I’m very glad people raise these points. Obviously, this is a concern when you’re recycling things to use in your garden, so I looked into it a little…
Tyres
Tyres, like many types of rubber, are treated with various chemicals during manufacture. The ones of most concern are plasticisers. These tend to mostly leach out in the first year or so – they’re what gives rubber that sharp, bitter smell when it’s still new.
Unfortunately, my only conclusion is that, without any proper research, it looks inconclusive. It seems like tyres should be safe enough to use, but I can’t say for certain. Best not to use them for growing food, I’d say. Better safe than sorry.
They’ll still work nicely for growing flowers and non-edible plants, though.
Wooden Pallets
Yes, these can be contaminated, so be careful. The biggest concern is if they’ve been treated with any chemicals – the worst of these chemicals are, to my knowledge, banned in the EU and no longer used in the US. Even so, here are some helpful links:
To summarise, wooden pallets for international use have markings to show if they’ve been treated. The best are marked DB and are untreated. Markings of EPAL, KD, or HY are also fine. These are heat treatments which have no lasting effects.
Ones to avoid are any which are painted in bright colours, or marked EUR (treated but non-specific – so it could be anything). If you find one marked MB, avoid it because that stuff is nasty.
If it has no markings, then it wasn’t intended for international use. These are mostly left untreated, but there’s no way to be sure, so use with caution.
I haven’t found so much about the collars, but I’m assuming the same rules apply.
