Quantification and characterization of manufactured nanomaterials shed from face masks

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Sipkens, Gregory J. Smallwood, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6995325/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 03 Feb, 2026 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Face masks are an important public health measure whose use became wide-spread during the pandemic. Manufactured nanomaterials (MNMs) have been used in face masks to enhance their anti-microbial and self-cleaning properties. There is currently a gap in the literature on the shedding potential of MNMs as it relates to potential inhalation uptake. Three face masks, containing titanium dioxide (TiO 2 ), were analyzed for their composition and particle shedding. The face masks were first analyzed to determine the mass fraction of TiO 2 and the composition of the particles detected. The face masks were then tested under continuous airflow with and without concurrent agitation. Particle shedding was quantified via multiple particle counters and sizers and captured on filters for additional analysis. The compositional analysis showed that all masks tested contained different levels of Ti, with TiO 2 particles observed at the surface of the fibers. Particle shedding was observed only for two of the masks with concurrent agitation. Further analysis of the shed particles did not indicate the presence of TiO 2 , but showed the presence of Si, Cu and Ca. This data adds to the body of evidence relating to inhalation uptake from shedding of MNMs and may inform future risk assessments. Earth and environmental sciences/Environmental sciences Health sciences/Health care Physical sciences/Materials science Biological sciences/Microbiology Physical sciences/Nanoscience and technology particle shedding facemask manufactured nanomaterial titanium dioxide risk assessment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction Due to their capabilities and the growing need for high quality personal protective equipment during the Covid-19 pandemic, nanomaterials have been incorporated into face masks to enhance their microbiocidal activity 1 – 5 and are found either blended into polymeric fibers or are coated on the surface of the fibers. Among the most commonly used nanomaterials in facemasks are nanoscale silver (Ag), nanoscale zinc oxide (ZnO), nanoscale copper oxide (CuO), and nanoscale titanium dioxide (TiO 2 ) 6 . Due to their photocatalytic properties, TiO 2 nanoparticles, which are the focus of this study, have been shown to exhibit microbiocidal activity when exposed to light, due to the generation of reactive oxygen species. Discussions related to the mechanism of nanoparticle microbiocidal activities can be found in 7 – 13 . The addition of these nanomaterials to facemasks raises the concern of their release (shedding) during normal or extended wear, causing a potential risk of exposure by inhalation to the wearer, which is currently not well elucidated. The inhalation of nanomaterials may cause adverse health effects, such as inflammation, oxidative stress, and lung damage 14 – 16 . Therefore, it is important to assess the potential release of nanomaterials from these facemasks. Most studies across the literature evaluated microplastic and nanoplastic release from facemasks, rather than metal-containing particle release, reporting mixed results. A recent review by Kisielinski et al. 17 compiled the results of multiple studies investigating the release of fibers, fiber components and chemical compounds from facemasks. The authors report a significant portion of microplastics and nanoplastics to be potentially released, with N95-certified products showing a consistently higher released fraction during leaching compared to surgical facemasks, largely attributed to the higher number of layers associated with N95 products. Studies on the release of such components are often performed via leaching 18 – 20 , representing an upper limit for particle release. Only a few studies have investigated this release in breathing-like apparatuses 20 , 21 to simulate inhalation exposure. Li et al. 21 investigated particle release in air from different types of facemasks under constant airflow, in an environment with no contamination control for a duration of 2–720 hours. The authors observed an increase in the fiber released count with time and disinfection processes, except for N95 masks, which in general, showed lower fiber release. Further analysis using Raman spectroscopy showed that the particles collected consisted of 12% silica and 42% confirmed microplastics with size ranging from 20–100 µm. Meier et al. 2022 20 investigated the release of fibers from facemasks over 8 hours using a breathing apparatus (Sheffield Head), with multiple donning and doffing and compared their findings to the fraction released liquid-based extractions. The authors found that under sinusoidal airflow, the fibers released from all masks were low, ranging between 6 to 24 fibres/g of mask. The number of fibers released slightly increased by a factor of 1.5 to 12.5 for different mask types when exposed to mechanical stress from donning and doffing. The number of fibers released using the breathing apparatus represented about 0.1 to 1.1% the fraction of liquid-based extractions for all masks tested. The above-mentioned studies and references within Kisielinski et al. mainly focused on the detection of volatile organic compound and microplastics/nanoplastics released from facemasks. However, little work has been performed to address manufactured nanomaterial release from facemasks. Bussan et al. 22 investigated multiple surgical and K95 facemasks for release of trace elements via leaching and from airflow under vacuum. While most facemasks tested were found not to contain trace elements (i.e. were below the method’s detection limit), a few facemasks were shown to contain traces of copper, antimony, zinc, and lead, where the latter (Pb) leached to ~ 60% after 6h. In a comprehensive study, Verleysen et al. 23 demonstrated, via scanning transmission electron microscopy coupled with energy dispersive X-ray (STEM-EDX) and inductively coupled plasma optical emission spectroscopy (ICP-OES), the presence of TiO 2 from various facemasks tested, with contents ranging from 17 to 4394 µg per mask available at the surface of the fibers, and median particle sizes ranging from 89 to 189 nm. A follow-up study by Montalvo et al. 24 investigated the release of Ag-based biocides and TiO 2 particles via leaching in artificial sweat. While Ag was released in amounts up to 36% of available Ag on the masks, TiO 2 was found in minimal amounts (0.35% of available Ti on the facemasks) in the released fraction. Similarly, Meier et al. 20 , Suwanroek et al. 25 and Pollard et al. 26 evaluated the leaching of multiple metals and metal oxides in multiple solutions (deionized water, detergent and artificial saliva), which were found to vary with mask and solution. These leached amounts represent a worst-case scenario for exposure estimates and may not be realistic for estimating the potential for inhalation. To our knowledge, there are currently no published studies reporting direct measurements of airborne shedding of component MNMs from commercial mask products accounting for the inhalable portion, which is crucial to support risk assessments with more realistic inhalation uptake and exposure estimates. Some attempts have been reported 27 to address this issue, however, no conclusions could be drawn from the experiments performed, due to the large variability in results observed. In this work, we performed an exploratory study to investigate potential airborne particle shedding from three different facemask products, all claimed to contain TiO 2 . We first characterized and quantified nanomaterials and metal content for each mask, which were subsequently tested for shedding using a custom-built setup, under controlled conditions and constant flow. Shed particles were analyzed based on their number, size and composition. 2 Results 2.1 Surface characterization and compositional analysis Following the methodology proposed in Section 4.2.1, all layers of each facemask were imaged with SEM (with the exception of layers 3–5 of Mask 3), with EDX performed on the detected particles. Particles were observed on all outer layers of the mask as well as the 1st middle layer of Mask 3 (identified as a carbon filter) and the inner layer of Mask 1. Figure 1 (panels a, d and g) show a low magnification of the outer layers of Mask 1, Mask 2 and Mask 3, respectively. Higher magnifications of these samples are shown in panels b, e and h with the elemental Ti map overlaid, showing the Ti distribution within the region of interest (ROI), outlined with a black box. Panels a, d and g show the corresponding EDX sum spectrum, representing the sum of all individual pixel spectra in the ROI. All layers displayed in Fig. 1 show a similar fiber network, characteristic of a non-woven spunbonded layer with approximate fiber dimeters of 16 µm, 20 µm and 30 µm for Mask 1, Mask 2 and Mask 3 respectively. Overall, the EDX analysis (spot analysis or elemental mapping) showed that the majority of particles observed on the outer layers contained Ti and O, with some particles containing Ag and Si occasionally found on the surface of Mask 2 and Mask 3 respectively. The particle size distribution for Mask 1, Mask 2 and Mask 3 (outer layer only), based on a total of 358, 250 and 355 particles, respectively, is shown in Fig. 2 as a function of the projected area-equivalent diameter. A lognormal distribution was fit to the data obtained. Similar distributions were observed for Masks 1 and 3, with larger particles detected for Mask 3 (modes: 0.52 µm and 0.79 µm for Mask 1 and Mask 3 respectively). This is mainly due to the presence of a Ti-coated layer observed on the fibers (e.g Fig. 1 h). This further corroborates the Mask 3 manufacturer’s claim of containing an outer layer TiO 2 coating. However, since no further details were provided regarding the coating material nor the coating process, no further conclusions could be drawn. Whereas a range of particle sizes were detected on the outer layers of Masks 1 and 3, a narrower size distribution was found for Mask 2 (mode: 0.37 µm), where the majority of the particles were found below 1 µm. In Fig. 2 , the obtained particle size distributions as a function of the minimum feret diameter are compared to the findings of Verleysen et al. 23 . In their study, Verleysen et al. analyzed 12 samples using a high-angle annular-dark-field scanning transmission electron microscope (HAADF-STEM) to image particles (agglomerates) detected within the fiber cross-section. Size distributions from Verleysen et al. for 10 of the 12 samples (outer layer only), were fitted using a lognormal distribution and compared to our findings. In general, narrower particles size distributions were found by Verleysen et al. for most samples with modes ranging between 0.1 to 0.3 µm. This difference stems from the different techniques and sample preparation used for imaging. In our study, since a small area of the outer layer of the facemask was imaged by SEM, as opposed to a thin cross-sectional area of the fibers imaged by HAADF-STEM for Verleysen et al., the resolution was constrained by the pixel size which was 10to 50 nm depending on the magnification used. Therefore, no particles below ~ 100 nm were included in this study due to the large uncertainties associated with the small particle sizes detected. The morphology of particles was not further assessed to distinguish between single particles or agglomerated particles as it is beyond the scope of this study. Analyzing the inner layers of the facemasks (S2 Fig), particles were only clearly detected on Mask 2. EDX performed on the particles detected, did not show the presence of TiO 2 in Mask 2. Consequently, the subsequent analysis mainly focused on the outer layer of the facemasks. 2.2 Total Ti content Analysis of the digested mask samples by ICP-MS revealed the presence of Ti in all studied facemasks, with varying quantities detected. The mass fractions of Ti per g of facemask is provided in Table 1 for all replicates as an average of 3–5 samples with corresponding standard deviation (SD). Mask 1 was found to have the highest content of Ti per g of mask, and hence was considered to be a good candidate for the subsequent shedding experiments. However, it should be noted that the mass fraction of Ti in this mask, is associated with high relative standard deviation (RSD, representing the ratio of the standard deviation to the mean) between subsamples of the same mask (range 19% − 43%, n = 5). This suggests that the TiO 2 coating of the mask fiber is not homogeneous although the RSD of total mass fraction of Ti among the replicates of mask 1 is within 9%. On the other hand, the TiO 2 coating on mask 2 seemed to be homogeneous (RSD range 3% − 5%, n = 3), but noticeable differences were observed among the mask replicates (RSD 16%). Mask 3 contained the lowest mass fraction of Ti and a large RSD was observed within the studied subsamples (range 7% − 35%, n = 4) as well as among the mask replicates (RSD 38%). Ti was found in Control 1, with similar mass fractions to Mask 3. Table 1 Average Ti mass fractions with associated standard deviation (SD). Mask n Ti Mass fraction ± SD [µg/g] Mask 1, Replicate 1 5 4070 ± 770 Mask 1, Replicate 2 5 4290 ± 860 Mask 1, Replicate 3 5 4870 ± 2105 Mask 2, Replicate 1 3 2200 ± 73 Mask 2, Replicate 2 3 1660 ± 45 Mask 2, Replicate 3 3 2230 ± 110 Mask 3, Replicate 1 4 160 ± 28 Mask 3, Replicate 2 4 80 ± 6 Mask 3, Replicate 3 4 95 ± 34 Control 1, Replicate 1 3 183 ± 34 Control 1, Replicate 2 3 217 ± 62 Control 1, Replicate 3 3 186 ± 44 Control 2 3 LOD LOD: below limit of detection, SD: standard deviation n: Number of subsamples for each replicate. 