Tractor tire toxicity question

In past years (see posts below) ) there was general consensus that big old tires are likely harmful to soil due to toxic components.  But recently I've heard Spirko, Geoff Lawton, and Nick Ferguson discuss normal microbial action in healthy permaculture soil that may in fact digest and reduce harmful elements found in old tires. Spirko in particular says use 'em.  

As they dry out over the decades that big tires last, I personally suspect that they become less toxic. You can smell new tires, just go in a tire store... but 15 year old tires seem rather more inert.

I just came upon 4 large machine tires, 37" tall and 15" wide. Wondering if I should just put them on a shooting berm, or find a more productive permie way to use them. One of our children is suburban gardening in limited space so I thought of cutting off one sidewall and giving them to her husband for use.

https://permies.com/t/74736/tires-dangerous-health-nature
https://permies.com/t/13430/Big-tires-keyhole-ish-design
https://permies.com/t/2889/tires-safe-gardens

Reno Husker wrote:As they dry out over the decades that big tires last, I personally suspect that they become less toxic. You can smell new tires, just go in a tire store... but 15 year old tires seem rather more inert.

That has been my experience as well. Tires that are truly old don't smell, even when you cut into them. I interpret that to mean that the largest part of the offgassing has already taken place.

For food production, I don't think most car/truck tires are old enough, so I wouldn't use them. And anyway, There are better methods that are cheap/free.

But a big, well-aged tractor-type tire? I've seen them half buried in playgrounds, and used in dog agility parks. For growing food? It's tempting, especially if some sort of liner could be used. I dunno.

I agree with you on both counts: there is clearly a toxin associated with tyre use (see The Guardian as one source). I have also read, but cannot find a source, that new tyres are more polluting than older ones. They give off more of the toxic dust and, as you say, they offgas the plasticisers and solvents used in their manufacture. On a related note, that 'new car smell" is incredibly toxic too.