Deposition of Microplastics in the Sea of Azov: A Critical Data Analysis in the Context of the Marginal Filter Concept

Abstract

This study investigated the accumulation of microplastics (MP) in the bottom sediments of the Sea of Azov and developed a detection method using pyrolysis gas chromatography-mass spectrometry (Pyr-GC-MS). Relationships between polymer concentration, sediment granulometric composition, depth of occurrence, hydrochemical parameters, and the distribution of benthic organisms were analyzed. Analysis of 20 samples revealed an average MP concentration of ~62 μg/g, with a maximum of 196 μg/g. Polyvinyl chloride (PVC) was the dominant polymer, reflecting its extensive use in regional industry. Correlation patterns were identified as inflection points on graphs of MP content and salinity versus sediment granulometric composition and depth. These points correspond to sampling stations near the western boundary of the Don River estuary (the Taganrog Bay area near Dolgaya Spit) and in the discharge zone of the Kuban River flow. It was established that the primary accumulation of MP occurs near anthropogenic sources (Taganrog, Berdyansk) and on the periphery of the Don and Kuban deltas in clay silts and sands. The estuarine sections of the rivers act as a natural barrier, facilitating MP deposition through coagulation with suspended organic particles. At the same time, no influence on fundamental ecological patterns was detected, with the relationships remaining within the logarithmic dependencies of benthic biomass on abundance. The obtained data provide a basis for standardizing MP assessment methods and for further research with a detailed station grid covering various sediment types and benthic habitat conditions.