Using citizen science data here allowed us to observe the temporal increase in littered masks, gloves and wipes as a result of national legislation, which would have been missed if these applications were not already in place. Potential sources of error can exist with this research methodology type such as: observer bias, poor and inconsistent tagging of items, lack of standardization of collection methods, regional biases in effort and temporal variation in effort27,28. Within this work we have reported at a national level due to the limited granularity of data available. There is potential that biases can occur between high and low population density areas and regions with greater participation. However, citizen science offers increasing access to data that would be complimentary to conventional research capabilities, especially under pandemic travel and work restrictions16,17.
We found a global increase in the proportion of COVID-19-related litter collected during the initial months of the pandemic. Masks showed the greatest increase and the clearest response to global and national pandemic interventions, increasing from <0.01 to >0.8% of all litter, a >80-fold increase by October 2020. In contrast, gloves and wipes were ~0.2% before the pandemic announcement, with gloves rising over tenfold and masks threefold in the initial months after the pandemic announcement, before decreasing to ~0.4% globally by October 2020. The global WHO advice for public mask wearing had a significant impact on the littering of masks compared to the announcements of an emergency and the pandemic (P < 0.01). This coincides with nations reducing their workplace restrictions from the initial higher level of 3 (require closing (or work from home) of all but essential workplaces), to that of 2 (require closing (or work from home) for some businesses), where mask use was used to support social distancing (Fig. 5). The United Kingdom shows a high proportion of mask litter peaking at 6% when compared to nations with reduced restrictions, such as New Zealand and Australia peaking at <0.2% (Fig. 2). Emerging research supports the presence and national variability in COVID-19 litter, with one study29 reporting a consistent <1% composition of COVID-19 litter over a 50-day survey of streets in South Africa. Whereas beach litter surveys in Kenya, 100 days after the first reported COVID-19 case, showed 16.5% of litter associated with COVID-19 (includes sanitizer and soap bottles)30.
In the initial months of the pandemic, when nations instigated their highest lockdown restrictions, gloves showed the greatest prevalence globally; for example, a survey study4 in Toronto Canada found proportionally 44% gloves, 31% masks and 25% wipes in May–June 2020, compared to 42% gloves, 27% masks and 31% wipes. As nations began to reduce lockdown restrictions, incidences of glove littering reduced, probably due to improved education on how the virus is likely to be transmitted, with wipes increasing during lower level restrictions as people begin to clean surfaces.
Estimates of the annual demand for PPE amount to billions of items per country, with the global market increasing in value from US$800 million in 2019 to over US$166 billion in 202014,20,31. Estimates for the United Kingdom alone place the general population use at over 24 billion items per year for single-use masks (if reusable ones are not widely used) and an estimated global monthly demand of 129 billion masks and 65 billion gloves6,14. Despite multiple vaccines becoming available, a high uptake by the global population will be needed and social distancing measures will need to remain in effect for some time32,33. Consequently, it is likely that the use of masks will remain high through 2021 into 2022 and there will be continued mask littering. Wipes and gloves will potentially remain in use whilst there is a high prevalence and transmission of the virus within the community, again with associated littering.
Our results suggest that, alongside addressing the threat to human health, targeted national-level pandemic responses are also necessary to address the threat to environmental health posed by related litter. As it is likely that higher mask use will continue following the immediate health pandemic, such responses must be sustained.
Occurrences of mask, glove and wipe litter has been influenced by the instigation of new legislation requiring the use of masks and the need to clean surfaces and hands (Fig. 5). Differences between nations’ mask littering are probably driven by multiple factors including national-level policies, such as mandatory wearing of masks and movement restrictions. The observed variations between nations are complex, with the quantity, composition and distribution dependent on appropriate ISB (infrastructure, service, behaviour)34: (1) infrastructure (for example, convenient and suitably placed litter bins), (2) service provision (for example, street cleansing, litter bin collections, communication materials and enforcement of penalties) and (3) desirable public behaviour (that is, choosing to not litter). Infrastructure and services are typically provided by local/national authorities, although some private companies, especially fast-foods outlets and convenience stores, recognize their role by providing and emptying bins on their property. In terms of behaviour, many surveys have demonstrated that the public are generally aware that it is unacceptable to litter but continue to do so anyway, for a range of reasons, including:
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Personal disposition towards littering (that is, particular and embedded: values, attitudes, knowledge, awareness, personalities, lifestyles, communities, social status and norms)
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Immediate personal circumstances (for example, being drunk, in a rush, a teenager, in someone else’s area and unlikely to be seen or caught)
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Factors deemed outside of a person’s control (for example, lack of bins in the ‘right’ places (including inside cars and public transportation), area is already run-down/dirty (so it doesn’t matter) or everyone else is doing it)
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‘Beneficial’ factors (for example, provides jobs for cleansing staff, revenue raised from fines, provides food for wildlife, food or peels are biodegradable so provide nutrients for soil)
Research has shown that people litter more in already-littered environments35. During the pandemic, waste collection authorities were under pressure due to staff absence and requirements for new working practices, potentially leading to reduced street cleaning and less frequent collection of waste from litter bins36,37. Further research is required to determine if this was a factor in the increase of littering which occurred, particularly after the lifting of strict lockdown periods. The increased proportion of PPE as litter could also point to the public being unprepared to deal with waste PPE outside of their homes. They may be concerned that taking waste home for disposal could potentially contaminate vehicles or shopping bags—therefore littering may appear to present less personal risk if no bins are available.
