Readily Biodegradable is a term used for substances that meet the very stringent testing criteria of a ready biodegradability test demonstrating ultimate biodegradation within a specified time period. Substances that are readily biodegradable are expected to be rapidly degraded in wastewater treatment plants or in the environment. Readily biodegradable is one of the key criterions for demonstrating a lack of persistence (P) in PBT assessments, hazard classifications, or "green chemistry" certifications.

Inherently Biodegradable is a term for substances that can be biodegraded under specific conditions. The inherent biodegradability test is not as stringent as a ready biodegradation study. It uses a greater amount of microorganism inoculum and doesn't have as strict of a time component. It is often used when a substance is not able to pass a readily biodegradable test, but will demonstrate whether or not the substance will eventually biodegrade.

Predicted to be Readily Biodegradable indicates that the substance has not been tested for biodegradation, but is predicted to be readily biodegradable based upon Quantitative Structure Activity Relationship (QSAR) modeling.

Glossary of Biodegradation Terms per REACH (Table R. 7.9-1, starting on p 156)