Recycled Car Tyres Have No Place In The Garden

Rhubarb is very efficient at bioaccumulating toxic heavy metals. Food garden, Moree, NSW.

Recycling is good, except when it is car tyres being up-cycled in food gardens. Permaculturists often misguidedly include tyres in ‘earth ship’ designs.
 What could possibly go wrong?

In June 2017, I posted 
about a ‘Dystopian treasure island’ on Facebook. It related to a news story about a playground created in Victoria, Australia, for Fitzroy public housing estate kids – dubbed a ‘sustainable sculpture’ – using old car tyres and recycled steel and rubber conveyor belts. The belts had been sourced from the mining industry and they contain a similar range of materials as car tyre rubber.

The re-use of car tyres for food growing cost this garden show exhibitor an award. Sydney, NSW.

Car tyre rubber leaches toxins over many years. The rate of leaching is faster in areas of higher rainfall, so in dry regions leaching occurs over longer periods. Leaching is also affected by soil acidity and other weathering effects, but many of the compounds released are not good for soil, crop, or human health.

Different impacts for animal and plant health complicate matters. As a horticulturist with a grounding in science, I know that humans can effortlessly excrete excess zinc from our diet with no negative health impacts. However, excess zinc in soil generally harms plant growth. I’ve had quite a bit of experience with damage caused by elevated zinc levels in products like artificial planting mixes containing ‘natural’ manures sourced cheaply from industrially farmed livestock, such as cow manure.

It is even more important to note that in terms of exposure to toxins, young children are not merely smaller versions of adult humans. The response of a child – which does not yet have a fully developed immune system to toxins – will not be the same as for an adult.

The best source of information I can find on the risks associated with up-cycling old tyres comes from the Brighton Permaculture Trust, England (BPT). The accuracy of the associated risks is complicated, BPT say, because “we don’t know the exact amount (of compounds) used because of commercial secrecy.” This secrecy means that even advocates of tyre up-cycling cannot predict the environmental impacts.

We have also known since the 1970’s that heavy metals contaminating soils are soaked up by plants – they can bioaccumulate in crops. Some very efficient bioaccumulators of heavy metals include silverbeet and rhubarb and root crops like turnip, potato, radish and beetroot. Toxins also accumulate in sediment in waterways, lakes and mangroves.

The practise of adding lead to petrol in the UK stopped many years before Australia phased out leaded petrol, however to this day lead contamination of soil close to busy roads will still exclude them from cropping certain food plants. Copper, another heavy metal released on roads by traffic, also accumulates in roadside soil. Have your nature strip soil laboratory tested before you start cropping. I contacted the National Measurement Institute for advice and had a test crop of silverbeet analysed before I started cropping my footpath garden. If you treat footpath food gardens as being constructed on semi-industrial land, you start appreciating the associated risks.

Car tyre contaminating an organic orchard. Cook Islands.

Millions of discarded car tyres pose significant environmental risks.Above ground stores can catch fire. They contain lots of empty air space, so they use up large amounts of space in landfill. Sometimes, in wet landfill locations, these pockets of air are sufficient to allow masses of tyres to ‘bubble up’ to the surface again. Old tyres are burned to generate electricity, releasing dioxins and furans amongst other highly hazardous, persistent wastes.

A particularly disastrous reuse of tyres is in the creation of artificial reefs as a method of disposal. Old tyre reefs have been constructed in the USA, the Gulf of Mexico, Indonesia, Malaysia, Australia, and Africa. None have ever succeeded in enhancing game fishing or conservation. Typically, when these ‘reef dumps’ break up during cyclones they pummel surrounding coral before being washed ashore, up river systems and into mangroves.

Waste tyres are found in many everyday items, including the soles of shoes, for shock absorbing play surfaces and as a flexible surface around tree bases (as an alternative to rigid structures made from bricks or concrete), in backfill for pipelines and roadworks and in making asphalt.

What do we know a typical tyre will contain? We know the following elements are found in an ‘average’ tyre:

Natural rubber, which is OK;
Synthetic rubber compounds, including butadiene, a known carcinogen;
Benzene, a solvent, and a known carcinogen;
Toluene, a solvent with negative health effects;
Xylene, an irritant;
Petroleum naphtha, a toxin;
Polycyclic aromatic hydrocarbons: These include phenols – some are endocrine-disruptors – and benzo(a)pyrene – compounds linked to cancer;
Heavy metals: zinc, chromium, nickel, lead, copper and cadmium. These are the most common contaminants found in foot path garden soil;
Carbon black, which is possibly carcinogenic;
Vulcanising agents: sulphur and zinc oxide;
Polychlorinated biphenyls, which are known carcinogens;

Recycling is, generally speaking, good. But some products are not simply or quickly made safe for everyday use. When you see recycled tyres and their products being used in food gardens or children’s play spaces, it is time to have an adult discussion about risk reduction and healthy childhood development.

A great source book for de-toxifying schools and playgrounds is ‘The Toxic Playground’ by Jo Immig, National Co-ordinator of the National Toxics Network Inc.

Up-cycled car tyre. Ho Chi Minh City, Vietnam.

Jerry Coleby-Williams
Patron, National Toxics Network
24th April 2019

Join Jerry Coleby-Williams on his Gardeners and Gourmets tour of Vietnam, 26th July to 14th August 2019. Click on this link to view the full itinerary

9 Comments Add yours

  1. roofingbird says:

    Thank you for re-addressing this!

  2. Lucinda Coates says:

    Excellent article, Jerry, and a topic that really needed to be aired. Thank you.

  3. Stephen Besnard says:

    I have always thought that they are a very high pollutant.

  4. aussiebeachgal says:

    Frightening stuff. This would be very useful knowledge to have on Gardening Australia, and will give more people visual exposure to the hazards they may inadvertently have lurking in their backyards. It could also act as a catalyst to prompt action from Save The Children who now caretaker the Cubbies project of children’s playgrounds, which includes the playground at Atherton Gardens in your article. Thanks for highlighting the pitfalls of these types of hazardous, disused products!

  5. Living Kilawe says:

    Thank you so much to educate use. I never know whether car tyres has toxic which can harm human.

  6. Eva says:

    Great Article. Thanks Jerry.

  7. Rowena Cavanagh says:

    Thank you for spelling out the details for not using car tyres in the garden. I have always been against them, but unfortunately Bill Mollison wasn’t. I am concerned newcomers to permaculture take his word as gospel without a second thought. It would be lovely to see more holistic permaculture designs rather than just repetitive copies. I firmly believe permaculture can be enhanced with results that also look wonderful.
    (Edited).

  8. Sharyn says:

    Thanks for this very informative article I have often wondered especially since a lot of people advocate the use of old tyres for potatoes, I will be dismantling my tyre garden ASAP!!!

  9. Lesley says:

    Super informative article Jerry! It caught my attention while planning my own nature play space in my garden after being inspired by this years Melbourne flower and garden show. Included in their amazing outdoor play area for children were 100 or so used tyres as stepping stones. Just goes to show, it’s worth doing more research 🙂 I really appreciate the information you’ve shared.

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