More Regulatory Control Required For Particles Found In Face Masks

Written by nature.com on August 30, 2022. Posted in Current News

A recent study of facemasks worn during the Covid pandemic showed that 70 percent of the examined face masks contained titanium dioxide in quantities ranging from 100 to 2000 mg kg⁻¹².

This suggests that TiO₂ is commonly applied in textiles of face masks, as in a wide variety of other textiles, e.g. to improve stability to ultraviolet light, as white colorant or as a matting agent^3,4.

In addition, to introduce new solutions to the challenges associated with the COVID-19 pandemic, textile companies are incorporating specific nanofiber, nanocomposite and nanoparticle technology into face masks^5,6.

Nanofibers containing TiO₂ nanoparticles have been produced to create antimicrobial filters⁷, also in combination with silver⁸ and graphene⁹. Coatings of TiO₂ nanoparticles on cotton fabric were applied for enhanced self-cleaning and antibacterial properties¹⁰.

In their recent opinion paper, Palmeiri et al.⁵ warn for the possible future consequences caused by a poorly regulated use of nanotechnology in textiles applied to improve the performance of face masks. In animal experiments, toxic effects were reported when TiO₂ particles were inhaled^11,12, as well as when they were ingested orally^13,14.

In 2017, the Risk Assessment Committee (RAC) of the European Chemical Agency (ECHA) reviewed the carcinogenic potential of TiO₂ and proposed to classify Titanium dioxide as Carc. 2, H351 (suspected human carcinogen)¹⁵ by inhalation. This CLP classification¹⁶ was adopted for titanium dioxide.

To evaluate whether the TiO₂ particles in face masks possibly present a health risk, their amounts, their physicochemical properties and their localization were analyzed in a selection of face masks. Supporting on these measurements, the amount of TiO₂ at the surface of the textile fibers was estimated and compared with the acceptable exposure level to TiO₂ by inhalation, expressed per mask (AEL_mask).

Although titanium dioxide (TiO₂) is a suspected human carcinogen when inhaled, fiber-grade TiO₂ (nano)particles were demonstrated in synthetic textile fibers of face masks intended for the general public. STEM-EDX analysis on sections of a variety of single use and reusable face masks visualized agglomerated near-spherical TiO₂ particles in non-woven fabrics, polyester, polyamide and bi-component fibers.

Median sizes of constituent particles ranged from 89 to 184 nm, implying an important fraction of nano-sized particles (< 100 nm). The total TiO₂ mass determined by ICP-OES ranged from 791 to 152,345 µg per mask. The estimated TiO₂ mass at the fiber surface ranged from 17 to 4394 µg, and systematically exceeded the acceptable exposure level to TiO₂ by inhalation (3.6 µg), determined based on a scenario where face masks are worn intensively.

No assumptions were made about the likelihood of the release of TiO₂ particles itself, since direct measurement of release and inhalation uptake when face masks are worn could not be assessed. The importance of wearing face masks against COVID-19 is unquestionable.

Even so, these results urge for in depth research of (nano)technology applications in textiles to avoid possible future consequences caused by a poorly regulated use and to implement regulatory standards phasing out or limiting the amount of TiO₂ particles, following the safe-by-design principle.

Twelve face masks meant to be worn by the general population and including both single-use (disposable) and re-usable masks were obtained from various suppliers in Belgium and the EU. The origin of the masks is worldwide. The selected masks consist of a variety of fibers, including synthetic fibers, such as polyester, polyamide and meltblown and thermobonded non-woven fabrics; and natural fibers, such as cotton (Table 1).

All masks are NIOSH uncertified, Mask04 and Mask07 have a CE logo; Mask03 and Mask07 are OEKO-TEX certified. Mask01, 04 and 05 are three ply type masks^17,18. Images of the examined masks are given as Supplementary Information 1.

Measurement of the total amount of titanium (Ti) in each face mask, as a proxy for the amount of TiO₂ particles, by inductively coupled plasma-optical emission spectroscopy (ICP-OES) showed that the amount of TiO₂ varied strongly, from 0.8 to 152 mg per mask (Table 1).

