Observation of the degradation of three types of plastic pellets exposed to UV irradiation in three different environments

Plastic debris represents one of the most prevalent and persistent pollution problems in the marine environment. In particular, microplastics that are mainly degraded from larger plastic debris have become a growing environmental concern. However, studies on the degradation of plastics in the aquatic environment that hydrobios reside in have been limited, while several studies regarding the degradation of plastics have been conducted under outdoor or accelerated weathering conditions. Thus, observation of the degradation of three types of virgin plastic pellets exposed to UV irradiation in three different environments (i.e., simulated seawater, ultrapure water, and a waterless (air) condition) was carried out. Data on the changes in physical and chemical properties were collected. The FTIR spectra showed that hydroxyl groups and carbonyl groups developed in three types of weathered plastic pellets under the air and ultrapure water environmental conditions after 3 months of UV irradiation, while only carbonyl groups were found in plastic pellets in the simulated seawater environment. In contrast, the Raman spectra showed no significant changes in the weathered plastic pellets, but there were different intensities of characteristic peaks after exposure to UV irradiation. In addition, SEM images illustrated that granular oxidation, cracks and flakes were common patterns during degradation, and the plastic pellets in the three different environments experienced different levels of chemical weathering. We suggest that further studies on the degradation processes of plastic debris are needed to predict the fate of plastic debris in the environment.

Liqi Cai, Jundong Wang, Jinping Peng, Ziqing Wu, Xiangling Tan, Science of The Total Environment, Volumes 628–629, 1 July 2018, Pages 740–747

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How plastics made from plants could be the answer to the world’s waste problem

(…) Using these platform molecules, the Green Chemistry Centre of Excellence at the University of York, has been working with the plastics industry to create a new generation of bio-based polyesters. These are often used to make fibres for clothing, as well as films and containers for liquids and foods. The resulting materials are entirely plant based, recyclable and – importantly – fully biodegradable. (…) (Theconversation.com, James William Comerford, 23/02/2018)

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Biodegradability of plastics: challenges and misconceptions

Plastics are one of the most widely used materials and, in most cases, they are designed to have long life times. Thus, plastics contain a complex blend of stabilizers that prevent them from degrading too quickly. Unfortunately, many of the most advantageous properties of plastics such as their chemical, physical and biological inertness and durability present challenges when plastic is released into the environment. Common plastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) are extremely persistent in the environment, where they undergo very slow fragmentation (projected to take centuries) into small particles through photo-, physical, and biological degradation processes1. The fragmentation of the material into increasingly smaller pieces is an unavoidable stage of the degradation process. Ultimately, plastic materials degrade to micron-sized particles (microplastics), which are persistent in the environment and present a potential source of harm for organisms.

Stephan Kubowicz and Andy M. Booth, Environ. Sci. Technol., Article ASAP, October 12, 2017

Biodegradable plastic bags on the seafloor: A future threat for seagrass meadows?

Marine plastic litter is a global concern. Carrier bags manufactured from non-biodegradable polymers constitute a large component of this litter. Because of their adverse impact on marine life, non-biodegradable bags have recently been replaced by biodegradable ones. However, growing evidence shows that these latter are not readily degradable in marine sediments and can alter benthic assemblages. The potential impact of biodegradable bags on seagrasses inhabiting sandy bottoms, which are the most widespread and productive ecosystems of the coastal zones, has been ignored. Mesocosm experiments were conducted to assess the effect of a commercialized biodegradable bag on a common seagrass species of the Mediterranean, Cymodocea nodosa, both at the level of individual plant (clonal growth) and of plant community (plant-plant relationships), under three culture regimes (plant alone, in combination with a neighbour of the same species or of the co-existing seagrass Zostera noltei) simulating different natural conditions (bare substrate, monospecific meadows or mixed meadows). The bag behaviour in marine sediment and sediment physical/chemical variables were also examined. After six months of sediment exposure, the bag retained considerable mass (85% initial weight) and reduced sediment pore-water oxygen concentration and pH. In the presence of bag, C. nodosa root spread and vegetative recruitment increased compared to controls, both intra- and interspecific interactions shifted from neutral to competitive, and the growth form changed from guerrilla (loosely arranged group of widely spaced ramets) to phalanx form (compact structure of closed spaced ramets) but only with Z. noltei. These findings suggest that biodegradable bags altering sediment geochemistry could promote the spatial segregation of seagrass clones and influence species coexistence.

