face masks was compared with the limit values, i.e. the fact that silver was present in multiple forms as for instance in the case of AgMask-3, was not taken into consideration albeit that it is more than possible that the release kinetics are different for silver particles and water droplets with dissolved silver. Some masks contained technologies designed for achieving a slow release of silver ions, e.g. the so-called Silvadur™ technology in Ag-Mask-03 (Carmona-Ribeiro and de Melo Carrasco, 2013). Also, no considerations were made with respect to the mechanisms of silver release. As one both inhales and exhales through the face masks, one could imagine that a part of the releasable silver is “blown”out of the mask during exhalation and it is more than likely that not the entire surface of the mask is involved when breathing through it. In addition, the calculations for the entire mask assume no influence of the different layers of the mask on silver exposure. Furthermore, all masks exceeding the limit values in this study are identified as “re-usable” and when they are used this way, this can reduce the daily exposure to silver because 1) the total amount of silver being released will be spread over a longer use period and 2) information is available that silver is released from silver-treated textiles during washing/dissolution (Benn et al., 2010; Pollard et al., 2021); the repeated wash cycles will as such generate a loss of the silver present in the face masks. Taking re-use into consideration can thus significantly impact the safety assessment of the facemasks; in a use scenario in which AgMask-14 is used at least 4 times, i.e. use time increased from 4 h to 16 h, the safety of the face mask can be demonstrated.

The amount of silver in AgMask-08 is very high and exceeds all limit values with several orders of magnitude. EM analyses demonstrated high amounts of Ag0 NP and indications that these are released. Therefore, this mask was considered unsafe and removed from the market by the Belgian competent authorities (Vandenbroucke, 2022). In AgMask-08, Ag0 NP were not only found on the fiber surface, but also in the fibers near the TiO2 particles. It can be assumed that these Ag0 NP are formed de novo at the negatively charged surface of the TiO2 particles, with known catalytic properties (Yonezawa et al., 2005), by reduction of Ag+ ions. In this mask, the amount of silver externally coating the fibers is very high, which can lead to high amounts of released Ag+ ions, for which it is known that, as opposed to Ag0 NP, they can migrate into the polymer fibers (Franz et al., 2020). It remains to be examined whether the combination of Ag+ ions with TiO2 particles can result in de novo formation of Ag0 NP in other masks, where the concentrations and the (reaction) environment are different. Although further research is necessary, this observation illustrates that the combination of silver ions and TiO2 must be critically examined in risk assessments to avoid unintended formation of and exposure to Ag0 NP. Probably, the additional risk from the presence of these Ag0 NP in AgMask-08 is low because the Ag0 NP in the fibers are surrounded by a polymer matrix. They are not likely to be released as opposed to the Ag0 NP that were shown detaching from the Ag0 coating of the fibers (Fig. S4).

The observation that in AgMask-16, containing the CuO biocide (93.337 %) (EPA, 2016), also Ag0 NP are present from a minor amount of contaminating silver (0.007 %), warrants for the application of a method, such a STEM-EDX, that allows to differentiate different types of particles to control the specifications and the quality of particulate biocides. In this specific case, the amount of CuO NP significantly exceeds that of Ag0 NP. Therefore, the question of possible health risks of CuO in AgMask-16 is relevant, but the characterization and risk analysis of the CuO particles was out of the scope of this study.

A major limitation for the safety assessment of silver biocides in face masks is the scarcity of quantitative (measured or modelled) information about the silver release during the use of face masks. Some information is available on the silver release from silver-treated textiles during washing/dissolution (Benn et al., 2010; Limpiteeprakan et al., 2016; Pollard et al., 2021) or abrasive conditions (Calderón et al., 2018; Lamb et al., 1990), but this information is difficult to extrapolate into inhalation exposure information during face mask use. Therefore we chose an approach which compares the silver content in the mask with limit values derived from existing inhalation exposure limits, thus restricting the number of required assumptions. A key assumption related to the use of the face mask was the 4 h during which a (re-useable) mask was used. In the absence of specific data, adding complex assumptions to the assessment about the form and the kinetics of the silver release combined with use patterns for different user groups (children, adults, elderly), made little sense or was not feasible. The calculations for the entire mask assume no interference of the different layers of the mask on silver exposure.

