Reusable masks promise protection, but new research reveals they can silently release toxic metals into waterways, raising urgent questions about their environmental cost.
Research: Washable face masks: an emerging source of metal and nanoparticle pollution in aquatic environments. Image credit: learesphoto/Shutterstock.com
Washable face masks marketed as containing metal nanoparticles are increasingly being used due to their touted antibacterial properties. recent papers environment and health reveals the other side of the story. These masks can be a source of metal contamination in the aquatic environment unless disposed of properly. This highlights the need for regulation throughout the lifecycle.
Metal nanoparticles accumulate and move through the aqueous system
Currently, tens of thousands of tons of metal nanoparticles (MNPs) are being produced. Comprised of metals such as silver (Ag) and copper (Cu), they have unique properties that make them useful in multiple medical, industrial, and consumer product environments.
Meanwhile, about 10 percent of the estimated 318 tons of MNP waste enters water bodies. they may experience There is bioaccumulation and transfer through the aquatic food chain, potentially leading to human exposure and adverse effects on human health.
Washable MNP-containing face masks have gained popularity during and after the recent coronavirus disease 2019 (COVID-19) pandemic due to their claims of better protection and longer duration of use. However, these masks can contribute to contamination with microplastics and released MNPs, especially due to exposure to detergents.
The authors of this paper performed an integrated assessment of the release of multiple MNPs and the fate of MNPs that were accidentally added to the product during manufacturing. This analysis may help understand their impact on human and ecosystem health.
There are 3 types of masks
This study evaluated three types of MNP-containing face masks marketed as containing Ag, Cu, and platinum (Pt) NPs. These different types of masks were obtained via e-commerce platforms for 5, 6, and 2 pieces, respectively. Everything was claimed to be reusable and washable.
These masks are composed of synthetic polymers produced using various metal or metalloid catalysts, so there is potential for inadvertent contamination by other particles. Additionally, additives such as flame retardants, pigments, and stabilizers often contain metals such as antimony, lead, and lead-cadmium compounds.
The ion and NP proportions of nine metals (Ag, Cu, Pt, arsenic, cadmium, chromium, nickel, lead (Pb), and antimony) were evaluated in the mask and 72-h leachate. To simulate natural leaching into water, the masks were exposed to ultrapure water and detergent solutions along with cleaning.
Initial surface electron microscopy (SEM) scans revealed that each mask contained primarily Ag and Cu, with the latter in some cases turning out to be copper sulfide. No Pt was detected in the Pt mask. Spectroscopic analysis confirmed that in addition to Ag and Cu, these masks contain other metals or metalloids such as chromium, nickel, lead, and antimony.
Leaching behavior
silver mask
In two of the five Ag masks, Ag was present at high levels of approximately 4000 ng/cm2 and 6,500 ng/cm2. These two released large amounts of Ag and Ag-NPs in both leaching scenarios.
At 72 h, the ionic Ag leachate measured 34% and 27% of the total Ag in ultrapure water, respectively. Ag-NPs constituted less than 0.5% of the leached Ag. In the detergent, 42% and 36% of the total Ag were released, respectively, and up to 2.7% of the leached Ag was in the NP form.
Ag masks also released Cu, with up to 42% of the total released into water and 47% into detergent. The release rate of Ag NPs decreased over time and finally reached a plateau at about 72 h.
with mask
Two of the six masks contained up to 1.7 × 106 ng/cm2 Cu mask. These masks leached more ionic Cu and Cu-NPs than the other masks, but the fraction of total Cu was less than the Ag or Pt masks.
Up to 0.44% of total copper was leached into water and up to 0.18% into detergent, respectively. In the first of these masks, Cu-NPs accounted for just less than 0.05% of the leached Cu, whereas in the second mask it was up to 5.6%.
These findings highlight the substantial variation between mask types and help explain the differences with previous reports suggesting higher Cu leaching.
These masks also contained silver. Water leaching released up to 24% of total Ag, while detergent released up to 14%. The leaching of Cu followed a similar trajectory as Ag.
Pt mask
The Pt mask contained no detectable Pt. This was probably due to undetectable morphology or label discrepancies, as also seen in some Ag or Cu masks, which do not contain as much of these metals as regular masks.
The Pt mask primarily contained 1,500 ng/cm2 of Ag, followed by much lower levels of antimony. Silver release by leaching in water was only up to 0.04% and in detergents up to 0.03%.
Up to 77% of the copper content was released into water and 32% into detergents. This is in contrast to the results of the other two masks, where detergent promoted copper release more than water.
The leaching behavior of Ag mainly depends on the amount retained in the mask fibers, but this was not the case for Cu. Here, both Ag and Pt masks released more Cu despite having lower total Cu content. This indicates that the release depends not only on the total metal content but also on the metal’s intrinsic properties and interaction with the mask matrix.
These results demonstrate that the release behavior does not depend solely on the bulk metal content, but is strongly influenced by metal-intrinsic properties and matrix interactions.
Magnitude of MNP in leachate
For all MNPs, immersion in detergent was associated with larger average MNP size than water. This is likely due to the surfactant-like nature of MNPs and the inherent thermodynamic instability that favors their growth.
The authors propose a model for particle migration and coalescence based on analysis of particle size distribution over time. However, there is not enough data to definitively establish this, and the mechanism remains speculative.
Other metals in the mask
Multiple metals were detected in all types of masks, and in some cases (e.g., Pt masks) metals other than the labeled component dominated the composition. These unintentionally added metals are not tightly bound to the mask fibers and can easily leach out.
Prolonged immersion leaches out all metal ions and MNPs. Antimony is more easily leached out in ultrapure water, and in most cases this is facilitated by cleaning agents.
Among the ionic metals, antimony had the highest concentration in the leachate, likely reflecting its high abundance and leachability in water. Other ions, chromium, lead, and nickel, were more leached into detergents.
Conversely, antimony NP levels were comparable to those of other unintentionally introduced metals. The detergent leachate contained larger particles of all metals and MNPs than the water leachate.
The authors also assessed the correlation between the leaching behavior of multiple metals and the simultaneous release of multiple metals, rather than a direct causal relationship to environmental risk. Cu and Pb are correlated with NP leachate concentration, suggesting that they occur together and are released together within the mask fiber during fabrication. The release pattern of NPs depends on both the specific metal and the leaching medium.
environmental hazards
Based on release scenarios modeled under defined assumptions, the researchers predict that most metals will leach into water at concentrations exceeding acceptable limits for drinking water, and for copper and antimony, exceeding acceptable limits for industrial wastewater. These concentrations exceed the algae toxicity thresholds for Ag and Cu and may have significant effects on aquatic organisms.
Other metals did not reach inhibitory concentrations. However, the combination of leaching of multiple metals can result in complex toxic effects. For example, nickel can increase the toxicity of chromium and copper.
Discarded masks represent an overlooked source of metal contamination
Evidence from this study indicates that improperly disposed of washable MNP face masks are an unrecognized source of heavy metal and nanoparticle contamination. This highlights the need for stricter regulations, clearer indication of metal release risks, and proper end-of-life disposal.
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