After the Organic Foods Production Act of 1990 launched, the Secretary of Agriculture was required by the act to create a National List of Allowed and Prohibited Substances (National List).
The National List identifies synthetic substances, materials and ingredients that may be used in organic farming and production operations. The List also highlights nonsynthetic substances, materials and ingredients that cannot be used.
Exclusions and Rules for the National List of Allowed and Prohibited Substances
It's possible to file a petition that requests inclusion for a specific substance on the National List. However, substances on the USDA petition site may not be used for organic production or handling operations before the substance is officially added to the final amendments of the National List, or until you see it on the current version of the National List.
The most current version of the National List of Allowed and Prohibited substances is available to views at the Electronic Code of Federal Regulations (e-CFR) website. To locate the current National List look under The National Organic Program subcategory "Subpart G-Administrative."
Each item on the National List has its own set of rules. The substance is either prohibited or approved. If approved there is further information about the substance if applicable. For example, on the National List, ammonium bicarbonate is allowed, but only for use as a leavening agent. Potassium carbonate is allowed but only if natural sodium carbonate is not an acceptable substitute.