Microplastics are everywhere on Earth, from the depths of the Mariana Trench to the summit of Everest, in the air, the water, in plants, animals and our bodies. The UN’s Food and Agriculture Organisation says soils contain more microplastic pollution than the oceans and that the use of plastics in the food and farming system has become pervasive, with most plastics currently single-use and buried, burned or lost after use.
Plastics also enter the environment through clothing; a single polyester garment can shed up to 700,000 fibres in one wash cycle. These enter the waste water and sewage system and can end up being spread on land as sludge. From here, the fibres enter the soil, are eaten by creatures like earthworms and move up the food chain, into the meat, milk and blood of farm animals, and also into food crops, and so into our bodies. We also breath in microplastics. Run-off from land transfers micropastics into the ocean, adding to the load generated by degradation of plastic waste washed down by rivers or discarded at sea.
Plankton consuming plastic microfibres in the sea off Devon. Photo: Dr Richard Kirby.
Plastics, due to their chemical composition, take centuries to decompose naturally. Fungi secrete a range of enzymes to break down their natural organic food sources, and reasearch is now looking at whether certain fungi are capable of breaking down plastic.
Two species in particular look promising. Pestalotiopsis microspora, discovered in the rainforest of Ecuador, can break down polyurethane in oxygen-free environment – such as occurs in parts of landfills. Aspergillus tubingensis, discovered in a dump site in Pakistan, can break down polyester in just a few weeks. The fungi attack certain chemical bonds in the plastic molecolues, breaking them into smaller, soluble units which the fungi can then use as food. Practical applications could include treating plastic waste in land fills, waste water treatment and developing plastics that can be more easily degraded by fungi.
Although these findings are encouraging, we are a long way off solving the plastics problem with fungi. All the results so far have been small scale, and under specific environmental conditions which don’t always exist in the real world. The chemistry of many plastics can’t be handled by fungi, and introducing plastic-eating fungi into the natural environment could have unforeseen effects on local ecosystems.
What about new types of plastic that are marketed as compostable or biodegradable? It is now becoming clear that these materials are also problematic, as most require industrial-scale composting facilities and they just fragment into into smaller and smaller pieces, thereby increasing the microplastics load. These ‘biodegradeable’ plastics are also incompatible with municipal plastics recycling schemes. Recently, the announcement of a new plastic that dissolves completely in sea water within hours has caused excitment. The plastic also disappears within 8-10 days when placed in soil, releasing “nutrients similar to fertiliser that can benefit plant life.” Again, we need to see such techniques working at scale and without unwanted side-effects in the natural environment.
The most effective way of tackling our planet’s plastics overload is international action to reduce the amount of plastic at source. All eyes are on the final negotiations of the Global Plastics Treaty, from 5-14 August in Geneva.The Treaty was debated in the House of Commons on 17 July, with cross-party consensus on the problem, and a strong call for the Treaty to address the entire life cycle of plastics, from production and design to disposal, rather than just focusing on waste management and recycling. We hope the UK Government will maintain a strong stance during the Treaty negotiations, in the face of concerted lobbying by the plastics and petrochemical industries. There is still time to sign Greenpeace’s petition for an ambitious and strong Global Plastics Treaty.