capable of being broken down by natural. organic processes and reabsorbed into the environment.
Merriam-Webster Online Dictionary
biodegradable (adjective)capable of being broken down especially into innocuous products by the action of living things (as microorganisms) - biodegradable trash bags
biodegradable (Wikipedia)
Yellow slime mold growing on a bin of wet paper
Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi.