Tebufenozide has a low solubility in water and a relatively high affinity for soils and sediments. It is not readily degraded by either hydrolysis or photolysis. The fate of tebufenozide was studied in two aerobic water/sediment systems and a single anaerobic system. The half-lives were 99-101 days in the aerobic systems and 179 days in the anaerobic.
These studies also confirmed the degradation pathways found in soil, with the ketone and two carboxylic acids as the main products, with further breakdown to carbon dioxide.
The octanol/water partition coefficient of tebufenozide indicates that some bioconcentration in aquatic organisms might occur. In a bioconcentration study with bluegill sunfish it was observed that the residues which accumulated in fish exposed to tebufenozide were depurated with half-lives of less than three days when they were removed from the system.
The analytical methods used in the reported studies involved extraction with methanol/acid or acetone, successive partitioning with hexane and methylene chloride or acetonitrile, and clean-up by column chromatography on basic alumina, Florisil or silica gel. Quantification is by HPLC with UV detection or by GLC with an NPD after methylation of the residues. The GLC method determines tebufenozide and HPLC determines tebufenozide and RH 6595 in the same extract.
The methods were validated with many crops. Recoveries of tebufenozide from fruits were above 80% with an LOD of 0.02 mg/kg by the GLC method, and about 80% with LODs of 0.01-0.02 mg/kg in most crops and 0.05 mg/kg in celery by HPLC. Confirmation by GC-MS or HPLC-MS was reported in some studies.
The storage stability of residues in frozen analytical samples has been studied with apples, apple juice, grapes and wine, rice, walnuts and lettuce. Tebufenozide, RH-6595, and RH-1788 were found to be stable at -20°C in apples for at least 200 days, nuts for 18 months, grapes for at least 12 months, lettuce for 6 months and dry tea for 65 days.
It was reported that studies on apples, walnuts and lettuce would be continued until data from the full 3 years of storage had been obtained.
The results of metabolism studies showed that tebufenozide is the major residue in plants to be found in supervised trials, and the Meeting concluded that the residue should be defined as tebufenozide. The residue is fat-soluble.
Tebufenozide is available as 200 and 240 g/l suspension concentrates, 70 and 10% wettable powders and also as a granulate formulation.
Residue data obtained from trials on about 12 crops in several countries, submitted to national registration authorities to support registered uses or uses pending registration, were evaluated.
Apples. The results of many trials from several countries around the world were reported. Trials in Australia and Greece were not according to GAP and were not considered for the estimation of maximum residue levels. In four US trials according to proposed GAP, residues ranged from 0.36 to 0.61 mg/kg. Residues from treatments complying with GAP were 0.08-1.1 mg/kg from 3-4 applications at 0.24 kg ai/ha, 14 days PHI in Canada, 0.01-0.18 mg/kg in 4 trials in France and 0.08-0.32 mg/kg in 4 trials in New Zealand (4-8 applications at 0.18 kg ai/ha, 14 days PHI). In two of these trials the residues at days 21 and 22 were taken because they were higher than at days 14 and 15. Residues from Italian GAP (3 applications at 0.288 kg ai/ha, 14 days PHI), were 0.28 to 0.55 mg/kg, and from Japanese GAP (two trials) 0.02 and 0.05 mg/kg. Eight trials in Germany (3 applications at 0.158-0.190 kg ai/ha, 28-day PHI) were evaluated against Belgian GAP and one trial in Spain against French GAP. Metabolites were not determined in any of the trials.
In summary, tebufenozide residues in apples from trials according to GAP were 0.08, 0.11, 0.12, 0.14, 0.16, 0.19, 0.265, 0.37, 0.43, 0.52, 0.75, 0.84 and 1.1 mg/kg in Canada; 0.01, 0.07, 0.14 and 0.18 mg/kg in France; <0.02, 0.08, 0.09, 0.11, 0.16, 0.16, 0.20 and 0.23 mg/kg in Germany; 0.28, 0.52 and 0.55 mg/kg in Italy; 0.02 and 0.05 mg/kg in Japan, and 0.08, 0.10, 0.26 and 0.32 mg/kg in New Zealand. The Meeting estimated a maximum residue level of 1 mg/kg for apples.
Pears. Supervised trials on pears were carried out according to GAP in Italy and New Zealand. The residues in two trials in New Zealand (4-9 applications at >0.18 kg ai/ha, 14 days PHI) were 0.09 and 0.10 mg/kg, and in one trial in Italy (3 applications at 0.216 kg ai/ha, 14 days PHI) 0.23 mg/kg.
Taking into account the similarity of the use patterns in apples and pears, the Meeting agreed to evaluate the combined data on apples and pears as applying to pome fruit.
This gave tebufenozide residues in pome fruit in rank order (median underlined) of 0.01, <0.02, 0.02, 0.05, 0.07, 0.077, 0.08, 0.08, 0.09, 0.09, 0.10, 0.10, 0.11, 0.11, 0.12, 0.14, 0.14, 0.16, 0.16. 0.16. 0.18, 0.19, 0.20, 0.23, 0.23, 0.26, 0.27, 0.28, 0.32, 0.37, 0.37, 0.43, 0.52, 0.52, 0.55, 0.75, 0.84 and 1.1 mg/kg.
The Meeting estimated a maximum residue level of 1 mg/kg and an STMR of 0.16 mg/kg for pome fruits.