2.3 Particle release in liquid Figure 3 shows the particle size distribution of the released TiO 2 particles in liquid (after 48h of agitation) analyzed using SP-ICP-MS for Mask 1, Mask 2 and Mask 3. A visual inspection of the supernatant revealed a discernable amount of fiber released from Mask 3, compared to Mask 1 and Mask 2. Analysis of the supernatants showed < 100 particles detected per sampling time for Mask 2, as opposed to ~ 200 and ~ 600 particles detected for Mask 1 and Mask 3 respectively. Interestingly, similar particle size distributions were observed for all facemasks (modes around ~ 60 nm), with Mask 2 showing slightly narrower range. However, due to the small number of particles detected for Mask 2, higher uncertainties are associated with the size distribution shown in Fig. 3 . The size distributions were fit using a multivariate lognormal distribution to account for the larger particle sizes detected. These particle sizes were not observed on the surface of the mask with the SEM analysis due to the limited image resolutions. However, it is important to note that projected aera-equivalent diameter is not equivalent to the volume-equivalent diameter obtained via SP-ICP-MS. A negligible number of particles was detected in the control samples and hence is not shown in Fig. 3 . Digestion and analysis of the agitated samples allows for a direct comparison with the original intact sample, providing better insights on the shedding potential of each facemask. Table 2 provides a comparison of the Ti mass fraction measured from digested samples of Mask 1, Mask 2 and Mask 3 before and after agitation. Only a small fraction of Ti (< 1%) could be displaced from Mask 1 and Mask 2, whereas about 53% of the Ti was found to be displaced from Mask 3. However, a high uncertainty is associated with the released portion due to the variability in measured Ti fraction between subsamples. Table 2 Average mass fractions (µg/g of mask) of Ti measured on the masks before and after 48 hours of agitation in ethanol and corresponding standard deviation (SD). Mask n Ti Mass fraction (original) ± SD [µg/g] Ti Mass fraction (after agitation) ± SD [µg/g] Portion released Mask 1, Replicate 2 3 4290 ± 860 4290 ± 690 < 1% Mask 2, Replicate 2 3 1660 ± 45 1680 ± 65 < 1% Mask 3, Replicate 2 3 80 ± 6 43 ± 7 ~ 53% Since liquid extraction would represent an upper limit for particle release 18 – 20 , these results imply a low airborne shedding potential of TiO 2 . 2.4 In-situ shedding during physical agitation The particle number concentration obtained by the downstream CPC for each test performed (as summarized in Table 4 ) was averaged across the duration of the test period and is shown, in Fig. 4 a and Fig. 4 b without and with inline agitation respectively, as a standalone test or an average of 2 to 4 tests performed (with associated standard deviation). As can be seen in the examples provided for Test 9 and Test 10, shedding was not observed continuously. Instead, an intermittent particle release was noted with varying concentrations between tests. Minimal shedding was observed (< 0.1 #/cm 3 ) under control conditions (continuous airflow with no inline agitation) for all facemasks tested. With the addition of inline agitation, a slight increase in particle count was noted for the Control 1, while a negligible number of particles was measured for Control 2. The highest concentrations were found for Mask 1 (average of 4 tests) and Mask 3 (1 test only) indicating a significant increase compared to conditions without agitation. Size distributions for Mask 1, Mask 2, Mask 3 and Control 2 under constant flow with inline agitation, as measured by the SMPS and OPC simultaneously, are shown in Fig. 5 integrated over the entire test period. These results again highlight the sporadic nature of the shedding observed. The majority of the particles detected were found generally in sizes below 50 nm, with varying particle concentrations in time. Note the number concentrations for Mask 2, which were found comparable to Control 2. For all tests performed, the larger particle counts and size distributions, as measured by the OPS, were found consistently below 1 #/cm 3 and thus are considered negligible. Characterization of the particles collected on PVC filters for Mask 1 with inline agitation using ICP-MS, after the complete digestion of the filter and particles, did not show the presence of Ti in any of the samples above the limit of detection. PVC filters collected from the 4-hour tests performed with Mask 1 without and with inline agitation (Test 9 and Test 10 respectively) were analyzed with STEM-EDX to investigate the composition of the particles collected. Consistent with the average particle number concentrations, an inspection of the filter surface revealed no detectable particles without agitation, whereas a limited number of particles (~ 20) were observed with the addition of inline agitation. Figure 6 shows images of three representative particles observed on the PVC filter from Test 10. EDX was performed across the ROI, through the particles and its surroundings, to provide a profile of the elements detected. The EDX analysis did not detect the presence of TiO 2 particles. The majority of the particles analyzed contained Si, Cu or Ca with two particles showing minimal levels of Mg. From these elements detected, only a small number of Si-containing particles were found on the surface of the facemasks. As no particles containing Ca or Cu were previously detected on the surface of the facemask, it remains unclear whether such particles originate from the mask itself or result from contamination during handling. Additionally, it is possible that the contact between the vibration motors and the mask may have caused particle release via physical abrasion, although such abrasion may still be representative of some real-world scenarios such as mask donning and mishandling. However, abrasion is expected to produce micron-sized particles, where only minimal concentrations were observed. Although, a limited number of detected particles were analyzed, the results, in conjunction with the total filter characterization performed using ICP-MS, suggest that minimal shedding would occur, even under extreme and unrealistic agitation conditions. The shedding potential is expected to decrease with the number of layers of the facemask, assuming the particles are only located on its most outer layer. 3 Discussion Due to the varying nature of the airborne shedding observed, definitive conclusions could not be drawn based on the three facemasks and repeats performed. Analyzing the facemasks selected, the highest and lowest levels of Ti were found for Mask 1 and Mask 3 respectively, with Mask 3 showing the highest number of TiO 2 particles released in liquid (representing ~ 50% of the mask content). Mask 2 showed high levels of Ti but a negligible number of TiO 2 particles released in liquid. Airborne shedding showed the highest nanoparticle concentration for Mask 3, with Mask 2 showing a negligible number of particles released. These results suggest that, although nanoparticles were detected on the surface of the facemask fibers, the released fraction, if any, would not be sufficient for comprehensive characterization. Moreover, considering the measured particle sizes, the mass fraction of the released particles is considered negligible. Our results align with the limited studies in the literature. Verleysen et al. 23 investigated the content of 12 facemasks for TiO 2 and Ag nanomaterials, using a similar approach to the one described in our study. The authors combined ICP-OES analysis to quantify the total amount of TiO 2 (ranging from 791 to 152,345 µg per mask) and TEM analysis to determine the particle fraction on the fiber surface (~ 2 to 4% of the particles detected). They reported 17 to 4394 µg per mask of TiO 2 available at the surface of the facemasks. Our findings are not directly comparable with the study of Verleysen et al. considering the different techniques used for the mask characterization. in this study, the titanium mass fraction analyzed by ICP-MS was quantified only in the outer layer, considering the SEM-EDX analysis performed prior. However, adopting a similar analysis, where only 2–4% of the particles are available on the fiber surface and all Ti is present as TiO 2 , we expect TiO 2 levels of approximately 1002 µg, 330 µg and 53 µg for each of Mask 1, Mask 2, and Mask 3, respectively (based on the weights reported in Table 3 ), which is within the range of levels reported by 23 . Montalvo et al. 24 further investigated the release of Ag-based biocides and TiO 2 particles from the same face masks analyzed in Verleysen et al. 23 , via leaching in artificial sweat. Out of 10 facemasks analyzed via ICP-MS, only 2 facemasks showed detectable Ag levels in the leachates, while Ti was detected for 1 facemask only. The Ti mass fraction leached (5.5–8.4 µg/g for two replicates) is comparable to our findings with levels ranging from ~ 1 to 37 µg/g in the supernatant of samples from Mask 1 and Mask 3 respectively. To our knowledge, this study is the first to report direct airborne shedding from facemasks providing released particle concentrations and composition and therefore cannot be directly compared to the literature. However, Mast et al. 27 reported an attempt to quantify airborne shedding from three replicates of three facemasks confirmed to contain TiO 2 and Ag 23 , on a Sheffield headform and breathing apparatus, following the guidelines outlines in the EN 149:2001 + A1:2009 standard testing procedure for respiratory protective devices. Although particles were detected on all samples, large variations were found between replicates and samples. When compared to experiments performed with a control facemask, no TiO 2 above the baseline measurements were detected. These conclusions are similar to our findings for airborne shedding where, although particles are observed, Ti levels were below our detection limits, for all techniques employed. Conclusions from our work and the literature, seems to indicate that nanomaterial shedding or resuspension from the different types of facemasks analyzed, would not likely occur under the tested conditions. Specifically, our analysis performed with NaCl loaded Control 2 facemasks during the experimental validation, detailed in the SI, shows insignificant resuspension (less than 0.6 particles resuspended per million particles in the mask). This is in agreement with multiple studies investigating the occurrence and mechanism of submicron ( 1 µm) particle shedding from textiles and fibrous materials. Particles depositing onto filter material will adhere by van der Waals forces, electrostatic forces or capillary forces 36 , which depends on the filter material, particle size and humidity levels. These particles can potentially shed if external forces are applied, such as high airflow or mechanical agitation, exceeding the adhesion force. However, extreme scenarios seem to be required for this to occur. Qian et al. 36 investigated the resuspension of polystyrene latex spheres, sodium chloride, corn oil and dust (ranging from 0.6–5.1 µm in aerodynamic diameter) from three types of filters – a respirator cartridge (glass fiber filter) and two half mask respirators (polypropylene filter) - by subjecting each sample to a maximum air velocity of 500 cm/s. The particles were detected downstream of the filter material using a combination of an Amherst Process Instruments (API) Aerosizer and a photometer. At the maximum air velocity tested, particle resuspension was found to be negligible (~ 0.3%) for particles below 1 µm and increased to 17% for the largest particles tested. The authors also report a minimum entrainment velocity of 130 cm/s to detect particles below 1 µm. Similar findings were reported by 37 when comparing shedding of inert particles with bacterial aerosol particles from N95 respirators, in which resuspension up to 0.025% for particles of 0.8 µm at 300 cm/s was observed. Fisher et al. 38 report a maximum of 0.21% MS2 bacteriophage resuspension (as a droplet and droplet nuclei) under cyclic flow. Other studies further investigated particle release from filter material beyond air currents such as material stretching or mishandling (drop from different heights), and report similar conclusions with a negligible fraction of particle released. The limited evidence from this study, corroborated with resuspension studies in the literature, demonstrate that the particle release from facemasks, and therefore inhalation exposure to TiO 2 , is potentially negligible. However, it is crucial to expand on these findings by testing a broader range of facemasks containing different MNMs with multiple repeats considering the variability in the results observed. 