You searched for: “most biodegradable
biodegradable (adjective), more biodegradable, most biodegradable
Relating to organic compounds that can be decomposed by natural processes: Environmentally friendly people are interested in using only biodegradable detergents, which can be broken down by biological agents, particularly by bacteria, when washing their clothes or dishes.

Most plastics, for example, are not biodegradable and will remain in the environment for ever!