In an evolving health landscape, emerging research continues to highlight concerns that could impact everyday wellbeing. Here’s the key update you should know about:
Reusable masks promise protection, but new research reveals they may quietly release toxic metals into waterways, raising urgent questions about their environmental cost.
Study: Washable Face Masks: An Emerging Source of Metal and Nanoparticle Contamination in Aquatic Environments. Image credit: learesphoto/Shutterstock.com
Washable face masks marketed as containing metal nanoparticles have become increasingly used due to their touted antimicrobial properties. A recent paper in Environment and Health reveals the other side of the story: these masks, unless properly discarded, may serve as a source of metal contamination in aquatic environments. This emphasizes the need for regulation throughout their lifecycle.
Metal nanoparticles accumulate and move through aquatic systems
Tens of thousands of tons of metal nanoparticles (MNPs) are produced today. Composed of metals such as silver (Ag) and copper (Cu), they possess unique properties that make them useful across multiple medical, industrial, and consumer product settings.
Meanwhile, about 10 % of the estimated 318 tons of MNP waste enters water bodies. They may undergo bioaccumulation and transfer through aquatic food chains, potentially leading to human exposure, with damaging effects on human health.
Washable MNP-containing face masks became popular during and after the recent coronavirus disease 2019 (COVID-19) pandemic due to claims of better protection and longer usable periods. However, these masks may contribute to pollution by microplastics and released MNPs, especially with detergent exposure.
The authors of this paper performed an integrated assessment of the release of multiple MNPs and the fate of MNPs inadvertently added to the product during manufacturing. This analysis could help understand their impact on human and ecological health.
Three types of masks
The study assessed three types of MNP-containing face masks, marketed as containing Ag, Cu, and platinum (Pt) NPs. There were five, six, and two masks of these distinct types, respectively, obtained via e-commerce platforms. All were claimed to be reusable and washable.
Since these masks comprise synthetic polymers produced with various metal or metalloid catalysts, inadvertent contamination with other particles is possible. Moreover, additives such as flame retardants, pigments, and stabilizers often contain metals, including antimony, lead, and lead-cadmium compounds.
The ionic and NP fractions of nine metals (Ag, Cu, Pt, arsenic, cadmium, chromium, nickel, lead (Pb), and antimony) were assessed in the masks and in 72-hour leachates. To simulate natural leaching into water, and with washing, the masks were exposed to ultrapure water and a detergent solution.
Initial surface electron microscopy (SEM) scanning revealed that the respective masks contained mainly Ag and Cu, with the latter, in some cases, identified as copper sulfides. No Pt was detected in the Pt-masks. Spectrometry confirmed that these masks contained, in addition to Ag and Cu, other metals or metalloids like chromium, nickel, lead, and antimony.
Leaching behavior
Ag-masks
Ag was present at high levels, ~4000 ng/cm² and 6,500 ng/cm² in two of five Ag-masks. These two released large amounts of Ag and Ag-NPs in both leaching scenarios.
At 72 hours, ionic Ag leachate measured 34 % and 27 % of total Ag, respectively, in ultrapure water. Ag-NPs comprised 0.5 % or less of the leached Ag. In detergent, they released 42 % and 36 % of total Ag, respectively, with up to 2.7 % of the leached Ag being in NP form.
The Ag-masks also released Cu, with up to 42 % of the total being released in water and 47 % in detergent. The rate of release of Ag NPs declined over time, eventually plateauing at about 72 hours.
Cu-masks
Cu-masks contained up to 1.7 × 106 ng/cm² in two of six masks. These masks leached more ionic Cu and Cu-NPs than the others, but a smaller fraction of total Cu than Ag or Pt masks.
They leached up to 0.44 % of the total Cu into water and up to 0.18 % into detergent, respectively. Cu-NPs comprised only <0.05 % of the leached Cu in the first of these masks, compared to up to 5.6 % in the second.
These findings highlight substantial variability across mask types and help explain differences from earlier reports suggesting higher Cu leaching.
These masks also contained Ag. Up to 24 % of total Ag was released by water leaching, compared with up to 14 % by detergent. Cu leaching followed a trajectory similar to Ag.
Pt-masks
Pt-masks contained no detectable Pt, perhaps because it was an undetectable form or labeling discrepancies, as seen also with some Ag or Cu masks, which contained no more of these metals than ordinary masks.
Pt-masks contained mainly Ag at 1,500 ng/cm², followed by antimony at much lower levels. They released only up to 0.04 % of their Ag by leaching in water, and up to 0.03 % in detergent.
They released up to 77 % of their Cu content in water and 32 % in detergent. This is in contrast to the findings with the other two masks, where detergent promoted Cu release more than water did.
While the leaching behavior of Ag was mostly dependent on the amount held in the mask fibers, this was not true of Cu. Here, both Ag and Pt masks released more of their Cu, though their total Cu content was less, indicating that release depends not only on total metal content but also on metal-specific properties and interactions with the mask matrix.
These results indicate that release behavior is not solely dependent on bulk metal content and is strongly influenced by metal-specific properties and matrix interactions.
MNP size in leachate
Detergent immersion was associated with a larger mean MNP size than water, for all MNPs. This is probably due to the surfactant-like properties of MNP and their inherent thermodynamic instability, which drives their growth.
The authors suggest a particle migration and coalescence model based on their analysis of particle size distribution over time. However, there is not enough data to establish this definitively, and the mechanism remains speculative.
Other metals in the masks
In all mask types, multiple metals were detected, and in some cases (e.g., Pt-masks), metals other than the labeled component dominated the composition. These unintentionally added metals are not firmly bound to the mask fibers and are readily leached out.
Prolonged immersion caused all metal ions and MNPs to leach, and this is enhanced by detergent in most cases, though antimony was leached more readily in ultrapure water.
Among ionic metals, antimony had the highest concentration in leachates, likely reflecting higher abundance and leachability in water. The other ions, chromium, Pb, and nickel, were more leachable in the detergent.
Conversely, antimony NP levels were comparable to those of the other unintentionally introduced metals. Detergent leachates contained larger particles of all metals and MNPs than water leachates.
The authors also assessed correlations in the co-release of multiple metals, rather than direct causal effects, on their leaching behavior and environmental risks. Cu and Pb were correlated in their NP leachate concentrations, suggesting that they occur together within the mask fibers during manufacture and are released together. The pattern of NP release varies with both the specific metal and the leaching medium.
Environmental hazard
The researchers predict that most metals would leach into water at concentrations exceeding permissible limits for drinking water and, for Cu and antimony, for industrial wastewater, based on modeled release scenarios under defined assumptions. These concentrations exceed algal toxicity thresholds for Ag and Cu, and could profoundly affect aquatic life.
Other metals did not reach inhibitory concentrations. However, the combined leaching of multiple metals may exert complex toxicological effects. For instance, nickel may increase the toxicity of chromium and Cu.
Discarded masks represent overlooked source of metal pollution
The evidence from this study indicates an unrecognized source of heavy-metal and nanoparticle contamination in improperly discarded washable MNP face masks. It highlights the need for stricter regulation, clearer labeling of metal-release risks, and proper end-of-life disposal.
