The study, led by Marco Reis, lecturer and researcher at the Chemical Engineering Department of the Faculty of Science and Technology of the University of Coimbra, Portugal (FCTUC), covered surgical masks, KN95 and social masks, and sought to “test simple and effective decontamination methods that can reach various sectors of society, especially small and medium-sized enterprises (SMEs) and the general public, in order to mitigate a complex environmental problem generated by the Covid-19 pandemic”.
After reviewing a “wide range of existing decontamination protocols”, the team decided to focus on three methods: “washing with a diluted sodium hypochlorite solution (the ordinary bleach), nebulisation with hydrogen peroxide (the so-called hydrogen peroxide) and microwave steam sterilisation”.
Depending on the context of use, “these methods are easily implemented and do not require large investments. For families, washing with a sodium hypochlorite solution and microwave steam sterilisation are the solutions with the greatest potential. In fact, steam sterilisation bags are already being used today, for example, to sterilise baby products”, says the researcher.
Nebulisation with hydrogen peroxide is an equally simple method, but it requires a small investment – the purchase of the nebuliser and a camera. “It’s an appropriate system for SMEs or for health centres, fire stations, police stations, municipalities, among others,” explains Marco Reis.
In this project, scientists not only evaluated the effectiveness of microbiological decontamination, but also the impact of the treatments on the filtration efficiency, permeability and structural characteristics of the masks, over 10 cycles of use. To carry out the experiments, the Environmental Microbiology group from the Centre for Mechanical Engineering, Materials and Processes used spores of bacteria as sterilisation indicators, which indicate the elimination of all living things, bacteria and viruses, including SARS-CoV-2.
The results of the study showed virtually 100% effectiveness in decontaminating the three types of masks tested. In general, “the treatments applied are highly effective in their decontamination action and can even reach the “sterilisation” level, i.e. a reduction of more than 99.9999% in the number of viable cells. The treatments that did not reach the sterilisation level presented at least one level of effectiveness classified as “disinfection”, corresponding to a reduction of more than 99.9% in the number of viable cells,” stresses the FCTUC scientist.
Regarding the studies on filtration efficiency, conducted at CITEVE, the results indicate that this important characteristic for the protection of users and third parties “was not significantly affected. There were only some effects on the permeability of the equipment, which, essentially, may interfere in the comfort of use (breathability). The impact of the treatments on the masks’ physical-chemical characteristics was also scrutinised (at the Research Centre of the Chemical Engineering Department, the CIEPQPF), and no relevant chemical changes were detected on the masks’ surfaces, even after 10 treatment cycles”, he adds.
However, the lecturer clarifies that only the use of microwave-generated steam can be applied immediately, “as long as masks with metallic components are not placed”. For the application of treatments with nebulised hydrogen peroxide and diluted sodium hypochlorite solution, “degasification studies are still necessary to ensure the inexistence of chemical residues resulting from these treatments”, he warns.
The project, called ‘Evaluation of the Efficacy of Decontamination and Safety of Reuse of Respiratory Protection Devices (APR)’ was funded by the Foundation for Science and Technology (FCT) under the measure ‘Research 4 Covid-19’. Paula Morais, Hermínio Sousa, Roberta Lordelo, Rafael Botelho, Rita Branco and Ana Dias participated in this study together with Marco Reis.