High angle annular dark field (HAADF)-scanning transmission electron microscopic (STEM) analysis of sections of the resin embedded face masks showed single and agglomerated constituent particles in synthetic fibers (Fig. 1a–c,e). The particles were observed in at least one layer of each examined face mask (Table 1 and Supplementary Information 2).

Energy dispersive X-ray spectroscopy (EDX) analysis confirmed that these particles consist of TiO₂ (Fig. 2 and Supplementary Information 3). A fraction of the TiO₂ particles was located at the surface of the fibers (Fig. 2b). TiO₂ particles were not observed in cotton fibers (Fig. 1d), in meltblown non-woven fabrics (Fig. 1f), and in some of the thermobonded non-woven fabrics (Table 1).

In general, the electron microscopy results confirm the ICP-OES measurements showing that the amount of TiO₂ particles was approximately a factor 10 lower in non-woven fabrics than in polyester and polyamide fibers.

Measurements of the size and shape (near-spherical morphology) of the constituent TiO₂ particles and agglomerates in the examined face masks (Table 1, Supplementary Information 4–6) show that, overall, the physicochemical properties of the TiO₂ particles in face masks are in agreement with the specifications of so-called fiber-grade TiO₂ applied in other textiles^19,20 and are similar to those of the E 171 food additive¹⁴.

Although the measured TiO₂ size distributions in the face masks do not all qualify the applied TiO₂ as nanomaterials according to the EC-definition²¹, each examined mask, besides Mask04, contained a notable fraction of nanoparticles (6% to 65%), requesting an appropriate risk analysis.

Because the hazard of inhaled TiO₂ particles is well documented^11,22,23, particularly exposure analysis is important for risk analysis. Exposure to TiO₂ (nano)particles in face masks, depends on their level of release. Migration of agglomerated TiO₂ particles completely incorporated in the fiber polymers of face masks can be excluded by theoretical considerations: only particles smaller than 5 nm can migrate in the polymers constituting the face masks²⁴.

Particles at the fiber surface might, however, be released when they are subjected to abrasion or to aerodynamic forces. Direct measurement of released particles is problematic because, to our knowledge, no standardized methods are available to determine whether particles are released from face masks during normal use, and which amount of TiO₂ is released. It is unknown if particles could be released as single particles, as agglomerates, as pieces of textile fibers containing agglomerates or a combination thereof, altering their fate.

Moreover, few literature data are available that provide information on desorption/erosion/abrasion of TiO₂ particles from TiO₂-containing fibers²⁵. Therefore, an indirect approach was applied comparing the mass of TiO₂ at the surface of the textile fibers of each mask with the mass of TiO₂ particles that can be inhaled without adverse effects, expressed per mask (AEL_mask).

This approach does not assume release of all particles at the fiber surface. It merely calculates which fraction of TiO₂ particles at the fiber surface has to be released to exceed the acceptable exposure level. Because the fate and release mechanisms of particles from face masks are currently unknown, no assumptions were made about the likelihood of the release of particles itself.

AEL_mask was estimated to be 3.6 µg using a threshold-based risk characterization for subchronic exposure with an intensive use scenario of face masks by the general adult population as described in Supplementary information 7. Lung inflammation was chosen as critical effect. A no observed adverse effect concentration of 0.5 mg/m³ was determined based on the repeated dose inhalation study with rats of Bermudez et al.¹² The risk was further characterized supporting on the approach to determine the professional acceptable exposure levels to TiO₂ nanoforms²⁶. The intensive use scenario assumed that 2 masks are worn over an 8-h period, with a recommended change of the masks every 4 h²⁷.

Furthermore, it was assumed that TiO₂ particles in the fiber matrix do not migrate and that only particles at the fiber surface can be released. The fraction (percentage) and the mass (µg) of TiO₂ particles at the fiber surface, were modelled assuming a homogenous particle distribution in the fibers as described in the methods section and Supplementary Information 9. This assumption is plausible because the TiO₂ particles are mixed with the fiber matrix during production and was confirmed by HAADF-STEM analysis.

For typical (near-)cylindrical synthetic fibers (polyester, polyamide and non-woven), percentages ranged from 2 to 4%. Estimated amounts of TiO₂ at the fiber surface per mask ranged from 17 to 4394 µg (Table 1). Because the structure of bi-component microfibers (Fig. 1c) results in a larger surface area²⁸, a correction factor was introduced resulting in higher percentages of particles at the surface (in the methods section and Supplementary Information 9).

