Photosensitizing properties of formulation adjuvants

Protein hydrolysed fertilizers (PHFs) are currently used to stimulate plant metabolism, mainly through foliar application, and are proposed for use as pesticide adjuvants. However, the effects of PHFs on pesticides upon irradiation are unknown. Here, several herbicides and model compounds were irradiated with simulated solar light in the presence of four PHFs extracted from animal proteins and from vegetal. PHFs enhanced the photodegradation of fenuron, mesotrione, 2-mercaptobenzothiazole and 2,4,6-trimethylphenol. Using the scavenging technique, we could evidence the direct reaction of triplet excited states of PHFs towards substrates and we evaluated the contribution of triplets, singlet oxygen and hydroxyl radicals. Hydroxyl radicals were not detected; they were either not formed or were efficiently scavenged by the PHFs. The four PHFs showed distinct photosensitizing abilities. Production processes, rather than origin of the PHFs, seem to govern the photochemical reactivity of the PHFs.