Bifenthrin was first evaluated at the 1992 Meeting 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 pending the receipt of information on the following points.
Efficiency of extraction by acetone of aged bifenthrin residues.
National MRLs for bifenthrin relating to uses on stored grains.
Fate during the commercial milling of wheat.
Fate during the baking of bread.
Fate during commercial malting of barley.
Information on milling and baking studies with bifenthrin-treated wheat was made available to the Meeting.
A method for the determination of residues in cereal grains relied on hexane/acetone extraction followed by solvent evaporation and capillary GLC analysis with EC detection. Recoveries were good and the LOD for bifenthrin on wheat was 0.01 mg/kg.
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 at day 1 were unchanged by week 12 in the storage trials suggests that the solvent adequately extracted aged residues.
A residue method for bifenthrin in flour, bran and bread involved acetone extraction followed by solvent evaporation, clean-up by Florisil column chromatography and capillary GLC with EC detection. Recoveries of bifenthrin were good from white flour, bran and wholemeal bread at 0.05, 1.0 and 0.2 mg/kg respectively. No data were available for recoveries from white bread.
In two grain storage trials wheat was treated with EC or UL formulations of a bifenthrin + malathion mixture at rates of 0.3 and 6.0 g ai/t for bifenthrin and malathion respectively, and then stored for 12 weeks or 180 days. The grain was sampled at intervals for analysis.
The results were consistent with those of the trials of bifenthrin used as a grain protectant evaluated by the 1995 Meeting. Bifenthrin residues are stable on stored grain at 20°C and 25°C and the levels of bifenthrin on the grain at the beginning and end of the storage will be essentially the same.
On the basis of the approved use of bifenthrin as a grain protectant on stored grain in Belgium at 0.3 g ai/t and its stability on wheat during storage the Meeting estimated a maximum residue level of 0.5 mg/kg for bifenthrin in wheat.
Data from 8 trials of bifenthrin on stored wheat in Belgium, France and the UK were evaluated by the 1995 JMPR. The highest bifenthrin residues recorded in each trial were 0.22, 0.19, 0.24 and 0.25 mg/kg in Belgium, 0.26 and 0.24 mg/kg in France and 0.28 mg/kg in the UK. The highest bifenthrin residues in each of the 6 trials evaluated by the present Meeting were 0.24 and 0.25 mg/kg in the UK and 0.26, 0.28, 0.31 and 0.32 mg/kg in France.
In summary the highest bifenthrin residues in each of the 14 grain protectant trials according to GAP in rank order (median underlined) were 0.19, 0.22, 0.24, 0.24, 0.24, 0.25, 0.25, 0.26, 0.26, 0.27, 0.28, 0.28, 0.31 and 0.32 mg/kg. The Meeting estimated an STMR of 0.255 mg/kg for bifenthrin on wheat.
In the milling studies grain was cleaned before milling with a Laboratory Carter Day Dockage Tester, which simulates commercial cleaning. Bifenthrin-treated wheat was taken for milling and baking on the first day and 8 weeks after treatment.
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 (3.1-3.8) times the level in the original wheat.
Residues of bifenthrin in white flour in the 4 milling trials (2 milling trials from each of 2 storage trials) were 0.06, 0.07, 0.07 and 0.09 mg/kg. Taking into account the possibility that bifenthrin residue levels on wheat could be higher than the levels on the wheat in these milling trials (0.23-0.25 mg/kg), the Meeting estimated a maximum residue level of 0.2 mg/kg for bifenthrin in flour.
The bifenthrin residues in the flour were 0.26, 0.28, 0.29 and 0.36 (mean 0.30) times those in the wheat. The Meeting therefore estimated an STMR-P of 0.076 mg/kg for bifenthrin in flour (0.30 x 0.255).
The bifenthrin residues in bran in the 4 milling trials were 0.75, 0.83, 0.88 and 0.92 mg/kg. Since the bifenthrin residue levels on wheat might be higher than those found in the trials (0.23-0.25 mg/kg) the Meeting estimated a maximum residue level of 2 mg/kg for bifenthrin in bran.
The concentration factors for bifenthrin residues in the processing of wheat to bran in the 4 milling trials were 3.1, 3.3, 3.7 and 3.8 (mean 3.5). The Meeting estimated an STMR-P of 0.89 mg/kg for bifenthrin in bran (3.5 x 0.255).
Wholemeal flour produced from bifenthrin-treated wheat on 4 occasions in each of the 2 storage trials contained bifenthrin residues of 0.17, 0.18, 0.19, 0.20, 0.20, 0.21, 0.22 and 0.22 mg/kg. These residues were 0.75, 0.77, 0.79, 0.80, 0.83, 0.88, 0.91 and 0.92 (mean 0.83) times those in the uncleaned wheat. The Meeting estimated a maximum residue level of 0.5 mg/kg and an STMR-P of 0.21 mg/kg (0.83 x 0.255) for bifenthrin in wholemeal.
Wholemeal bread and white bread were produced from the wholemeal and white flours generated in the milling studies. Residues in the bread and flour were reported on both a fresh and a dry weight basis. The results 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 largely 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.