Our results support the opinion of ANSES that it is impossible to reach a single conclusion that can be generalized to all silver nanoparticles with regard to their identification, the evaluation of their dangerousness, their antibacterial activity and the possible phenomena of bacterial resistance, whatever the planned or existing applications (ANSES, 2015). The results further support the conclusions of Blevens et al. (Blevens et al., 2021) that although many face masks have substantiated claims to contain silver with antiviral and antimicrobial properties, “these certifications or patents are not enough to determine credibility, and stricter regulations by federal agencies on product testing for manufacturers that make claims are necessary to ensure the efficacy of the product advertised, as well as a cloth face mask inhalation standard.”

5. Conclusions

The proposed methodologies allow characterizing silver-based biocides applied in face masks by measuring their silver content and determining the type(s) and in situ localization of silver-based biocides. Thirteen of 20 selected masks contained detectable amounts of silver ranging from 3 μg to 235 mg. Four of these masks contained silver nanoparticles, and in one of these masks, the nanoparticles were present in a coating. Application of this information in the approach, which compares the silver content in the mask with limit values derived from existing inhalation exposure limits for a specific silver biocide making a minimum of assumptions, allows identifying face masks containing silver-based biocide that can be considered intrinsically safe (safe-by-design), and also face masks that require a more extensive safety assessment. This can contribute to set up specifications for safe face masks and for their quality control. With limited adaptations, the proposed methodologies can be adapted for evaluation of applications of metallic and metal oxide biocides other than silver-based biocides, and for other types of consumer products and medical devices. Furthermore, these results raise questions about the safety of some face masks and their intended use. In line with ANSES's recommendations (ANSES, 2020) to limit the use of silver nanoparticles (production, processing, use) to applications whose usefulness has been clearly demonstrated, more data and methodologies should become available to assess the balance of benefits of silver-based biocide on face masks for human health in relation to their health and environmental risks.

The reported findings urge for in-depth research on the applications of silver-based biocides in face masks, and on (nano)technology applications in face masks in general. Phasing out applications that can be unsafe, product development based on the safe-by-design principle, and implementing regulatory standards and guidelines taking in account nanosafety concerns, can avoid possible future consequences caused by a poorly designed nanotechnology in consumer and medical products, while maintaining nanotechnology's important potential to improve (medical) products such as face masks.

The following are the supplementary data related to this article.

Table S1

Overview of the examined face masks intended for general use.

mmc1.docx (19.8KB, docx)

CRediT authorship contribution statement

All authors contributed to the writing of the manuscript. Conceptualization, Jan Mast, Erik Van Miert and Eveline Verleysen; Data curation, Karlien Cheyns and Eveline Verleysen; Formal analysis, Nadia Waegeneers and Eveline Verleysen; Funding acquisition, Jan Mast, Nadia Waegeneers and Eveline Verleysen; Methodology, Jan Mast, Erik Van Miert, Karlien Cheyns, Marie-Noëlle Blaude, Nadia Waegeneers, Ruud Bernsen, Christiane Vleminckx and Eveline Verleysen; Project administration, Jan Mast and Eveline Verleysen; Resources, Jan Mast, Nadia Waegeneers and Eveline Verleysen; Software, Lisa Siciliani and Eveline Verleysen; Supervision, Jan Mast, Christiane Vleminckx, Joris Van Loco; Validation, Jan Mast, Joris Van Loco and Eveline Verleysen; Visualization, Lisa Siciliani and Eveline Verleysen; Writing – Review and editing, Charlotte Wouters, Joris Van Loco, Christiane Vleminckx.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors are grateful to the financial support received from the Belgian federal government which provided Sciensano additional funding for scientific research to overcome the COVID-19 pandemic allowing to realize the COVID-19 AgMask project; (Evaluation of the types, efficient use and health risks of application of silver-based biocides to provide antimicrobial properties to face masks applied during the COVID-19 crisis | sciensano.be). We would like to thank Marina Ledecq, Ronny Machiels and Regis Nkenda for their expert technical assistance and Jill Alexandre for her administrative support ordering the face masks.

Editor: Damià Barceló

Data availability

Data will be made available on request.

