BOUND XENOBIOTIC RESIDUES IN FOOD COMMODITIES OF PLANT AND ANIMAL ORIGIN (TECHNICAL REPORT)

In order to assess the dietary risk resulting from the use of pesticid es or veterinary drugs the nature of the chemical residues on food com modities needs to be determined. Elucidation of the nature of the chem ical residue is carried out using radiolabelled studies where the radi olabelled xenobiotic is applied or dosed in a manner which reflects us e conditions. Food commodities are exhaustively extracted to remove th e individual components of the residue. Once extracted the identity an d toxicological significance of the components. can be assessed and, w here appropriate, analytical methods developed to quantitatively deter mine the amount of the components in food items. Depending on the char acteristics of the components of the residue, the extraction regime ma y not remove all the chemical residue from the sample matrix. These re sidues are frequently characterised as being ''bound'', however the am ount and nature of this residue will be highly dependant on the extrac tion 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 avail ability of enzyme systems which effectively solubilise the entire matr ix rather than extracting the residue. It is also recommended that whe re the extraction falls short of the full definition then the residues should be termed as ''unextractable'' and the conditions of the extra ction should also be defined. Where residues are bound the assessment of the dietary risk cannot be directly assessed thus raising issues re lating to the significance of the bound residue. The overall toxicolog ical significance of a bound residue will depend primarily on its bioa vailability and the level of exposure. In order to determine the bioav ailability, study design is crucial in order to perform a critical saf ety assessment.