Nanofragmentation of Expanded Polystyrene Under Simulated Environmental Weathering (Thermooxidative Degradation and Hydrodynamic Turbulence)

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Abstract

Fragmentation of macroplastics into microplastics in the marine environment is probably one of the processes that have generated most drive for developing the microplastics research field. Thus, it is surprising that the level of scientific knowledge on the combinative effect of oxidative degradation and mechanical stressors on fragmentation is relatively limited. Furthermore, it has been hypothesized that plastic fragmentation continues into the nanoplastic size domains, but environmentally realistic studies are lacking. Here the effects of thermooxidative aging and hydrodynamic conditions relevant for the shoreline environment on the fragmentation of expanded polystyrene (EPS) were tested in laboratory simulations. The pre-degraded EPS was cut into pieces and subjected to mechanical, hydrodynamic simulations during four-day stirring experiments. Subsamples were filtered and subsequently analyzed with light microscopy with automated image analysis particle size distribution determinations, polymer identification with Raman spectroscopy, Scanning Electron Microscopy (SEM) with automated image analysis particle size distribution. The nanoplastic size fraction was measured using nanoparticle tracking analysis. In addition, the degree of polymer oxidation was spectroscopically characterized with Fourier transform infrared (FTIR) spectroscopy. The results illustrate that fragmentation of the mesoplastic objects is observed already after 2 days, but that is more distinct after 4 days, with higher abundances for the smaller size fractions, which imply more release of smaller sizes or fragmentation in several steps. For the nanoplastic fraction, day four shows a higher abundance of released or fragmented particles than day two. The conclusions are that nanofragmentation is an important and understudied process and that standardized test protocols for both thermooxidative degradation and mechanical treatments mimicking realistic environmental conditions are needed. Further testing of the most common macro- and mesoplastic materials to assess the rates and fluxes of fragmenting particles to micro- and nanoplastic fractions should be conducted.

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Microplastics in the marine environment.

Anthony Andrady (2011)

This review discusses the mechanisms of generation and potential impacts of microplastics in the ocean environment. Weathering degradation of plastics on the beaches results in their surface embrittlement and microcracking, yielding microparticles that are carried into water by wind or wave action. Unlike inorganic fines present in sea water, microplastics concentrate persistent organic pollutants (POPs) by partition. The relevant distribution coefficients for common POPs are several orders of magnitude in favour of the plastic medium. Consequently, the microparticles laden with high levels of POPs can be ingested by marine biota. Bioavailability and the efficiency of transfer of the ingested POPs across trophic levels are not known and the potential damage posed by these to the marine ecosystem has yet to be quantified and modelled. Given the increasing levels of plastic pollution of the oceans it is important to better understand the impact of microplastics in the ocean food web. Copyright © 2011 Elsevier Ltd. All rights reserved.

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Microplastics in the marine environment: a review of the methods used for identification and quantification.

Valeria Hidalgo-Ruz, Lars Gutow, Richard Thompson … (2012)

This review of 68 studies compares the methodologies used for the identification and quantification of microplastics from the marine environment. Three main sampling strategies were identified: selective, volume-reduced, and bulk sampling. Most sediment samples came from sandy beaches at the high tide line, and most seawater samples were taken at the sea surface using neuston nets. Four steps were distinguished during sample processing: density separation, filtration, sieving, and visual sorting of microplastics. Visual sorting was one of the most commonly used methods for the identification of microplastics (using type, shape, degradation stage, and color as criteria). Chemical and physical characteristics (e.g., specific density) were also used. The most reliable method to identify the chemical composition of microplastics is by infrared spectroscopy. Most studies reported that plastic fragments were polyethylene and polypropylene polymers. Units commonly used for abundance estimates are "items per m(2)" for sediment and sea surface studies and "items per m(3)" for water column studies. Mesh size of sieves and filters used during sampling or sample processing influence abundance estimates. Most studies reported two main size ranges of microplastics: (i) 500 μm-5 mm, which are retained by a 500 μm sieve/net, and (ii) 1-500 μm, or fractions thereof that are retained on filters. We recommend that future programs of monitoring continue to distinguish these size fractions, but we suggest standardized sampling procedures which allow the spatiotemporal comparison of microplastic abundance across marine environments.

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Life in the "plastisphere": microbial communities on plastic marine debris.

Erik Zettler, Tracy J. Mincer, Linda A Amaral-Zettler (2013)

Plastics are the most abundant form of marine debris, with global production rising and documented impacts in some marine environments, but the influence of plastic on open ocean ecosystems is poorly understood, particularly for microbial communities. Plastic marine debris (PMD) collected at multiple locations in the North Atlantic was analyzed with scanning electron microscopy (SEM) and next-generation sequencing to characterize the attached microbial communities. We unveiled a diverse microbial community of heterotrophs, autotrophs, predators, and symbionts, a community we refer to as the "Plastisphere". Pits visualized in the PMD surface conformed to bacterial shapes suggesting active hydrolysis of the hydrocarbon polymer. Small-subunit rRNA gene surveys identified several hydrocarbon-degrading bacteria, supporting the possibility that microbes play a role in degrading PMD. Some Plastisphere members may be opportunistic pathogens (the authors, unpublished data) such as specific members of the genus Vibrio that dominated one of our plastic samples. Plastisphere communities are distinct from surrounding surface water, implying that plastic serves as a novel ecological habitat in the open ocean. Plastic has a longer half-life than most natural floating marine substrates, and a hydrophobic surface that promotes microbial colonization and biofilm formation, differing from autochthonous substrates in the upper layers of the ocean.