Monitoring moss reveals widespread deposition of airborne microplastics across the UK – practical lessons and recommendations

Moss presents an excellent candidate for biomonitoring the atmospheric deposition of microplastics across wide spatial scales and to monitor trends over time due to its relative ease of sampling compared to alternative approaches such as conventional wet and dry deposition atmospheric sampling. Approaches for sampling mosses and quantifying other pollutants such as metals and nutrients are already well established. Using moss to monitor for microplastics carried in the air has been shown to have promise. However, evaluation of representative sampling and processing procedures must be performed to ensure that quantification of microplastics in moss maintains integrity to the original sample. Using data from a sampling campaign of 52 locations across United Kingdom, we explore these key considerations and aspects of study design, to evaluate the potential use of moss as a bio-monitor for microplastic atmospheric deposition. A method for the isolation of microplastics from moss biomass using flow displacement and filtration is optimised for the extraction of microplastics approximately > 25 µm in size, appropriate for quantification by vibrational spectroscopy methods such as µ-FTIR. The approach is then applied to samples from six major genus of moss, common to the United Kingdom, across 52 natural or semi-natural landscapes. The survey design and analysis methodology are evaluated against quality assurance and control criteria, whilst the findings are critically discussed in light of relevant literature. This study represents the first survey of the extent of microplastic contamination of mosses across United Kingdom, investigating correlations between location characteristics and microplastic polymer diversity and abundance. It shows ubiquitous contamination of mosses with microplastics, irrespective of their location across the United Kingdom, and indicates that a diffuse atmospheric source may play a role in this widespread contamination of moss.