Plastics labelled “biodegradable” are not quite so innocuous after all, and can add considerably to the physical and chemical pollution of marine ecosystems, a newly-released UN report says.
Some ‘biodegradable’ plastics need industrial composters and exposure to temperatures over 50°C to completely disintegrate — and “such conditions are rarely if ever met in the marine environment,” says the United Nations Environment Programme (UNEP) report titled “Biodegradable Plastics and Marine Litter: Misconceptions, Concerns and Impacts on Marine Environments”.
Every year, around 280 million tonnes of plastic are produced globally, of which 20 million tonnes enter oceans, choking coral reefs, entangling marine wildlife, and when breaking down into microplastic (plastic particles of 5mm or less) then ingested by sea birds, fish and other marine organisms.
Divya Gandhi To speed up the degradation of plastic, such as polyethylene, a metal-based additive is included that catalyses its oxidation and breakdown. While these “oxo-degradable” plastics may fragment into microplastics sooner, “there is a lack of independent scientific evidence that biodegradation will occur any more rapidly than unmodified polyethylene,” says the report.
Slow degradation In marine environments, oxo-degradable plastic can take up to five years to degrade, during which time it continues to pollute the ocean. “The fate of these fragments (microplastics) is unclear, but it should be assumed that oxo-degradable polymers will add to the quantity of microplastics in the oceans, until overwhelming independent evidence suggests otherwise.”
Another report released last year by UNEP estimated that plastic waste cost marine ecosystems $13 billion in damages every year. Toys, athletic goods, and household goods sectors used the largest amount of plastic in their products while soft drinks companies and the pharmaceutical industry used the most plastic in their packaging, the report, “Valuing plastic”, said.
The new UNEP report says that there is, ironically, some evidence to suggest that “labelling a product as ‘biodegradable’ will result in a greater inclination to litter on the part of the public.” For instance, a bag with a ‘biodegradable’ stamp “is more likely to be discarded inappropriately,” it says. The report cites a survey of littering behaviour conducted in Los Angeles, which revealed that when a product was labelled as “biodegradable”, it encouraged littering. And although a plastic product may be marketed as ‘biodegradable’, “this may only apply to a limited range of environmental conditions, which are probably not encountered in the natural environment.”
In conclusion, “the adoption of plastic products labelled as ‘biodegradable’ will not bring about a significant decrease either in the quantity of plastic entering the ocean or the risk of physical and chemical impacts on the marine environment, on the balance of current scientific evidence,” it says.
Poor waste management and even deliberate release has led to “the ubiquitous presence” of plastic in oceans, spelling significant physical or chemical pollution of marine ecosystems. Marine wildlife – ranging from toothed whales to sea turtles and seagulls – has been found to contain large quantities of plastic within their guts. “It is thought that plastic items are mistaken for prey and, when swallowed, block the gut and cause starvation,” it says. Another study published in December 2014 in the journal PLOS One estimated that “at least 5.25 trillion plastic particles weighing 268,940 tonnes are currently floating at sea”.
However, biodegradable polymers, although considerably costlier, do have their uses, says the UNEP report. For instance, when used in fishing gear, it reduces “ghost fishing” or the inadvertent entanglement of marine life when the equipment is lost or discarded.
divya.gandhi@thehindu.co.in
