The "white sand mussels" are edible bivalves inhabiting the littoral shores usually buried in the sand. Тhey are invasive species for the Bulgarian waters of the Black Sea. The samples for this study were collected from different points on the northern and southern Black Sea Bulgarian coast in the period January 2020 to December 2020. The study of different types of microorganisms was performed by using the microbial identification system model: MicroLog M® BIO45101 BiologInc and the software product GEN III. The physic-chemical parameters of the waters – temperature, pH, salinity and dissolved O2 were also determined. In the different species, we had detected specific microbiological complexes. The species Pseudomonas viridilivida and Citrobacter farmer were isolated only from Donax trunculus. The species Escherichia hermannii was found only in Mya arenaria, and Acinetobacter johnsonii was detected only in Chamelea gallina. The isolated species Acinetobacter gyllenbergii and Acinetobacter johnsonii are related to humans and are indicators for pollution of the water with channel waste waters. Our results demonstrated an increase ofhe quantity of the coliforms the region of Sveti Vlas from August, where they were 50 the norms. In the region of Arkutino in July and Ahtopol in August, the quantity of the fecal coliforms is 190 and 30 times the norms prescribed in the Ordinanceo. 4 from 20.10.2000 for the quality of fisheries water and the breeding of shellfish (the amount of fecal coliforms in the inter-shell content should be less than 300 NVB). We noticed also seriousollution of the Varna lake even months after an accident with a leaky pipe.

The accumulation of microplastics in the world oceans is one of the main global problems of the modern world. The Black Sea is the main source of seafood for people from several countries, including Bulgaria. The pollution of the Black sea is a result of various factors, especially anthropogenic. The aim of this study was to determine the presence and accumulation of microplastics in the Black Sea mussel Mytilus galloprovincialis L., 1819, harvested from different locations along the northern Bulgarian Black Sea coast. Within each microplastic morphological group, three size classes were recognized: 100-200 μm, 25-100 μm, and ≤ 25 μm. Microplastics were found in the soft tissues of all studied specimens but in a different ratio of pellets, fibers and fragments. Generally, the pellets were the most often registered particles, followed by irregularly-shaped fragments, whereas fibers were less numerous. The dominant part of the isolated plastics are made of polyethylene (PE), and polyethylene terephthalate (PET). Our results pointed out serious pollution with plastic particles in the Bulgarian Black Sea aquatory, which in the future may seriously affect the health of the mussel population and also human health.