4 Methods 4.1 Facemask selection A survey of commercially available facemasks on the market was performed to identify specific masks claiming to either provide “antimicrobial” properties, provide “self-cleaning” capabilities or simply contain nanomaterials. Most commercially available masks surveyed claimed to contain Ag, with a small number of masks containing TiO 2 , ZnO, SiO or CuO. We selected three masks claiming to contain TiO 2 referred to herein as Mask 1, Mask 2 and Mask 3, all of which were general purpose facemasks available to consumers. The breakdown of the layers in these masks is provided in Table 1 , with images of the masks available in the supplemental information (SI, S1 Fig). Table 3 Description of selected Mask 1, 2 and 3. Layer 1 refers to the material facing outward from the wearer, while the highest layer refers to the layer in contact with the wearer’s face. Facemask Type Weight ± SD (g) * Layers Mask 1 general purpose facemasks Disposable 3.42 ± 0.02 Layer 1: SB non-woven PP (outermost) Layer 2: MB non-woven PP Layer 3: MB non-woven PP Layer 4: SB non-woven PP (innermost) Mask 2 general purpose facemasks Disposable 3.09 ± 0.02 Layer 1: SB non-woven PP Layer 2: MB non-woven PP Layer 3: SB non-woven PP Mask 3 general purpose facemasks Reusable 10.58 ± 0.04 Layer 1: Not disclosed Layer 2: Activated carbon Layer 3: Electrostatic Mesh Layer 4: MB non-woven PP Layer 5: Not disclosed Layer 6: Cotton layer Control 1 Surgical mask Disposable 2.95 ± 0.02 Layer 1: SB non-woven PP Layer 2: MB non-woven PP Layer 3: SB non-woven PP Control 2 general purpose facemasks Reusable 2.39 ± 0.02 Layer: Nanospun non-woven PVDF, PLGA/PAN BFC: Barrier face covering, SB: Spunbond, MB: Meltblown, PP: polypropylene, PVDF: Polyvinylidene fluoride, PLGA: poly(lactic-co-glycolic acid), PAN: Polyacrylonitrile * Reported weight is based on measurements of three replicates of each facemask. Two additional facemasks with no claims of TiO 2 presence, were selected as control samples. The first control facemask (Control 1) represents a generic 3-layer surgical facemask while the second facemask (Control 2) represents a 1-layer non-woven nanofiber mask. The selected face masks were analyzed to determine the content, particle size, composition and location (layer of the face mask) of TiO 2 particles in the masks, as well as their shedding potential. 4.2 Facemask characterization 4.2.1 Surface characterization Each layer of all facemasks (with the expectation of layers 3–5 of Mask 3) were analyzed using scanning electron microscopy 15 and further analyzed with energy dispersive X-ray (EDX) where particles were observed. For this purpose, the layers of each facemask were separated and cut into 100 mm × 100 mm samples, which were imaged on both sides (outer and inner facing). To minimize charging effects on the sample due to an accumulation of charge from the electron beam, carbon was sputter-coated on each sample prior to SEM, resulting in a 10–25 nm coating. The samples were visualized using high resolution SEM (S-4800, Hitachi Ltd., Japan) for large scale images from 3.6 by 2.5 mm down to 84 by 60 µm. For further characterization, ultrahigh resolution SEM (S-5500 Hitachi Ltd., Japan), coupled with EDX analysis, was performed on smaller sample areas of 84 × 60 to 50 × 35 µm. EDX elemental mapping was also performed simultaneously in some instances, to determine the element distribution across the scanned area. Image analysis, using ImageJ software (National Institutes of Health, USA), was performed on several SEM images to obtain a size distribution of observed particles available on the surface of each facemask. For this purpose, most particles were outlined with an ellipsoid, with the exception of large irregular particles observed, which were outlined following their shape. Size distributions were obtained based on minimum feret diameter and the projected area-equivalent diameter calculated from the projected area of the particle. 4.2.2 Analysis of dissolved and particulate TiO 2 by (ICP-MS) For the total metal content, samples were acid-digested as described elsewhere 28 . Briefly, an accurately weighed portion of mask (10 mg) was digested in 2 mL of concentrated nitric acid (HNO 3 ) and 4 mL concentrated sulfuric acid (H 2 SO 4 ) in a closed microwave system (Multiwave 7000, Anton Parr GmbH, Austria) using the following digestion program: 15 min ramp to 280°C followed by a hold period of 60 min at 280°C. Each sample was digested in triplicate and each digestion cycle contained at least one method blank and one certified reference material (SRM 1898 – Titanium dioxide nanomaterial). Digested samples were diluted to a final HNO 3 acid concentration of 2% and analyzed using an Agilent 8900 ICM-MS/MS (Agilent Technologies, Santa Clara, CA, USA) introduced using an Agilent SPS 4 autosampler with a cover (Agilent Technologies, Santa Clara, CA, USA). The instrument was equipped with a standard sample introduction system consisting of a MircoMist glass concentric nebulizer, a quartz spray chamber, and a quartz torch with 2.5 mm id injector. The interface was equipped with a nickel-plated copper sampling cone and nickel skimmer cone. The instrument was operated in MS/MS mode using a mixed cell gas containing oxygen (O 2 ) and hydrogen (H 2 ) for detection of Ti. The method was applied to resolve the isobaric interferences, mainly arising from 48 Ca and the matrix-based polyatomic interferences, such as those derived from C, S, and P. Q1 was set to m/z 48 (the mass of the precursor 48 Ti + ion) and Q2 was set to m/z 64 (the mass of the target product ion 48 Ti 16 O + ). The introduction of O 2 in the reaction/collision cell led to formation of 48 Ti 16 O + product ion, and added H 2 facilitated formation of 48 Ca 16 O 1 H + , thereby eliminating interference on 48 Ti 16 O + by 48 Ca 16 O + . The instrument was optimized daily for maximum sensitivity and stability with cerium oxide ratios of < 1% and doubly charged ions ( 70 Ce + / 140 Ce ++ ) < 2%. An online internal standard of scandium (Sc) and rhodium 17 was continuously mixed with calibration standards and samples during the analysis. Monitored Sc isotope ( m/z 45 → 61) and Rh isotope ( m/z 103) were used to compensate for possible instrument instability and matrix effects by calculating the ratio between the m/z of the element of interest and the internal standard. Quantitation was performed using the external calibration method; quality control samples of medium concentration, as well as blank, were measured every 13 samples. For characterization of particle shedding potential by leaching, three accurately weighed samples from each facemask (10 mg) were placed in a vial containing 30 mL of ethanol. The samples were agitated on a rotary shaker (Roto-Shake Genie, Scientific industries Inc., USA) for 48 hours. The supernatant was collected from each sample, evaporated to near dryness, reconstituted in 10 mL of MilliQ water and analyzed by ICP-MS in single particle mode (SP-ICP-MS). The instrument’s introduction system was identical to the one used for dissolved metal analysis with the exception of a quartz torch with 1.0 mm id injector. The analysis was performed in time-resolved analysis (fast TRA) mode, using a dwell time of 0.1 ms per point without settling time between measurements. The flow rate was measured at the start and end of each sequence and was typically between 0.30 to 0.35 mL min − 1 . The instrument was operated in the same MS/MS mode as for total metal analysis and optimization was performed the same way. The raw data were exported and processed with the SPCal software (version 1.3.2) 29 using automatic threshold detection with 5-sigma criteria for Gaussian filtering and Formula C for Poisson filtering. The remaining mask samples (after shaking) were dried and digested for analysis of their remaining Ti content, following the methodology outlined above. 4.3 Particle shedding 4.3.1 Experimental setup Particle shedding was measured by making modifications to the custom-built system 30 , 31 used previously for particle number-based filtration efficiency and pressure resistance measurements of various facemasks 32 , 33 . The experimental setup consisted of a testing chamber; a pair of condensation particle counters (CPCs Model 3752 and Model 3750, TSI Inc., USA), placed one before and one after the testing chamber; a scanning mobility particle sizer (SMPS), which consists of an electrostatic classifier (Model 3082, TSI Inc., USA), an aerosol neutralizer (Model 3088, TSI Inc., USA) and a CPC (Model 3752 and Model 3750, TSI Inc., USA), placed after the testing chamber; and a vacuum pump which drew HEPA filtered air through the system. The mask samples were sealed to a mounting plate with an O-ring. The plate and facemask samples were mounted in the testing chamber with the outer side of the mask facing the incoming air to mimic the direction of air flow from inhalation during mask use. The relative humidity and temperature were maintained at 40 ± 10% and 21 ± 2 ºC, respectively, in the chamber. Clean and humidified air, filtered through a set of HEPA filters, traversed the testing chamber. The upstream particles were sampled with the first CPC, while the particles downstream were sampled with the second CPC, SMPS and an optical particle sizer (Model 3330, TSI Inc., USA) accounting for a broad range of sizes from 5 nm to 10 µm. The flow rate was controlled via a mass flow controller (EL-Flow, Bronkhorst, Netherlands) and was maintained at 50 ± 5 L/min. Background measurements (without a mask on the mounting plate and for a control mask) were performed prior to each sample measurement day. Intensive inline mask agitation (vibration) of the sample was also implemented using two vibration motors (10 × 3 mm, stainless steel, 12000 RPM) placed on the inner surface of the mask within the testing chamber, as shown in Fig. 7 . Each vibration motor was placed onto the surface of the mask using magnets, ensuring a rapid connection and minimizing damage to the surface of the facemask. The vibration was controlled via a voltage adjuster allowing a vibration frequency of up to 200 Hz (cycles/sec). This high agitation frequency does not represent the agitation of a facemask during typical breathing, where a normal breathing rate of 10–20 breaths per minutes corresponds to a breathing frequency of 0.16–0.33 Hz, but rather provides an upper limit for potential particle release. Such agitation could also be understood to represent the agitation that occurs in a person’s pocket or during other mishandling of a mask. 4.3.2 Procedure and particle collection Unless otherwise stated, all tests were performed with the outer layer of each mask only, facing the incoming air, to avoid variability due to inconsistency between the number of layers in each mask. Prior to testing, the seams of each mask were cut to release the pleats and separate the mask layers. A blank test (no mask in the holder) was performed with and without vibration at the beginning of each measurement day, providing a baseline to all instruments. Once the facemask was sealed in the testing chamber, humidified filtered air (~ 40% relative humidity) was passed at a constant flow of 50 L/min for a test duration ranging between 20 min to 4 h. All mask samples were then tested without further manipulation. Shed particles were continuously monitored using a CPC for small particle sizes below 3 µm, a SMPS (1 minute scan) for small particle sizing below 1 µm and an OPS (1 minute collection) for larger particle sizing and counting (> 300 nm to 10 µm). The remaining particles were further collected on Polyvinyl chloride (PVC) membrane filters, with a 5 µm nominal pore size (Millipore Sigma, USA) for metal content analysis using ICP-MS (following the same digestion procedure outlined in Section 4.2.2) and/or STEM-EDX Analysis. Although a large nominal pore size was used, the PVC filters were shown to have high collection efficiencies at different particle sizes 35 . TEM grids collecting the shed particles were not assessed in this study due to the low particle concentration < 4% loading on the grids. The complete list of all tests performed is detailed in Table 4 . Table 4 List of experiments performed, detailing the different experimental conditions for each test. Test Facemask Duration (min) Vibration Analysis 1 Control 1 (x2) 20 No - 2 Control 1 (x2) 20 Yes - 3 Control 1, 3 layers 20 Yes - 4 Control 2 (x2) 20 No - 5 Control 2 (x2) 20 Yes - 6 Mask 1 20 No ICP-MS 7 Mask 1 (x2) 20 Yes ICP-MS 8 Mask 1, 4 layers 20 Yes ICP-MS 9 Mask 1 240 No STEM-EDX 10 Mask 1 240 Yes STEM-EDX 11 Mask 1 60 Yes SP-ICP-MS 12 Mask 2 20 Yes SP-ICP-MS 13 Mask 3 20 Yes SP-ICP-MS The air upstream was monitored via a CPC to ensure no room air contamination is present in the system. The apparatus (counting and sizing instruments) was validated using a sodium chloride loaded Control 2 facemask (detailed in the SI) and shown to effectively capture a small portion of the loaded particles. 