Temperature-mediated biodegradation of plastics in marine environments

Zhang, Yuanmei (2025) Temperature-mediated biodegradation of plastics in marine environments. Masters thesis, Memorial University of Newfoundland.

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Abstract

The global ocean accumulates massive plastic waste, raising concerns over environmental impacts. Plastic biodegradation is a promising solution; however, the efficiency of this process is highly temperature-dependent. Despite its importance, the comprehensive understanding of how temperature affects microbial dynamics in plastic degradation across diverse marine climates, particularly in colder regions, remains limited. This study begins with a literature review on temperature-mediated biodegradation of plastics in marine environments. Evidence suggests that elevated temperatures generally promote biofilm growth and enzymatic activity. Cold-tolerant bacteria produce extracellular polymeric substances (EPS) to stabilize biofilms at lower temperatures. At moderate temperatures, Proteobacteria dominate the initial degradation phase, while Actinobacteria, Firmicutes, and Cyanobacteria contribute to various stages of degradation. Psychrophilic and thermophilic bacteria facilitate degradation in extreme climates. Enzymes such as cutinases, lipases, and depolymerases facilitate partial degradation of hydrolyzable plastics, while non-hydrolyzable plastics remain recalcitrant, relying on enzyme-generated reactive oxygen species (ROS) for gradual breakdown. Additionally, controlled laboratory experiments were conducted to evaluate the biodegradation of petroleum-based low-density polyethylene (LDPE), bio-based polylactic acid (PLA), and polyhydroxyalkanoates (PHAs) at various temperatures (4, 15, and 22 °C) using a cold-tolerant Alcanivorax strain isolated from North Atlantic Ocean. Compared to LDPE and PLA, results showed that PHA films supported substantial bacterial growth, displayed considerable morphological damage, and released more microplastics (MPs) and dissolved organic carbon (DOC) across all temperatures. Notably, degradation by-products of PHA at 22°C exhibited the highest toxicity to Vibrio fischeri, highlighting temperature’s role in biodegradation rates and associated ecological risks. These findings from both the literature review and experiment studies underscore the critical influence of temperature on plastic biodegradation and provide fundamental knowledge for mitigating plastic pollution in diverse marine climates.

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