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The future of plastic waste disposal could be a fungus

A Pakistani scientist has discovered a fungus that can break down plastic
by Mahrukh Sarwar

The ground around the once popular tourist destination is polluted with rubbish. Plastic bags, bottles and other disposable waste is strewn around Keenjhar, the second largest freshwater lake in Pakistan. Located 122 km from Karachi city and a mere 18 km from the town of Thatta, it remains a vital source of potable water for people in both localities.

The lake sees a high influx of visitors on a daily basis so they can swim, fish and enjoy picnics there. The plastic pollution they leave behind chokes sewers and open drainage systems, and contributes to the spread of vector-borne diseases. When burnt, it gives off toxic fumes in the air which is being inhaled by humans.

Synthetic plastics, which take years to decompose, pose a huge risk to the environment. Approximately 300 million tons of plastic is produced globally each year. Of that, only 10 percent is recycled. Most of it is simply thrown away. Some types of plastics can even take up to 1,000 years to biodegrade. The average time for an ordinary plastic bag to decompose is at least 500 years.

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A Pakistani researcher has made an  important discovery that could have implications for waste management in the country. Dr Sehroon Khan, of World Agroforestry Centre and Kunming Institute of Biology, and his team of researchers have found a fungus in a garbage dump in Sector H-10 in Islamabad which can break down plastic in a matter of weeks.

Khan’s research, published in Environmental Pollutionan international journal – focuses on the discovery of a type of soil fungus, Aspergillus tubingensis, that uses enzymes to break down plastics such as polyester polyurethane (PU) in a matter of weeks. The fungus was found in a garbage dump in Sector H-10 in Islamabad, Pakistan. Researchers collected soil samples as well as various pieces of plastics, wood and pebbles in the hope of isolating and identifying a PU biodegrading fungi.

Aspergillus tubingensis is generally found growing in soil but researchers found that it could also colonize and thrive on plastic surfaces. It breaks them down by secreting enzymes which weaken the chemical bonds between individual molecules and uses the mechanical force of its thread-like hyphae to break them apart. This process takes only a few weeks.

According to the research, the plastic degrading ability of the fungus was tested in three different ways: on a Sabouraud Dextrose Agar (SDA) plate, in liquid mineral salt medium (MSM), and after burial in soil. Researchers discovered that the biodegradation of PU by the fungus was the highest when the SDA plate culture method was used, followed by the liquid culture method and soil burial technique. In fact, after just two months in the liquid medium the fungus had completely degraded the PU film into smaller pieces.

The team of researchers also found that the performance of the fungi was affected by the temperature, pH balance of its surroundings and the carbon source of the culture medium. They are now looking into the conditions required to replicate the process.

Talking to MIT Technology Review, Dr Khan said, “I did some of the work in Pakistan as an MPhil student and some of the work was done in my postdoc in China. Kunming Institute of Botany (KIB), Chinese Academy of Sciences (CAS) give me an opportunity when I had no job after my contract with the HEC ended. This was between 2012 and 2013. Then I joined KIB, CAS for postdoctoral studies. Thanks to China for providing a platform and giving me four grants in three years.”

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The study was conducted by nine researchers from Pakistan and China.

Goodbye plastic pollution?

Since it is low-cost, lightweight and durable, plastics such as PU have various applications and are used in the manufacturing of plastic foam, tyres, bumpers, adhesive paints, synthetic leathers, refrigerator insulation and in automobiles. All this xenobiotic material eventually ends up in landfills, pollutes water resources and increases soil surface littering. Identification of this environment-friendly fungus could be useful in providing new means to deal with the large amount of plastic waste that has been accumulated across the world.

In 2016 researchers from Kyoto Institute of Technology and Keio University also discovered a new species of bacteria that could break down Polyethylene terephthalate (PET), a plastic that is commonly found in disposable water bottles and makes up approximately one-sixth of the world’s annual plastic production.

Previous attempts to deal with plastic waste through burying or burning had produced toxic residue, such as aldehydes, isocyanates, ammonia, cyanide, vinyl chloride and nitrogen oxides – which are not only dangerous for vegetation, animal and human health, but also disrupt ecological processes.

Some questions have been raised about the effectiveness of the fungus discovered by Dr Khan’s team in dealing with the substantial waste management problem in Pakistan.

“Since it is a living organism, there would be concerns about the biological and ecological implications of propagating one species of fungus,” said Tabitha Spence, an environmental activist in Pakistan.

“Maybe all the plastic would disappear but there would also be a by-product from this process and chemically, the by-product might have many of the same components of plastic that were ingested in the first place,” she added.

Spence said there is a tendency to look towards solutions to problems which are recognised as risks without examining the source of the problem. “A better way might be to look into the root of the problem – be it overproduction of disposable containers or something else,” she said.

A national survey by the Pakistan Environmental Protection Agency in 2018 found that roughly 55 billion plastic shopping bags were being used each year in the country and their use was expected to increase by 15 percent per annum.

Punjab province introduced legislation regarding polythene bags (black or any other polythene bags below fifteen micron thickness). In 2014, the province of Sindh banned the use of non-degradable plastic products. Section 14(3) of the Sindh Environment Protection (SEP) Act, 2014 reads, “no person shall import, manufacture, stockpile, trade, supply, distribute or sell any scheduled plastic product which is non-degradable and can’t be broken down by natural process.” Similar bans also exist in Balochistan and Khyber Pakhtunkhwa. However, implementation of the ban remains abysmal with plastic bags frequently exchanging hands in marketplaces.

According to Spence, the strategy for dealing with plastic waste had to include recycling. The environmental activist noted that cities in Pakistan needed to take responsibility and come up with a formalized strategy for recycling – not just plastic but also glass, tin, metals and any other material that is recyclable. “There are a lot of models around the world that show how it could be done,” she said.

Dr Muhammad Anwar Baig, a veteran environmental expert and professor of Environmental Science at the National University of Sciences and Technology (NUST) said that there were also other ways of dealing with plastic waste. “Some material could be added to the plastic using nanotechnology [which promotes biodegradability] so that the plastic can decompose quickly,” he explained.

Future of the Fungus

“We need to find the end product of degraded plastics, figure out how safe they are and their effect on the environment,” said Dr Khan. He added that additional research was needed to understand the implications for waste disposal.

While updating MIT Technology Review on the research, he said they had continued working on the same project over the last years and also found other promising fungi in the process that were good at plastic degradation. The paper is currently under review in an international academic journal and the results have been submitted for a patent.

However, until a sustainable solution is found and implemented, Pakistan’s mountains of waste keep on getting higher.

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The writer is a member of staff.

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