Elena Balestri, Virginia Menicagli, Flavia Vallerini, Claudio Lardicci, Science of The Total Environment, Volumes 605–606, 15 December 2017, Pages 755–763

Study to provide information supplementing the study on the impact of the use of “oxo-degradable” plastic on the environment”

Oxo-degradable or oxo-biodegradable plastics are conventional plastics, such as High Density Polyethylene (HDPE), commonly used in carrier bags, which also include additives which are designed to promote the oxidation of the material to the point where it embrittles and fragments. This may then be followed by biodegradation by bacteria and fungi at varying rates depending upon the environment. It has been debated for some time whether or not these additives perform in the way in which their manufacturers claim they will, whether they cause harm to the environment, and whether they effectively make plastics recycling more problematic. In November 2014, Members of the European Parliament proposed an outright ban on “oxo-degradable” plastics within the EU. Although this measure was blocked, an amendment to the Packaging and Packaging Waste Directive, adopted in May 2015, commits the Commission to examine the impact of the use of oxo-degradable plastic on the environment; “By 27 May 2017, the Commission shall present a report to the European Parliament and to the Council, examining the impact of the use of oxo-degradable plastic carrier bags on the environment and present a legislative proposal, if appropriate.” This study has been undertaken in response to that request and compiles the requisite information regarding environmental impacts of this material, to the extent that such information is available, in order to form an opinion on any appropriate actions to be taken. The report presented here draws on the available scientific literature in order to investigate the claims from the industry with regard to biodegradation in different environments, and compatibility with current recycling processes. Input from key stakeholders—including the industry itself—has been used during the review to understand the impacts of the use of these materials.

European Commission, Final report, April 2017, 166 pages

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Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonella

Plastics are synthetic polymers derived from fossil oil and largely resistant to biodegradation. Polyethylene (PE) and polypropylene (PP) represent ∼92% of total plastic production. PE is largely utilized in packaging, representing ∼40% of total demand for plastic products (www.plasticseurope.org) with over a trillion plastic bags used every year [1] . Plastic production has increased exponentially in the past 50 years ( Figure S1 A in Supplemental Information , published with this article online). In the 27 EU countries plus Norway and Switzerland up to 38% of plastic is discarded in landfills, with the rest utilized for recycling (26%) and energy recovery (36%) via combustion (www.plasticseurope.org), carrying a heavy environmental impact. Therefore, new solutions for plastic degradation are urgently needed. We report the fast bio-degradation of PE by larvae of the wax moth Galleria mellonella, producing ethylene glycol.

Paolo Bombelli, Christopher J. Howe, Federica Bertocchini, Current Biology, Volume 27, Issue 8, pR292–R293, 24 April 2017

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Biodegradation of polyethylene microplastics by the marine fungus Zalerion maritimum

Plastic yearly production has surpassed the 300 million tons mark and recycling has all but failed in constituting a viable solution for the disposal of plastic waste. As these materials continue to accumulate in the environment, namely, in rivers and oceans, in the form of macro-, meso-, micro- and nanoplastics, it becomes of the utmost urgency to find new ways to curtail this environmental threat. Multiple efforts have been made to identify and isolate microorganisms capable of utilizing synthetic polymers and recent results point towards the viability of a solution for this problem based on the biodegradation of plastics resorting to selected microbial strains.

Herein, the response of the fungus Zalerion maritimum to different times of exposition to polyethylene (PE) pellets, in a minimum growth medium, was evaluated, based on the quantified mass differences in both the fungus and the microplastic pellets used. Additionally, molecular changes were assessed through attenuated total reflectance Fourier transform Infrared Spectroscopy (FTIR-ATR) and Nuclear Magnetic Resonance (NMR).

Results showed that, under the tested conditions, Z. maritimum is capable of utilizing PE, resulting in the decrease, in both mass and size, of the pellets. These results indicate that this naturally occurring fungus may actively contribute to the biodegradation of microplastics, requiring minimum nutrients.

Ana Paço, Kátia Duarte, João P. da Costa and al., Science of The Total Environment, Volume 586, 15 May 2017, Pages 10–15

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