5 Conclusions Three facemasks claimed to contain TiO 2 , were characterized and analyzed under constant air flow for potential MNM release. We demonstrated and quantified the presence of TiO 2 on the outer layer of each facemask with variable and high mass fractions detected for Mask 1 and Mask 2, which was found to be within the same range of previous studies. TiO 2 particles detected on all facemasks showed similar size distributions on the surface of the facemask or collected from the supernatant after 48h of agitation in liquid ethanol. The method for in-situ shedding outlined in this study enables the evaluation of facemasks under a worst-case scenario by testing a single particle-containing layer, under continuous flow and allowing for vigorous agitation. The three masks selected were subsequently tested under the stated conditions. Results demonstrated that continuous flow alone was not sufficient to dislodge particles, while particles below 100 nm were detected with concurrent inline agitation for Mask 1 and Mask 3 only. Further analysis of the shed particles did not indicate the presence of TiO 2 , but showed the presence of Ca, Cu and Si containing particles, with no high aspect ratio fibres detected. At a minimum, this study provides evidence that dislodging particles from the masks is difficult and that resuspension of either particles added to the mask or captured by the mask is unlikely. Definitive conclusions remain challenging, given that the low rates of particle shedding make airborne measurement challenging. This combined with the potentially high toxicity of inhaled nanomaterials adds uncertainties to risk assessments. Nevertheless, the low TiO 2 shedding potential from facemasks in this work adds to the body of evidence relating to inhalation exposure to MNM indicating that shedding is unlikely. Declarations Competing interests The authors declare no competing interests. Author Contribution R.M, Z.G, T.S, G.S and A.B contributed to the conceptualization of the study. R.M and Z.G performed the investigation and data analysis. R.M wrote the original draft and all authors reviewed the manuscript. Acknowledgement We would like to thank the Kai Cui and Mark Salomons from the NRC's Quantum and Nanotechnologies Research Centre microscopy facility for all STEM imaging and EDX analysis. We would also like to thank Chase Sun for his help in implementing the inline agitation. This work was funded by the New Substances Assessment and Control Bureau, Health Canada. Data Availability The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request. 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Supplementary Files S1File.pdf S1 File. Supplemental information to “Quantification and characterization of manufactured nanomaterials shed from face masks”. Cite Share Download PDF Status: Published Journal Publication published 03 Feb, 2026 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 23 Jul, 2025 Reviews received at journal 20 Jul, 2025 Reviews received at journal 04 Jul, 2025 Reviewers agreed at journal 04 Jul, 2025 Reviewers agreed at journal 02 Jul, 2025 Reviewers invited by journal 02 Jul, 2025 Editor assigned by journal 02 Jul, 2025 Editor invited by journal 30 Jun, 2025 Submission checks completed at journal 30 Jun, 2025 First submitted to journal 28 Jun, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6995325","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":480072746,"identity":"8f87a09f-8e1f-4db3-b271-e4118526509b","order_by":0,"name":"Rym Mehri","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7ElEQVRIiWNgGAWjYPCCAwxs7A0ka+E5QKoWBokEItWaz8hOYLpRcSefT/LtsQ8/GOzyzNsPML8AMuRxaZG5kbuBOefMM8s26bzkmT0MycUyZxLYLIEMwwYcWiQkgFpy2w4bsEnnGDMz/juQOEOCgc0Y6FRG/Fr+AbVInjFmBqqEa7HHr6UBqEWCB66F+TGIgVMLz9sNh3OOAbXw5BgzAr2QOIMnsY2xxyA5GacW9tyNj3NqDhvIt58xZgAGVOIM9sOHP/yosLPFpYVBIAEUKSiAsU2CwQCXeiDgR9cABMwf8GgYBaNgFIyCkQcAa+hOrnAjboAAAAAASUVORK5CYII=","orcid":"","institution":"National Research Council Canada","correspondingAuthor":true,"prefix":"","firstName":"Rym","middleName":"","lastName":"Mehri","suffix":""},{"id":480072747,"identity":"a9b60bb2-43d2-4231-a9be-fd22ca68defe","order_by":1,"name":"Zuzana Gajdosechova","email":"","orcid":"","institution":"National Research Council Canada","correspondingAuthor":false,"prefix":"","firstName":"Zuzana","middleName":"","lastName":"Gajdosechova","suffix":""},{"id":480072748,"identity":"e3775f36-38df-4d2a-89ba-59af251ec250","order_by":2,"name":"Timothy A. 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The corresponding sum spectrum of the EDX elemental mapping is shown in (c), (f) and (i) for Mask 1, Mask 2 and Mask 3 respectively.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/b744fe45d4494996cbbb11ce.png"},{"id":86001740,"identity":"9c03b9a4-0992-4db3-b846-e91073f91f17","added_by":"auto","created_at":"2025-07-04 07:40:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":179172,"visible":true,"origin":"","legend":"\u003cp\u003eParticle size distribution for Mask 1, Mask 2 and Mask 3 as a function of the projected area-equivalent diameter (left panel) and minimum feret diameter (right panel), with corresponding lognormal distribution fit to the data. These results are compared size distributions of agglomerated TiO\u003csub\u003e2\u003c/sub\u003e particles obtained by Verleysen et al. \u003csup\u003e23\u003c/sup\u003e for 10 facemasks.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/e1a8e74e0c2a1401db026e58.png"},{"id":86000504,"identity":"c0ff8056-d59f-4528-9d58-233ae990596f","added_by":"auto","created_at":"2025-07-04 07:25:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":136408,"visible":true,"origin":"","legend":"\u003cp\u003eSize distribution of TiO\u003csub\u003e2\u003c/sub\u003enanomaterials detected by single particle ICP-MS in Mask 1, Mask 2 and Mask 3.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/d4d1f6aebe3785644978ec37.png"},{"id":86000480,"identity":"dda5cf02-8c70-4183-87b1-4d1b6a2d721d","added_by":"auto","created_at":"2025-07-04 07:24:58","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":170539,"visible":true,"origin":"","legend":"\u003cp\u003eParticle number concentration obtained from average measurements of each test performed in Table 4for both control facemasks and all three facemasks tested (a) without and (b) with inline agitation (vibration). The inset time series show example test runs for each case.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/5870b08f84f9b69bcfb61650.png"},{"id":86000482,"identity":"cf2dcc79-1be8-46f9-8449-c0c1048c4432","added_by":"auto","created_at":"2025-07-04 07:24:58","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":203817,"visible":true,"origin":"","legend":"\u003cp\u003eNumber size distribution in time for Mask 1, Mask 2 and Mask 3 tested under constant flow with inline agitation, as measured by SMPS (left panel) and OPS (right panel). SMPS size distributions were fitted using a lognormal distribution.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/38676c68a79766bb6c04ed35.png"},{"id":86000488,"identity":"a006210b-9846-4314-b1aa-2fe088e2b6b4","added_by":"auto","created_at":"2025-07-04 07:24:58","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":480037,"visible":true,"origin":"","legend":"\u003cp\u003eSTEM images and EDX line spectrum for three representative particles observed on the PVC filter, collected from Mask 1 under constant flow and inline agitation (Test 10). Particles were found to contain mostly Ca, Cu or Si, while no TiO\u003csub\u003e2\u003c/sub\u003e particles were detected.\u0026nbsp;\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/21d882a0cf2f859d5ac443f7.png"},{"id":86000484,"identity":"01a133e1-8add-472e-97c5-d35ac80587e2","added_by":"auto","created_at":"2025-07-04 07:24:58","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":315062,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental setup for particle release in air. The setup is based on a custom-built system used for particle filtration efficiency measurements but is modified to accommodate for particle detection downstream using a condensation particle counter (CPC), a scanning mobility particle sizer (SMPS), an optical particle sizer \u003csup\u003e34\u003c/sup\u003e and a filter sampler for all particle collection. MFC: mass flow controller, PVC: polyvinyl chloride.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/5ba777a27e649f2fb0a52b26.png"},{"id":102234080,"identity":"b49c28c4-d027-4cea-9589-734c178b17c0","added_by":"auto","created_at":"2026-02-09 16:05:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3066418,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/cf810a0d-f281-4834-a33f-c6fad3a82413.pdf"},{"id":86001741,"identity":"3b8e27de-3295-40d1-b86c-517b1a5ddded","added_by":"auto","created_at":"2025-07-04 07:40:59","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":438525,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eS1 File\u003c/strong\u003e. Supplemental information to “Quantification and characterization of manufactured nanomaterials shed from face masks”.\u003c/p\u003e","description":"","filename":"S1File.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6995325/v1/513d9f1e0c3018855cf340a3.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Quantification and characterization of manufactured nanomaterials shed from face masks","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eDue to their capabilities and the growing need for high quality personal protective equipment during the Covid-19 pandemic, nanomaterials have been incorporated into face masks to enhance their microbiocidal activity \u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e and are found either blended into polymeric fibers or are coated on the surface of the fibers. Among the most commonly used nanomaterials in facemasks are nanoscale silver (Ag), nanoscale zinc oxide (ZnO), nanoscale copper oxide (CuO), and nanoscale titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e) \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Due to their photocatalytic properties, TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles, which are the focus of this study, have been shown to exhibit microbiocidal activity when exposed to light, due to the generation of reactive oxygen species. Discussions related to the mechanism of nanoparticle microbiocidal activities can be found in \u003csup\u003e\u003cspan additionalcitationids=\"CR8 CR9 CR10 CR11 CR12\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe addition of these nanomaterials to facemasks raises the concern of their release (shedding) during normal or extended wear, causing a potential risk of exposure by inhalation to the wearer, which is currently not well elucidated. The inhalation of nanomaterials may cause adverse health effects, such as inflammation, oxidative stress, and lung damage \u003csup\u003e\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Therefore, it is important to assess the potential release of nanomaterials from these facemasks.\u003c/p\u003e \u003cp\u003eMost studies across the literature evaluated microplastic and nanoplastic release from facemasks, rather than metal-containing particle release, reporting mixed results. A recent review by Kisielinski et al. \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e compiled the results of multiple studies investigating the release of fibers, fiber components and chemical compounds from facemasks. The authors report a significant portion of microplastics and nanoplastics to be potentially released, with N95-certified products showing a consistently higher released fraction during leaching compared to surgical facemasks, largely attributed to the higher number of layers associated with N95 products. Studies on the release of such components are often performed via leaching \u003csup\u003e\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, representing an upper limit for particle release. Only a few studies have investigated this release in breathing-like apparatuses \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e to simulate inhalation exposure. Li et al. \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e investigated particle release in air from different types of facemasks under constant airflow, in an environment with no contamination control for a duration of 2\u0026ndash;720 hours. The authors observed an increase in the fiber released count with time and disinfection processes, except for N95 masks, which in general, showed lower fiber release. Further analysis using Raman spectroscopy showed that the particles collected consisted of 12% silica and 42% confirmed microplastics with size ranging from 20\u0026ndash;100 \u0026micro;m. Meier et al. 2022 \u003csup\u003e20\u003c/sup\u003e investigated the release of fibers from facemasks over 8 hours using a breathing apparatus (Sheffield Head), with multiple donning and doffing and compared their findings to the fraction released liquid-based extractions. The authors found that under sinusoidal airflow, the fibers released from all masks were low, ranging between 6 to 24 fibres/g of mask. The number of fibers released slightly increased by a factor of 1.5 to 12.5 for different mask types when exposed to mechanical stress from donning and doffing. The number of fibers released using the breathing apparatus represented about 0.1 to 1.1% the fraction of liquid-based extractions for all masks tested.