The solubility of tebufenozide in water was determined by the shake-flask method, using aqueous mixtures of the labelled test compound to provide concentrations of 5, 10, 25 and 50 mg/l if all the tebufenozide dissolved. The concentration after the final equilibrium averaged 0.83 mg/l in the four tubes (Kelly, 1992b).
The hydrolysis of tebufenozide was studied in sterile aqueous solutions buffered to pH 5, 7, and 9, containing 0.5 mg/l of [14C]tebufenozide and less than 1% by volume of acetonitrile, and maintained at 25 ± 1°C for 30 days in the dark. Aliquots of the solutions were analysed after 0, 3, 7, 14, 21, and 30 days for the test compound and possible hydrolysis products by solid-phase extraction, LSC, TLC and HPLC.
The total recoveries of applied radioactivity averaged 105-109% for the three systems. The only significant radioactive compound in the solutions was confirmed by normal-phase TLC and reverse-phase HPLC to be tebufenozide. No hydrolysis products were detected (Reynolds, 1992a).
The photolysis of tebufenozide, labelled in the A-ring, was studied in a 0.5 mg/l solution in natural pond water maintained at 25 ± 1°C. The sample tubes were irradiated with a Xenon lamp, with 12-hour light/dark cycles, for 30 days. CO2 and other volatile materials in the head-spaces of the sample tubes were retained in a series of traps. Duplicate sample tubes were removed from the photolysis chamber and the solutions analysed for the test compound and possible photoproducts at 0, 3, 7, 14, 21 and 30 days.
Analyses were by partition with organic solvent and liquid scintillation counting of the two phases, followed by TLC and HPLC of the organic phase with radiometric detection. No aqueous phase contained more than 5% of the applied radioactivity and no significant amount of volatile material was formed.
Tebufenozide was degraded with a half-life of 67 days under the conditions of the experiment. The major product was the ketone RH-6595, produced at a maximum level of 5.3% of the original 14C. Eight other photoproducts were detected, none exceeding 3.5% of the applied activity in any sample. Almost no degradation occurred in the dark control. Recoveries of the applied radioactivity were 96-106% (Reynolds, 1992c).
In a study of aerobic aquatic degradation two hydrosoils and their respective paddy waters were incubated with tebufenozide labelled at all three sites at a nominal rate of 1 mg/kg in the dark at 25 ± 1°C for one year. The sediments were Arkansas silty clay and California clay loam (Reynolds, 1992g). The characteristics of the two systems are shown in Table 17.
Table 17. Characteristics of water/sediment systems.
|
|
Arkansas silty clay |
California clay loam |
||
|
soil |
water |
soil |
water |
|
|
Sand, % |
12 |
|
30 |
|
|
Silt, % |
42 |
|
34 |
|
|
Clay, % |
46 |
|
36 |
|
|
Organic matter, % |
2.0 |
|
2.6 |
|
|
pH |
6.9 |
6.7 |
7.8 |
6.9 |
|
O2 (dissolved, ppm) |
|
8.10 |
|
6.85 |
Duplicate samples were taken for analysis on days 0, 1, 3, 7, 14, 30, 60, 120, 180, 270 and 365. Volatile compounds were trapped throughout the study. At each sampling, the soil and supernatant water were separated by decanting and centrifuging and analysed separately. The radioactive components in each phase were extracted and determined by TLC and/or HPLC, and the identities of the parent compound and the major products were confirmed by mass spectrometry. The distribution of radioactivity and the nature and amounts of the products from the three labels were similar. The results are summarized in Tables 18 and 19.
Table 18. Average distribution of radioactivity at various intervals in Arkansas and California soils.
|
Days incubation |
% of 14C |
|||||||
|
Arkansas |
California |
|||||||
|
Supernatant |
Solids |
PES1 |
Traps |
Supernatant |
Solids |
PES1 |
Traps |
|
|
0 |
55.8 |
43.4 |
0.74 |
0 |
53.4 |
45.9 |
0.69 |
0 |
|
1 |
45.2 |
48.8 |
0.5 |
0.02 |
39.7 |
63.0 |
2.4 |
0.01 |
|
3 |
36.4 |
54.6 |
3.18 |
0.04 |
40.6 |
60.4 |
3.7 |
0.01 |
|
7 |
26.0 |
64.6 |
2.1 |
0.05 |
22.4 |
75.1 |
5.9 |
0.02 |
|
14 |
17.5 |
75.1 |
5.8 |
0.05 |
19.8 |
78.4 |
7.0 |
0.03 |
|
30 |
16 |
74.7 |
7.5 |
0.27 |
12.7 |
74.8 |
15.3 |
0.06 |
|
59-60 |
21.3 |
57.4 |
15.2 |
1.2 |
13.0 |
79.7 |
12.9 |
0.4 |
|
88-90 |
23.9 |
64.5 |
8.2 |
2.9 |
15.9 |
78.3 |
9.3 |
1.9 |
|
120 |
24.4 |
59.4 |
10 |
5.2 |
19.1 |
65.0 |
14.9 |
6.9 |
|
179 |
21.4 |
51.2 |
13.7 |
10.5 |
18.4 |
48.4 |
20.3 |
18.6 |
|
270 |
31.1 |
29.9 |
15.4 |
20 |
11.7 |
23 |
24 |
34.2 |
|
360 |
29.2 |
24.5 |
20.7 |
30.1 |
5.56 |
11.5 |
22.7 |
47.4 |
1 Post-extraction solids
Three major compounds were observed in the study in addition to tebufenozide and CO2. These were the ketone RH-6595 and the two carboxylic acids RH-2651 and 2703, all products of oxidation of the ethyl group on the A-ring of molecule. Five additional degradation products were also found and characterized by their chromatographic behaviour but not identified. None of these accounted for more than 5.7% of the applied activity in any sample. Up to 47% of the total applied 14C was converted to 14CO2 by the end of the study.
