Appraisal

Diazinon was first evaluated by the 1965 JMPR and has been reviewed several times since. In 1993 a periodic review was conducted and in 1994 a new MRL was recommended for hops. The 1993 JMPR recommended, among other items, an increase in the CXL for pome fruits from 0.5 to 2 mg/kg and the withdrawal of the CXLs for animal commodities in the absence of animal transfer studies and data from uses as an ectoparasiticide.

The CCPR in 1995 and 1996 endorsed most of the recommendations of the 1993 JMPR with the exception of the proposed MRL for pome fruits and the recommended withdrawal of the CXLs for milks and the meat of cattle, pigs and sheep.

Several countries were concerned that the proposed MRL for pome fruit, and to some extent the proposed limits for tomatoes and cabbages, might imply a high dietary intake. Insufficient new data were provided to review the recommendation, which was based on trials in the USA. It was the understanding of the Meeting that US GAP for pome fruits has been revised since 1993, and that additional trials which had been carried out according to the new GAP might support a lower limit. It is desirable that details of these trials be provided to a future JMPR. In order to provide a better estimate of dietary intake, the Meeting estimated STMR levels for pome fruit, tomatoes and cabbages from the data in the 1993 JMPR monograph on trials which complied with GAP at that time. These levels were 0.12, 0.12 and 0.16 mg/kg respectively. The respective proposed MRLs are 2, 0.5 and 2 mg/kg.

The main focus of the present evaluation was the review of submissions in support of MRLs for animal products. The 1993 JMPR considered animal transfer studies and information on veterinary uses to be desirable, and the 1995 CCPR retained the CXLs for animal products pending review by the JMPR of new data on animal feeding trials to be submitted by Australia and the manufacturer. The Meeting reviewed new submissions on animal transfer studies and supervised trials involving approved uses for ectoparasite control together with reports of additional analytical methods (mainly for animal products) and animal metabolism studies, some of which were provided to the 1993 JMPR, but not to the FAO Panel.

Some studies of animal metabolism were resubmitted at the request of the Meeting, in particular on poultry metabolism which had not been reviewed in 1993. These confirmed that metabolism in hens is essentially similar to that in mammals and that diazinon, diazoxon and hydroxydiazinon generally constitute a small proportion of the total radioactive residue, which consists largely of the pyrimidinol metabolite and hydroxy derivatives of it, together with glucuronide and other conjugates.

The Meeting reviewed nine analytical methods submitted for the first time in addition to re-submissions of methods reviewed in 1993. The new submissions are mainly methods for animal products based on GLC with phosphorus- or NP-selective detectors. Most of them determine only diazinon per se, with limits of determination ranging from 0.01 to 0.05 mg/kg. Two methods determine hydroxydiazinon and diazoxon in addition to diazinon, although in most trials only residues of diazinon were reported.

A feeding trial on dairy cows at levels equivalent to 40, 120 and 400 ppm of diazinon in the diet was reported. The manufacturer considered 40 ppm to be a reasonable estimate of intake but the dietary burden based on Codex MRLs for those commodities with the greatest potential for residues in cattle feed, maize forage, sugar beet tops and apple pomace, is likely to be lower. If the maximum percentage of the feed dry weight for dairy and beef cattle is assumed to be 80 and 40% maize forage, 10 and 20% sugar beet tops, and 20 and 40% apple pomace, it can be estimated that the dry weight dietary burden would not exceed about 25 ppm for dairy or 15 ppm for beef cattle. This is based on adjusting the CXLs to a dry weight basis, assuming that they are not already so expressed. Since some countries include other feed items which might contain more diazinon, 40 ppm is a reasonable worst-case assumption, if not needed for estimates based on Codex MRLs.

The study at the 40 ppm level indicated that no residues (<0.01 mg/kg) of diazinon, diazoxon or hydroxydiazinon would be expected in the liver, kidney, muscle, or milk of cattle, but residues of diazinon up to 0.04 mg/kg occurred in omental fat. Intakes calculated from Codex MRLs would be expected to produce residues of <0.02 mg/kg in the fat of beef cattle. Diazinon residues in the fat were roughly proportional to the intake of diazinon. Diazinon was detectable in milk only at the tenfold dosing level: the pattern of residues in the milk of individual cows dosed at this rate suggests that residues of diazinon may peak after about 3-7 days and then decrease.