\u003c/p\u003e \u003cp\u003eThe above-mentioned studies and references within Kisielinski et al. mainly focused on the detection of volatile organic compound and microplastics/nanoplastics released from facemasks. However, little work has been performed to address manufactured nanomaterial release from facemasks. Bussan et al. \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e investigated multiple surgical and K95 facemasks for release of trace elements via leaching and from airflow under vacuum. While most facemasks tested were found not to contain trace elements (i.e. were below the method\u0026rsquo;s detection limit), a few facemasks were shown to contain traces of copper, antimony, zinc, and lead, where the latter (Pb) leached to ~\u0026thinsp;60% after 6h. In a comprehensive study, Verleysen et al. \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e demonstrated, via scanning transmission electron microscopy coupled with energy dispersive X-ray (STEM-EDX) and inductively coupled plasma optical emission spectroscopy (ICP-OES), the presence of TiO\u003csub\u003e2\u003c/sub\u003e from various facemasks tested, with contents ranging from 17 to 4394 \u0026micro;g per mask available at the surface of the fibers, and median particle sizes ranging from 89 to 189 nm. A follow-up study by Montalvo et al. \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e investigated the release of Ag-based biocides and TiO\u003csub\u003e2\u003c/sub\u003e particles via leaching in artificial sweat. While Ag was released in amounts up to 36% of available Ag on the masks, TiO\u003csub\u003e2\u003c/sub\u003e was found in minimal amounts (0.35% of available Ti on the facemasks) in the released fraction. Similarly, Meier et al. \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, Suwanroek et al. \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e and Pollard et al. \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e evaluated the leaching of multiple metals and metal oxides in multiple solutions (deionized water, detergent and artificial saliva), which were found to vary with mask and solution. These leached amounts represent a worst-case scenario for exposure estimates and may not be realistic for estimating the potential for inhalation.\u003c/p\u003e \u003cp\u003eTo our knowledge, there are currently no published studies reporting direct measurements of airborne shedding of component MNMs from commercial mask products accounting for the inhalable portion, which is crucial to support risk assessments with more realistic inhalation uptake and exposure estimates. Some attempts have been reported \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e to address this issue, however, no conclusions could be drawn from the experiments performed, due to the large variability in results observed.\u003c/p\u003e \u003cp\u003eIn this work, we performed an exploratory study to investigate potential airborne particle shedding from three different facemask products, all claimed to contain TiO\u003csub\u003e2\u003c/sub\u003e. We first characterized and quantified nanomaterials and metal content for each mask, which were subsequently tested for shedding using a custom-built setup, under controlled conditions and constant flow. Shed particles were analyzed based on their number, size and composition.\u003c/p\u003e"},{"header":"2 Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Surface characterization and compositional analysis\u003c/h2\u003e \u003cp\u003eFollowing the methodology proposed in Section 4.2.1, all layers of each facemask were imaged with SEM (with the exception of layers 3\u0026ndash;5 of Mask 3), with EDX performed on the detected particles. Particles were observed on all outer layers of the mask as well as the 1st middle layer of Mask 3 (identified as a carbon filter) and the inner layer of Mask 1. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (panels a, d and g) show a low magnification of the outer layers of Mask 1, Mask 2 and Mask 3, respectively. Higher magnifications of these samples are shown in panels b, e and h with the elemental Ti map overlaid, showing the Ti distribution within the region of interest (ROI), outlined with a black box. Panels a, d and g show the corresponding EDX sum spectrum, representing the sum of all individual pixel spectra in the ROI.\u003c/p\u003e \u003cp\u003eAll layers displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e show a similar fiber network, characteristic of a non-woven spunbonded layer with approximate fiber dimeters of 16 \u0026micro;m, 20 \u0026micro;m and 30 \u0026micro;m for Mask 1, Mask 2 and Mask 3 respectively. Overall, the EDX analysis (spot analysis or elemental mapping) showed that the majority of particles observed on the outer layers contained Ti and O, with some particles containing Ag and Si occasionally found on the surface of Mask 2 and Mask 3 respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe particle size distribution for Mask 1, Mask 2 and Mask 3 (outer layer only), based on a total of 358, 250 and 355 particles, respectively, is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e as a function of the projected area-equivalent diameter. A lognormal distribution was fit to the data obtained. Similar distributions were observed for Masks 1 and 3, with larger particles detected for Mask 3 (modes: 0.52 \u0026micro;m and 0.79 \u0026micro;m for Mask 1 and Mask 3 respectively). This is mainly due to the presence of a Ti-coated layer observed on the fibers (e.g Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh). This further corroborates the Mask 3 manufacturer\u0026rsquo;s claim of containing an outer layer TiO\u003csub\u003e2\u003c/sub\u003e coating. However, since no further details were provided regarding the coating material nor the coating process, no further conclusions could be drawn. Whereas a range of particle sizes were detected on the outer layers of Masks 1 and 3, a narrower size distribution was found for Mask 2 (mode: 0.37 \u0026micro;m), where the majority of the particles were found below 1 \u0026micro;m.\u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the obtained particle size distributions as a function of the minimum feret diameter are compared to the findings of Verleysen et al. \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. In their study, Verleysen et al. analyzed 12 samples using a high-angle annular-dark-field scanning transmission electron microscope (HAADF-STEM) to image particles (agglomerates) detected within the fiber cross-section. Size distributions from Verleysen et al. for 10 of the 12 samples (outer layer only), were fitted using a lognormal distribution and compared to our findings.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn general, narrower particles size distributions were found by Verleysen et al. for most samples with modes ranging between 0.1 to 0.3 \u0026micro;m. This difference stems from the different techniques and sample preparation used for imaging. In our study, since a small area of the outer layer of the facemask was imaged by SEM, as opposed to a thin cross-sectional area of the fibers imaged by HAADF-STEM for Verleysen et al., the resolution was constrained by the pixel size which was 10to 50 nm depending on the magnification used. Therefore, no particles below ~\u0026thinsp;100 nm were included in this study due to the large uncertainties associated with the small particle sizes detected. The morphology of particles was not further assessed to distinguish between single particles or agglomerated particles as it is beyond the scope of this study.\u003c/p\u003e \u003cp\u003eAnalyzing the inner layers of the facemasks (S2 Fig), particles were only clearly detected on Mask 2. EDX performed on the particles detected, did not show the presence of TiO\u003csub\u003e2\u003c/sub\u003e in Mask 2. Consequently, the subsequent analysis mainly focused on the outer layer of the facemasks.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Total Ti content\u003c/h2\u003e \u003cp\u003eAnalysis of the digested mask samples by ICP-MS revealed the presence of Ti in all studied facemasks, with varying quantities detected. The mass fractions of Ti per g of facemask is provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e for all replicates as an average of 3\u0026ndash;5 samples with corresponding standard deviation (SD). Mask 1 was found to have the highest content of Ti per g of mask, and hence was considered to be a good candidate for the subsequent shedding experiments. However, it should be noted that the mass fraction of Ti in this mask, is associated with high relative standard deviation (RSD, representing the ratio of the standard deviation to the mean) between subsamples of the same mask (range 19% \u0026minus;\u0026thinsp;43%, n\u0026thinsp;=\u0026thinsp;5). This suggests that the TiO\u003csub\u003e2\u003c/sub\u003e coating of the mask fiber is not homogeneous although the RSD of total mass fraction of Ti among the replicates of mask 1 is within 9%. On the other hand, the TiO\u003csub\u003e2\u003c/sub\u003e coating on mask 2 seemed to be homogeneous (RSD range 3% \u0026minus;\u0026thinsp;5%, n\u0026thinsp;=\u0026thinsp;3), but noticeable differences were observed among the mask replicates (RSD 16%). Mask 3 contained the lowest mass fraction of Ti and a large RSD was observed within the studied subsamples (range 7% \u0026minus;\u0026thinsp;35%, n\u0026thinsp;=\u0026thinsp;4) as well as among the mask replicates (RSD 38%). Ti was found in Control 1, with similar mass fractions to Mask 3.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAverage Ti mass fractions with associated standard deviation (SD).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTi Mass fraction\u0026thinsp;\u0026plusmn;\u0026thinsp;SD [\u0026micro;g/g]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 1, Replicate 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4070\u0026thinsp;\u0026plusmn;\u0026thinsp;770\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 1, Replicate 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4290\u0026thinsp;\u0026plusmn;\u0026thinsp;860\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 1, Replicate 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4870\u0026thinsp;\u0026plusmn;\u0026thinsp;2105\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 2, Replicate 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2200\u0026thinsp;\u0026plusmn;\u0026thinsp;73\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 2, Replicate 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1660\u0026thinsp;\u0026plusmn;\u0026thinsp;45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 2, Replicate 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2230\u0026thinsp;\u0026plusmn;\u0026thinsp;110\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 3, Replicate 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e160\u0026thinsp;\u0026plusmn;\u0026thinsp;28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 3, Replicate 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e80\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 3, Replicate 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e95\u0026thinsp;\u0026plusmn;\u0026thinsp;34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eControl 1, Replicate 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e183\u0026thinsp;\u0026plusmn;\u0026thinsp;34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eControl 1, Replicate 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e217\u0026thinsp;\u0026plusmn;\u0026thinsp;62\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eControl 1, Replicate 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e186\u0026thinsp;\u0026plusmn;\u0026thinsp;44\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eControl 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLOD\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003eLOD: below limit of detection, SD: standard deviation\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003en: Number of subsamples for each replicate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Particle release in liquid\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the particle size distribution of the released TiO\u003csub\u003e2\u003c/sub\u003e particles in liquid (after 48h of agitation) analyzed using SP-ICP-MS for Mask 1, Mask 2 and Mask 3. A visual inspection of the supernatant revealed a discernable amount of fiber released from Mask 3, compared to Mask 1 and Mask 2. Analysis of the supernatants showed\u0026thinsp;\u0026lt;\u0026thinsp;100 particles detected per sampling time for Mask 2, as opposed to ~\u0026thinsp;200 and ~\u0026thinsp;600 particles detected for Mask 1 and Mask 3 respectively. Interestingly, similar particle size distributions were observed for all facemasks (modes around ~\u0026thinsp;60 nm), with Mask 2 showing slightly narrower range. However, due to the small number of particles detected for Mask 2, higher uncertainties are associated with the size distribution shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The size distributions were fit using a multivariate lognormal distribution to account for the larger particle sizes detected. These particle sizes were not observed on the surface of the mask with the SEM analysis due to the limited image resolutions. However, it is important to note that projected aera-equivalent diameter is not equivalent to the volume-equivalent diameter obtained via SP-ICP-MS. A negligible number of particles was detected in the control samples and hence is not shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDigestion and analysis of the agitated samples allows for a direct comparison with the original intact sample, providing better insights on the shedding potential of each facemask. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e provides a comparison of the Ti mass fraction measured from digested samples of Mask 1, Mask 2 and Mask 3 before and after agitation. Only a small fraction of Ti (\u0026lt;\u0026thinsp;1%) could be displaced from Mask 1 and Mask 2, whereas about 53% of the Ti was found to be displaced from Mask 3. However, a high uncertainty is associated with the released portion due to the variability in measured Ti fraction between subsamples.