Sediment-bound residues increased gradually as the study progressed to 19-23% of the 14C from all three labels in both hydrosoils. The bound residues after 358-366 days were characterized by means of various techniques. Mild acidic extraction solubilized 5-6% of the total applied 14C and acid hydrolysis released about 4%. The remainder was fractionated into humic and fulvic acids and humin, with the activity predominantly in the fulvic acid fraction.
The half-lives of the parent compound under the aerobic aquatic test conditions (average of the three labels) were 101 days in the California clay loam and 99 days in the Arkansas silty clay.
Table 19. Distribution of residues in the aquatic degradation of tebufenozide.
|
Day |
Percentage of 14C present as |
||||
|
Tebufenozide |
RH-6595 |
RH-2651 |
RH-2703 |
CO2 |
|
|
Arkansas silty clay, A-ring label |
|||||
|
0 |
98.29 |
0 |
0 |
0 |
0 |
|
1 |
91.70 |
0.13 |
0 |
0 |
0.02 |
|
3 |
89.53 |
0.92 |
0 |
0 |
0.04 |
|
7 |
88.11 |
2.26 |
0 |
0 |
0.05 |
|
14 |
90.01 |
0 |
0 |
0.07 |
0.05 |
|
30 |
76.77 |
5.52 |
0 |
0 |
0.27 |
|
59 |
60.17 |
2.14 |
2.63 |
8.71 |
1.23 |
|
90 |
64.31 |
4.88 |
4.16 |
8.78 |
2.94 |
|
120 |
49.05 |
6.92 |
9.49 |
9.43 |
5.19 |
|
178 |
30.78 |
6.56 |
14.26 |
11.14 |
10.53 |
|
269 |
12.71 |
2.56 |
32.07 |
2.59 |
20.02 |
|
366 |
7.02 |
1.07 |
35.45 |
0 |
30.08 |
|
California clay loam, B-ring label |
|||||
|
0 |
98.48 |
0 |
0 |
0 |
0 |
|
1 |
96.92 |
0.29 |
0 |
0 |
0 |
|
3 |
94.92 |
0.70 |
0 |
0 |
0.01 |
|
7 |
95.67 |
0.32 |
0 |
0 |
0.01 |
|
14 |
91.46 |
0.42 |
0 |
0 |
0.02 |
|
30 |
86.63 |
0 |
0 |
0 |
0.05 |
|
60 |
80.80 |
5.10 |
0 |
0 |
0.35 |
|
88 |
64.99 |
8.10 |
2.57 |
4.74 |
2.04 |
|
120 |
58.18 |
4.99 |
2.86 |
4.62 |
6.09 |
|
179 |
31.11 |
4.26 |
8.46 |
4.66 |
18.08 |
|
270 |
15.17 |
2.50 |
6.40 |
1.11 |
35.78 |
|
358 |
7.94 |
0.78 |
1.88 |
0.05 |
47.00 |
A companion study of anaerobic aquatic degradation with a flooded silt loam hydrosoil, was again in the dark at 25 ± 1°C for one year at a nominal rate of 1 mg/kg of tebufenozide, uniformly labelled with 14C in the A-ring and also with 14C in the two methyl groups on the B-ring to aid mass spectral identification if needed. Duplicate samples were taken for analysis on days 0, 3, 7, 14, 30, 60, 90, 120, 179, 270 and 365. Volatile products were trapped throughout the study (Reynolds, 1992f).
Two significant compounds were found apart from tebufenozide and CO2: the ketone, which reached a maximum of 8.0% of the applied activity at day 179, and the carboxylic acid RH-2651 which reached 11.6% at day 120. Eight other compounds were found and characterized. One was the carboxylic acid RH-2703, the others were not identified. None of these minor products exceeded 4% of the applied activity in any sample. The calculated half-life of tebufenozide was 179 days.