Information on the freezer storage stability of diazinon in milk and of diazoxon and hydroxydiazinon in meat and milk is desirable to confirm the above conclusions.

In a feeding study on poultry no residues (<0.01 mg/kg) of diazinon, diazoxon or hydroxydiazinon were found in any sample from hens fed for 28 consecutive days at rates equivalent to 0.5, 1.5 or 5 ppm in the diet. The basis for considering 0.5 ppm as a likely level in poultry feed was not explained. The only commodity with a Codex MRL which is a significant poultry feed item is maize, which might be up to 80% of a poultry diet. However the CXL for maize is at the limit of determination of 0.02 mg/kg, so a feeding level of 0.5 ppm is more than adequate. A maximum residue level of 0.02 mg/kg (limit of determination) could be supported for poultry meat, fat and eggs.

Eight trials of uses against ectoparasites were reviewed by the JMPR from 1967 to 1975 and 3 ear tag trials were reviewed in 1993. All of these were re-submitted for review by the present Meeting, together with a number of studies not previously reviewed: 10 spray trials (6 on cows, 2 on goats, 1 on sheep, 1 on pigs), 4 ear tag trials on cattle, 3 sheep dip trials, 1 wound-dressing study on sheep and 1 backrub study on cattle.

Dust applications. Data from one very old study could not be related to GAP. The residues in milk increased from 0.02 mg/kg after two hours to 0.1 mg/kg after 9 hours.

Wound dressings. In a 1974 Australian study residues of diazinon were determined in the fat, muscle and liver of fly-struck sheep (5 animals/treatment rate) 10 days after treatment with a 2% ai powder formulation applied as a wound dressing at 10 and 30 g/animal. It could not be confirmed with the label provided that 10 g/animal is the GAP rate. The maximum residues from the 10 g treatment after ten days compared to the 14-day Australian GAP slaughter interval were 0.01 mg/kg in liver, 0.03 mg/kg in muscle and 0.08 mg/kg in omental fat. The corresponding median residue levels were <0.01, 0.01 and 0.06 mg/kg.

Backrubber trials. The Meeting could not evaluate the results of a 1967 trial in the USA with both handrubbed and burlap bag applications for which no relevant GAP was available.

In a recent Australian trial on cattle in accordance with Australian GAP the maximum, median and mean diazinon residues were 0.66, 0.24 and 0.29 mg/kg in loin fat and 0.26, 0.16 and 0.16 mg/kg in renal fat 5 days after 19 days of exposure to a typical backrubber application. The GAP withdrawal period is 3 days and the recommended export slaughter interval 10 days. Residues had generally decreased substantially by 7 or more days after exposure ceased. The maximum, median and mean residues of diazinon were 0.3, 0.04 and 0.1 mg/kg in loin fat one day after 10 days of exposure. Residues in renal fat were on average about half those in loin fat. The residues in loin fat were higher after prolonged exposure. The Meeting concluded that residues would not be expected to exceed 0.7 mg/kg in the fat of cattle from applications of EC formulations in backrubbers according to Australian GAP if exposure does not exceed 19 days and a withdrawal interval of 5 days is observed, or 0.1 mg/kg after the 10-day export slaughter interval. The Meeting had no information about exposures greater than 19 days.

Ear tags. Three Canadian and 4 Australian trials were reported. The Canadian reports were rather abbreviated summaries: although most of the essential information was provided, analytical methods were only referenced and details were meagre on intervals from sampling to analysis, sample storage and handling conditions, and confirmation by analysis of the claimed levels of diazinon in the tags. No reference, or confirmation of adherence, to GLP was provided. The Canadian trials are probably according to GAP. The Canadian withdrawal interval is reported to be "Nil" and the label simply refers to removal before slaughter. The Meeting interpreted this to imply essentially a 0-day withholding period.

In the 1987 Canadian trials residues in whole milk were <0.5 mg/kg 1 day after tag application and reached a maximum, median and mean of 1.7, 1.4 and 1.4 mg/kg after 7 days. Residues in back fat and kidney fat were respectively 0.03 and 0.035 mg/kg after 14 days. No residues (<0.01 mg/kg) were reported in muscle, liver or tongue. Similar results were reported in the 1989 study, with a maximum of 0.05 mg/kg in back fat. The Meeting concluded that the Canadian trials were not reported in sufficient detail to draw firm conclusions.

