Potential Role of Mosses in Evaluating Airborne Microplastic Deposition in Terrestrial Ecosystems

The deposition of airborne microplastics (MPs) poses potential risks to human health and terrestrial ecosystems. Therefore, suitable mitigation efforts are needed, as is knowledge of their deposition patterns in inhabited and remote regions. Currently, there are no standardized protocols for monitoring airborne MPs, and implementing and managing automatic monitoring systems would be costly and feasible only in a few fixed locations. Over the past few decades, several species of cryptogams have proven to be reliable biomonitors of persistent atmospheric contaminants. Due to the lack of standardized methodologies, the results of preliminary biomonitoring surveys for MPs have been inconsistent and difficult to compare. However, they clearly indicate higher MP concentrations in epigeic mosses than in epiphytic lichens (collected at the same site or experimentally exposed in parallel in bags). This review discusses the morphophysiological features that favor the entrapment and retention of intercepted MPs in mosses, as well as the field and laboratory activities necessary to determine whether these organisms progressively accumulate airborne MPs as a function of the exposure time. Steps for future research needed to develop a cost-effective, reliable and easily applicable biomonitoring methodology are suggested. Evaluating the advantages of active moss biomonitoring over sampling atmospheric bulk deposition or exposing suitable commercial materials is recommended.