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‘Biodegradable’ mulches contributing to plastic pollution

Doubts have been raised over the biodegradability credentials of bio-based plastics such as agricultural mulches after a study in the Netherlands found high levels of contamination on farmland.

Research commissioned by Dutch environmental charity Plastic Soup Foundation found that high concentrations of bioplastics marketed as ‘biodegradable’ remained in soils and ditches for longer than the two-year industry standard, contributing to the more widespread problem of microplastic pollution.

Researchers at Wageningen University in the Netherlands took samples from eight flower farms in the Netherlands in September 2022 and at eight coriander farms in Spain in November 2022. They found 48 different types of microplastics across the tested samples of which 61% were found to be fossil fuel-based, with the remaining 39% bio-based.

Plastic mulch used to warm up the soil and prevent weed growth was found to be the main reason for the microplastic pollution in soils. The results of the study found high concentrations of microplastics derived from bio-degradable plastic mulches that did not degrade within a two year period under field conditions; this violates the industry standard (EN 17033) which states biodegradable plastic mulches should be biodegraded in soils by 90% within two years.

Campaigners said the study raises serious questions about the biodegradability credentials of bio-based plastics and have called for tighter regulations on the environmental claims made by manufacturers.

“Biodegradable plastic mulches are increasingly used by farmers. Mulch is sold to farmers with the false promise of degradability within two years,” said Maria Westerbos, director of Plastic Soup Foundation. “This study shows that these mulches risk contaminating the soils in which the food we eat is grown.”