Plastic leaching into farmer’s fields at alarming rate

Plastics are ubiquitous in agriculture, accumulating in the world's soils and affecting human health, according to a new publication by the United Nations Environment Program (UNEP).

Elaine Baker, a researcher at Australia's University of Sydney and co-author of the report, said: "We are beginning to understand that the accumulation of plastic can have wide-ranging repercussions on soil health, biodiversity and productivity, all of which are vital for food security.”

The 29th edition of UNEP's "Foresight Brief" charted how plastics widely used in agriculture, from plastic-coated fertilizers to mulch films, pollute soil and potentially threaten crop production.

They are also affecting human health when transferred to people through the food chain. It is estimated that 12.5 million tons of plastic products are used annually in agricultural production and livestock.

Of these, macroplastics are used as protective wrappers for mulch and forage. They cover greenhouses and protect crops from the elements. They are also used in irrigation tubes, bags and bottles.

Over time, macroplastics slowly break down into microplastics, fragments less than five millimetres in length, which seep into the soil and end up in our food chain.

“We are beginning to understand that the accumulation of plastic can have wide-ranging repercussions on soil health, biodiversity and productivity, all of which are vital for food security”:

Elaine Baker

Then there are the intentionally added microplastics, which are even used as coatings for fertilizers, pesticides and seeds.

Microplastics can change the physical structure of the soil and limit its water-holding capacity, which can affect plants by reducing root growth and nutrient uptake.

Chemical additives from plastics that seep into the ground can also affect food value chains and have health consequences.

According to the report, the largest source of microplastic contamination in the soil is fertilizers produced from organic matter such as manure and which, known as biosolids, can be cheaper and better for the environment than manufactured fertilizers.

But in that case, the manure is laced with microbeads, tiny synthetic particles commonly used in soaps, shampoos, makeup, and other personal care products, which is cause for concern.

Some countries have banned plastic microbeads, but many other microplastics continue to enter the water system. These include everything from cigarette filters to tire components and synthetic fibres in clothing.

Experts say the variable size and composition of microplastics make it difficult to remove once they're in wastewater.

On the other hand, UNEP admits that progress is being made in improving the biodegradability of polymers used in agricultural products. Some mulch films, used to modify soil temperatures, limit weed growth and prevent moisture loss, are now marketed as fully biodegradable and compostable.

To reduce dependence on hydrocarbon-based polymers, the use of biobased polymers is becoming more widespread. But not all are biodegradable, some can be as toxic as fossil fuel-based polymers, and their price remains an issue.

Experts say that the production of bio-based polymers must include considerations of sustainable agriculture and can be replaced by nature-based solutions.

For example, so-called cover crops can be used, which protect the soil and are not intended to be harvested.

That strategy can suppress weeds, counteract soil diseases and improve soil fertility, although there are concerns that they may reduce yields and increase costs.

"None of the (nature-based) solutions is a silver bullet," Baker said. "Plastic is cheap and easy to work with, which makes trying to introduce alternatives a hard sell," she acknowledged.

According to her, governments must "disincentivize the use of agricultural plastics", following the path of the European Union, which earlier this year restricted the use of certain types of polymers in fertilizers.

Baker said that more research is needed to develop products, such as some of textile origin, that do not release microplastics.

For the expert "now is the time to adopt the precautionary principle and develop specific solutions to stop the flow of plastic from the source to the environment". After all, "there is only a finite amount of agricultural land available," she concluded.

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