Slow-release fertilizers can spread microplastics on US cropland

Yahoo

11-03-2025

Fertilizers that shed microplastics are increasingly spreading on America's cropland, research shows, raising new worry about the soil contamination and safety of the US food supply.
A peer-reviewed University of Missouri paper found common types of slow-release fertilizers are often encapsulated with plastic and can be so small that they could be considered microplastics. Those are designed to break down into even smaller pieces of plastic once spread in fields.
The tiny bits of plastic can end up in water and soil at alarming levels, the paper's lead author said, and the substance is likely taken up by crops. Until now, the slow fertilizers have been thought to be safe, said Maryam Salehi, a lead author and researcher with the University of Missouri.
'We need to inform farmers,' Salehi said. 'When they choose their products, they need to know that these have some potential risks.
Microplastics are tiny bits of plastic either intentionally added to consumer goods, or which are products of larger plastics breaking down. The particles contain any number of 16,000 plastic chemicals, of which thousands, such as BPA, phthalates and Pfas, present serious health risks.
The substance has been found throughout the human body, and is linked to an increased risk of heart attack and cancer. It's also considered to be a neurotoxicant that can cause multiple forms of brain dysfunction, such as Parkinson's disease.
Salehi said it is unclear which other chemicals are in the fertilizer plastic.
Testing has found microplastics in a wide range of foods, including produce.
Some of the slow release fertilizer pieces are less than five millimeters, which makes them microplastics by definition. But once they are in the soil, they 'break down into tiny, tiny particles' when a tractor runs over them, or someone walks on ground where they've been spread, Salehi said.
That is worrying because smaller bits can more easily move through the environment than larger pieces of plastic, Salehi said. The study found most of the microplastics stayed in the soil, but some were washed into nearby water sources by rain or irrigation processes.
The paper did not measure how much of the microplastics ended up in crops, but previous research has found that they can be taken up. Other papers have found that the bits of plastic may actually reduce soil quality.
'There is additional concern about the impact on food safety,' Salehi said.
But the problem may be rather easy to solve. There are many types of slow release fertilizers, including those that are encapsulated with biodegradable materials, Salehi said. However, the plastic versions work well so the industry for now seems to be sticking with them, she added.