From macro to micro: Comprehensive marine beach litter analysis using portable NIR

The exponential growth of plastic production, combined with inadequate management of plastic waste, is increasing plastic pollution across all environments. Over the past decade, many countries have developed national strategies to monitor litter in marine environments, and on beaches these often involve monitoring either macrolitter and/or microlitter. Understanding the dynamics between different size fractions in the environment is crucial for a better understanding of the plastic cycle. Challenges remain in linking the information obtained from existing monitoring strategies: detailed categorisation of macrolitter based on the Joint List of Litter Categories developed by the Marine Strategy Framework Directive Technical Group on Marine Litter, and the analysis of microplastics from beach sediments, which usually includes determining morphological characteristics, colour, size, and chemical composition. The determination of polymer types in plastic macrolitter is not part of current monitoring. This study presents the first comprehensive analysis of marine beach litter in Slovenia, focusing on all three size classes of marine litter: macrolitter, mesolitter, and microlitter, and demonstrates the difficulties in comparing data between these size classes. The average densities observed were 0.38 macrolitter m^-2, 29.42 mesolitter m^-2 and 27.51 microlitter kg^-1 dry sediment. The majority of macrolitter originated from building and construction, as well as items related to food consumption. By introducing polymer type identification, the accuracy and efficiency of litter categorisation can be improved, contributing to a more precise understanding of the correlation between different size classes, litter composition, dynamics, and sources of plastic pollution in coastal areas.