Moss as a biomonitor for the atmospheric deposition of anthropogenic microfibres

Microplastics, which are plastic particles < 5 mm, have been found throughout the environment. However, few studies have focused on their transport via atmospheric deposition. Bryophytes have been used as biomonitors for the atmospheric deposition of trace elements, persistent organic pollutants and particulate matter, and may potentially be used to monitor the atmospheric deposition of microplastics or anthropogenic microfibres (mf). Hylocomium splendens was collected from three lake catchments, which are remote from anthropogenic disturbance and emissions sources. Anthropogenic mf were observed in all moss samples; the average number was 24 mf g^-1 dry weight (range: 15-30 mf g^-1) across the three study sites. The average length of mf was 1.02 mm (range: 0.83-1.20 mm). Plastic mf were identified using five rigorous visual criteria; 27% of the observed mf passed four criteria and 13% passed all five, suggesting at most a quarter of the mf may be plastic. Annual average atmospheric deposition of anthropogenic mf across the three lake catchments was estimated at ~47,700 mf m^-2 (~12,000 plastic mf m^-2), based on a moss biomass of 2 kg dry weight m^-2. These preliminary findings suggest that moss may be a useful biomonitor for the atmospheric deposition of mf (and microplastics).