Uses as an ectoparasiticide

Eight trials were reviewed by the JMPR from 1967 to 1975 and 3 trials with ear tags were reviewed in 1993. All of these were re-submitted to the present Meeting, together with studies not previously reviewed: 9 with sprays (6 on cows, 2 on goats, 1 on pigs), 4 with cattle ear tags, 3 with sheep dips and one trial each on sheep dressing, sheep jetting and cattle backrubbing.

Dust application. In one very old briefly described study 3 cows were hand-dusted from a sprinkler can with 2% w/w diazinon dust (124 g/animal) and milk was analysed by GLC 2, 5, 9 and 24 hours after application (Chilwell et al., 1967). Analytical recoveries averaged 79% at a fortification level of 0.1 mg/kg. The residues (mg/kg) were as shown below.

	2 h	5 h	9 h	24 h
Range	0.01-0.02	0.03-0.05	0.05-0.1	0.05-0.07
Mean	0.01	0.04	0.09	0.06

No GAP was reported for this use.

Wound dressing. In an old Australian study residues of diazinon were determined in the fat, muscle and liver of fly-struck sheep 10 days after treatment (5 animals at each rate) with a 2% ai powder formulation applied as a wound dressing at 10 and 30 g/animal (Bull, 1974). The lower rate was reported to be according to GAP but this could not be confirmed with the label provided. Residues (mg/kg) were as shown below.

	g/sheep	Liver	Muscle	Omental fat
Range	10	0.01-0.01	0.01-0.03	0.05-0.08
Mean		<0.01	0.01	0.06
Range	30	<0.01-0.01	0.01-0.02	0.08-0.1
Mean		0.01	0.02	0.09

Backrubs. Two studies were available. The first (Bourne and Arthur, 1967) was a very old published US study in one part of which 56.6 g of 2% diazinon dust formulated on Pyrex ABB with 1% motor oil was hand-rubbed on the backs of 5 cows daily for 4 days. Half a day after the last treatment diazinon residues in the milk ranged from <0.05 to 0.52 mg/kg and after intervals of 1 to 15 days they were <0.05 mg/kg.

In the second part of the study 5 different cows were rubbed several times across the back with a burlap backrubber (1.2 m long X 10.2 cm diameter) impregnated with 0.45 kg of 2% diazinon dust. It was not clear whether the applications were daily but they were probably daily for four consecutive days as in the other part of the study. Diazinon residues in the milk as determined spectrophotometrically ranged from <0.05 to 0.23 mg/kg 0.5 days after the last treatment to <0.05 mg/kg in all samples from 1 to 15 days after treatment. There was no information on relevant US GAP

The second study was a recent Australian trial on 2- to 3-year old Brahman male cattle in which the backrubber was charged with 500 ml of 200 g/1 diazinon EC per 101 of sump oil (i.e. 10 g ai/l oil). This is reported Australian GAP, which also includes a 3-day withdrawal period (Rose, 1995;

Queensland and New South Wales, 1996). Groups of 5 cattle were exposed for 10 days and slaughtered 1 or 2 days after treatment, or for 19 days and slaughtered after 4, 7 or 10 days. Samples of renal and/or loin fat were taken from the 5 cattle in each group at each interval. The residues are shown in Table 8.

Table 8. Residues of diazinon in renal and loin (subcutaneous) fat of groups of 5 cattle 1 to 10 days after backrubber treatment at 10 g ai/l with EC formulation ((Rose, 1995; Queensland and New South Wales, 1996)

Diazinon, mg/kg, at interval, days, after treatment
11	21	42		72		102
Loin	Loin	Loin	Renal	Loin	Renal	Loin
0.07	0.08	0.66	0.26	0.1	0.08	0.03
0.04	0.05	0.24	0.16	0.05	0.08	0.03
<0.02	0.04	0.07	0.05	0.14	0.06	0.03
0.31	0.12	0.16	0.16	0.15	0.06	0.1
0.04	0.03	0.34	0.17	0.08	0.04	0.07

¹ Exposed for 10 days
² Exposed for 19 days

Ear tags. Reports of three Canadian and four Australian trials were available. The results are shown in Table 9.

