Animal metabolism
Information was made available to the Meeting on studies of ziram metabolism in lactating goats.
Residues in the tissues, milk and excreta residues were measured in 2 lactating goats each weighing about 40 kg, dosed orally once daily after morning milking for 6 consecutive days by capsule with [thiocarbonyl-14C]ziram at 11.9 and 13.2 mg/kg bw/day, equivalent to 300 ppm ziram in the feed (Bodden, 1993). The feed consumption was 1 kg/animal/day of a grain-based milking ration as well as alfalfa grass hay provided ad libitum; the mean total daily feed consumption was 1.7 kg. The goats were milked twice daily, producing 1.9-2.7 kg per day. Milk and excreta were collected throughout, and the animals were slaughtered 6 hours after the final dose for tissue collection.
A large part of the administered 14C was not accounted for (54% and 34%). By analogy with the animal metabolism of thiram losses as CS2 and CO2 in expired air would be expected, but 14C was not measured in the expired air. More of the 14C dose was in the faeces (42% and 61%) than in the urine (3%), tissues (0.93% and 0.78%) or milk (0.28% and 0.51%).
The levels of 14C in the milk increased for the first 2 or 3 days of feeding and then reached a plateau (Table 1). The levels of 14C were higher in the liver than in other tissues (Table 2).
Tissues, milk and urine were analysed for dithiocarbamate residues by a colorimetric CS2 evolution method with a detection limit of 0.5 mg/kg as CS2. In the liver approximately 10% of the 14C was present as CS2-liberating compounds (1.1 and 1.2 mg/kg as CS2). CS2 was not detected in the other tissues and milk, but the total 14C levels were generally too low to expect its detection. In the urine samples on day 5 from the 2 goats 14% and 27% of the 14C was present as CS2-liberating compounds.
Nitrosodimethylamine was not detected in the milk, tissues or urine (LOD 1 mg/kg).
The 14C residues in milk, liver, kidney, muscle and fat were not extractable with a chloroform/methanol/water mixture until after protease treatment. The liberated 14C was present in polar water-soluble compounds. 14C was present in lactose and casein isolated from milk and urea isolated from urine, showing that some of the 14C had been incorporated into natural products.
Table 1. Levels of 14C in milk produced by 2 goats dosed daily with [thiocarbonyl-14C]ziram equivalent to 300 ppm in the feed (Bodden, 1993).
|
Day |
14C (as ziram), mg/kg milk |
|||
|
Goat 1, am milking |
Goat 1, pm milking |
Goat 2, am milking |
Goat 2, pm milking |
|
|
1 |
|
0.44 |
|
1.02 |
|
2 |
0.25 |
0.56 |
0.41 |
1.34 |
|
3 |
0.61 |
0.74 |
1.85 |
1.74 |
|
4 |
0.92 |
0.95 |
1.54 |
1.47 |
|
5 |
0.86 |
0.87 |
1.74 |
1.75 |
|
6 |
0.74 |
0.78 |
1.66 |
1.44 |
Table 2. Levels of 14C in samples from 2 goats dosed daily with [14C]ziram equivalent to 300 ppm in the feed and slaughtered 6 hours after the final dose (Bodden, 1993).
|
Sample |
14C as ziram, mg/kg, |
|
|
Goat 1 |
Goat 2 |
|
|
Bile |
3.1 |
2.3 |
|
Blood |
0.87 |
1.6 |
|
Fat (omental) |
0.16 |
0.20 |
|
Fat (renal) |
0.17 |
0.18 |
|
Kidney |
2.9 |
3.4 |
|
Liver |
28.0 |
22.0 |
|
Muscle |
0.45 |
0.81 |
Plant metabolism
Information was made available to the Meeting on ziram metabolism in apples.
Apples and apple leaves on trees were treated once by hand-spraying with [thiocarbonyl-14C]ziram at a rate equivalent to 34 kg ai/ha, which is 5 times the label rate (Wyss-Benz, 1994). The apples were 3.5-5.0 cm at the time of treatment. Leaves and apples were sampled for analysis at intervals of 0, 14, 28, 56 and 80 days after treatment, the final occasion at apple maturity. The distribution and levels of 14C in the apples and leaves at the various sampling intervals are shown in Table 3. Residues on the surface of the apples and leaves (found in washings) disappeared more quickly than incorporated residues.
Extracts of apple peel and pulp were analysed by a head-space GLC CS2 evolution procedure. No CS2-related residues were detected in the extracts of apple pulp (LOD ~ 0.02 mg/kg as CS2); they constituted 3.6%, 1.6% and 5.4% of the total 14C residues in apple peel on days 0, 14 and 80, but were not detected in the peel sampled on days 28 and 56. On a whole-apple basis the highest level of CS2-related residue was 0.016 mg/kg CS2 in the day 80 sample.
Parent ziram was detected in washings from apples and leaves sampled on days 0, 14 and 28 after treatment. The levels became too low for identification at later samplings. TLC showed that 14C was present in more polar fractions than ziram. [14C]ziram was detected by HPLC in apple pulp (0.014 mg/kg) from apples sampled on the day of treatment, but not at later sampling times. The extractable incorporated 14C at the various sampling times was in polar material. Reference compounds which were possible metabolites did not correspond to any of the radioactive fractions.
Table 3. Distribution and levels of 14C (as ziram) in apples and leaves after treatment with [thiocarbonyl-14C]ziram at a rate equivalent to 34 kg ai/ha (Wyss-Benz, 1994).
|
Days after applic. |
Apples |
Leaves |
||||||||
|
washings |
peel |
pulp |
washings |
washed leaves |
||||||
|
mg/kg |
%1 |
mg/kg |
%1 |
mg/kg |
%1 |
mg/kg |
%2 |
mg/kg |
%2 |
|
|
0 |
94 |
97 |
2.5 |
2.6 |
0.63 |
0.7 |
5930 |
98 |
117 |
1.9 |
|
14 |
2.4 |
24 |
4.0 |
40 |
3.5 |
36 |
93 |
45 |
114 |
55 |
|
28 |
1.0 |
19 |
2.3 |
41 |
2.2 |
40 |
37 |
26 |
107 |
74 |
|
56 |
0.15 |
4.6 |
1.3 |
40 |
1.8 |
56 |
3.4 |
6.6 |
48 |
93 |
|
80 |
0.11 |
4.2 |
1.2 |
46 |
1.3 |
50 |
2.9 |
6.1 |
45 |
94 |
1 Of total 14C in apples
2 Of total 14C in leaves