Table 1 shows that for all examined face masks, the amount of TiO₂ particles at the surface of the textile fibers notably exceeds the AEL_mask. This systematic exceedance indicates that by applying an approach relying on conservative assumptions while uncertainties regarding hazard and exposure remain (Supplementary Information 7), a health risk cannot be ruled out when face masks containing polyester, polyamide, thermobonded non-woven and bi-component fibers, are used intensively.

Exceedance of the AEL_mask for reusable face masks is higher (87 to 1220 times) than for single use masks (5 to 11 times), implying that for the reusable masks uptake of only a very small percentage of the particles at the fiber surface may already pose a health risk. Reusable masks typically have higher TiO₂ amounts in the matrix, have a higher mass (more textile corresponds with more TiO₂), and have smaller mean fiber diameters than single use masks.

For all examined masks, the combined measurement uncertainty (k = 1) on the total mass of TiO₂ (Table 1, Supplementary Information 8) was larger than AEL_mask. Consequently, TiO₂ release in the order of AEL_mask, measured as the change in TiO₂ before and after wearing the mask, cannot be demonstrated since it falls within the uncertainty range of the total mass measurement.

Face mask have an important role in the measures against the COVID-19 pandemic¹. So far, no data are available that indicate that the possible risk associated with the presence of TiO₂ particles in face masks outweighs the benefits of wearing face masks as protection measure. That is why we do not call for people to stop wearing face masks. However, the warning of Palmeiri et al.⁵ for the possible future consequences caused by a poorly regulated use of nanotechnology in textiles should be extended to face masks where TiO₂ particles are applied conventionally, as a white colorant or as a matting agent, or to assure durability reducing polymer breakdown by ultraviolet light^3,4.

These properties are not critical for the functioning of face masks, and synthetic fibers suitable for face mask can be produced without TiO₂²⁹ as was observed in the layers of several masks (Table 1). Moreover, uncertainties regarding the genotoxicity of TiO₂ particles remain¹⁴. Therefore, these results urge for the implementation of regulatory standards phasing out or limiting the amount of TiO₂ particles, according to the ‘safe-by-design’ principle.

The applied approach allowed to assess one of the quality parameters of face masks quantitatively: the amount of TiO₂ at the fiber surface. Such quantitative parameter is important to evaluate the face masks present on the market, to develop product specifications and regulatory standards, and to produce better products.

In the course of this study, we identified several major challenges related to the analysis, characterization and risk assessment of TiO₂ in face masks, which go beyond the scope of the study: (i) In general, scientific data on the presence of (nano)particles in face masks, their characteristics, the exposure and the risks for the population is limited. (ii) Methodologies for characterizing TiO₂ particles in face masks are time consuming and expensive. (iii)

Even though this study focused on face masks intended for the general public, this does not exclude TiO₂ from being present in other types of masks containing synthetic fibers, such as medical masks, even when they are certified. The presented study on face masks for the general population should be extended to assess the potential health risks associated with the presence of TiO₂ particles in medical and personal protection equipment face masks and consequent occupational exposure. (iv)

The fate and release mechanisms of particles from face masks are currently unknown, e.g. particles could be released as single particles, as agglomerates, as pieces of fibers containing agglomerates or a combination thereof. Agglomerates are sensitive to changes in the environment such as pH, ionic strength, presence of proteins and motion of the carrier medium, and can de-agglomerate or agglomerate further depending on the environment^30,31.

While this induces complex behavior of nanoparticles in exposure scenarios and in tissue uptake and bio-distribution, influence on toxicity or biological responses remain poorly understood^30,32. (v)

Key information about the toxicity of TiO₂ particles is missing for risk assessment: data about the hazard (inhalation toxicity threshold) of the specific TiO₂ particles present in face masks should be determined in a robust, repeated dose inhalation study with fiber-grade TiO₂ particles.

Furthermore, more toxicity and epidemiological research is needed to assess the risk of vulnerable populations, especially children.

This is taken from a long document. Read the rest here: nature.com

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