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAverage mass fractions (\u0026micro;g/g of mask) of Ti measured on the masks before and after 48 hours of agitation in ethanol and corresponding standard deviation (SD).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTi Mass fraction (original)\u0026thinsp;\u0026plusmn;\u0026thinsp;SD [\u0026micro;g/g]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTi Mass fraction (after agitation)\u0026thinsp;\u0026plusmn;\u0026thinsp;SD [\u0026micro;g/g]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePortion released\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 1, Replicate 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e4290\u0026thinsp;\u0026plusmn;\u0026thinsp;860\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e4290\u0026thinsp;\u0026plusmn;\u0026thinsp;690\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;1%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 2, Replicate 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1660\u0026thinsp;\u0026plusmn;\u0026thinsp;45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1680\u0026thinsp;\u0026plusmn;\u0026thinsp;65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;1%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMask 3, Replicate 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e80\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e43\u0026thinsp;\u0026plusmn;\u0026thinsp;7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e~\u0026thinsp;53%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSince liquid extraction would represent an upper limit for particle release \u003csup\u003e\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, these results imply a low airborne shedding potential of TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 In-situ shedding during physical agitation\u003c/h2\u003e \u003cp\u003eThe particle number concentration obtained by the downstream CPC for each test performed (as summarized in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) was averaged across the duration of the test period and is shown, in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb without and with inline agitation respectively, as a standalone test or an average of 2 to 4 tests performed (with associated standard deviation). As can be seen in the examples provided for Test 9 and Test 10, shedding was not observed continuously. Instead, an intermittent particle release was noted with varying concentrations between tests.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMinimal shedding was observed (\u0026lt;\u0026thinsp;0.1 #/cm\u003csup\u003e3\u003c/sup\u003e) under control conditions (continuous airflow with no inline agitation) for all facemasks tested. With the addition of inline agitation, a slight increase in particle count was noted for the Control 1, while a negligible number of particles was measured for Control 2. The highest concentrations were found for Mask 1 (average of 4 tests) and Mask 3 (1 test only) indicating a significant increase compared to conditions without agitation. Size distributions for Mask 1, Mask 2, Mask 3 and Control 2 under constant flow with inline agitation, as measured by the SMPS and OPC simultaneously, are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e integrated over the entire test period. These results again highlight the sporadic nature of the shedding observed. The majority of the particles detected were found generally in sizes below 50 nm, with varying particle concentrations in time. Note the number concentrations for Mask 2, which were found comparable to Control 2. For all tests performed, the larger particle counts and size distributions, as measured by the OPS, were found consistently below 1 #/cm\u003csup\u003e3\u003c/sup\u003e and thus are considered negligible.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCharacterization of the particles collected on PVC filters for Mask 1 with inline agitation using ICP-MS, after the complete digestion of the filter and particles, did not show the presence of Ti in any of the samples above the limit of detection.\u003c/p\u003e \u003cp\u003ePVC filters collected from the 4-hour tests performed with Mask 1 without and with inline agitation (Test 9 and Test 10 respectively) were analyzed with STEM-EDX to investigate the composition of the particles collected. Consistent with the average particle number concentrations, an inspection of the filter surface revealed no detectable particles without agitation, whereas a limited number of particles (~\u0026thinsp;20) were observed with the addition of inline agitation. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows images of three representative particles observed on the PVC filter from Test 10. EDX was performed across the ROI, through the particles and its surroundings, to provide a profile of the elements detected. The EDX analysis did not detect the presence of TiO\u003csub\u003e2\u003c/sub\u003e particles. The majority of the particles analyzed contained Si, Cu or Ca with two particles showing minimal levels of Mg. From these elements detected, only a small number of Si-containing particles were found on the surface of the facemasks. As no particles containing Ca or Cu were previously detected on the surface of the facemask, it remains unclear whether such particles originate from the mask itself or result from contamination during handling. Additionally, it is possible that the contact between the vibration motors and the mask may have caused particle release via physical abrasion, although such abrasion may still be representative of some real-world scenarios such as mask donning and mishandling. However, abrasion is expected to produce micron-sized particles, where only minimal concentrations were observed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAlthough, a limited number of detected particles were analyzed, the results, in conjunction with the total filter characterization performed using ICP-MS, suggest that minimal shedding would occur, even under extreme and unrealistic agitation conditions. The shedding potential is expected to decrease with the number of layers of the facemask, assuming the particles are only located on its most outer layer.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Discussion","content":"\u003cp\u003eDue to the varying nature of the airborne shedding observed, definitive conclusions could not be drawn based on the three facemasks and repeats performed. Analyzing the facemasks selected, the highest and lowest levels of Ti were found for Mask 1 and Mask 3 respectively, with Mask 3 showing the highest number of TiO\u003csub\u003e2\u003c/sub\u003e particles released in liquid (representing\u0026thinsp;~\u0026thinsp;50% of the mask content). Mask 2 showed high levels of Ti but a negligible number of TiO\u003csub\u003e2\u003c/sub\u003e particles released in liquid. Airborne shedding showed the highest nanoparticle concentration for Mask 3, with Mask 2 showing a negligible number of particles released. These results suggest that, although nanoparticles were detected on the surface of the facemask fibers, the released fraction, if any, would not be sufficient for comprehensive characterization. Moreover, considering the measured particle sizes, the mass fraction of the released particles is considered negligible.\u003c/p\u003e \u003cp\u003eOur results align with the limited studies in the literature. Verleysen et al. \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e investigated the content of 12 facemasks for TiO\u003csub\u003e2\u003c/sub\u003e and Ag nanomaterials, using a similar approach to the one described in our study. The authors combined ICP-OES analysis to quantify the total amount of TiO\u003csub\u003e2\u003c/sub\u003e (ranging from 791 to 152,345 \u0026micro;g per mask) and TEM analysis to determine the particle fraction on the fiber surface (~\u0026thinsp;2 to 4% of the particles detected). They reported 17 to 4394 \u0026micro;g per mask of TiO\u003csub\u003e2\u003c/sub\u003e available at the surface of the facemasks. Our findings are not directly comparable with the study of Verleysen et al. considering the different techniques used for the mask characterization. in this study, the titanium mass fraction analyzed by ICP-MS was quantified only in the outer layer, considering the SEM-EDX analysis performed prior. However, adopting a similar analysis, where only 2\u0026ndash;4% of the particles are available on the fiber surface and all Ti is present as TiO\u003csub\u003e2\u003c/sub\u003e, we expect TiO\u003csub\u003e2\u003c/sub\u003e levels of approximately 1002 \u0026micro;g, 330 \u0026micro;g and 53 \u0026micro;g for each of Mask 1, Mask 2, and Mask 3, respectively (based on the weights reported in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), which is within the range of levels reported by \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eMontalvo et al. \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e further investigated the release of Ag-based biocides and TiO\u003csub\u003e2\u003c/sub\u003e particles from the same face masks analyzed in Verleysen et al. \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, via leaching in artificial sweat. Out of 10 facemasks analyzed via ICP-MS, only 2 facemasks showed detectable Ag levels in the leachates, while Ti was detected for 1 facemask only. The Ti mass fraction leached (5.5\u0026ndash;8.4 \u0026micro;g/g for two replicates) is comparable to our findings with levels ranging from ~\u0026thinsp;1 to 37 \u0026micro;g/g in the supernatant of samples from Mask 1 and Mask 3 respectively.\u003c/p\u003e \u003cp\u003eTo our knowledge, this study is the first to report direct airborne shedding from facemasks providing released particle concentrations and composition and therefore cannot be directly compared to the literature. However, Mast et al. \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e reported an attempt to quantify airborne shedding from three replicates of three facemasks confirmed to contain TiO\u003csub\u003e2\u003c/sub\u003e and Ag \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, on a Sheffield headform and breathing apparatus, following the guidelines outlines in the EN 149:2001\u0026thinsp;+\u0026thinsp;A1:2009 standard testing procedure for respiratory protective devices. Although particles were detected on all samples, large variations were found between replicates and samples. When compared to experiments performed with a control facemask, no TiO\u003csub\u003e2\u003c/sub\u003e above the baseline measurements were detected. These conclusions are similar to our findings for airborne shedding where, although particles are observed, Ti levels were below our detection limits, for all techniques employed.\u003c/p\u003e \u003cp\u003eConclusions from our work and the literature, seems to indicate that nanomaterial shedding or resuspension from the different types of facemasks analyzed, would not likely occur under the tested conditions. Specifically, our analysis performed with NaCl loaded Control 2 facemasks during the experimental validation, detailed in the SI, shows insignificant resuspension (less than 0.6 particles resuspended per million particles in the mask). This is in agreement with multiple studies investigating the occurrence and mechanism of submicron (\u0026lt;\u0026thinsp;1 \u0026micro;m) and supermicron (\u0026gt;\u0026thinsp;1 \u0026micro;m) particle shedding from textiles and fibrous materials. Particles depositing onto filter material will adhere by van der Waals forces, electrostatic forces or capillary forces \u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, which depends on the filter material, particle size and humidity levels. These particles can potentially shed if external forces are applied, such as high airflow or mechanical agitation, exceeding the adhesion force. However, extreme scenarios seem to be required for this to occur.\u003c/p\u003e \u003cp\u003eQian et al. \u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e investigated the resuspension of polystyrene latex spheres, sodium chloride, corn oil and dust (ranging from 0.6\u0026ndash;5.1 \u0026micro;m in aerodynamic diameter) from three types of filters \u0026ndash; a respirator cartridge (glass fiber filter) and two half mask respirators (polypropylene filter) - by subjecting each sample to a maximum air velocity of 500 cm/s. The particles were detected downstream of the filter material using a combination of an Amherst Process Instruments (API) Aerosizer and a photometer. At the maximum air velocity tested, particle resuspension was found to be negligible (~\u0026thinsp;0.3%) for particles below 1 \u0026micro;m and increased to 17% for the largest particles tested. The authors also report a minimum entrainment velocity of 130 cm/s to detect particles below 1 \u0026micro;m. Similar findings were reported by \u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e when comparing shedding of inert particles with bacterial aerosol particles from N95 respirators, in which resuspension up to 0.025% for particles of 0.8 \u0026micro;m at 300 cm/s was observed. Fisher et al. \u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e report a maximum of 0.21% MS2 bacteriophage resuspension (as a droplet and droplet nuclei) under cyclic flow.