Marine pollution /
Marine pollution / Marine degradation UNEP Report on biodegradable plastics & marine litter Summarized and interpreted by Karen Laird and Michael Thielen Photo: Ludwig Tröller / CreativeCommons In November 2015 the United Nations Environment Programme (UNEP) published a report, entitled “Biodegradable Plastics and Marine Litter. Misconceptions, Concerns and Impacts on Marine Environments”. The objective of (the) briefing paper is to provide a concise summary of some of the key issues surrounding the biodegradability of plastics in the oceans, and whether the adoption of biodegradable plastics will reduce the impact of marine plastics overall [1]. Plastic debris is ubiquitous in the marine environment, comes from a multitude of sources and is composed of a great variety of polymers and copolymers [1]. It has been suggested that plastics considered to be biodegradable may play an important role in reducing the impact of ocean plastics. Environmental biodegradation is the partial or complete breakdown of a polymer as a result of microbial activity, into CO 2 , H 2 O and biomasses, as a result of a combination of hydrolysis, photodegradation and microbial action (enzyme secretion and within-cell processes). Although this property may be appealing, it is critical to evaluate the potential of ‘biodegradable’ plastics in terms of their impact on the marine environment, before encouraging wider use [1]. The report found that complete biodegradation of plastics occurs in conditions that are rarely, if ever, met in marine environments, with some polymers requiring industrial composters and prolonged temperatures of above 50 °C to disintegrate. There is also limited evidence suggesting that labelling products as biodegradable increases the public’s inclination to litter, as some people are attracted by technological solutions as an alternative to changing behaviour. Labelling a product as biodegradable may be seen as a technical fix that removes responsibility from the individual, resulting in a reluctance to take action. As stated in the report, plastics most commonly used for general applications, such as polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) are not biodegradable in marine environments (nor in any other, MT). Polymers, which biodegrade under favourable conditions on land, such as acetyl cellulose (AcC), UN Photo Martine Perret 24 bioplastics MAGAZINE [02/16] Vol. 11
Marine pollution / Marine degradation polybutylene succinate (PBS), polycaprolactone (PCL), polyvinyl alcohol (PVA) and others are much slower to break up in the ocean and their widespread adoption is likely to contribute to marine litter and consequent undesirable consequences for marine ecosystems. “Recent estimates from UNEP have shown as much as 20 million tonnes of plastic end up in the world’s oceans each year,” said Achim Steiner, Executive Director of the UN Environment Programme (UNEP) in a press release. “Once in the ocean, plastic does not go away, but breaks down into microplastic particles. This report shows there are no quick fixes, and a more responsible approach to managing the lifecycle of plastics will be needed to reduce their impacts on our oceans and ecosystems.” These microplastics have, in recent years, become a source of growing concern. Microplastics are particles up to five millimetres in diameter, that are either manufactured or created when plastic breaks down. Their ingestion has been widely reported in marine organisms, including seabirds, fish, mussels, worms and zooplankton. The UNEP study also analyzed the environmental impacts of oxo-degradable plastics, enriched with a pro oxidant, such as manganese, which precipitates their fragmentation. It found that in marine environments even this fragmentation is fairly slow and can take up to 5 years, during which products made from this type of plastic continue to pollute the ocean. Moreover, convincing evidence showing that oxo-degradable polymers completely biodegrade to CO 2 and water after fragmentation is still lacking. According to UNEP, oxo-degradable plastics can pose a threat to marine ecosystems even after fragmentation. The report says it should be assumed that microplastics created in the fragmentation process remain in the ocean, where they can be ingested by marine organisms and facilitate the transport of harmful microbes, pathogens and algal species. The report also quotes a UK government review that stated that “oxo-degradable plastics did not provide a lower environmental impact compared with conventional plastics”. The recommended solutions for dealing with end-of-life oxo-degradable plastics were incineration (first choice) or landfill. In addition, the authors observed that: as the (oxo-degradable) plastics will not degrade for approximately 2 – 5 years, they will still remain visible as litter before they start to degrade. The report more or less confirms what many in the industry have known for a long time, and it contains important information for the public at large – both as regards oxo-degradable plastics and biodegradable plastics. Well-written and well-researched, the report is by no means an attack on biobased plastics, but rather an attempt to get a message out and to create awareness. As its authors put it: “Assessing the impact of plastics in the environment, and communicating the conclusions to a disparate audience is challenging. The science itself is complex and multidisciplinary. Some synthetic polymers are made from biomass and some from fossil fuels, and some can be made from either. Polymers derived from fossil fuels can be biodegradable. Conversely, some polymers made from biomass sources, such as maize, may be non-biodegradable. Apart from the polymer composition, material behaviour is linked to the environmental setting, which can be very variable in the ocean. The conditions under which biodegradable polymers will actually biodegrade vary widely.” And the report closes with the final conclusion: On the balance of the available evidence, biodegradable plastics will not play a significant role in reducing marine litter [1]. [1] UNEP 2015. Biodegradable Plastics & Marine Litter. Misconceptions, Concerns and Impacts on Marine Environments. Nairobi. a pdf-version is available at bit.ly/1R7IALI Photo: M. Thielen, bioplastics MAGAZINE [02/16] Vol. 11 25
