Intertwined synergistic abiotic and biotic degradation of polypropylene pellets in marine mesocosmsIntertwined synergistic abiotic and biotic degradation of polypropylene pellets in marine mesocosms Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2025-03-202023enThe accumulation of plastic waste in the oceans has caused growing concern for its effects on marine life. The interactions of plastics with environmental factors have been linked to fragmentation to micro- and nanoparticles with different properties and consequences, but the mechanism of fragmentation has not been fully understood yet. In this work, we investigate the combined effect of marine communities and ultraviolet (UV) radiation towards the degradation of virgin and artificially weathered polypropylene (PP) pellets after a long-term incubation period in marine mesocosms. The surface chemical alterations and deterioration of the polymer, in conjunction with the attachment and evolution of marine bacterial communities, the development of biofilm and exopolymeric substances (EPS), as well as the colloidal properties (zeta-potential and hydrodynamic diameter) of the mesocosms were studied. The surface area of both types of pellets decreased over time, despite no concrete weight change being observed. Cell growth, EPS production and colloid particle size were correlated to the loss of area. Therefore, we propose that surface area could be effectively monitored, instead of weight loss, as an alternative indicator of polymer degradation in biodegradation experiments. Changes in the chemical structure of the polymer, in addition to the evolution of the biological factors, implied that a complex degradation process alternated between two phases: an abiotic phase, when UV irradiation contributes to the deterioration of the polymer surface layers and a biotic phase, when marine communities degrade the weathered polymer surface to reveal the underlying layer of virgin polymer. Finally, microscopic particles, produced as a result of the decrease in pellet area, promoted the aggregation of colloidal particles. The role and impacts of these colloidal particles in marine ecosystems are yet as unidentified as that of micro- and nano-sized plastic particles and call for further investigation.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). In addition, funding by the European Union H2020 project INMARE (grant agreement No. 634486) is highly appreciated.http://creativecommons.org/licenses/by/4.0/Journal of Hazardous Materials457 Karkanorachaki Aikaterini Καρκανοραχακη Αικατερινη Syranidou Evdokia Συρανιδου Ευδοκια Maravelaki Pagona Μαραβελακη Παγωνα Kalogerakis Nikos Καλογερακης Νικος Elsevier Marine environment Microplastics Nanoplastics Degradation Aggregation ATR-FTIR