Composition, properties and other factors influencing plastics biodegradability

Plastic litter has become increasingly abundant in the environment, with entire products and fragments found worldwide in practically all environmental matrices. The global oceans are especially exposed to plastic debris, as they are natural sinks for pollution. A proportion of land-based plastic materials find their way to the marine environment. As part of the work toward a solution to the increasing amounts of plastic litter, interest in plastic biodegradation processes has grown. This plastic litter is subjected to various extrinsic environmental conditions (e.g., temperature, moisture, pH, salinity, oxygen concentration, UV exposure, microbial community structure, and variations in mechanical energy) to influence its biodegradation potential and the rate at which that biodegradation takes place. Plastics comprise a wide range of polymers with distinct intrinsic physical and chemical properties (polymer type, crystallinity, molecular weight, morphology, additive chemical content, and composition) that significantly influence their susceptibility to particular degradation mechanisms, including biodegradation. As a result of large variations in these intrinsic and extrinsic parameters, the biodegradation and biodegradability of plastics within the natural environment is a complex process not conducive to a simple or generic description. Despite a steadily increasing research focus on plastic biodegradation, much remains unknown about the interactions among microorganisms, environments, and plastic materials. This chapter provides an overview of biodegradation mechanisms. It combines this with current knowledge about the intrinsic and extrinsic parameters that influence plastic biodegradability, emphasizing biodegradation in the marine environment. Topics for further research and development are also highlighted.