This column appears as part of the Winds of Change newsletter.

The circular economy is a fantastic idea. Let’s all stop sending them off to landfill or incinerators and make them into something useful - money-making, even - instead.

What’s not to like? Except when it doesn’t work, and when it is a cause of the dissemination of pollution, rather than a clean, safe answer to the problem.

I wrote about an example of when the circular economy stinks last week when I recovered a new report by the Environmental Rights Centre Scotland (ERCS) and the environmental charity Fidra, which highlighted growing concerns over the spreading of sludge, a by-product of wastewater and sewage treatment on agricultural land.

Over half a million tonnes of this 'low-cost fertiliser', was spread on Scotland's fields between 2020 and 2024. But, according to the report, this type of fertiliser contains plenty of toxic and polluting substances, including PFAS (often dubbed forever chemicals), microplastics, heavy metals, bisphenols, pathogens, pharmaceuticals, antibiotic-resistant bacteria and antibiotic-resistance genes.

It also points out that the spreading of sewage sludge has been banned or restricted in other countries, including the Netherlands, Switzerland, and parts of the United States, because of concerns about the risks.

The sewage sludge problem struck me as very similar to the 'end of life' tyres issue which I wrote about a few years ago.

Used car tyres are a challenge. Every year, more than 50 million end-of-life tyres are generated across the UK. The seemingly good news is that, following a landfill ban, the country recovers almost all of its waste tyres.

'Repulsive': The fight for a sewage sludge-spreading ban

Report calls for ban on spreading of sewage sludge on farms

Ban toxic 3G crumb rubber pitches in Scotland, says report

As a result, according to industry recycling website Grade All, around 15% of tyres are retreated or regrooved, 35% are exported, primarily for cement kilns or pyrolysis operations in other countries, some are used in civil engineering and landscaping projects, and 25% are processed into rubber crumb.

But the problem is those old tyres, a composite of natural and synthetic rubber and other chemicals, contain multiple pollutants which potentially are spread when shredded, and, when burned, produce a toxic cocktail of hazardous gases, oil and heavy metals.

Certainly exporting them for incineration is unethical. A BBC documentary last year revealed how millions of tyres being sent from the UK to India for recycling are actually being "cooked" in makeshift furnaces causing serious health problems and environmental damage.

But, also, incorporating them into a sports pitch, where athletes might roll or fall in them, or workers handle them, doesn't really seem all that safe either?

Professor Andrew Watterson Emeritus Professor of Health at Stirling University has been working hard to draw attention to the hazards of the dissemination of crumb in sports pitches across Scotland and the UK.

He is enthusiastic about the circular economy as a concept, but not this element. “In theory,” he says, “like supporting good over evil, we should all be in favour of the ‘circular economy’ after making every effort to reduce or remove the use of unwanted and harmful materials first."

However, end of life tyres, he says, present “a major challenge” and “adopting a ‘circular economy’ approach to them makes sense by safely recycling them”.

But the way we are doing it now, he says, is not safely recycling. “Shredding tyres and then spreading them on sports pitches and other surfaces as crumb when they will inevitably enter the environment is an example of a non-circular economy practice.

Winds of change on when the circular economy goes wrong (Image: Derek McArthur)

“A rubber crumb is usually less that 1millimetre in diameter. In the 1990s, Canadians were already aware that it took 12,000 tyres in crumb form to make some of their artificial sports pitches so producing enormous numbers of crumbs.

"The practice now looks like a form of madness. Despite attempts to reduce crumb losses on such surfaces, it’s visible to any 3G pitch user or passer by that such pitches cannot contain all the crumb used in their construction and then continued maintenance.”

This was a big idea that came with a massive pollution potential. The European Union found, in 2023, that the crumb infill material used on artificial sport surfaces was the largest source of releases of intentionally added microplastics in the environment.

"For that reason, " Professor Watterson says, "linked to their plastics pollution plan and evidence of microplastic ecotoxicity to living organisms, the EU agreed to phasing out the use by October 2031. The EU recognised crumb could never form part of a circular economy when used on sports pitches. Scotland should follow suit.”

Tyre recycling comes at a cost to both public and the environment, and meanwhile, he observes, the industry gets rid of end-of-life tyres in crumb form "relatively cheaply and profitably".

Fidra, meanwhile, points out that with practices like this we risk creating an “unsafe pseudo-circular economy”. The charity has campaigned against both the spreading of sewage sludge and the use of rubber infill on sports pitches, and also published a review paper on creating a safe circular economy.

"Unless chemicals and plastic are addressed," a spokesperson tells me, "Scotland risks developing an unsafe pseudo-circular economy that produces pollution and contaminated materials. Without addressing chemicals at source, we cannot achieve true circularity. What goes around must be safe to come around again. Chemical safety must be integrated into Scotland’s circular economy strategy from the start.”

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The charity lists other ways that potential unsafe chemicals could mar a circular economy, including what to do with furnishing and electricals that have high levels of flame retardants, which are now classified as persistent organic pollutants (POPs) under the Stockholm Convention.

Tyres and sludge are just two examples – but they are others. They are reminders that to create a safe circular economy, we need to manufacture safer products in the first place.

© Herald Scotland