Microplastics in potting soils, "À bon entendeur" broadcast

Last week, Swiss Radio and Television aired a report as part of the programme "À bon entendeur", in which Fanny Berset, a doctoral student in environmental physical chemistry at the F.-A. Forel Department of the University of Geneva, was interviewed about the presence of microplastics in bags of potting soil.

The report, by Alexandre Willemin, aimed to assess the microplastic content of six bags of potting soil sold in garden centres across French-speaking Switzerland. The six soils were sent for analysis to specialised laboratories in Norway. The result: only one bag, Ricoter from Hornbach, contained no detectable plastics. All others contained microplastics ranging in size from 0.027 to 1 millimetre, with some containing up to 20,800 micrograms of microplastics per litre of potting soil.

More worryingly, polystyrene and PVC were detected — two plastics considered potentially problematic for human health. As Fanny Berset explains, if these plastics are small enough, they can cross physiological barriers, end up in plants and the fruit and vegetables we eat, and by extension, in our organs and bloodstream.

The quality of potting soil, which is often derived from composted organic waste, depends directly on how well the population sorts its waste — something that remains insufficient today, as demonstrated by Thomas Servant, head of the Châtillon SIG unit, who was also interviewed in the report.

Despite this, bags of potting soil remain compliant with the Ordinance on the Reduction of Risks from Chemical Products, which sets a limit of 0.1% by weight of undesirable materials in potting soils. There is currently no standard for microplastics, which are invisible to the naked eye.

The "À bon entendeur" episode "Des microplastiques dans les terreaux universels ?", broadcast on 12 May 2026, is available on the RTS website.

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