How Canada’s plan to curb farm emissions could make plastic pollution worse

Slow-release nitrogen fertilizers, central to Canada's plan to reduce greenhouse gas emissions on farms, are filling fields with microscopic plastic pollution, environmentalists warn.

The high-tech granular fertilizers are coated in a thin layer of plastic designed to slow down the release of nitrogen into the soil, making it easier for plants to absorb. Excess nitrogen in the soil is the main source of nitrous oxide, a potent greenhouse gas responsible for over a third of emissions from Canadian farms.

Plastic-coated fertilizers are part of a larger group of so-called "enhanced efficiency" fertilizers the federal government estimates could reduce emissions by 15 to 35 per cent. Fertilizer and farming industry groups have pitched them as a key tool in meeting Canada's climate goals — a perspective recently embraced by the federal government.

However, once the nitrogen has been absorbed or dissolved, the fertilizer's plastic coating stays in the soil. These tiny plastic particles can then accumulate in the ground or leach into waterways, absorbing other chemicals along the way that can harm people and the environment.

Studies show microplastics can travel widely through the ocean and air and in human bodies; they act like sponges, absorbing harmful chemicals from the environment before releasing them into people or animals. While there is a rapidly growing body of research that highlights microplastics' harmful effects on oceans, little research has been done on their impact on soil or on human health if they are absorbed by crops.

That worries Carroll Muffett, president of the Center for International Environmental Law. The environmental organization recently published a report, which was not peer-reviewed, calling for greater scrutiny of the use of agrochemicals.

Unlike loose trash, plastic mulches and other sources of microplastic pollution, the use of plastic-coated fertilizers is an "intentional" decision to put irretrievable plastic pollution in the soil, Muffett said.

The UN Food and Agriculture Organization (FAO) estimates fertilizer companies use about 100,000 tonnes of plastic to make about 400,000 tonnes of fertilizers each year, but public sales data from major fertilizer companies suggests the true amount of plastic-coated fertilizers used each year could be far higher.

Microplastics can also travel into or onto crops, eventually making their way into human food. Because plastic-coated fertilizers and pesticides put microplastic "in direct and sustained contact with highly toxic materials," they pose an extra health and environmental risk, Muffett said.

"The convergence of microplastics with pesticides and fertilizers essentially takes two enormous problems and combines them into one."

But not everyone believes plastic-coated fertilizers are harmful.

"You can think of it as an environmentally friendly approach because nitrogen in the environment can lead to greenhouse gases … and water-quality issues," said Mario Tenuta, a professor of soil ecology at the University of Manitoba. He is the lead researcher at a soil ecology laboratory partly funded by Fertilizer Canada, the country's main fertilizer industry lobby group.

Plastic-coated fertilizers don't release enough plastic into the environment to be a major concern and there is "no evidence" the products are impacting soil biology or human health, Tenuta said. While he acknowledged the chemicals intentionally put plastics into the soil and contribute to broader plastic pollution problems, he argued their ability to reduce runoff and greenhouse gas emissions outweighs the negative impact of plastic pollution.

It's an argument Muffett doesn't buy. Plastic pollution is a well-known environmental problem, even if the scale of the problem on the world's soils has been largely overlooked by media and policymakers. That should be cause for concern, he said.

"We're in a world in which plastic pollution is so pervasive, it's been recognized as an indicator of an entire geological epoch," he said. "The Anthropocene epoch, you measure it by plastic pollution."