I can get huge loads of leaves dropped off by landscaping companies. I figure that this is fairly good. There are of course contamination issues. Here is how I have broken them down in my mind.
I will be using them in a hot, turned compost pile with manure and wood chips. Once it has been turned a couple of times, it will sit for the rest of the winter.
Heavy Metals: not really a problem
Most chemicals: will not be able to survive a hot compost pile, survive a fungi loaded sheet mulch, and still somehow be able to get into the plant and affect me.
Persistant herbicides: will not have been sprayed on the trees (otherwise there would be a load of dead trees.) I carefully sourced the manure to avoid this problem.
Junk: will be able to be picked out, either before composting or after. The lawn care companies said they would try to keep plastic, etc, out.
Dog droppings: This is where it gets interesting. However, we are in a fairly well to do suburban area. Most people clean up after their dogs. Lawn companies are collecting leaves. A few dog droppings might have got mixed in. Once the leaves get mixed with the manure and wood chips, any droppings would be pretty diluted. Then they would have to run the thermal and biological gauntlet.
Also, almost any urban area has dogs and cats everywhere. Almost any rural area has coyotes, foxes, and or mountain lions. We certainly are not going to just stop growing food. That beautiful supermarket produce could easily be contaminated.
There is very little possibility of cat droppings, which are potentially more dangerous. Also, after reading a recent article in acres USA Exposing the Lies: Prions, Organophosphates & Mad Cow Disease, I am not really worried about prions. I am not injecting this stuff into my brain, after all.
So, my position is that I should not be at all worried about this.
Of course, I use cardboard too. I know some people don't. That's fine too. But when they fed one group of rats on puffed grain cereal, and another set on the cereal box, the cereal rats died first— in convulsions. But I would certainly compost puffed grain cereal, box and all, if someone gave me some. (The rat story is from Nourishing Traditions. )
I will be interested in hearing your take on this.
Of course, I will make sure that parents know: Children should not eat dirt! But then again, there is interesting research on the role of parasites in health, and that a lack of dirt can make us sick!
I still would not add dog droppings to my compost pile. But given all the above, I don't think I have to worry about using these leaves.