Plastics which are non-biodegradable are actually resistant to acidic attack. Volatile materials can also be stored in non-biodegradable containers like plastic. Food stored in plastic containers...
Material that's nonliving (excluding dead organic matter) is non-biodegradable. Plastic, metal, styrofoam, and corrugated cardboard are non-biodegradable, while a dead tree, animal waste, and skin...