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 Because of their adverse impact on marine life, non-biodegradable bags have recently been replaced by biodegradable ones.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

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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

The report

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

The article 

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

The article

Invisible plastic particles from textiles and tyres a major source of ocean pollution – IUCN study

Tiny plastic particles washed off products such as synthetic clothes and car tyres could contribute up to 30% of the ‘plastic soup’ polluting the world’s oceans and – in many developed countries – are a bigger source of marine plastic pollution than plastic waste, according to a new IUCN report.  (…) (IUCN, 22/02/2017)

The news and report (Primary microplastics in the oceans : a global evaluation of sources, authors: Julien Boucher, Damien Friot)

Preparation and degradation mechanisms of biodegradable polymer: a review

Polymers are difficult to degrade completely in Nature, and their catabolites may pollute the environment. In recent years, biodegradable polymers have become the hot topic in people’s daily life with increasing interest, and a controllable polymer biodegradation is one of the most important directions for future polymer science. This article presents the main preparation methods for biodegradable polymers and discusses their degradation mechanisms, the biodegradable factors, recent researches and their applications. The future researches of biodegradable polymers are also put forward.

S H Zeng, P P Duan, M X Shen, Y J Xue and Z Y Wang, IOP Conference Series: Materials Science and Engineering, Volume 137, Number 1, 2016 (Open access)

The article

Compostable and edible packaging: the companies waging war on plastic

However, more sustainable alternatives have proved controversial. Earlier this year the UN’s chief scientist, Jacqueline McGlade, described biodegradable plastics as “well-intentioned but wrong” since those that end up the oceans do not have the right conditions to break down.

Other plastics, including so-called oxo-degradables (pdf), break down into microplastics, which are also thought to be highly damaging if they find their way into the ocean.

Now a new generation of plastic makers is working to tackle the global plastic waste crisis head on by developing home-compostable plastics. (…) (theguardian.com, October 2016)

The news