Furthermore, it is readily biodegraded in soil. Food waste can be biodegraded by composting, and reused to fertilize soil. MTBE is biodegraded by the action of bacteria. In 2005, "Shewanella oneidensis" biodegraded a high percentage of PCBs in soil samples. It can be biodegraded by some bacteria, including "Sphingobium chlorophenolicum". Some of the oil does not appear to have biodegraded at all. Heavy metals including cadmium, chromium, lead and uranium are elements so they cannot be biodegraded. Gangliosides are made and biodegraded rapidly in early life as the brain develops.