A whale shark swims beside a plastic bag in the Gulf of Aden near Yemen. Although whale sharks are the biggest fish in the sea, they're still threatened by ingesting small bits of plastic. Both the United Nations and the European Union have staked out positions against biodegradables. The UN, in a report published in , flatly declared that biodegradable plastics are not the answer to marine plastic pollution. Thompson and his team tested five types of bags, including one compostable bag, one conventional high-density polyethylene bag, and three kinds of biodegradable bags.
Two of the biodegradable bags were oxo-biodegradable. The other biodegradable bag was manufactured in a way that promotes its breakdown differently. Bags were exposed to environmental conditions in three different sites. For the experiment, some of the bags were cut into strips and placed in mesh pouches that exposed them to outdoor elements at each of three different test sites. Whole bags were also used in each of the test locations. For the soil test in the university garden, samples were buried almost ten inches deep.
For the outdoor exposure test, samples were placed on a wall in the garden with a southern exposure. For the marine test, samples were submerged more than three feet beneath the surface of Plymouth Harbor. A fourth laboratory test site was set up as a control. Samples were set out July 10, , and inspected regularly for signs of surface loss, holes, or disintegration. Samples were also measured for tensile strength, meaning how easily they broke under tension.
At the harbor site, all the bags and test strips had acquired a microbial biofilm on the surface after a month. The compostable bag disappeared after three months. At the open-air site in the garden, all of the bags and test strips had become too brittle to test further or had disintegrated into microplastics after nine months. They could not be tested further. At the soil site in the garden, the bags remained intact. Although the compostable bag survived in its original shape for 27 months, it was unable to hold any weight without tearing.
Narayan, the chemist, says the study provides real world data revalidating the limitations of biodegradables. The Plymouth study says that in it was estimated that Awareness of the problem of plastic pollution and the impact on the environment has led to a growth in so-called biodegradable and compostable options.
But Napper said the results showed none of the bags could be relied on to show any substantial deterioration over a three-year period in all environments. The research showed that the way compostable bags were disposed of was important. They should biodegrade in a managed composting process through the action of naturally occurring micro-organisms. But the report said this required a waste stream dedicated to compostable waste — which the UK does not have. Vegware, which produced the compostable bag used in the research, said the study was a timely reminder that no material was magic, and could only be recycled in its correct facility.
Compostable materials can compost with five key conditions — microbes, oxygen, moisture, warmth and time. After 9 months in the open air environment, all the bags either became too brittle to continue testing or had shattered into microplastic pieces one of the primary complaints about oxo-biodegradables is that they include additives to speed up break down and this results in micro-plastic pollution. The EU even recommended banning them last year. If a biodegradable bag ends up in a recycling bin, for example, it has the potential to contaminate a whole batch of recyclables making them unviable.
Compostable materials can compost with five key conditions — microbes, oxygen, moisture, warmth and time. The researchers voiced concerns over the way biodegradable products get marketed. Their marketing seems to suggest they can be thrown right into the natural environment, but the results of this most recent study suggest otherwise. The researchers suggest that standards need to be developed for compostable, biodegradable and oxo-biodegradable materials, such as clearly outlining appropriate disposal and the rates of degradation that can be expected.
The lack of consumer education about the differences between compostable, biodegradable and oxo-biodegradable materials and where to properly dispose of them, coupled with a lack of facilities to deal with their decomposition, further challenges the notion that these products are better for the environment. But that should not be the end of the conversation. We need to challenge the single-use product model itself. As resistance to the plastic epidemic swells and cities and countries carry out bans against single-use plastic products worldwide, we need to carefully consider the implications of this research study.
At the heart of the issue remains a key question: is the single-use, throwaway model sustainable in the first place? Or, to put it another way, the problem is pursuing, on the one planet known to harbour life, a four-planet lifestyle.
Last year, someone tweeted at Starbucks to request they replace their plastic coffee cups with cups made from corn starch. This tweet was retweeted over 60, times before being deleted when someone raised a big red flag: those who were supporting this call failed to consider the environmental impacts of producing corn starch.
As it turns out, an enormous amount of land needs to be cleared to grow it, displacing food production. The challenge is to get all of the pieces of the puzzle to slot into place. Join one million Future fans by liking us on Facebook , or follow us on Twitter or Instagram. If you liked this story, sign up for the weekly bbc. Share using Email. By Kelly Oakes 5th November But could they help to fix our food waste problem? The desert soil that could save lives The fight to bring a deadly illegal industry to justice Biodegradable plastics are one set of materials that are becoming a popular replacement as consumers demand green alternatives.
The problem with labels To test how different kinds of plastic bag fare in different environments, Imogen Napper at the University of Plymouth collected carrier bags with various claims about biodegradability, and put them in three different natural environments over a period of three years: buried in soil, left in the sea, and hung up in the open air.
Bioplastics might not solve our marine plastic pollution problem, but they are well suited to tackling another big environmental problem: food waste. Cleaning up our act The biggest potential area of impact for compostable plastics is in food service. There are some other applications suited to biodegradables, too. A load of compostables are going to end up incinerated, and a lot of plastics are going to end up in composting plants, it's just the way it is for the next two years or three years — David Newman.
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