Bound xenobiotic residues in food commodities of plant and animal origin: IUPAC Reports on Pesticides (40)

In order to assess the dietary risk resulting from the use of pesticides or veterinary drugs the nature of the chemical residues on food commodities needs to be determined. Elucidation of the nature of the chemical residue is carried out using radiolabelled studies where the radiolabelled xenobiotic is applied or dosed in a manner which reflects use conditions. Food commodities are exhaustively extracted to remove the individual components of the residue. Once extracted the identity and toxicological significance of the components. can be assessed and, where appropriate, analytical methods developed to quantitatively determine the amount of the components in food items. Depending on the characteristics of the components of the residue, the extraction regime may not remove all the chemical residue from the sample matrix. These residues are frequently characterised as being "bound", however the amount and nature of this residue will be highly dependant on the extraction regime used. To provide guidance and standardisation a definition of the term "bound residues" is recommended. This definition builds on a previous IUPAC definition but takes account of the current availability of enzyme systems which effectively solubilise the entire matrix rather than extracting the residue. It is also recommended that where the extraction falls short of the full definition then the residues should be termed as "unextractable" and the conditions of the extraction should also be defined. Where residues are bound the assessment of the dietary risk cannot be directly assessed thus raising issues relating to the significance of the bound residue. The overall toxicological significance of a bound residue will depend primarily on its bioavailability and the level of exposure. In order to determine the bioavailability, study design is crucial in order to perform a critical safety assessment.