Table 9. Residues of diazinon in milk, milk fat and tissues of cows or calves treated with diazinon ear tags.

Country, year, ref, dose	Sample	Days after tag application	Residue, range and (mean)1
Canada 1987 Surgeoner, et al., 1987a Vol 2 of 3 ref. 9 Two tags/cow 11% diazinon	whole milk'	5 h through 1 day	m g/kg this study only
			ND (= <0.5 mg/kg) (ND)
		3	ND - 1.4 (0.64)
		7	1.2-1.7 (1.4)
		14	1.1-1.7 (1.4)
		21	ND-1.8 (0.53)
		28	0.73-1.4 (1.1) 3 cows
Canada 1987 Surgeoner et al., 1987b Vol. 2 of 3 ref. 10 Two tags/steer, 9.6% diazinon	back fat (omental)	14	0.032, ND (= £ 0.01 mg/kg)
		³ 100	ND
	kidney fat (perirenal)	14	0.035, ND
		³ 100	ND
	muscle or liver	14 to ³ 100	ND
	tongue	³ 100	ND 3 cows
Canada 1989 Surgeoner et al., 1989 Vol. 2 of 3 ref. 11 Two 20% diazinon tags/steer	back fat (centre,	7	0.01
	subcutaneous)	14	0.05
			0.03. 0.02
	kidney fat (perirenal)	7	0.03
		14	0.04
		28	0.03, 0.03
	kidney, liver or muscle	7, 14, 28	all ND (= <0.01)
	tongue	7	ND
		14	0.02
		28	ND -0.02 4 steers
Australia, 1989 Bull and Wicker, 1989 Vol. 2 of 3, ref. 19 Two 18% diazinon tags/cow	Milk fat (butter)	1	<0.01-0.02 (<0.01)
		7	<0.01-0.01 (<0.01)
		14	<0.01-0.01 (<0.01)
		28	0.01-0.02 (0.0125)
			4 cows
	Milk (not analysed, but estimate based on the milk fat residue)	1-28	<0.01
Australia, 1990 Mawhinney, 1990 Vol. 2 of 3, ref. 18 One 18% diazinon tag/calf or cow (1/2 max. GAP)	fat (biopsy, subcutaneous tail	calves
	butt)	7	<0.01-0.03 (0.02)
		42	0.01-0.03 (0.02)
		43	<0.01-0.01
		cows
		7	<0.01-0.01
		44	<0.01
Australia, 1992	milk fat (butter)	1	0.04-0.08 (0.06)
		7	0.12-0.26 (0.19)
		14	0.06-0.18 (0.13)
			5 cows
Bull and Swindale, 1992 Vol. 2 of 3, ref. 15 Two 15 g 20% diazinon tags/cow	whole milk (highest residues	1	0.003
	assuming 4% fat)1	7	0.01
		14	0.007
Australia, 1993 Strong and Bull, 1993 Vol. 2 of 3, ref. 16 Two 15 g 20% diazinon tags/cow	fat of milk	1	<0.01-0.02 (<0.01))
		2	<0.01-0.01 (<0.01))
		3	<0.01-0.02 (<0.01))
		7	0.01-0.02 (0.02)
		10	0.01-0.02 (0.02)
		14	0.02(4) (0.02)
		28	0.02(4) (0.02)
		42	0.01-0.03 (0.02)
		56	0.01-0.02 (0.02)
		84	<0.01-0.01 (<0.01)

¹ mg/kg unless otherwise indicated

The three Canadian trials were reviewed by the 1993 JMPR and will not be described in detail here. In the first (Surgeoner et al., 1987a) the highest residues in milk during the 28 days of the trial were 0.0018 mg/kg (on day 21) with two 11% diazinon ear tags applied to each of three dairy cows. In the second study (Surgeoner et al., 1987b) with two 9.6% diazinon ear tags on each of three steers, the maximum diazinon residues were 0.035 mg/kg in perirenal fat and 0.032 mg/kg in omental fat 14 days after the application of the tags. No residues (£0.01 mg/kg) were found in muscle or liver. Residues in the fat decreased to <0.01 mg/kg after 100 days. In the third study (Surgeoner et. al., 1989) with two 20% diazinon tags on each of 4 steers, the highest residues in the 28-day treatment occurred after 14 days with 0.45 mg/kg in back subcutaneous fat, 0.041 mg/kg in perirenal fat and 0.016 mg/kg in tongue. No residues (£0.01 mg/kg) were reported in muscle, liver or kidney. This study appears to be in accordance with Canadian GAP (see Table 6).

