Phosphonic acid is regularly detected in products of both conventional and organic fruit and vegetable farming. Phosphonic acid is a substance that has systemic effects on fungal infections, in particular helping combat downy mildew. Phosphonic acid residue can appear as a result of the usage of fungicides with the active substance fosetyl-aluminum or with phosphonic acid itself. Both substances are approved in the European Union as active substances in fungicides and are included in the scope of Regulation (EC) No 396/2005 regardless of how they enter the product.
Fosetyl-aluminum, also known as fosetyl-Al, is used in conventional farming in various ways. In organic farming, though, its usage is not permitted. When fosetyl-Al degrades, the active substance phosphonic acid is produced via the intermediary product fosetyl. Based on this fact, Regulation (EC) No 396/2005 defines the residue of fosetyl-Al as the sum of fosetyl and phosphonic acid and its salts, expressed as fosetyl.
Aside from fungicidal origins, phosphonic acid contamination can also potentially occur as a result of plant fortifiers or (leaf) fertilizers that contain phosphonates (phosphonic acid salts). However, this application is no longer permitted due to phosphonate being classified as a fungicide. Nevertheless, there are indications that permanent crops such as fruit trees may store phosphonic acid and can excrete it even in subsequent years.
The GBA Group has years of experience analyzing phosphonic acid as well as fosetyl-Al, carrying out these analyses routinely by means of LC-MS/MS technology. If you have any questions, we will gladly assist you.