Physio-chemical degradation of single-use plastics in natural weather and marine environments.

Plastic pollution has reached concerning levels globally, with single-use plastic products (SUPs) comprising at least 50% of plastic waste. This study investigates the physical and chemical degradation of frequently used SUPs, including petroleum-based and bio-based plastics, in natural Northern European coastal weather and marine environments over a three-year period from 2019 to 2022. Addressing a critical knowledge gap, this research was based on a hypothesis that real-world ageing studies on SUPs would produce more accurate time- and process-lines for their transformation from macro-to microplastics than are available today based on the modeling studies more frequently used. The study employs optical examination, mechanical testing, Fourier Transform Infrared (FTIR) spectroscopy, and Gas Chromatography-Mass Spectrometry (GC-MS) to determine and relate physical and chemical changes with time. The results indicate that SUPs undergo significantly faster degradation in natural weather than predicted to date. Photooxidation emerges as the primary degradation pathway for all SUPs, emphasizing the role of light in plastic breakdown. Importantly, physical degradation to microplastics in natural environments is not always associated with significant chemical changes such as breaking chemical bonds. Black SUPs exhibit greater resistance to visible light and ultraviolet radiation than equivalent white and transparent examples. In marine environments, SUPs degrade measurably slower than in air, their degradation slowing with increasing distance from the water surface. Our findings indicate the urgent need for strategies that mitigate the impacts of photo-oxidation of SUPs. Such strategies may include a focus on the removal of post-use SUPs from pavements, roads, beaches, and water surfaces where photo-oxidation is faster than underwater and underground. Preferential use of black SUPs over white or transparent should also be considered.

Real time degradation studies on polyurethane household sponges in Danish weather and marine environments.

Polyurethane (PUR) ether sponges represent a widely-used cleaning tool with a short service lifetime resulting in the production of high quantities of waste. However, the fate of PUR in natural environments is poorly understood. In this study, sponges were exposed to the natural environments of Danish weather and seawater for two years. Physiochemical changes were monitored using visual, microscopic, spectroscopic and chromatographic techniques. Results from Attenuated Total Reflection-Fourier Transform Infrared spectroscopy and change in mass indicated that photo-oxidation was the primary degradation pathway of polyurethane ether- based sponges with a specific surface degradation rate of 12,500 µm year-1 in Danish weather. Significantly, analysis by gas chromatography-mass spectrometry showed the release to the environment of toxic substance TDI as a product of photo-oxidation. Although PUR degraded more slowly in seawater than in weather, flame retardant TMCP leached from sponges to water, indicating potential health risks of PUR waste to aquatic life.

Mastication of polyolefins alters the microbial composition in Galleria mellonella.

Recent studies have indicated that Galleria mellonella larvae ingest polyethylene films and the degradation mechanism could inspire biotechnological exploitation for degrading plastic to eliminate global pollution from plastic waste. In this study, we tested the chemical compositions of masticated and ingested different plastic types by G. mellonella. High throughput sequencing of 16S rRNA gene was used to characterize the alteration of the microbial communities derived from salivary glands, gut contents and whole G. mellonella larvae. Our results indicated that G. mellonella is able to masticate polyethylene (PE), expanded polystyrene (EPS) and polypropylene (PP) and convert it to small particles with very large and chemically modified surfaces. The characteristics of the polymer affect the rate of damage. Formation of functional carbonyl groups on the appearance of oxidized metabolic intermediates of polyolefins in the frass samples observed. We found that the mastication of EPS, PP or PE could significantly alter the microbial composition in the gut content while it did not appear to influence the salivary glands microbial community. Representatives of Desulfovibrio vulgaris and Enterobacter grew with the PE diet while mastication of polystyrene and polypropylene increased the abundance of Enterococcus. The evaluation of bacterial communities in whole larvae confirmed the obtained result and additionally showed that the abundance of Paenibacillus, Corynebacterium and Commamonadaceae increased by Styrofoam (EPS) consumption.

Impact of polyethylene on salivary glands proteome in Galleria melonella.

Polyethylene pollutions are considered inert in nature and adversely affect the entire ecosystem. Larvae of greater wax moth (Galleria mellonella) have the ability to masticate and potentially biodegrade polyethylene films at elevated rates. The wax moth has been thought to metabolize PE independently of gut flora, however the role of the microbiome is poorly understood and degradation by the wax moth might be involved. To determine whether the salivary glands of the wax moth were potentially involved in the PE degradation, it was investigated how surface changes of polyethylene were affected by mastication and consumption. Formation of pitting and degradation intermediates including carbonyl groups, indicated that salivary glands could assist in polyethylene degradation. We investigated the biochemical effect of exposure by PE on the composition of the salivary gland proteome. The expression of salivary proteins was found to be affected by PE exposure. The proteins that were significantly affected by the exposure to PE revealed that the wax moth are undergoing general changes in energy levels, also enzymatic pathways associated to fatty acid beta oxidation during consumption to PE were induced.