In the first of four Australian trials two ear tags (18% diazinon, 4% a-cypermethrin; tag weights unspecified) were applied to each of three Fresian dairy cows and milk samples (two milkings/day) were taken 1, 7, 14 and 28 days after application (Bull and Wicker, 1989). Butter was immediately separated and stored at -15°C until analysis for diazinon by method 132A. The residues were <0.01-0.02 mg/kg on days 1 and 28 and <0.01-0.01 mg/kg on days 7 and 14. Mean procedural recoveries of diazinon from butter of 90% and a limit of determination of 0.01 mg/kg were reported, although sample chromatograms were not included.

In the second trial three Bos indicus calves (c. 200 kg) and three Brahman cows (400-660 kg) were each treated with a single ear tag impregnated with 18% diazinon and 4% a-cypermethrin (tag weights unspecified). Subcutaneous fat was taken by biopsy from fat pads on the side of the tail butt at 7, 42 and 83 days after treatment from the calves and after 7 and 44 days from the cows (Mawhinney, 1990). The highest diazinon residues in the fat from the calves were 0.03 mg/kg after. 7 and 42 days and 0.01 mg/kg after 83 days. In the cows the residues were <0.01-0.01 mg/kg at 7 days and <0.01 at 44 days, with controls for both calves and cows <0.01 mg/kg.

The analytical procedure consisted in extraction of the fat with hexane, partitioning with acetonitrile, clean-up on a Florisil column and determination of diazinon by GLC with an NP detector. The reported limit of "detection" was 1 ng/g (0.001 mg/kg at a signal noise ratio of 5:1). Sample chromatograms suggest that detection at 0.001 mg/kg is possible and that 0.01 mg/kg would probably be a reasonable limit of determination, although controls were not included among the sample chromatograms. At the 0.01 mg/kg fortification level procedural recoveries of diazinon averaged 82%. Diazinon in fat samples from treated animals was confirmed by mass spectrometry.

In the third Australian study two 15 g tags (20% diazinon) were applied to each of 5 Friesian cows and milk was sampled after 1, 7, and 14 days (Bull and Swindale, 1992). Cream was separated from the milk and stored in a refrigerator for 5 days. Butter was then made and stored at -15°C until analysis. The analytical phase was reported to be according to OECD GLP.

The highest residue in the butter of any one cow was 0.26 mg/kg on day 7 with mean residues for the 5 cows of 0.06 mg/kg on day 1, 0.19 mg/kg on day 7 and 0.13 mg/kg on day 14.

The analytical method was 132B with procedural recoveries from butter ranging from 73 to 103% (n=4, mean 91.5%), excluding one recovery of 58% with fortification at 0.05 mg/kg. No sample chromatograms were provided.

In the fourth Australian trial (Strong and Bull, 1993) diazinon residues were determined in the milk fat of four Friesian cows treated with two 15g, 20% diazinon, ear tags for up to 3 months. Milk was sampled 1, 2, 3, 7, 10, 14, 28, 42, 56 and 84 days after attachment of the tags, immediately separated, and made into butter which was stored at -15°C until analysis. The study was started in October 1992 and the analyses were completed by January 1993: they were reported to be in accordance with OECD GLP.

The residues did not exceed 0.03 mg/kg in any sample. The mean residue for the four cows increased to 0.02 mg/kg by day 7 and remained at that level until day 56, decreasing to <0.01 mg/kg by day 84.

The method of analysis was again 132B with a mean procedural recovery of 87% at 0.02 mg/kg and a reported limit of determination of 0.01 mg/kg. No sample chromatograms were provided.