RESIDUE AND ANALYTICAL ASPECTS
Bifenthrin was first evaluated at the 1992 JMPR and MRLs of 0.05* mg/kg were recommended for barley, maize and wheat to cover field applications. The 1995 JMPR reviewed information about the use of bifenthrin as a grain protectant but made no recommendations and sought further clarification on a number of points.
Information on milling and baking studies on wheat treated with bifenthrin was made available to the Meeting.
No specific information was available on the efficiency of extraction of aged bifenthrin residues from grain by hexane/acetone, but the fact that the bifenthrin residue levels on wheat in storage trials at day 1 were unchanged by week 12 suggests that the solvent adequately extracts aged residues from grain.
Bifenthrin residues were stable on grain stored at 20°C and 25°C and their levels on the grain at the beginning of storage were essentially the same as at the end.
Approximately 16% of the bifenthrin residues were lost in producing wholemeal flour from uncleaned wheat. The bifenthrin level in white flour was about 30% (26-36%), and the level in bran about 3.5 times (3.1-3.8) the level in the uncleaned wheat.
Wholemeal bread and white bread were baked from the wholemeal and white flour produced in the milling studies. The results from these baking trials suggest that about 70% of the bifenthrin disappears on baking wholemeal or white bread. This is not consistent with the behaviour of other pyrethroids, which are mostly retained through the baking process.
The Meeting was reluctant to draw a firm conclusion on the fate of bifenthrin during baking until some aspects of the analytical method had been clarified. Validation of analytical recoveries from bread at the bifenthrin residue levels which occur in practice and at the LOD is needed, as is investigation into the possibility that bifenthrin residues are bound in the bread and not extractable by the current method.
Recommendations for MRLs and estimated STMR levels are listed in Annex I.
FURTHER WORK OR INFORMATION
Desirable
1. Validation of the analytical method for recoveries of bifenthrin residues from bread at the levels occurring in practice and at the LOD.
2. Information on the degree of extraction of bifenthrin residues from bread by the current procedure.
3. Information on national registrations and MRLs for bifenthrin covering its use on stored grain.
4. Information on the fate of bifenthrin during the commercial malting of barley treated with it post-harvest. The studies should simulate the commercial process (from 1995 JMPR).
