Qualitative and quantitative assessment of microplastics in three sandy Mediterranean beaches, including different methodological approaches

Microplastics are small plastic particles ( < 5 mm) that are found in most marine habitats around the world. Currently, several studies are trying to determine their exact effects. Microplastics can be introduced into the marine ecosystem directly as manufactured microplastics, or indirectly through the decomposition of larger plastic particles. They can enter the food chain, and can be found as vectors for the movement of microbial communities and chemical pollutants. In our study, two different ways of measuring microplastics were tested at three Mediterranean beaches, each subject to different types of human pressure. The purpose of the study was to compare different sampling approaches for assessing the microplastics present in sediment, taking into account temporal variability across the summer and winter seasons. Statistically significant differences were found between the beaches, which reflect the distinct uses made of each of them. At the same time, significant differences were found in the contents of microplastics, which were due to seasonal variability. Our analysis showed that microplastics can be found in deeper sediment layers with different concentrations to that of the surface layer. Therefore sampling methods that do not sample the same sediment layer do not seem to produce comparable results. In addition, classic categorizations of microplastics (as microfibers, membranes, etc.) may not always be sufficient. Rather, a classification based on microplastic properties, the specificities of each region and each study's objectives is recommended.