\u003c/p\u003e \u003cp\u003eOther studies further investigated particle release from filter material beyond air currents such as material stretching or mishandling (drop from different heights), and report similar conclusions with a negligible fraction of particle released.\u003c/p\u003e \u003cp\u003eThe limited evidence from this study, corroborated with resuspension studies in the literature, demonstrate that the particle release from facemasks, and therefore inhalation exposure to TiO\u003csub\u003e2\u003c/sub\u003e, is potentially negligible. However, it is crucial to expand on these findings by testing a broader range of facemasks containing different MNMs with multiple repeats considering the variability in the results observed.\u003c/p\u003e"},{"header":"4 Methods","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Facemask selection\u003c/h2\u003e \u003cp\u003eA survey of commercially available facemasks on the market was performed to identify specific masks claiming to either provide \u0026ldquo;antimicrobial\u0026rdquo; properties, provide \u0026ldquo;self-cleaning\u0026rdquo; capabilities or simply contain nanomaterials. Most commercially available masks surveyed claimed to contain Ag, with a small number of masks containing TiO\u003csub\u003e2\u003c/sub\u003e, ZnO, SiO or CuO. We selected three masks claiming to contain TiO\u003csub\u003e2\u003c/sub\u003ereferred to herein as Mask 1, Mask 2 and Mask 3, all of which were general purpose facemasks available to consumers. The breakdown of the layers in these masks is provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, with images of the masks available in the supplemental information (SI, S1 Fig).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDescription of selected Mask 1, 2 and 3. Layer 1 refers to the material facing outward from the wearer, while the highest layer refers to the layer in contact with the wearer\u0026rsquo;s face.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFacemask\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWeight\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (g)\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayers\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eMask 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003egeneral purpose facemasks\u003c/p\u003e \u003cp\u003eDisposable\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e3.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 1: SB non-woven PP (outermost)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 2: MB non-woven PP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 3: MB non-woven PP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 4: SB non-woven PP (innermost)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eMask 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003egeneral purpose facemasks Disposable\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3.09\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 1: SB non-woven PP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 2: MB non-woven PP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 3: SB non-woven PP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003eMask 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003egeneral purpose facemasks Reusable\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e10.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 1: Not disclosed\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 2: Activated carbon\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 3: Electrostatic Mesh\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 4: MB non-woven PP\u003c/p\u003e \u003cp\u003eLayer 5: Not disclosed\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 6: Cotton layer\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eControl 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSurgical mask\u003c/p\u003e \u003cp\u003eDisposable\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e2.95\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 1: SB non-woven PP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 2: MB non-woven PP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer 3: SB non-woven PP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eControl 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003egeneral purpose facemasks\u003c/p\u003e \u003cp\u003eReusable\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e2.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLayer: Nanospun non-woven PVDF, PLGA/PAN\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eBFC: Barrier face covering, SB: Spunbond, MB: Meltblown, PP: polypropylene, PVDF: Polyvinylidene fluoride, PLGA: poly(lactic-co-glycolic acid), PAN: Polyacrylonitrile\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003e*\u003c/sup\u003eReported weight is based on measurements of three replicates of each facemask.\u003c/p\u003e \u003cp\u003eTwo additional facemasks with no claims of TiO\u003csub\u003e2\u003c/sub\u003e presence, were selected as control samples. The first control facemask (Control 1) represents a generic 3-layer surgical facemask while the second facemask (Control 2) represents a 1-layer non-woven nanofiber mask. The selected face masks were analyzed to determine the content, particle size, composition and location (layer of the face mask) of TiO\u003csub\u003e2\u003c/sub\u003e particles in the masks, as well as their shedding potential.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Facemask characterization\u003c/h2\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e4.2.1 Surface characterization\u003c/h2\u003e \u003cp\u003eEach layer of all facemasks (with the expectation of layers 3\u0026ndash;5 of Mask 3) were analyzed using scanning electron microscopy \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e and further analyzed with energy dispersive X-ray (EDX) where particles were observed. For this purpose, the layers of each facemask were separated and cut into 100 mm \u0026times; 100 mm samples, which were imaged on both sides (outer and inner facing).\u003c/p\u003e \u003cp\u003eTo minimize charging effects on the sample due to an accumulation of charge from the electron beam, carbon was sputter-coated on each sample prior to SEM, resulting in a 10\u0026ndash;25 nm coating. The samples were visualized using high resolution SEM (S-4800, Hitachi Ltd., Japan) for large scale images from 3.6 by 2.5 mm down to 84 by 60 \u0026micro;m. For further characterization, ultrahigh resolution SEM (S-5500 Hitachi Ltd., Japan), coupled with EDX analysis, was performed on smaller sample areas of 84 \u0026times; 60 to 50 \u0026times; 35 \u0026micro;m. EDX elemental mapping was also performed simultaneously in some instances, to determine the element distribution across the scanned area.\u003c/p\u003e \u003cp\u003eImage analysis, using ImageJ software (National Institutes of Health, USA), was performed on several SEM images to obtain a size distribution of observed particles available on the surface of each facemask. For this purpose, most particles were outlined with an ellipsoid, with the exception of large irregular particles observed, which were outlined following their shape. Size distributions were obtained based on minimum feret diameter and the projected area-equivalent diameter calculated from the projected area of the particle.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e4.2.2 Analysis of dissolved and particulate TiO\u003csub\u003e2\u003c/sub\u003e by (ICP-MS)\u003c/h2\u003e \u003cp\u003eFor the total metal content, samples were acid-digested as described elsewhere \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Briefly, an accurately weighed portion of mask (10 mg) was digested in 2 mL of concentrated nitric acid (HNO\u003csub\u003e3\u003c/sub\u003e) and 4 mL concentrated sulfuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e) in a closed microwave system (Multiwave 7000, Anton Parr GmbH, Austria) using the following digestion program: 15 min ramp to 280\u0026deg;C followed by a hold period of 60 min at 280\u0026deg;C. Each sample was digested in triplicate and each digestion cycle contained at least one method blank and one certified reference material (SRM 1898 \u0026ndash; Titanium dioxide nanomaterial).\u003c/p\u003e \u003cp\u003eDigested samples were diluted to a final HNO\u003csub\u003e3\u003c/sub\u003e acid concentration of 2% and analyzed using an Agilent 8900 ICM-MS/MS (Agilent Technologies, Santa Clara, CA, USA) introduced using an Agilent SPS 4 autosampler with a cover (Agilent Technologies, Santa Clara, CA, USA). The instrument was equipped with a standard sample introduction system consisting of a MircoMist glass concentric nebulizer, a quartz spray chamber, and a quartz torch with 2.5 mm id injector. The interface was equipped with a nickel-plated copper sampling cone and nickel skimmer cone. The instrument was operated in MS/MS mode using a mixed cell gas containing oxygen (O\u003csub\u003e2\u003c/sub\u003e) and hydrogen (H\u003csub\u003e2\u003c/sub\u003e) for detection of Ti. The method was applied to resolve the isobaric interferences, mainly arising from \u003csup\u003e48\u003c/sup\u003eCa and the matrix-based polyatomic interferences, such as those derived from C, S, and P. Q1 was set to \u003cem\u003em/z\u003c/em\u003e 48 (the mass of the precursor \u003csup\u003e48\u003c/sup\u003eTi\u003csup\u003e+\u003c/sup\u003e ion) and Q2 was set to \u003cem\u003em/z\u003c/em\u003e 64 (the mass of the target product ion \u003csup\u003e48\u003c/sup\u003eTi\u003csup\u003e16\u003c/sup\u003eO\u003csup\u003e+\u003c/sup\u003e). The introduction of O\u003csub\u003e2\u003c/sub\u003e in the reaction/collision cell led to formation of \u003csup\u003e48\u003c/sup\u003eTi\u003csup\u003e16\u003c/sup\u003eO\u003csup\u003e+\u003c/sup\u003e product ion, and added H\u003csub\u003e2\u003c/sub\u003e facilitated formation of \u003csup\u003e48\u003c/sup\u003eCa\u003csup\u003e16\u003c/sup\u003eO\u003csup\u003e1\u003c/sup\u003eH\u003csup\u003e+\u003c/sup\u003e, thereby eliminating interference on \u003csup\u003e48\u003c/sup\u003eTi\u003csup\u003e16\u003c/sup\u003eO\u003csup\u003e+\u003c/sup\u003e by \u003csup\u003e48\u003c/sup\u003eCa\u003csup\u003e16\u003c/sup\u003eO\u003csup\u003e+\u003c/sup\u003e. The instrument was optimized daily for maximum sensitivity and stability with cerium oxide ratios of \u0026lt;\u0026thinsp;1% and doubly charged ions (\u003csup\u003e70\u003c/sup\u003eCe\u003csup\u003e+\u003c/sup\u003e / \u003csup\u003e140\u003c/sup\u003eCe\u003csup\u003e++\u003c/sup\u003e)\u0026thinsp;\u0026lt;\u0026thinsp;2%. An online internal standard of scandium (Sc) and rhodium \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e was continuously mixed with calibration standards and samples during the analysis. Monitored Sc isotope (\u003cem\u003em/z\u003c/em\u003e 45 \u0026rarr; 61) and Rh isotope (\u003cem\u003em/z\u003c/em\u003e 103) were used to compensate for possible instrument instability and matrix effects by calculating the ratio between the \u003cem\u003em/z\u003c/em\u003e of the element of interest and the internal standard. Quantitation was performed using the external calibration method; quality control samples of medium concentration, as well as blank, were measured every 13 samples.\u003c/p\u003e \u003cp\u003eFor characterization of particle shedding potential by leaching, three accurately weighed samples from each facemask (10 mg) were placed in a vial containing 30 mL of ethanol. The samples were agitated on a rotary shaker (Roto-Shake Genie, Scientific industries Inc., USA) for 48 hours. The supernatant was collected from each sample, evaporated to near dryness, reconstituted in 10 mL of MilliQ water and analyzed by ICP-MS in single particle mode (SP-ICP-MS). The instrument\u0026rsquo;s introduction system was identical to the one used for dissolved metal analysis with the exception of a quartz torch with 1.0 mm id injector. The analysis was performed in time-resolved analysis (fast TRA) mode, using a dwell time of 0.1 ms per point without settling time between measurements. The flow rate was measured at the start and end of each sequence and was typically between 0.30 to 0.35 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The instrument was operated in the same MS/MS mode as for total metal analysis and optimization was performed the same way. The raw data were exported and processed with the SPCal software (version 1.3.2) \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e using automatic threshold detection with 5-sigma criteria for Gaussian filtering and Formula C for Poisson filtering.\u003c/p\u003e \u003cp\u003eThe remaining mask samples (after shaking) were dried and digested for analysis of their remaining Ti content, following the methodology outlined above.