An environmentally-friendly method is disclosed for transforming preserved wood, for example creosote-treated or CCA-treated wood with supercritical water. The product of treating weathered creosote-treated wood is a mixture that is similar to fresh creosote. The novel system is akin to a closed-loop system for recovering and rejuvenating creosote. In another aspect of the invention, acidic supercritical water is used to extract copper, chromium, and arsenic from CCA-treated wood, or more generally, to extract metals from an organic matrix.