References

  1. Adenaiye, O.O., Lai, J., de Mesquita, P.J.B., Hong, F.H., Youssefi, S., German, J.R., Tai, S.-H.S., Albert, B.J., Schanz, M., Weston, S., 2021. Infectious SARS-CoV-2 in exhaled aerosols and efficacy of masks during early mild infection. medRxiv. [DOI] [PMC free article] [PubMed]
  2. Ahmed T., Ogulata R.T., Sezgin Bozok S. Silver nanoparticles against SARS-CoV-2 and its potential application in medical protective clothing–a review. J. Text. Inst. 2021:1–14. [Google Scholar]
  3. Almanza-Reyes H., Moreno S., Plascencia-López I., Alvarado-Vera M., Patrón-Romero L., Borrego B., Reyes-Escamilla A., Valencia-Manzo D., Brun A., Pestryakov A. Evaluation of silver nanoparticles for the prevention of SARS-CoV-2 infection in health workers: in vitro and in vivo. PLoS One. 2021;16 doi: 10.1371/journal.pone.0256401. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. ANSES . ANSES; Maisons-Alfort, France: 2015. AVIS et rapport de l’Anses relatif à l’expertise concernant la mise à jour des connaissances sur l’évaluation des risques sanitaires et environnementaux liés à l’exposition aux nanoparticules d’argent (no. 2011-SA-0224) [Google Scholar]
  5. ANSES . ANSES; Maisons-Alfort, France: 2020. ANSES Opinion on the Estimation of Potential Risks Associated With Wearing Masks Treated With Silver Zeolite and Silver-Copper Zeolite (no. 2020- SA- 0134) [Google Scholar]
  6. Belgian Federal Public Service Public Health, Safety of the Food Chain and Environment Face Masks. I protect you, you protect me. [WWW Document] 2022. https://www.info-coronavirus.be/en/facemask/ URL. (accessed 11.16.22)
  7. Benn T., Cavanagh B., Hristovski K., Posner J.D., Westerhoff P. The release of nanosilver from consumer products used in the home. J. Environ. Qual. 2010;39:1875–1882. doi: 10.2134/jeq2009.0363. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Blevens M.S., Pastrana H.F., Mazzotta H.C., Tsai C.S.-J. Cloth face masks containing silver: evaluating the status. ACS Chemical Health & Safety. 2021;28:171–182. doi: 10.1021/acs.chas.1c00005. [DOI] [PubMed] [Google Scholar]
  9. Calderón L., Yang L., Lee K.-B., Mainelis G. Characterization of airborne particle release from nanotechnology-enabled clothing products. J. Nanopart. Res. 2018;20:1–15. doi: 10.1007/s11051-018-4435-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Carmona-Ribeiro A., de Melo Carrasco L. Cationic antimicrobial polymers and their assemblies. IJMS. 2013;14:9906–9946. doi: 10.3390/ijms14059906. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Christensen F.M., Johnston H.J., Stone V., Aitken R.J., Hankin S., Peters S., Aschberger K. Nano-TiO2–feasibility and challenges for human health risk assessment based on open literature. Nanotoxicology. 2011;5:110–124. doi: 10.3109/17435390.2010.504899. [DOI] [PubMed] [Google Scholar]
  12. Commission implementing decision(EU) 2021/1283 of 2 August 2021 on the non-approval of certain active substances in biocidal products pursuant to Regulation (EU) No 528/2012 of the European Parliament and of the Council OJEU. 2021;279:32–34. [Google Scholar]
  13. Current intelligence bulletin 70: health effects of occupational exposure to silver nanomaterials., 2021. . U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. doi:10.26616/NIOSHPUB2021112
  14. Durán N., Durán M., de Jesus M.B., Seabra A.B., Fávaro W.J., Nakazato G. Silver nanoparticles: a new view on mechanistic aspects on antimicrobial activity. Nanomedicine. 2016;12:789–799. doi: 10.1016/j.nano.2015.11.016. [DOI] [PubMed] [Google Scholar]
  15. ECHA Recommendation no. 14 of the BPC Ad hoc Working Group on Human Exposure. Default human factor values for use in exposure assessments for biocidal products. (revision of HEEG opinion 17 agreed at the Human Health Working Group III on 12 June 2017) [WWW Document] 2017. https://echa.europa.eu/documents/10162/21664016/recom_14+_default+human_factor_values_biocidal+products_en.pdf/88354d31-8a3a-475a-9c7d-d8ef8088d004 URL.