Grapes. Numerous field trials on vines have been conducted in Australia, France, Germany, Italy and Thailand. Those in Australia, Italy and Thailand, and several from France, were not according to GAP. Residues in nine trials in Germany in accordance with proposed GAP ranged from 0.21 to 0.42 mg/kg. Nine trials in France complied with GAP (3 applications at 0.144 kg ai/ha, 21 days PHI) and the residues in these in rank order were 0.05, 0.06, 0.07, 0.08, 0.12. 0.18, 0.26, 0.28 and 0.28 mg/kg.
The Meeting estimated a maximum residue level of 0.5 mg/kg and an STMR of 0.12 mg/kg for tebufenozide in grapes.
Kiwifruit. Several field trials were carried out in New Zealand and the USA, but the Meeting could not relate these trials to GAP in New Zealand and was unable to estimate a maximum residue level for kiwifruit.
Leafy vegetables. Several field trials on lettuce were carried out at different locations in the USA according to proposed GAP. Residues in head lettuce ranged from 0.01 to 6.6 mg/kg and in leaf lettuce from 0.4 to 3.2 mg/kg. Head lettuce samples were stored before analysis for 264 to 1186 days.
Six of nine field trials on spinach at different locations in the USA were according to proposed GAP (7 applications at 0.140 kg ai/ha, 7 days PHI). The residues from them ranged from 1 to 4.2 mg/kg. The storage period before analysis was about 750 days.
Several supervised trials on mustard greens were carried out in the USA. According to the proposed GAP of 7 applications at 0.067-0.135 kg ai/ha with a 7-day PHI. The reported storage period before analysis ranged from 139 to 930 days. The residues were 0.65 to 5.6 mg/kg.
The evaluation of data on leafy vegetables can be reconsidered when GAP has been established and studies on the storage stability of residues in lettuce have been completed.
Celery. Several field trials were conducted in the USA with 7, 8 or 9 applications at 0.14 kg ai/ha. In trials where both stalk and stalk with foliage were analysed, the residues in the stalk with foliage were significantly higher than those in the stalk. The residues ranged from 0.1 to 1.3 mg/kg (1.3 mg/kg in stalk with foliage).
Since there is no existing GAP for celery, the Meeting could not estimate a maximum residue level.
Several supervised trials on cabbage and broccoli were carried out in the USA according to proposed GAP: 7 applications at 0.067-0.135 kg ai/ha and a 7-day PHI. The reported storage period before analysis ranged from 110 to 938 days. The residues in broccoli were 0.1-0.33 mg/kg (3 samples) and in cabbage <0.01-0.53 mg/kg (5 samples). The residues in head cabbage without wrapper leaves were 0.01 mg/kg.
The evaluation of data on these crops can be reconsidered when GAP has been established and studies on the storage stability of residues in vegetables have been completed.
Field trials on Chinese kale and chilli peppers in Thailand were reported but they were not according to GAP. The Meeting could not estimate a maximum residue level.
Rice. Eight supervised trials were carried out in Japan according to GAP, with two different formulations (0.75 DL and 10 WP). The residues in the husked grain at 14-21 days PHI ranged from 0.005 to 0.07 mg/kg and in the straw from 2.2 to 7.7 mg/kg. Metabolite residues (sum of alcohol and ketone) were at or below the LOD in the grain and 0.2-0.3 mg/kg in the straw, but increased at longer PHIs to maxima of 0.008 mg/kg in grain and 0.42 mg/kg in straw.
Two trials on rice in Spain were not according to GAP.
The residues in the Japanese trials in rank order were <0.005, 0.007, 0.008, 0.02, 0.03, 0.05, 0.06 and 0.07 mg/kg. The Meeting estimated a maximum residue level of 0.1 mg/kg and an STMR of 0.03 mg/kg for rice, husked.
Pecans. Eight field trials in the USA were all with more applications than the number in the proposed GAP, but four of them were at the proposed application rate. All the residues were below the LOD of 0.01 mg/kg and only one was above the limit of detection (0.003 mg/kg). The Meeting estimated a maximum residue level of 0.01* mg/kg but could not recommend it for use as an MRL because there is no existing GAP.
Walnuts. The highest residue found in nut-meat was 0.05 mg/kg, when the compound was applied at twofold rate (0.560 kg ai/ha). In six field trials in the USA according to GAP (4 applications at 0.28 kg ai/ha, 30 days PHI), the residues ranged from <0.003 to 0.02 mg/kg. In two trials in France considered to comply with GAP the residues were undetectable (<0.003 mg/kg).
Tebufenozide residues in walnuts in rank order (median underlined) were <0.003, 0.003, <0.003, <0.003, <0.003, 0.006, 0.007, 0.02 and 0.02 mg/kg. The Meeting estimated a maximum residue level of 0.05 mg/kg and an STMR of 0.003 mg/kg for walnuts. A maximum residue level of 0.05 mg/kg, rather than 0.02 mg/kg was estimated, because in two trials the residues were determinable at 0.02 mg/kg.
Tea. Trials were conducted in Japan and Sri Lanka but those in Sri Lanka were not adequately reported. The residues in dry tea from the two Japanese trials according to GAP were 11.5 and 11.6 mg/kg at a 14-day PHI. Residues of the combined alcohol and ketone metabolites determined as the alcohol were 0.23-0.24 mg/kg.
The Meeting concluded that the data were insufficient to estimate a maximum residue level for dry tea.