Our results highlight the impact that legislation can have on the composition of litter. As mentioned, it is likely that PPE litter will persist throughout the pandemic, which can create a series of environmental and health impacts if mitigation is not undertaken.
If littered PPE and cleaning products are allowed to persist in the environment they present hazards to humans, the environment and infrastructure. These impacts are dependent on the duration since an item was littered and the environmental conditions it was deposited into. This can be separated into three categories: short term, medium term and long term.
Short-term impacts
Within the first few hours and days, littered PPE and wipes pose a potential viral vector of COVID-19 if used by an infected person38. Littered items create a visual pollutant that can encourage further littering within that area35,39.
Littered items can be transported by weather conditions into drains and sewerage systems, creating potential blockages where they entangle with other solids (for example, leaf litter)40,41. Where combined sewerage systems are used this can create a direct route from the terrestrial into the marine environment42 or into rivers/streams43. Masks are manufactured in a similar way to that of wipes, presenting similar problems in sewerage systems, with the added complication of elastic ties.
Medium-term impacts
For megafauna, there is a risk of choking and entanglement with discarded litter, with the difficulty to mechanically break down the material and the straps/elastic causing entanglement44. If ingested, malnourishment can occur whereby non-digestible plastics accumulate impacting survival45,46. Where there are high volumes of waste, smothering can occur, whereby organisms experience difficulty surviving and propagating47.
Long-term impacts
Once in the environment, littered items can continue to have the impacts mentioned above, with the addition of becoming vectors for other pathogens and pollutants. Chemical, physical and biological weathering will break the littered items down from macro-plastics (>5 mm) into micro-plastics (<0.5 mm) and nano-plastics (<100 nm) that have the potential to enter the lower food chain and have toxicological effects including the leaching of metals9,27,28,48,49.
Authorities have been under huge pressure during this pandemic and waste management solutions to address littering of PPE have not been high on their agenda. However, as vaccines emerge and the scale and impacts of littering have become apparent, local and national action is necessary. As highlighted by the ISB model, measures must address all factors that contribute to inadequate waste management, in this case, PPE littering (that is, building appropriate infrastructure and service provision alongside actions to influence appropriate behaviour change)34. Such measures are likely to include development of policy, legislation, producer responsibility, improvements in waste management infrastructure (new bins in ‘hot spots’ for littered PPE) and service provision (more frequent bin emptying), targeted communication campaigns and signage. Preventing the need for single-use PPE, especially masks and gloves, will require greater access to reusable items and guidance on frequency and conditions for safe and suitable washing.
Individual nations’ policy and legislation on mask use has required citizens to purchase and use, often for the first time, single-use masks. This has resulted in an increase of mask litter collected from September 2019 to October 2020. Within several countries reported here, this is an increasingly abundant form of litter. All nations that legislated the use of masks saw an increase in the occurrence of mask littering. However, nations have differing littering behaviours regarding masks, with some littering substantially more than others. This study supports the anecdotal accounts of COVID-19-related litter but it cannot differentiate the main drivers causing the differences between nations which may be based on population behaviour (influenced by regional values, attitudes and cultural/social norms), accessibility of urban waste management systems, mismanagement of waste, strictness of mask legislation and social distancing/lockdown legislation, all probably contributing to varying degrees among others.
The primary focus of COVID-19 responses have been on human health and reducing impact on society. Our results support other studies in showing the occurrence of a litter problem associated with our human-health focused response. Our results also show intercountry differences in response to to similar COVID-19-related policies. Identifying and understanding interactions among the processes driving litter, especially PPE, should be included in future research and policies, especially as coronavirus-related diseases such as COVID-19 are likely to persist for years to come. Ultimately the differences between nations are probably an artefact from the existing waste management practices and embedded littering behaviours before the pandemic. This will require a combined investment in infrastructure, services and legislation to reduce littering occurrence whilst public PPE use is essential. There is a clear correlation between policies that require the use of masks and their occurrence as litter. As such, future policies should be designed to promote the use of reusable items; facilitate the collection and disposal of single-use items at points where their use is mandatory; and support waste management infrastructure in the recovery and subsequent disposal of the material.