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Particle shedding\u003c/h2\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e4.3.1 Experimental setup\u003c/h2\u003e \u003cp\u003eParticle shedding was measured by making modifications to the custom-built system \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e used previously for particle number-based filtration efficiency and pressure resistance measurements of various facemasks \u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. The experimental setup consisted of a testing chamber; a pair of condensation particle counters (CPCs Model 3752 and Model 3750, TSI Inc., USA), placed one before and one after the testing chamber; a scanning mobility particle sizer (SMPS), which consists of an electrostatic classifier (Model 3082, TSI Inc., USA), an aerosol neutralizer (Model 3088, TSI Inc., USA) and a CPC (Model 3752 and Model 3750, TSI Inc., USA), placed after the testing chamber; and a vacuum pump which drew HEPA filtered air through the system. The mask samples were sealed to a mounting plate with an O-ring. The plate and facemask samples were mounted in the testing chamber with the outer side of the mask facing the incoming air to mimic the direction of air flow from inhalation during mask use. The relative humidity and temperature were maintained at 40\u0026thinsp;\u0026plusmn;\u0026thinsp;10% and 21\u0026thinsp;\u0026plusmn;\u0026thinsp;2 \u0026ordm;C, respectively, in the chamber. Clean and humidified air, filtered through a set of HEPA filters, traversed the testing chamber. The upstream particles were sampled with the first CPC, while the particles downstream were sampled with the second CPC, SMPS and an optical particle sizer (Model 3330, TSI Inc., USA) accounting for a broad range of sizes from 5 nm to 10 \u0026micro;m. The flow rate was controlled via a mass flow controller (EL-Flow, Bronkhorst, Netherlands) and was maintained at 50\u0026thinsp;\u0026plusmn;\u0026thinsp;5 L/min. Background measurements (without a mask on the mounting plate and for a control mask) were performed prior to each sample measurement day.\u003c/p\u003e \u003cp\u003eIntensive inline mask agitation (vibration) of the sample was also implemented using two vibration motors (10 \u0026times; 3 mm, stainless steel, 12000 RPM) placed on the inner surface of the mask within the testing chamber, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Each vibration motor was placed onto the surface of the mask using magnets, ensuring a rapid connection and minimizing damage to the surface of the facemask. The vibration was controlled via a voltage adjuster allowing a vibration frequency of up to 200 Hz (cycles/sec).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis high agitation frequency does not represent the agitation of a facemask during typical breathing, where a normal breathing rate of 10\u0026ndash;20 breaths per minutes corresponds to a breathing frequency of 0.16\u0026ndash;0.33 Hz, but rather provides an upper limit for potential particle release. Such agitation could also be understood to represent the agitation that occurs in a person\u0026rsquo;s pocket or during other mishandling of a mask.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e4.3.2 Procedure and particle collection\u003c/h2\u003e \u003cp\u003eUnless otherwise stated, all tests were performed with the outer layer of each mask only, facing the incoming air, to avoid variability due to inconsistency between the number of layers in each mask. Prior to testing, the seams of each mask were cut to release the pleats and separate the mask layers.\u003c/p\u003e \u003cp\u003eA blank test (no mask in the holder) was performed with and without vibration at the beginning of each measurement day, providing a baseline to all instruments. Once the facemask was sealed in the testing chamber, humidified filtered air (~\u0026thinsp;40% relative humidity) was passed at a constant flow of 50 L/min for a test duration ranging between 20 min to 4 h. All mask samples were then tested without further manipulation. Shed particles were continuously monitored using a CPC for small particle sizes below 3 \u0026micro;m, a SMPS (1 minute scan) for small particle sizing below 1 \u0026micro;m and an OPS (1 minute collection) for larger particle sizing and counting (\u0026gt;\u0026thinsp;300 nm to 10 \u0026micro;m). The remaining particles were further collected on Polyvinyl chloride (PVC) membrane filters, with a 5 \u0026micro;m nominal pore size (Millipore Sigma, USA) for metal content analysis using ICP-MS (following the same digestion procedure outlined in Section 4.2.2) and/or STEM-EDX Analysis. Although a large nominal pore size was used, the PVC filters were shown to have high collection efficiencies at different particle sizes \u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTEM grids collecting the shed particles were not assessed in this study due to the low particle concentration\u0026thinsp;\u0026lt;\u0026thinsp;4% loading on the grids. The complete list of all tests performed is detailed in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eList of experiments performed, detailing the different experimental conditions for each test.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTest\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFacemask\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDuration (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eVibration\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAnalysis\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl 1 (x2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl 1 (x2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl 1, 3 layers\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl 2 (x2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl 2 (x2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMask 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eICP-MS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMask 1 (x2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eICP-MS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMask 1, 4 layers\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eICP-MS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMask 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSTEM-EDX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMask 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSTEM-EDX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMask 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSP-ICP-MS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMask 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSP-ICP-MS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMask 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSP-ICP-MS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe air upstream was monitored via a CPC to ensure no room air contamination is present in the system. The apparatus (counting and sizing instruments) was validated using a sodium chloride loaded Control 2 facemask (detailed in the SI) and shown to effectively capture a small portion of the loaded particles.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eThree facemasks claimed to contain TiO\u003csub\u003e2\u003c/sub\u003e, were characterized and analyzed under constant air flow for potential MNM release. We demonstrated and quantified the presence of TiO\u003csub\u003e2\u003c/sub\u003e on the outer layer of each facemask with variable and high mass fractions detected for Mask 1 and Mask 2, which was found to be within the same range of previous studies. TiO\u003csub\u003e2\u003c/sub\u003e particles detected on all facemasks showed similar size distributions on the surface of the facemask or collected from the supernatant after 48h of agitation in liquid ethanol.\u003c/p\u003e \u003cp\u003eThe method for in-situ shedding outlined in this study enables the evaluation of facemasks under a worst-case scenario by testing a single particle-containing layer, under continuous flow and allowing for vigorous agitation.\u003c/p\u003e \u003cp\u003eThe three masks selected were subsequently tested under the stated conditions. Results demonstrated that continuous flow alone was not sufficient to dislodge particles, while particles below 100 nm were detected with concurrent inline agitation for Mask 1 and Mask 3 only. Further analysis of the shed particles did not indicate the presence of TiO\u003csub\u003e2\u003c/sub\u003e, but showed the presence of Ca, Cu and Si containing particles, with no high aspect ratio fibres detected. At a minimum, this study provides evidence that dislodging particles from the masks is difficult and that resuspension of either particles added to the mask or captured by the mask is unlikely.\u003c/p\u003e \u003cp\u003eDefinitive conclusions remain challenging, given that the low rates of particle shedding make airborne measurement challenging. This combined with the potentially high toxicity of inhaled nanomaterials adds uncertainties to risk assessments. Nevertheless, the low TiO\u003csub\u003e2\u003c/sub\u003e shedding potential from facemasks in this work adds to the body of evidence relating to inhalation exposure to MNM indicating that shedding is unlikely.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eR.M, Z.G, T.S, G.S and A.B contributed to the conceptualization of the study. R.M and Z.G performed the investigation and data analysis. R.M wrote the original draft and all authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe would like to thank the Kai Cui and Mark Salomons from the NRC's Quantum and Nanotechnologies Research Centre microscopy facility for all STEM imaging and EDX analysis. We would also like to thank Chase Sun for his help in implementing the inline agitation. This work was funded by the New Substances Assessment and Control Bureau, Health Canada.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003ePalmieri, V., De Maio, F., De Spirito, M. \u0026amp; Papi, M. 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Hyg.\u003c/em\u003e \u003cb\u003e56\u003c/b\u003e, 315\u0026ndash;325. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1093/annhyg/mer101\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1093/annhyg/mer101\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2012).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"particle shedding, facemask, manufactured nanomaterial, titanium dioxide, risk assessment","lastPublishedDoi":"10.21203/rs.3.rs-6995325/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6995325/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFace masks are an important public health measure whose use became wide-spread during the pandemic. Manufactured nanomaterials (MNMs) have been used in face masks to enhance their anti-microbial and self-cleaning properties. There is currently a gap in the literature on the shedding potential of MNMs as it relates to potential inhalation uptake.\u003c/p\u003e \u003cp\u003eThree face masks, containing titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e), were analyzed for their composition and particle shedding. The face masks were first analyzed to determine the mass fraction of TiO\u003csub\u003e2\u003c/sub\u003e and the composition of the particles detected. The face masks were then tested under continuous airflow with and without concurrent agitation. Particle shedding was quantified via multiple particle counters and sizers and captured on filters for additional analysis.\u003c/p\u003e \u003cp\u003eThe compositional analysis showed that all masks tested contained different levels of Ti, with TiO\u003csub\u003e2\u003c/sub\u003e particles observed at the surface of the fibers. Particle shedding was observed only for two of the masks with concurrent agitation. Further analysis of the shed particles did not indicate the presence of TiO\u003csub\u003e2\u003c/sub\u003e, but showed the presence of Si, Cu and Ca. This data adds to the body of evidence relating to inhalation uptake from shedding of MNMs and may inform future risk assessments.\u003c/p\u003e","manuscriptTitle":"Quantification and characterization of manufactured nanomaterials shed from face masks","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-04 07:24:53","doi":"10.21203/rs.3.rs-6995325/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-23T11:05:50+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-20T15:37:51+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-04T14:29:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"138435007121864559986558946067583926296","date":"2025-07-04T14:11:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"98415148513119956019838310767818458787","date":"2025-07-02T15:07:07+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-02T14:05:26+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-02T14:02:36+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-06-30T18:45:29+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-30T04:20:19+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-06-28T04:01:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"701d7802-801d-4bfd-af74-58a059c5f837","owner":[],"postedDate":"July 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":50979709,"name":"Earth and environmental sciences/Environmental sciences"},{"id":50979710,"name":"Health sciences/Health care"},{"id":50979711,"name":"Physical sciences/Materials science"},{"id":50979712,"name":"Biological sciences/Microbiology"},{"id":50979713,"name":"Physical sciences/Nanoscience and technology"}],"tags":[],"updatedAt":"2026-02-09T16:01:57+00:00","versionOfRecord":{"articleIdentity":"rs-6995325","link":"https://doi.org/10.1038/s41598-025-34482-6","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-02-03 15:57:52","publishedOnDateReadable":"February 3rd, 2026"},"versionCreatedAt":"2025-07-04 07:24:53","video":"","vorDoi":"10.1038/s41598-025-34482-6","vorDoiUrl":"https://doi.org/10.1038/s41598-025-34482-6","workflowStages":[]},"version":"v1","identity":"rs-6995325","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6995325","identity":"rs-6995325","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}