Safety concerns regarding CUMasks provided by the Hong Kong government

Safety concerns regarding CUMasks provided by the Hong Kong government


On 8 May 2020, Professor Wallace Leung from the Department of Mechanical Engineering at the Hong Kong Polytechnic University questioned the safety of CUMasks distributed for free by the Hong Kong government. One issue is the copper layer of the mask, which the Hong Kong Research Institute of Textiles and Apparel (HKRITA) touted as having microbial properties that would "immobilize bacteria and common viruses". After repeated washes, however, Professor Leung worried that the copper nanoparticles (NPs) may diminish adhesion to the fabric and risk inhalation.

The HKRITA claims that the CUMask fulfills the ASTM F2100 Level 1 standard, which incorporates the F2299 standard that can filter out at least 95% of aerosol particles with a diameter of 100 nm. The diameter of SARS-CoV-2 ranges between 50 to 200 nm. Level 1 is a low-barrier and typically recommended for general use. NPs of copper and its compounds, copper(II) oxide and copper(I) oxide, have known for the antimicrobial applications and their sizes can range anywhere from 1 to 200 nm or larger. At the time of writing this article, we have not received any information on the size or nature of NPs in the CUMask. Taking these unknowns into consideration, we looked into the existing research with the goal of keeping our readers informed about the potential risks. However, any conclusions should be avoided until the specifications of the CUMask are revealed. 

Previous studies in mice have found inflammatory responses in the lungs after exposure to 25nm copper NPs. Adverse effects also occurred in two experiments on the physiological effects of mice after inhaling 10-12 nm NPs of copper and its compounds. The first experiment found that five days' exposure was sufficient for lung inflammation even at a very low concentration. Depending on the amount inhaled, lung inflammation did not completely dissipate even after the 21-day recovery period. NPs accumulated and stayed in the lungs during the exposure period but fully dissolved during recovery. While the solid organs (e.g. kidney, liver, etc.) do not show increased copper levels after inhalation, ingesting copper NPs have presented toxicity in other studies and other NPs are known to move outside of the lung after inhalation. Consistent with the first study, the second experiment also showed increased inflammation in the lower respiratory system immediately followed the exposure period. This experiment exposed the mice to copper NPs for a total of 10 days and then infected them with a pneumonia-causing bacteria. Compared to the unexposed group, they were less capable of fighting the bacteria "despite the purported anti-bacterial activity of" copper. 

A different study countered this qualm, however. The previous study's pneumonia-causing bacteria was Gram-negative and Gram-positive* options were not considered. This new experiment used both Gram-positive and Gram-negative bacteria from the gut. It found that copper(II) oxide NPs effectively inhibited both types. Intended to test the antimicrobial effectiveness of incorporating copper(II) oxide into nanofibers for mask production, the experiment did not test against viruses. The NP size used in the experiment was around 37 nm. A more problematic feature of this experiment was its toxicity test, which showed that the amount of NPs within the mask fabric was directly correlated to cell death.

These studies demonstrated the efficacy of copper NPs and its compounds as a safe antimicrobial barrier are questionable. A few key pieces of information are necessary to determine if the CUMask's copper layer will at least do no harm:

(1) What is the size and chemical nature of NPs in the copper layer?

(2) Its protective and filtration layers separate the copper layer from the wearer's face. What size of particles can pass through those layers?

(3) If the virus and other NPs are properly filtered, will the protective and filtration layers chemically react with the NPs?

Keep in mind that ASTM F2100 "does not address all aspects of medical face masks design and performance".

Editor's Note:

* Gram-positive and Gram-negative bacteria have different protective outer layers. Knowing the type of bacteria informs healthcare providers' decisions on the most effective treatment or protection methods.

Sources: Apple Daily

HKRITA video on Technology behind CUMask 

ASTM Standards,

Cu Nanoparticle: Synthesis, Characterization and Application (2019)

Organ burden and pulmonary toxicity of nano-sized copper (II) oxide particles after short-term inhalation exposure (2016)

Effects of copper nanoparticle exposure on host defense in a murine pulmonary infection model (2011)

Copper oxide (CuO) loaded polyacrylonitrile (PAN) nanofiber membranes for antimicrobial breath mask applications (2019)

Further Reading:

Guide to Face Mask Selection and Use (ASTM Levels)