Description of status quo, state of the art
There are a number of veterinary drugs for which Codex has not adopted an MRL. An ADI/MRL may not have been established because the veterinary drug may not have been evaluated by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) or in the JECFA evaluation, the toxicological data did not support an ADI, the residue data were insufficient, a suitably validated analytical method was not identified, or good agricultural practices would result in exceeding the MRL. JECFA is an expert scientific committee independent of Codex which provides risk assessment advice to Codex and member countries.
In the absence of ADI/MRL, national authorities commonly resort to zero tolerance regulatory approaches (where no detectable residue of the veterinary drug in the food is acceptable), with the prevalence of residues of concern potentially changing as analytical method detection capabilities improve. Additional tools are needed to evaluate risk when the existing approach of establishing an ADI and MRL cannot be applied.
The change in technology, for example LC-diode array to LC-MS, has resulted in an improvement in detection capability so that a residue that was previously non-detectable now becomes reportable. The change in reported levels is independent of any toxicological risk posed by the food product.
Analysis of gaps, identification of problems
An MRL cannot be established if the toxicological data do not support the derivation of an ADI, nor can an MRL be established if no data are provided for evaluation, as is the case for an unapproved use of a veterinary drug.
Low level residues of veterinary drugs without ADIs or MRLs may be present at concentrations approaching those of environmental contaminants. Considering that there may be environmental sources of the drug substance (that may differ regionally), it is not clear when residues of a banned veterinary drug should be evaluated as a contaminant. While the toxicological evaluations in the risk assessments would be the same, other considerations may be different.
Identification of the data requirements for evaluation by JECFA can be a problem for some national authorities. Similarly, the collection of sufficient data for an evaluation of veterinary drugs by the JECFA has been a problem for some compounds.
