Marine biodegradation of plastic films by Alcanivorax under various ambient temperatures: Bacterial enrichment, morphology alteration, and release of degradation products

The global ocean has been receiving massive amounts of plastic wastes. Marine biodegradation, influenced by global climate, naturally breaks down these wastes. In this study, we systematically compared the biodegradation performance of petroleum- and bio-based plastic films, i.e., low-density polyethylene (LDPE), polylactic acid (PLA), and polyhydroxyalkanoates (PHAs) under three ambient temperatures (4, 15, and 22 °C). We deployed the our previously isolated cold-tolerant plastic-degrading Alcanivorax to simulate the accelerated marine biodegradation process and evaluated the alteration of bacterial growth, plastic films, and released degradation products. Notably, we found that marine biodegradation of PHA films enriched more bacterial amounts, induced more conspicuous morphological damage, and released more microplastics (MPs) and dissolved organic carbon (DOC) under all temperatures compared to LDPE and PLA. Particularly, MPs were released from film edges and cracks with a mean size of 2.8 μm under all temperatures. In addition, the degradation products released by biodegradation of PHA under 22 °C induced the highest acute toxicity to Vibrio fischeri. Our results highlighted that: (1) marine biodegradation of plastics would release millions of MPs per cm2 exposed surface area even in cold environments within 60 days; (2) different marine biodegradation scenarios of these plastics may raise disparate impacts and mitigation-related studies.