First landscape-scale survey of the background level of COVID-19 face mask litter: Exploring the potential for citizen science data collection during a ‘pollution pilgrimage’ of walking a 250-km roadside transect

The COVID-19 pandemic has generated a global problem through the cavalier or deliberate disposal of personal protective equipment (PPE) by the general public. This has raised concerns that the billions of discarded face masks pose a threat to wildlife through entanglement or, when broken down, through ingestion of derived microplastics. Previous quantitative surveys of the magnitude of such litter have focused on areas where people congregate, such as tourist beaches and large cities. The present survey is the first to provide data on the background level of face mask litter through a landscape of variable land-use. A 250-km transect along an historic road between Montreal and Quebec City (Canada) was surveyed during a walking pilgrimage, revealing an overall density of 0.0001 ± 0.00006 face masks m. Average densities were significantly higher in areas of human occupation compared to agricultural and forested rural land. However, there was no significant correlation between population size of communities and the number of face masks encountered, nor in litter extent and proximity to municipalities. This may be due to the confounding influence of inter-community differences in scheduled street cleaning operations. Seventy-six percent of face masks were of the disposable surgical variety, with the remaining 24% being reusable cloth masks. This, and the fact that only 10% of the former and none of the latter exhibited broken ear straps, insinuates that the litter could be due to accidental loss rather than inappropriate discarding by individuals en route. Scaling-up these findings in relation to the global road network generates a preliminary background estimate for roadside litter of >17 million face masks. The present study endorses the call made by others to engage citizen scientists in surveying PPE litter, in particular, the thousands who each year walk the medieval pilgrimage routes through the landscape of Europe.