Reconciling human health with the environment while fighting the COVID-19 pandemic through improved eco-design of face masks
Before calculating the environmental impacts, we analyzed the inventory data and entered it into the software for the simulations. With respect to reusable masks, on-site measurements of raw materials, energy requirements for processing (e.g. fitting, cutting, sewing, etc.), packaging material configurations, reuse, cleaning activities and transport distances were provided by the Italian Social District. In particular, the reusable face mask washing requirements were adapted from Schmutz et al.9 in accordance with the information provided by the producer. Additionally, data on waste disposal scenarios for both types were collected from the preprint by Allison et al.23 Finally, single-use mask inventory data was collected from independent producers via certified laboratories. The final set of background and foreground data is provided in “Supplementary Table S1”.
Single-use face masks are made of three layers of polypropylene nonwovens. Inner and outer fabric layers are Spunbond and the middle filter layer is 99% Meltblown24. Reusable face masks (Type IIR) are also made up of three layers: an inner layer of antibacterial-grade cotton, a middle layer of Meltblown, and an outer layer of Spunbond. The quality of the mask is determined by the quality of the components and is therefore traceable back to the component suppliers. Information on vendors and product component types (including certifications and features) is provided in “Supplementary Table S2”. The Meltblown (provided by Ramina) forms the central part of the reusable masks. This component guarantees a filtering performance of more than 99% which, together with the high quality water-repellent anti-drip C6 antibacterial cotton (supplied by Olmetex) of the inner layer, resists up to 10 washes by immersion. These materials, forged together using specialized machinery, improve Type IIR surgical masks above all else, in terms of their superior performance in the overall trade-off between filtering quality, reuse and environmental sustainability. In addition, the cotton interior fabric of these masks has the same effectiveness as single-use masks in reducing the transmission of respiratory viruses.25.
For elastic bands, nose clip material (for single-use masks) and fabric layers, no direct datasets are available in the ecoinvent database. Thus, for the present study, non-allergenic latex-free elastic bandages, produced using a “polyurethane, soft foam” process, were selected. The nose clip material, which is only used for single-use masks, was assumed to be modeled using a “polyvinyl chloride resin (B-PVC)” process. Finally, we assumed that a “polypropylene, pellet” process was used for the TnT Spunbond and Meltblown layers. Regarding packaging materials, reusable masks are packed in biodegradable plastic bags, while single-use masks are packed in plastic bags. Both types of masks are packaged in packs of 10 and delivered in recycled boxes. In the present study, packaging materials were entered into the software as “biopolymer of starch complexed with polyester”, “packaging film, low density polyethylene” and “corrugated boxes: 16.6 % primary fibres, 83.4% recycled fibres”. For transport, a “transport, freight, truck 16-32 metric ton, EURO6” process was adopted from the manufacturing plant and national distribution by road, using Euro 6D vans.
To calculate the number of face masks used in Italy in 2020, we estimated the Italian population at 60.6 million, based on statistics from the Organization for Economic Co-operation and Development (OECD).26. We assumed one mask per person, per day, for both types of masks, per WHO recommendations27. As reusable face masks can be washed up to 10 times without losing their virus filtration performance (according to the manufacturer’s own specifications), we have assumed the maximum number of washes for the use phase. As a result, the total number of face masks used in Italy was calculated at 2.18 and 22.1 billion for reusable and single-use masks, respectively. The total amount of waste was calculated based on the number of masks used, as well as their packaging materials (i.e. plastic wraps and cardboard boxes) (Table 2). Single-use face masks have been found to generate nearly 10 times more waste for each waste category, compared to reusable face masks.
Regarding mask use, our baseline scenario was based on WHO recommendations27, which state that reusable masks should be washed daily with soap/detergent and hot water (60°C). We assumed that the whole household (2.3 people for the Italian case) the masks are washed together with other clothes in a standard 7 kg washing machine, in accordance with both the literature9 and manufacturer’s instructions. Schmutz et al.9 indicated that the requirements for a half-full washing machine (a typical situation in Europe) are 84 g of detergent, 52.3 L of tap water and 1.1 kWh of electricity per load. Accordingly, the average wash consumables required for each mask are calculated by normalizing the specified requirements to a mask (i.e. multiplying a half-full requirement by 0.2%).
It should be noted, however, that user behavior is not easy to predict and the washing machine is not always considered the preferred option. Therefore, in a further step, we investigated different user behaviors as sensitivity cases. First, handwashing was introduced as the main sensitivity scenario9,23,28. In this case, we have assumed that the set of household masks will be washed together every day after use, in a 5 L bowl filled with up to 3 L of water at 60°C and then rinsed with water without soap. /detergent. Approximately 6.24 g of liquid detergent and 6 L of water are needed for each manual washing session23. As in the case of machine washing, the average washing consumables required for each mask are calculated by normalizing the specified requirements to one mask (i.e. the requirements per mask and per wash are 2.609 L of tap water, 2.713 g of detergent, 447.7 kJ of energy supplied by the gas boiler).
Additionally, we also considered other possible user behavior scenarios, assuming that reusable masks could be washed for longer than the recommended lifespan (i.e. 10 washes). Accordingly, a second case of sensitivity was modeled for reusable masks washed 15 times before disposal. Finally, with reference to single-use masks, we have taken into consideration a longer wearing time. Although the recommended face mask usage is one mask per day (or 4-8 hours), many users wear single-use surgical masks for longer than this recommended period. So, in this case of sensitivity, we assumed that users would wear the same mask for 2 consecutive days. It should be noted, however, that the last two cases of sensitivity, i.e. concerning a longer wearing period of both types, could compromise the level of protection of the masks and therefore human health.
Regarding packaging and waste disposal activities, the Italian social district provided data from its ongoing studies regarding the biodegradability of packaging materials for reusable face masks (type IIR). However, this study could not consider actual waste disposal activities (i.e. recycling, reuse) due to the lack of approved assessments. Thus, waste disposal was primarily based on previous studies indicating that incineration and landfilling were viable options.23.29. We assumed that contaminated masks and discarded packaging materials would go directly to waste disposal sites, and 43% of mixed waste would be landfilled while 57% of mixed waste would be incinerated23. Regarding alternative disposal activities, we considered two sensitivity cases: one that assumed that all masks of each type would be fully incinerated9.30 and another that assumed that all masks of each type would be fully landfilled31.