Animal metabolism
Ruminants. Two lactating goats were dosed with [phenyl-U-14C]haloxyfop in gelatin capsules twice daily for ten consecutive days at a rate equivalent to 16 ppm in the diet (Yackovich and Miller, 1983a). Urine and faeces were collected each morning during the test period. Blood samples were taken daily and expired air was collected from one goat for a ten-hour period. Milk was collected each morning and evening. Twelve hours after the final dose the animals were slaughtered and tissue samples and gut contents taken.
The recovery of the administered radioactivity was 90-96%. Most was excreted in the urine (84-92% of total administered dose) as unchanged haloxyfop; milk contained 1.9-3.2% and faeces 1.5-1.9%. No radioactivity was found in the expired air. Radioactivity as haloxyfop equivalents was 0.02 mg/kg in muscle, 0.1 mg/kg in fat, 0.4 mg/kg in liver and 1.3 mg/kg in kidney.
The liver and kidneys contained only haloxyfop, while the fat contained a non-polar conjugate which was easily hydrolysed to yield haloxyfop under alkaline conditions. The residue in muscle was not identified because the radioactivity was too low.
The radioactivity in the milk reached a plateau within two days after the first dose at 0.2 to 0.3 mg/kg haloxyfop equivalent, representing about 2 to 3% of the daily dose. The residue was primarily in the milk fat fraction in the form of non-polar conjugate(s) which were easily hydrolysed to yield haloxyfop under alkaline conditions. Enzymatic hydrolysis with lipase (triacylglycerol-acyl-hydrolase) indicated that the conjugates were triacylglycerols.
The recovery of radioactivity and its distribution are shown in Table 1.
Table 1. Recovery and distribution of radioactivity following the feeding of [14C]haloxyfop to lactating goats.
|
Sample |
Recovery of radioactivity, % of total dose |
Radioactivity as mg/kg haloxyfop equivalent |
% of haloxyfop in residual radioactivity |
|
Fat |
0.04-0.06 |
0.06-0.111 |
>903 |
|
Heart |
<0.01 |
0.02-0.071 |
|
|
Kidneys |
0.09-0.11 |
1.07-1.451 |
>904 |
|
Liver |
0.14-0.16 |
0.31-0.451 |
>904 |
|
Muscle |
0.09-0.11 |
<0.01-0.021 |
|
|
Gut contents |
0.25-0.40 |
- |
|
|
Milk (whole) |
1.92-3.18 |
0.23-0.332 |
|
|
Milk (fat) |
- |
1.53-3.412 |
>933 |
|
Urine |
84.4-91.7 |
- |
995 |
|
Faeces |
1.48-1.88 |
- |
|
|
Expired air |
<0.01 |
- |
|
|
Total |
89.8-96.2 |
- |
|
1 At 12 hours after the final dose
2 Average concentration from third day
3 Non-polar conjugate
4 Free haloxyfop or polar conjugate
5 Free haloxyfop
Poultry. Four laying hens were dosed with [phenyl-U-14C]haloxyfop in gelatin capsules once a day for eleven consecutive days at a rate equivalent to 12 ppm in the diet (Yackovich and Miller, 1983b). Eggs and faeces were collected each morning during the test period. The hens were killed 24 hours after the final dose and tissue samples and gut contents taken.
The recovery of the administered radioactivity was 93-102%, mostly from the excreta with small amounts in eggs (82-90% and 1.1-2.6% of total administered dose respectively). In the tissues the radioactivity as haloxyfop equivalent was 0.12 mg/kg in muscle, 0.99 mg/kg in fat, 1.8 mg/kg in liver and 4.2 mg/kg in the kidneys.
The excreta, liver and kidneys contained mainly haloxyfop with some polar and/or non-polar conjugates, while most of the radioactivity in the fat was due to a non-polar conjugate of haloxyfop. Both the polar and non-polar conjugates were easily hydrolysed to yield haloxyfop under alkaline conditions. The residue in muscle was not identified because its radioactivity was too low.
The residue in the eggs was mainly in the yolk, where its radioactivity reached a plateau within seven days after the first dose at about 3 mg/kg haloxyfop equivalent, representing about 2 to 3% of the daily dose. As in goat milk fat, the residue in the egg yolk was identified as non-polar conjugate(s) of haloxyfop, easily hydrolysed by alkali to yield haloxyfop and shown by enzymatic hydrolysis with lipase to be triacylglycerol(s). The recovery and distribution of radioactivity are shown in Table 2.
Table 2. Recovery and distribution of radioactivity following the feeding of [14C]haloxyfop to laying hens.
|
Sample |
Recovery of radioactivity, % of total dose |
Radioactivity as mg/kg haloxyfop equivalent |
% of haloxyfop in residual radioactivity |
|
Fat |
0.15 |
0.991 |
99 (3) |
|
Heart |
- |
0.281 |
|
|
Kidneys |
0.23 |
4.221 |
90 (4) |
|
Liver |
0.37 |
1.821 |
91 (4) |
|
Muscle |
0.25 |
0.121 |
|
|
Gut contents |
7.5 |
- |
|
|
Egg (whole) |
1.58 |
- |
|
|
Egg (white) |
- |
0.252 |
|
|
Egg (yolk) |
- |
2.942 |
92 (3) |
|
Developing yolk |
0.49 |
- |
|
|
Faeces |
86.54 |
- |
97 (3) |
|
Total |
97.95 |
- |
|
1 At 24 hours after final dose
2 Average concentration from 7th day
3 Non-polar conjugate
4 60-70% as free haloxyfop, non-polar and polar conjugates
5 Free haloxyfop or polar conjugates
