A new method for analyzing microplastic particle size distribution in marine environmental samples

Abstract

Microplastics (MPs) are recognized as a global emerging threat to aquatic ecosystems and biodiversity worldwide. Though the number of publications and interest to the MP research have been increased rapidly, it is still hamper to compare the obtained data due to the usage of different methodologies in MP assay. Thus, there is an urgent need for a standardized approach to the procedures of MP quantification in order to produce comparative assessments. In this pilot study, the conventional NOAA protocol of MP extraction from seawater was combined with a simple and inexpensive method for analyzing shape and size spectrum of all MP particles making up the sample. A common flatbed scanner equipped with slide adapter was applied for image acquisition while MP dispersive properties (particle abundance, shape and size spectrum) were quantified using ImageJ software. Feret’s diameter and circularity (or roundness) appeared to be the most efficient shape descriptors for the particle analysis. The total silhouette area of MP particles was shown to produce a confident approximation of the MP overall mass. The first reliable estimates of MP concentrations in the Black Sea coastal waters (Sevastopol Bay) accounted for 0.6 to 7 items m-3 and 6 to750 µg m-3 in terms of abundance and mass, respectively. No steady-state gradients have been revealed in MP distribution along the transect from the mouth of the bay to its corner. Inflow of MP to the bay waters and their transport along the bay seemed to be controlled by a complex combination of factors including rainfalls, wind regimes, currents and the Black river discharge.