I have the opportunity to get lots of leaves (Mulch!) from a neighbor. The only catch is that it's from a lawn that was treated with a grub killer last spring. The leaves will be collected with a lawn-vacuum-thingy.
See my thread about fixing contamination with mushrooms and you need not have any worries about lawn chemicals. What you might want to do is pile these leaves up on one place, douse them liberally with any mushrooms you can find and put through the blender, and let it sit for a few weeks. That should be plenty of time for the fungi to do their detoxifying magic.
You'll have to determine your own standards as to what level of contamination you are willing to accept.
How much of the slug poison was used, did it rain much since it was applied, was it applied in huge amount across the entire lawn, did they spray the trees, how long between the praying and the leaves falling, do the leaves have an unacceptable amount of contaminants, what will you do with the leaves, will they be used as mulch around ornamental plants, will they be used as fuel, will they be bagged and used as winter insulation, will they be spread as mulch over vegetable plants, how long will it take for the leaves to decompose over the vegetable plants, will you be rotting them down for a year or more to make leaf mold, will you be diluting those leaves with some amount of pristine leaves? Most importantly, how much of that slug spray that was used 6 month ago will transfer from the neighbors lawn, onto the leaves, and eventually into the soil in which you grow vegetables, and is that acceptable to you?
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