Concerns over plastic pollution have prompted many consumers to reach for products labelled “biodegradable”. A United Nations study, however, has found that widespread use of such items does little to solve the problem of plastic in the world’s oceans and the damage it does to marine creatures and the environment.
The report Biodegradable Plastics and Marine Litter – Misconceptions, Concerns and Impacts on Marine Environments says that in the oceans, biodegradable plastic rarely disintegrates. There is also evidence suggesting that labelling products as “biodegradable” makes people more inclined to litter.
Plastics have great benefits and advantages for society. Their durability makes them useful for food preservation, medical product efficacy, electrical safety and improved thermal insulation, among other things. Unfortunately, their hard-wearing characteristic becomes a bane when they end up in the environment, especially oceans.
The United Nations Environment Programme (UNEP) estimates that about 280 million tonnes of plastic are produced globally each year and of that, only a small percentage is recycled. Because of littering and poor waste management, some of that plastic waste ends up in the world’s oceans, costing several billion dollars annually in environmental damage to marine ecosystems.
In recent years, concern has grown over microplastics – particles up to 5mm in diameter, either manufactured (such as plastic exfoliating beads in personal care products) or created when plastic breaks down (such as fibres from clothes when washed). Ingestion of microplastics has been seen in marine organisms, including seabirds, fish, mussels and worms.
“Recent estimates show that as much as 20 million tonnes of plastic end up in the world’s oceans each year. Once in the ocean, plastic does not go away but breaks down into microplastic particles. This new report shows there are no quick fixes, and a more responsible approach to managing the life-cycle of plastic will be needed to reduce their impacts on our oceans and ecosystems,” says UNEP executive director Achim Steiner.
The report – commissioned by the Global Programme of Action for the Protection of the Marine Environment from Land-based Activities, an intergovernmental mechanism hosted by UNEP – was to verify whether biodegradable plastics can lessen the negative environmental impact that conventional plastics pose to the marine environment. The conclusion? Switching to biodegradable plastic will not significantly decrease the volume of plastic entering oceans.
Biodegradation of plastic occurs when none of the original polymer remains – that is, it has been broken down to carbon dioxide, methane and water. The extent of biodegradation is influenced by properties of the polymer and environmental factors, such as temperature.
The report says that the conditions that trigger complete breakdown of biodegradable plastics are rarely, if ever, met in the marine environment. For example, a plastic shopping bag marked “biodegradable” may require conditions found only in an industrial composter (such as high and constant temperatures of 50°C) to break down.
The report author, marine biologist Dr Peter John Kershaw, says plastic polymers which disintegrate under favourable conditions on land are much slower to break up in the ocean, so their widespread use is likely to contribute to marine litter. He says to be considered biodegradable, these products need to meet certain industrial standards but these do not match what actually goes on in the environment.
In the oceans, ultraviolet radiation is the dominant weathering process. It causes plastic to turn brittle, crack and break up. Fragmentation is greatest when plastic debris is directly exposed to UV radiation on shorelines. Once they are buried in sediment, submerged in water or covered in organic and inorganic films (which happens readily in sea water), then the speed of fragmentation declines. The report states that plastic objects observed on the seabed, such as PET bottles, plastic bags and fishing nets, show insignificant deterioration. In addition, the inclusion of additive chemicals such as UV- and thermal-stabilisers inhibit the fragmentation process.
The study also analyses the environmental impact of oxo-biodegradable plastics which are gaining popularity. These are conventional polymers such as polyethylene, which are manufactured with a metal-based additive (such as manganese) to promote rapid fragmentation when discarded. The study finds that in marine environments, the fragmentation is fairly slow and can take up to five years, during which the plastic objects continue to foul the sea. When these plastics eventually shatter, their fate is still poorly understood. “It should be assumed that the microplastics remain in the ocean, where they can be ingested by marine organisms and facilitate the transport of harmful microbes, pathogens and algal species,” says the report. The study finds a lack of independent scientific evidence showing that oxo-biodegradable plastics biodegrade completely in the environment, except under industrial composting conditions.
Biodegradable plastic also poses a problem for recycling. When it gets mixed with standard plastic, the properties of the original plastic are compromised. To ensure proper recycling, both types of plastic have to be segregated. The report also cites research that found that labelling products as “biodegradable” increases people’s tendency to litter because they think they are not creating waste. The report suggests minimal use of plastic and proper recycling as ideal actions to eliminate plastic pollution.
Download the report at unep.org/gpa/documents/publications/BiodegradablePlastics.pdf.