Disintegration of Biodegradable Plastic Bags in Marine Mesocosm Conditions: The Effects of Time and Temperature

Plastic pollution in the marine environment is a persistent and ubiquitous issue. Biodegradable and compostable plastics may present a positive alternative to traditional non-biodegradable polymers for marine applications such as aquaculture. Mater-Bi (MB) is a starch-based polymer used in compostable films and plastic carrier bags and has been proven to completely biodegrade in a variety of laboratory conditions. However, degradation rates in the natural environment differ from static laboratory tests and depend on the specific physicochemical and environmental conditions of a particular location. This study examined the degradation of Mater-Bi in coastal marine conditions in a flow-through mesocosm system, in comparison to polyhydroxybutyrate (PHB), a well-known biopolymer, and high-density polyethylene (HDPE), a traditional plastic polymer. Mass and area loss were both used as proxies for disintegration across a nine-month time span. Results indicate that both Mater-Bi and polyhydroxybutyrate disintegrate when exposed to shallow water column and sediment conditions, losing on average 25 to 47% of area or mass, whereas high-density polyethylene showed no evidence of degradation. Loss of area and mass of Mater-Bi and polyhydroxybutyrate were especially pronounced, averaging 0.87%/week after 30 weeks of submergence when water temperature increased to 20 °C. The disintegration of biodegradable plastics through microbial action over time and in warmer temperatures likely contributed to these results. Biodegradable plastics such as Mater-Bi may therefore have a lower environmental impact and persist in the marine environment for shorter periods of time than conventional non-biodegradable polymers.