Thursday, January 16, 2014

Is It Safe To Grow Potatoes In Car Tyres

Source: Brighton Permaculture
Last year I collected a lot of car tyres, which I planned to use to grow potatoes in an arid area of my backyward which was ugly and unusable, but which is too close to the house and foot traffic to ignore.

I also wanted to grow potatoes on a large scale, as my family eats a large quantity of them.

I'd read about, and seen a lot of respected gardeners on TV advocate the use of tyres in growing potatoes.

Even corporates funded schools and other feeding schemes to start gardens using garden tyres, and no one mentioned that there could be a problem with the system.

That is, until I mentioned my plan on the Simple Living Forum and one of the members argued against it, citing the potential leaking of chemical toxins into the soil and my food.

My gut response was, "of course it's safe! Why would no one speak up if there is an issue with it?"

But then, thinking about it some more, I had to wonder. Tyres are made of rubber and other synthetic materials, none of which I would volunatarily eat directly, so why was I OK with eating them if they slipped into my food?

I wasn't going to easily give up on the idea though, because I already have an experimental crop  growing and I didn't want to give it up.

So I decided to do some research, hoping to find some information or data that would disprove my forum member's theory. And don't say that the idea of toxins leaching into food and soil is a no-brainer, because for me, and millions of people out there growing their food in tyres, it doesn't seem to be one.

Anyhoo, the websites I read so far agree with my forum friend: growing food in tyres is not safe. Not for the soil, and certainly not for the food.

Here is what Mischa Hewitt is the author of Earthships in Europe  says on Brighton Permaculture:

Tyres are extremely durable. During manufacture, natural rubber is combined with synthetic rubber and treated with a cocktail of chemicals, some toxic or known carcinogens, others more innocuous, to make the tyre withstand all the forces that will act upon it on the road. For a list of some of the chemicals involved and their known health impacts, see box out.

The forces that tyres have to resist on the road are: sunlight, water, acidity, abrasion and friction with the road surface. Each of these forces works in a different way on the tyre, but over time collude to break it back down into its constituent parts.

During this process, the various chemicals and compounds are slowly released through off-gassing, particulate matter or 'tyre dust', or as chemicals, leaching out into water.

As an aside, the Environment Agency [Great Britain. Environment Agency (1998) Tyres in the Environment. Environment Agency, Bristol ISBN 1873160755, p.43] calculates that every tyre loses 20% of its weight during its lifetime on the road, getting slowly ground down and blowing away in the wind.

 Read the full article

Also check out the EU Commission's directive on landfill waste:

The following wastes may not be accepted in a landfill:
  • liquid waste;
  • flammable waste;
  • explosive or oxidising waste;
  • hospital and other clinical waste which is infectious;
  • used tyres, with certain exceptions;
  • any other type of waste which does not meet the acceptance criteria laid down in Annex II.
Many articles talk a lot about toxic chemicals in tyres. So I asked myself, what are these chemicals? Why would I mind having them in my food? According to wikipedia, tyres are made of the following ingredients:

  • Natural rubber, or polyisoprene is the basic elastomer used in tire making
  • Styrene-butadiene co-polymer (SBR) is a synthetic rubber which is often substituted in part for natural rubber based on the comparative raw materials cost
  • Polybutadiene is used in combination with other rubbers because of its low heat-buildup properties
  • Halobutyl rubber is used for the tubeless inner liner compounds, because of its low air permeability. The halogen atoms provide a bond with the carcass compounds which are mainly natural rubber. Bromobutyl is superior to chlorobutyl, but is more expensive
  • Carbon Black, forms a high percentage of the rubber compound. This gives reinforcement and abrasion resistance
  • Silica, used together with carbon black in high performance tires, as a low heat build up reinforcement
  • Sulphur crosslinks the rubber molecules in the vulcanization process
  • Vulcanizing Accelerators are complex organic compounds that speed up the vulcanization
  • Activators assist the vulcanization. The main one is zinc oxide
  • Antioxidants and antiozonants prevent sidewall cracking due to the action of sunlight and ozone
  • Textile fabric reinforces the carcass of the tire
 So yeah, maybe I don't want to eat a casserole of potatoes, carbon black, sulphur and polybutadiene. Do you?


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