MINAGRIS - Farmers give up using municipal compost due to high plastic content.

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Our UK team has recently finished sampling agricultural fields for plastics large and small as part of the MINAGRIS project. During this time, it has become increasingly clear that we have a compost problem.

Municipal compost is made with our kitchen countertop and garden green waste collections. When it first arrived at scale as an option for farmers to apply this valuable source of organic matter to their fields and boost their soil carbon, it seemed like a win-win. It had the potential to bring otherwise wasted nutrients back into the food system, saving them from stinking out our bins before ending up in landfill or an incinerator. This was a bold shift towards a more circular economy, which had the potential to be great for soils and farm profitability.

The problem is the high plastic content. Farmers and growers initially eager to make use of this black gold to improve their soil health quickly realised that the plastic content of municipal compost was so high that they were no longer happy putting it on their land. This came up repeatedly in our farmer interviews and whilst we were sampling. Our initial enquiries indicate that this seems to be a widespread understanding within the farming and market gardening communities, not just in the UK but Europe-wide.

So, what are these plastics? Where are they coming from? Well, seemingly, they are food wrappers, straws, disposable cutlery, fruit stickers and cling film that are somehow finding their way into kitchen waste caddies. They are garden twine, netting, fragments of pots, plant labels and litter that get swept up with leaves and garden waste. In all likelihood, they are also the bioplastics produced from alternatives to fossil oil, but that, confusingly, are not necessarily biodegradable.

In the UK, the Environment Agency consider high levels of plastic contamination from compost to be attributable to ‘kerbside collections’, recognising that plastic contamination overall has ‘reduced market confidence’ in municipal compost. There are standards that must be adhered to by processors before collected kerbside biowaste can be reclassified as compost, including removing all non-compostable plastic ‘to levels that are as low as reasonably practicable’. A lack of funding is cited as the reason there is no quantifiable threshold or accompanying monitoring programme to ensure adherence to this.

Prevention in this case may well be better than cure, as mechanical processes for screening out plastics are costly and risk fragmenting them into smaller pieces. A combined approach of reducing contamination in kerbside collections, improved screening by processors, and reducing the prevalence of single use plastics in the wider economy will likely be necessary.

Municipal compost is just one of several routes through which plastics enter agricultural soils. The evidence is building that plastics in soils can impact their health and functionality, including their ability to absorb and retain water, and support healthy crops and ecosystems. From soils, plastic can be washed into the wider ecosystem. The public conversation on ocean plastics has exploded in recent years, but this very domestic source of plastics in our environment is something that remains well-known only within select communities.

We need to get this conversation out beyond those farmers and growers with working experience of using municipal compost to get us on the road to solving this particular plastic problem.

Farmers give up using municipal compost due to high plastic content.

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