The recently highlighted ubiquity of plastics in the marine environment has been a cause for rising concern, due to their size-dependent negative effects on marine and human life. Environmental factors, such as solar radiation, temperature, mechanical stress or microbial degradation, lead to the in-situ fragmentation of plastics into secondary particles, namely microplastics, with a nominal diameter smaller than 5 mm, or even nanoplastics (< 1 μm). In this work, the fate of 3 fossil-based plastic (polypropylene (PP), high-density polyethylene (HDPE) and polystyrene (PS)) and 4 bioplastic pellets (polylactic acid (PLA), thermoplastic starch (TPS), bio-polyethylene (bio-PE) and recycled thermoplastic starch (rTPS)) was monitored in marine mesocosms for 5 months. The surface chemical alterations and deterioration of pellets along with the biofilm development were studied. At the same time, the micro/nanoplastic generation was determined using microscope, dynamic light scattering (DLS) and Nanoparticle Tracking Analysis (NTA) in order to estimate the concentration and size distribution. Biofilm developed on the surface of all pellets since the first month and the concentration of biofilm cells displayed an increasing trend. An increase in the concentration of secondary bioplastic particles was also detected along experimental period. The surface area of all fossil-based pellets decreased over time and changes in the chemical structure of the surface of all polymer types were detected but at a different extent. It seems that a complex, polymer dependent degradation process occurs and the fate of the so-called biodegradable polymers should be more carefully investigated in the marine environment.

Acknowledgement: This research was co-financed by Greece and the European Union (European Social Fund-ESF) through the Operational Program «Human Resources Development, Education and Lifelong Learning» in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research”(MIS-5000432), implemented by the State Scholarships Foundation (IKY). The financial support by the Erasmus+ Programme is greatly appreciated.