Marine degradation of plastics in Western Mediterranean Sea: Comparison between biodegradable and conventional polymers
Patricia Feijóo, Anna Marín, Estefania Sánchez‐Safont, José Tena‐Medialdea, José Rafael García‐March, José Gámez‐Pérez, Luís Cabedo
Abstract
• Degradation performance of biopolymers (PHBV, PLA) and conventional polymers (PA, PP, PE) was assessed over 12 months in a specific marine environment: a harbor of the Mediterranean Sea. • Biopolymer PLA mimicked the behavior of conventional polymers, showing minimal marine degradation only influenced by abiotic factors. • Only PHBV showed biodegradation signs confirming to be a dual-function material: physical support and energy resource for microorganisms. • Specific conditions of the marine habitat and excessive biofouling contributed to deceleration of PHBV disintegration rate from month 6. Biodegradable polymers have been proposed as a possible solution to plastic pollution in the ocean but there is still a lack of knowledge about their behavior in this particular ecosystem due to the great variability of marine habitats. The abiotic and biotic deterioration of biodegradable polymers -polylactic acid (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), (PHBV) - and conventional polymers - polyamide 6/6.6 copolymer (PA), polypropylene (PP) and polyethylene (PE) - were studied throughout 12 months of immersion in the western Mediterranean sea. The behavior of PLA was not distinct from that of the non-biodegradable plastics. PA, PE and PP only showed small changes derived from their interaction with the marine environment. Their low mass reduction and attrition of mechanical properties were ascribed to abiotic factors. Biodegradation was clearly observed only for the PHBV, reaching a 16 % of weight loss in the registered period and showing an increased surface roughness, and higher biofilm density than the rest of materials. However, as time progressed, a noticeable reduction in the biodegradation rate was observed. This decline may be attributed to a limitation of optimal conditions for microorganisms on the material's surface, likely influenced by the unique characteristics of the surrounding environment, such as biofouling, pollution, and temperature variations. FTIR experiments confirmed the layer-by-layer degradation mechanism starting from amorphous zones. This is a step forward in understanding the degradability of polymers in specific marine environments required for developing prediction systems of plastics’ lifetime in the ocean.