Oxytetracycline Fruit Residues
Posted August 2025
Researchers: Ute Albrecht , Gabriel Pugina
Contact: Ute Albrecht, UF/IFAS SWFREC ualbrecht@ufl.edu
Summary:
The currently allowed maximum residue level (MRL) of oxytetracycline (OTC) in the fruits is 10 parts per billion (ppb) or 0.01 parts per million (ppm). A study was conducted to determine whole fruit (peel and juice) residues in response to different doses of OTC and different months of injection. The trees in this study were 18-year-old ‘Valencia’ on Swingle rootstock. Trees were injected with OTC in 2023 and 2024 using 100 ml of a 5,500 ppm, 8,250 ppm, or 11,000 ppm solution (0.55 g, 0.825 g, or 1.1 g OTC per tree). Injections were performed on one side of the tree using FLexInject™ injectors. In year 1, injections were performed either in June or September. In year 2, injections were performed either in June or August. Fruits were harvested in March 2024 and 2025. A random subset of fruits was collected from each treatment and homogenized in a blender. The homogenate was analyzed for OTC by an ISO/IEC 17025 accredited laboratory using LC-MS/ MS. In both years, OTC fruit residues were below the MRL when injections were performed in June, regardless of the OTC dose. When injections were performed in September (year 1), residues were considerably higher than the allowed MRL, and a higher OTC dose resulted in higher residues. When injections were performed in August (year 2), average OTC residues were below the MRL, but individual samples exceeded the allowed level of 0.01 ppm. It is therefore recommended to complete all injections before August.
Take Home Message:
- The maximum allowed residue level of OTC in the fruits is 0.01 parts per million (10 parts per billion).
- Fruit OTC residues depend on the month in which injections are performed.
- Injections performed in late summer/ fall generate high OTC residues.
