Characterising the deterioration of different plastics in air and seawater

Abstract

In situ studies of plastic deterioration can help us understand the longevity of macroplastic as well as the generation of microplastics in the environment. Photo-oxidation contributing to the generation of microplastics in the marine environment was explored using four types of plastic (polyethene, polystyrene, poly(ethylene terephthalate) and Biothene exposed in light and in shade, in both air and sea water. Metrics for deterioration were tensile extensibility and oxidation rate. Measurements were conducted at intervals between 7 and 600 days' exposure. Deterioration was faster in air than in sea water and was further accelerated in direct light compared to shade. Extensibility and oxidation were significantly inversely correlated in samples exposed in air. Samples in sea water lost extensibility at a slower rate. Polystyrene, which enters the waste stream rapidly due to its wide application in packaging, deteriorated fastest and is, therefore, likely to form microplastics more rapidly than other materials, especially when exposed to high levels of irradiation, for example when stranded on the shore.

Laboratory model for plastic fragmentation in the turbulent ocean

“…Let us consider an elongated object with a Young modulus E ≈ 1 GPa and a diameter d ≈ 50 µm. These values are rather classical for plastic materials, as plastic films for example [57,58] which have a typical thickness of 50 µm. The turbulent flow near the ocean surface experienced by plastic debris is most of the time weakly turbulent, with turbulent dissipation rates of the order of ε ≈ 10 −6 − 10 −3 m 2 /s 3 caused by wind shear on the ocean surface [21].…”

Degradation of bio-based and biodegradable plastics in a salt marsh habitat: Another potential source of microplastics in coastal waters

“…These first few weeks of exposure were marked by the least amount of biofilm, and consequently, the greatest amount of UV transmittance, which would have facilitated photo-oxidation reactions. The role of photo-oxidation in the degradation of plastics has been previously noted in a study by Biber et al (2019) , who found that the deterioration of polyethylene, PET, PS, and Biothene® was faster in direct sunlight compared to shade, and in air compared to water. These results corroborate those of an earlier study by Pegram and Andrady (1989) , who found little evidence of weathering of polyethylene samples floating in seawater over an 8-week period, whereas those exposed to air nearly embrittled over the same period.…”

Degradation of Biodegradable Single-Use Plates and Waste Bags in Terrestrial and Marine Environments

“…In the context of this study, the lowest rate of degradation was observed in open-air conditions for all four of the studied environments. Contrary to that of previous studies, the non-degradable plastic fragmented in open-air faster when compared to the marine environment [7], [17]. However, in these previous studies the impact of grazers was limited as the sampled products were shielded by dense mesh.…”