Phosphoric Acid

Are there non-synthetic sources of phosphoric acid? Under the Canada Organic Regime (COR) standards, what restrictions apply to phosphoric acid used as a formulant in livestock health care products?

By Cesar Cartagena

As one of the six macrominerals, phosphorus is an essential element for life. Its elemental forms, white and red phosphorous, are highly reactive, and phosphorous is most often found in nature as the insoluble rock phosphate mineral apatite.

Phosphorous is better absorbed when in soluble form, such as the dihydrogen phosphate ion (H₂PO₄⁻), derived from orthophosphoric acid (H₃PO₄) and water. Phosphoric acid’s uses in organic production vary. It is used as a pH adjustor in liquid fish fertilizers, as an inert ingredient in pesticide products, and as a sanitizer for dairy equipment. Under the Canadian Organic Standards, phosphoric acid used in livestock production must meet the requirements of individual Permitted Substances List (PSL) Table entries within CAN/CGSB-32.311-2020, specifically either Table 5.3, Formulants (inerts, excipients); or Table 7.4, Phosphoric Acid. In order to determine whether a given phosphoric acid product is allowed for organic use, OMRI reviews the function of the material in the final product, and use instructions on the label and Safety Data Sheet (SDS) as applicable.

Phosphoric acid is produced commercially via two main methods: the “wet process” and the “thermal process.” Wet-process phosphoric acid involves reacting sulphuric acid with naturally-occurring phosphate rock, and is used in fertilizer production. Thermal-process phosphoric acid, produced via oxidation or burning of liquid elemental phosphorous, is of a much higher purity, and is used in the manufacture of high-grade chemicals, pharmaceuticals, detergents, food products, beverages, and other non-fertilizer products. These two methods both render the phosphoric acid a synthetic material as defined in Terms and Definitions 3.78 (synthetic substance) in CAN/CGSB-32.310-2020. Non-synthetic sources of phosphoric acid are not available, as the manufacturing processes currently available require chemical reactions. 

Despite the extensive changes within the 2020 standards update, the compliance of phosphoric acid remains unchanged in livestock production. Under the 2015 PSL Table 5.3 Acids entry, non-synthetic acids were permitted for all livestock health care and production aid uses. As discussed earlier, available sources of phosphoric acid are synthetic. However, under the updated 2020 entry, the annotation has been edited to remove the non-synthetic origin and include specific acids by name—but phosphoric acid is not included. The acids included in the annotation are usually produced through non-synthetic means, unlike phosphoric acid. 

Even though the wording and compliance criteria for “Acids” has changed, the allowance for phosphoric acid has not. PSL Table 5.3, Health care products and production aids, continues to include an allowance for phosphoric acid in organic livestock production. Depending on its declared use, phosphoric acid may be considered an excipient under the “Formulants” entry in a livestock health care product. The annotation in the “Formulants” entry requires that the material “shall be used in conjunction with substances listed in Table 5.3” and that “Formulants are not subject to 1.4 of CAN/CGSB-32.310 […]” In order to determine the compliance of the material as a formulant (specifically, an excipient in livestock health care products), OMRI requires the submission of a full ingredient declaration of the final product, as well as a final product label and SDS. 

Under the revised 2020 standards, phosphoric acid remains allowed as an active ingredient in cleaners, disinfectants and sanitizers on dairy equipment, provided that it is removed prior to contact with organic product (PSL Table 7.4). Phosphoric acid is not allowed as an active ingredient in other livestock health care products. 

This article first appeared in the winter 2020 issue of the OMRI Materials Review Newsletter. It was reviewed and updated by Senior Technical Coordinator Peter Bungum in March 2021.