Plastics are accumulating in the world’s soils at a worrying rate, according to a new report from the United Nations Environment Programme (UNEP).
The 29th edition of UNEP’s Foresight Brief highlights how plastics used extensively in farming – from plastic coated plastic fertilizers to mulch film – are contaminating the soil and potentially threatening food security. Microplastics are also impacting human health when transferred to people through the food chain.
“There is only a finite amount of agricultural land available,” says Professor Elaine Baker from the University of Sydney, the report’s co-author. “We are starting to understand that the build-up of plastic can have wide-ranging impacts on soil health, biodiversity and productivity, all of which are vital for food security,” she says.
Plastics are ubiquitous in agriculture. Macroplastics are used as protective wraps around mulch and fodder. They cover greenhouses and shield crops from the elements. They are used in irrigation tubes, sacks and bottles — and intentionally added microplastics are even used as coatings on fertilizers, pesticides and seeds.
But over time, macroplastics slowly break down into microplastics of shards less than 5mm long – and seep into the soil. These microplastics can change the physical structure of earth and limit its capacity to hold water. That can affect plants by reducing root growth and nutrient uptake. Chemical additives in plastics that leach into the soil can also impact food value chains and lead to health implications.
None of these solutions are a magic bullet. Plastic is inexpensive and easy to work with, which makes trying to introduce alternatives a hard sell.
According to the Foresight Brief, the single-biggest source of microplastic pollution in soil is fertilizers produced from organic matter, such as manure. Known as biosolids, these can be cheaper and better for the environment than manufactured fertilizers. But manure is mixed with microspheres, tiny synthetic particles commonly used in soap, shampoo, makeup and other personal care products, which is cause for concern.
Some countries have banned plastic microspheres, but many other microplastics continue to enter the water system. These include everything from cigarette filters to tire components to synthetic fibres from clothes. Experts say the varying size and composition of microplastics make them difficult to remove once they are in sewage.
Progress is being made to improve the biodegradability of polymers used in agricultural products. Some mulch films – used to modify soil temperature, limit weed growth and prevent moisture loss – are now being marketed as fully biodegradable and compostable which is not always the case.
To reduce the reliance on hydrocarbon-based polymers, the use of bio-based polymers is expanding. But, not all are biodegradable – some may be as toxic as fossil fuel-based polymers – and their price is still an issue. Experts say that the production of bio-based polymers should not generate land competition with food, and considerations on their growth should include those for sustainable agriculture
So-called cover crops, which shield the soil and are not meant to be harvested, can also be used. These nature-based solutions can suppress weeds, counter soil diseases and improve soil fertility, but there are concerns they could reduce yields and increase costs.
“None of these solutions are a magic bullet,” says Baker. “Plastic is inexpensive and easy to work with, which makes trying to introduce alternatives a hard sell.”
She said governments need to “disincentivize” the use of agricultural plastics, following the path of the European Union, which earlier this year restricted certain types of polymers from being used in fertilizer.
Baker said more research needs to be done to develop products – such as some alternative textiles – that don’t shed microplastics. Encouraging consumers to rethink their plastic consumption and manufacturers to reduce the amount of plastic they use is also essential, she said.
“While there is still only limited research on the impacts of plastics in soil, there is evidence of negative effects on soil health and productivity,” she says. “Now is the time to adopt the precautionary principle and develop targeted solutions for stopping the flow of plastic from the source and into the environment.”
About The Foresight Briefs
The Foresight Briefs are published by the UNEP to highlight a hotspot of environmental change, feature an emerging science topic, or discuss a contemporary environmental issue. The 29th edition of UNEP’s Foresight Brief explores the use of plastic in agriculture and the significant waste problem this entails, which impacts soil health, biodiversity, productivity and food security.
