Chomated copper arsenate treated wood has been functionally banned in the US since 2003, and replaced with Alkaline copper quaternary or copper azole preservatives, which are generally safe, though I wouldn't go eating off a plate made from them or anything. The bigger issure with wood foundations is that even when treated they're necessarily going to have a limited lifespan -- wood still degrades from groundwater contact over time without insect or fungal attack, and water will wash the preservative agent out of the wood over time, eventually letting fungus and termites in.