Microstructure Characterization of Oceanic Polyethylene Debris

Abstract

Plastic pollution has become a worldwide concern. It was demonstrated that plastic breaks down to nanoscale particles in the environment, forming so-called nanoplastics. It is important to understand their ecological impact, but their structure is not elucidated. In this original work, we characterize the microstructure of oceanic polyethylene debris and compare them to the nonweathered objects. Cross-sections are analysed by several emergent mapping techniques. We highlight deep modifications of the debris within a layer a few hundred microns thick. The most intense modifications are macromolecule oxidation and a considerable decrease in the molecular weight. The adsorption of organic pollutants and trace metals is also confined to this outer layer. Fragmentation of the oxidized layer of the plastic debris is the most likely source of nanoplastics. Consequently nanoplastic chemical nature differ greatly from plastics.

Evidence for protein misfolding in the presence of nanoplastics

“…Nonetheless, it must be mentioned here that in a recent article, Rowenczyk et al found that some oxidation occurs on PE in marine environments not only at the surface but even up to depths of 500‐6000 μm from the plastic's interface, albeit to a significantly lower extent. [ 18 ] Thus, these novel results suggest that the reasoning above has its limitations, and in future studies oxidized polymers might also be interesting to consider.…”

“…[ 1–4 ] It has been shown repeatedly that through the mechanical, chemical, and biological fragmentation of plastics microscopic pieces of polymers are formed in the form of microplastics (MPs, d < 1 mm) and nanoplastics (plastic nanoparticles [PNPs], d < 100 nm), which are being distributed all over the planet. [ 4–21 ] There are estimates that through the consumption of sea salt and sea food from polluted waters, food packed in plastic, and bottled water, humans consume several grams plastic everey week. [ 22–24 ] Presently, the actual risks these plastics pose to the environment and to health are mostly unknown, [ 25 ] beyond the fact that their mere occurrence is not natural in the bodies of humans and other living organisms.…”

Ionic Liquids as Extractants for Nanoplastics

“…Secondly, PNPs are often not pristine, but they contain – next to the actual polymer – additional compounds. These can be amphiphilic molecules adsorbed onto the PNPs surface (e. g. amino acids with non‐polar side chains), and thereby solubilizing it in a micelle‐like structure, or polar substituents on the polymer chains, produced by the partial oxidation of the PNP surface by air and sunlight or oxidative wastewater treatment . For weathered macroscopic polyethylene species, both processes have been observed through spectroscopic measurements .…”

“…These can be amphiphilic molecules adsorbed onto the PNPs surface (e. g. amino acids with non‐polar side chains), and thereby solubilizing it in a micelle‐like structure, or polar substituents on the polymer chains, produced by the partial oxidation of the PNP surface by air and sunlight or oxidative wastewater treatment . For weathered macroscopic polyethylene species, both processes have been observed through spectroscopic measurements . Whilst the former structures can be removed from the PNP during the phase transfer, solvated thereafter separately from the PNP in either of the two phases, the latter ones are covalently attached to the particle, and therefore they must enter the IL phase together with the rest of the PNP.…”

“…The RDF peaks indicate that the association of the polar moieties of the IL to the oxidized functional groups of the PNP is roughly independent of the side chain length, as the slight increase for the longer side chains can be partly attributed to the lower concentration of polar group in a unit volume of the IL, which causes through dilution effects an increase in the peak heights when calculating the g(r). Therefore, taking into consideration the high degree of oxidation in waste plastic, [87,88] ILs should be excellent solvents for PNP extraction from realistic environmental samples.…”