The reason why some substances are biodegradable and some are non-biodegradable is because microorganisms such as bacteria and decomposers as saprophytes have a specific role to play. They can only degrade natural products such as paper, wood, etc. According to this, some things are degradable and some are not.
Why are some substances biodegradable and some non-biodegradable?
Why are some substances biodegradable and some non-biodegradable?