Here's the thing. our civilization produces an awful lot of crap that has to be disposed of. When it is concentrated in landfills, normal biological processes cannot break down harmful chemicals for a variety of reasons, inadequate heat and oxygen leading the list. Very often chemicals cannot break down when brought into the home as well, such as organiphosphates which are processed pretty well in low concentrations outside. (I realize some of you will debate this but I'm not interested in that tired contraversy right now.) Using a little carpet as mulch seems to be an ideal way of dealing with one form of waste. Everything leaches chemicals but I think it is counterproductive to be excessively conservative. The concern about produce near a highway doesn't have anything to do with ground pollution but with direct contact of chemicals in the air attaching to leaves and fruit. Plants do not pull everthing in the ground into their systems and if carpet does not create a huge health risk in someones home where they are breathing in its fibers and absorbing its chemicals through their skin how could it pose a significant risk as a mulch? It is possible I suppose but not likely enough to advise against it in my opinion. Someone can google the issue of whether plants selectively absorb lead through their roots if they like, but it's something I haven't heard about. The danger of industrial pollution is not how it kills us one at a time- individuals are living longer than they ever have. The danger of industrial pollution is that it is altering the entire planet in ways that threaten the existence of our entire species. This is a fact that the organic agriculture movement seems to overlook. When the oceans themselves are dying, mostly from chemicals unrelated to agriculture, eating organic brocolli doesn't do a whole lot of good.

Thanks to everyone for the insights and suggestions. Am now confident that our shingles are not CCA treated and very doubtful that anything else was applied for a variety of reasons. One other relevant observation is that subterranean termites had tunneled through a defect in the slab ledge, up the back of the brick veneer, and into the cedar shingles. There were thousands (tens of thousands?) of the little beasts found eating a large section of cedar when the contractor pulled off the composition roof the previous owner had installed over the original. Just recalled this wouldn't have happened in the presence of CCA, though unsure how much they would have been bothered by other possible preservative/retardant chemical treatments. I probably gave too much emphasis to CCA in the initial post because it was my greatest concern in using as mulch for reasons discussed earlier. The broader question is whether there were any chemical treatments for cedar shingles in common use at the build time and location that would still pose a danger in mulch/compost. I couldn't find any that would not have leached, eroded, or otherwise broken down sufficiently by now. If you have an interest or are bothered with insomnia one night, Performance of Preservative-treated Wood Shingles and Shakes (pdf) gives a good summary of treatment options at around 1995. Also read somewhere that a tablespoon of ash from CCA treated wood is considered a lethal dose for humans. That's a lot to ingest unintentionally, but a reminder of how dangerous this stuff can become if mishandled.

Yes. Until it disintegrates into just a powdery, almost sawdust like substance, it is still perfectly good as a mulch.

in a world where words mean things ... what you now have is compost.. and no longer a mulch .. and to confuse you more ... compost can be a mulch ... lol .. what you have.. would be what you find in the bottom of an overly wet compost pile ... and if you have a compost pile.. just throw this muck in it.. and let it return to a usable form as it dries ... and is turned into the pile ... i agree.. muck is hard to apply in that form ... but dont waste it ... ken