  16. Egger S., Lehmann R.P., Height M.J., Loessner M.J., Schuppler M. Antimicrobial properties of a novel silver-silica nanocomposite material. Appl. Environ. Microbiol. 2009;75:2973–2976. doi: 10.1128/AEM.01658-08. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. EPA . U.S. Environmental Protection Agency; 2011. HeiQ AGS-20 (Notice of Pesticide No. 85249–1) [Google Scholar]
  18. EPA . vols. Argo9825 (No. 91367–1) U.S. Environmental Protection Agency; 2016. Notice of Pesticide. [Google Scholar]
  19. Ferdous Z., Nemmar A. Health impact of silver nanoparticles: a review of the biodistribution and toxicity following various routes of exposure. IJMS. 2020;21:2375. doi: 10.3390/ijms21072375. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Franz R., Bott J., Störmer A. Considerations for and guidance to testing and evaluating migration/release of nanoparticles from polymer based nanocomposites. Nanomaterials. 2020;10:1113. doi: 10.3390/nano10061113. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Kim J.B., Kim J.Y., Yoon T.H. Determination of silver nanoparticle species released from textiles into artificial sweat and laundry wash for a risk assessment. Hum. Ecol. Risk Assess. 2017;23:741–750. doi: 10.1080/10807039.2016.1277417. [DOI] [Google Scholar]
  22. Lamb G.E., Kepka S., Miller B. Particle release from fabrics during wear. Aerosol Sci. Technol. 1990;13:1–7. [Google Scholar]
  23. Limpiteeprakan P., Babel S., Lohwacharin J., Takizawa S. Release of silver nanoparticles from fabrics during the course of sequential washing. Environ. Sci. Pollut. Res. 2016;23:22810–22818. doi: 10.1007/s11356-016-7486-3. [DOI] [PubMed] [Google Scholar]
  24. Lorenz C., Windler L., von Goetz N., Lehmann R.P., Schuppler M., Hungerbühler K., Heuberger M., Nowack B. Characterization of silver release from commercially available functional (nano)textiles. Chemosphere. 2012;89:817–824. doi: 10.1016/j.chemosphere.2012.04.063. [DOI] [PubMed] [Google Scholar]
  25. Mast J., Blaude M.-N., Siciliani L., Cheyns K., Waegeneers N., Van Loco J., Vleminckx C., Verleysen E. Sciensano; Brussels: 2021. Identification, Physicochemical Characterisation and Preliminary Risk Analysis of Titanium Dioxide Particles in Face Masks. (No. D/2021/14.440/72) [Google Scholar]
  26. Memon H., Wang H., Yasin S., Halepoto A. Influence of incorporating silver nanoparticles in protease treatment on fiber friction, antistatic, and antibacterial properties of wool fibers. J. Chem. 2018;2018:1–8. doi: 10.1155/2018/4845687. [DOI] [Google Scholar]
  27. Mercier, G.M., Cheyns, K., Nkanda, R., Machiels, R., Dewinne, A., Waegeneers, N., Mast, J., Grijalva, D.M., 2022. Acid digestion of nonwoven textiles for measuring their trace element content by ICP techniques.
  28. Mitrano D.M., Rimmele E., Wichser A., Erni R., Height M., Nowack B. Presence of nanoparticles in wash water from conventional silver and nano-silver textiles. ACS Nano. 2014;8:7208–7219. doi: 10.1021/nn502228w. [DOI] [PubMed] [Google Scholar]
  29. Morozova O.V., Manuvera V.A., Grishchechkin A.E., Barinov N.A., Shevlyagina N.V., Zhukhovitsky V.G., Lazarev V.N., Klinov D.V. Targeting of silver cations, silver-cystine complexes, Ag nanoclusters, and nanoparticles towards SARS-CoV-2 RNA and recombinant virion proteins. Viruses. 2022;14:902. doi: 10.3390/v14050902. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Palmieri V., De Maio F., De Spirito M., Papi M. Face masks and nanotechnology: keep the blue side up. Nano Today. 2021;37 doi: 10.1016/j.nantod.2021.101077. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Pollard Z.A., Karod M., Goldfarb J.L. Metal leaching from antimicrobial cloth face masks intended to slow the spread of COVID-19. Sci. Rep. 2021;11:1–8. doi: 10.1038/s41598-021-98577-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Radetić M. Functionalization of textile materials with silver nanoparticles. J. Mater. Sci. 2013;48:95–107. doi: 10.1007/s10853-012-6677-7. [DOI] [Google Scholar]
