Bleach Emissions Interact Substantially with Surgical and KN95 Mask Surfaces

Abstract

Mask wearing and bleach disinfectants became commonplace during the COVID-19 pandemic. Bleach generates toxic species including hypochlorous acid (HOCl), chlorine (Cl 2 ), and chloramines. Their reaction with organic species can generate additional toxic compounds. To understand interactions between masks and bleach disinfection, bleach was injected into a ventilated chamber containing a manikin with a breathing system and wearing a surgical or KN95 mask. Concentrations inside the chamber and behind the mask were measured by a chemical ionization mass spectrometer (CIMS) and a Vocus proton transfer reaction mass spectrometer (Vocus PTRMS). HOCl, Cl 2 , and chloramines were observed during disinfection and concentrations inside the chamber are 2−20 times greater than those behind the mask, driven by losses to the mask surface. After bleach injection, many species decay more slowly behind the mask by a factor of 0.5−0.7 as they desorb or form on the mask. Mass transfer modeling confirms the transition of the mask from a sink during disinfection to a source persisting >4 h after disinfection. Humidifying the mask increases reactive formation of chloramines, likely related to uptake of ammonia and HOCl. These experiments indicate that masks are a source of chemical exposure after cleaning events occur.

Emissions from Hydrogen Peroxide Disinfection and Their Interaction with Mask Surfaces

“…One possible reason for this is adsorption of H 2 O 2 onto the mask surface and gradual desorption of this compound over time. This would be consistent with prior work by Kumkrong et al, in which elevated concentrations of H 2 O 2 over a 0.5–5 h period were observed after N95 masks had been disinfected for reuse, as well as in similar work on bleach emissions and their interactions with mask surfaces . The chamber acts as a source of the detected compounds, either directly from injection or indirectly from reactive formation or desorption, possibly involving some water layers on surfaces .…”

“…A more detailed description of the sampling locations and chamber setup can be found elsewhere. 32 The chamber temperature was not observed to change substantially over the course of an experiment, and the chamber RH was observed to increase by 10−20% during injection with no substantial change recorded during mask humidification. These increases in RH are unsurprising based on the proportion of water in the hydrogen peroxide solution and may increase the thickness of adsorbed water layers on chamber surfaces.…”

Influence of Application Method on Disinfectant Byproduct Formation during Indoor Bleach Cleaning: A Case Study on Phenol Chlorination

“…The behind-mask concentration profiles (Figure c,d) and our prior work suggest that K/N95 masks may serve as adsorbent sites, thereby lessening initial exposure. However, primary compounds and DBPs were observed to accumulate in the mask over time during disinfectant injection, and the mask eventually acted as a source for these species for several hours after disinfection application finished, as discussed in more detail in the work of Bhattacharyya et al (2023) . DBPs that do not effectively volatilize and favorably partition to and reside on surfaces can be incorporated into indoor dust or removed through surface contact (such as human touch or wiping) and may remain a potential exposure concern well after a disinfection event.…”

“…Experiments were done with a dry or pre-humidified mask, with other experimental conditions identical, to approximate wearing either a fresh or well-worn mask. The pre-humidified mask was prepared before the experiment by “exhaling” humid air through the manakin onto the mask, leading to approximately 1 g of water uptake to the mask . Mask humidification also led to an increase in chamber RH (measured with a LI-COR LI-850 H 2 O/CO 2 analyzer) to approximately 45% RH, compared to the ∼20% in the dry mask experiment that was typical of these chamber experiments .…”

“…Environmental chamber experiments are described in more detail in separate publications − and are described only briefly here. Experiments were conducted in a 67 m 3 (5.5 m × 4.5 m × 2.7 m) stainless steel chamber operating at ∼23 °C with an ∼2.3 h –1 air change rate.…”