  33. Reed R.B., Zaikova T., Barber A., Simonich M., Lankone R., Marco M., Hristovski K., Herckes P., Passantino L., Fairbrother D.H., Tanguay R., Ranville J.F., Hutchison J.E., Westerhoff P.K. Potential environmental impacts and antimicrobial efficacy of silver- and nanosilver-containing textiles. Environ. Sci. Technol. 2016;50:4018–4026. doi: 10.1021/acs.est.5b06043. [DOI] [PubMed] [Google Scholar]
  34. Regulation No 528/2012 of the European Parliament and of the Council of 22 May 2012 Concerning the Making Available on the Market and Use of Biocidal Products Off. J. Eur. Union. 2012:L167/1. [Google Scholar]
  35. Rujido-Santos I., Herbello-Hermelo P., Barciela-Alonso M.C., Bermejo-Barrera P., Moreda-Piñeiro A. Metal content in textile and (nano)textile products. IJERPH. 2022;19:944. doi: 10.3390/ijerph19020944. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Seiffert J., Buckley A., Leo B., Martin N.G., Zhu J., Dai R., Hussain F., Guo C., Warren J., Hodgson A., Gong J., Ryan M.P., Zhang J.(Jim), Porter A., Tetley T.D., Gow A., Smith R., Chung K.F. Pulmonary effects of inhalation of spark-generated silver nanoparticles in Brown-Norway and Sprague–Dawley rats. Respir. Res. 2016;17:85. doi: 10.1186/s12931-016-0407-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Swamy S. Wash-durable face mask with antimicrobial properties and/or improved washability. EP. 2018;3:287 028 A1. [Google Scholar]
  38. Theodorou I., Ryan M., Tetley T., Porter A. Inhalation of silver nanomaterials—seeing the risks. IJMS. 2014;15:23936–23974. doi: 10.3390/ijms151223936. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Vandenbroucke F. Naar een strikte regelgeving voor álle mondmaskers op de Belgische markt | Frank Vandenbroucke [WWW Document] 2022. https://vandenbroucke.belgium.be/nl/naar-een-strikte-regelgeving-voor-%C3%A1lle-mondmaskers-op-de-belgische-markt URL. accessed 11.16.22.
  40. Verleysen E., Ledecq M., Siciliani L., Cheyns K., Vleminckx C., Blaude M.-N., De Vos S., Brassinne F., Van Steen F., Nkenda R. Titanium dioxide particles frequently present in face masks intended for general use require regulatory control. Sci. Rep. 2022;12:1–9. doi: 10.1038/s41598-022-06605-w. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Weldon B.A., Faustman E.M., Oberdörster G., Workman T., Griffith W.C., Kneuer C., Yu I.J. Occupational exposure limit for silver nanoparticles: considerations on the derivation of a general health-based value. Nanotoxicology. 2016;10:945–956. doi: 10.3109/17435390.2016.1148793. [DOI] [PubMed] [Google Scholar]
  42. Wouters C., Siciliani L., Ledecq M., Verleysen E., Mast J. Identification and characterization of TiO2 nanoparticles in face Masks by TEM. Protoc. Exch. 2022 doi: 10.21203/rs.3.pex-1902/v1. [DOI] [Google Scholar]
  43. Yonezawa Y., Kometani N., Sakaue T., Yano A. Photoreduction of silver ions in a colloidal titanium dioxide suspension. J. Photochem. Photobiol. A Chem. 2005;171:1–8. doi: 10.1016/j.jphotochem.2004.08.020. [DOI] [Google Scholar]
  44. Zhang F., Wu X., Chen Y., Lin H. Application of silver nanoparticles to cotton fabric as an antibacterial textile finish. Fibers Polym. 2009;10:496–501. doi: 10.1007/s12221-009-0496-8. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Table S1

Overview of the examined face masks intended for general use.

mmc1.docx (19.8KB, docx)

Data Availability Statement

Data will be made available on request.

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