Details were also lacking from the first two Australian trials (1989, 1990), although the storage conditions were indicated for the first and sample chromatograms were provided for the second. The 1989 study appears to reflect Australian GAP, but in 1990 only one ear of each animal was tagged whereas two tags conform to GAP. The maximum, median and mean residues in milk fat in 1989 were 0.02, 0.01 and 0.0125 mg/kg after 28 days, and were not significantly different from those after 1 day. The maximum residue would be equivalent to 0.01 mg/kg in whole milk assuming 4% fat. The Meeting placed less reliance on these trials than the better documented 1992/93 Australian trials.

The 1992 and 1993 Australian trials were similar in principle and appear to reflect Australian GAP. Both were reported to comply with OECD GLP. In the 1992 trial diazinon residues in the milk fat peaked after 7 days with maximum, median and mean residues of 0.26, 0.2 and 0.19 mg/kg, corresponding to a maximum of 0.01 mg/kg in whole milk assuming 4% fat. In the 1993 trial residues increased from a maximum, median and mean of 0.02, <0.01 and 0.0125 mg/kg milk fat after 1 day to 0.02, 0.01 and 0.02 mg/kg after 7 days and 0.03, 0.02 and 0.02 mg/kg after 42 days, then decreased to 0.01 mg/kg after 84 days of continuous exposure. Maximum and mean residues in whole milk would be 0.01 mg/kg assuming 4% milk fat.

Although the Meeting was more confident of the documentation for the 1992/93 Australian trials, there is an apparent inconsistency between the higher residue levels (up to 0.3 mg/kg) found in milk fat in 1992 compared with 0.03 mg/kg in 1993 and 0.02 mg/kg in the 1989 Australian trials. Before completion of the 1993 study this was attributed to the use of 15 g tags in 1992 compared with 10 g in 1989, but the 1993 tags were also 15 g and the residues were comparable to those in 1989.

After the 1993 study the authors speculated that the inconsistencies were due to differences in the extent of self-grooming by the cattle. This varies according to buffalo fly pressure, which was not recorded. The only other obvious differences between the trials were that in 1992 the cream was stored in a refrigerator for 5 days before the preparation of butter whereas preparation was immediate in 1993, and the ear tags were from different manufacturers. Unfortunately no reference was made to analysing the tags to confirm the diazinon content before the study.

Overall the Meeting gave greater weight to the more recent, better described Australian studies and concluded that diazinon residues from the use of ear tags on cattle according to GAP should not exceed 0.2 mg/kg (mean) in butter, 0.05 mg/kg in back fat or renal fat, 0.01 mg/kg (mean) in milk, or the limits of determination of 0.01 mg/kg in kidney, liver and muscle and 0.02 mg/kg in tongue.

Dipping. Of 8 trials, 3 on cattle and 1 on sheep were very old and insufficiently documented by current standards to provide a basis for estimating maximum residue levels. Only the sheep trial of these four (in 1962) appears to comply approximately with current GAP: it showed maximum and mean residues of 1.4 and 0.8 mg/kg in sheep kidney fat. Even in that study the sheep were dipped for 20 seconds, considered to be twice the recommended time. The Meeting placed little emphasis on these four studies. Since the other three very old trials were the only ones with cattle there are no useful cattle trials and any conclusions on likely residues in dipped cattle must be largely based on sheep dipping, which would normally produce higher residues.

The sheep trials in 1973 and 1974 were fairly well documented. In 1973 the residues in milk from treatments according to GAP were 0.01 and 0.02 mg/kg after the 4-day GAP milking interval. In 1974 the maximum residues were 0.4 mg/kg in muscle, 0.02 mg/kg in liver and 2.6 mg/kg in omental fat, but the dip concentration was 3 times the GAP level. In a reasonably well described Australian trial in 1986 sheep were slaughtered in pairs at intervals after a single dip. The maximum and mean residues after the 14-day GAP pre-slaughter interval were 0.03 and 0.02 mg/kg in muscle, 0.01 and 0.01 mg/kg in liver, 0.02 and 0.02 mg/kg in kidney, and 0.67 and 0.65 mg/kg in kidney fat. The mean residues were also the medians.

The best documented trial was in 1989 in the UK. The dip concentration was 1.6 times the GAP concentration in the UK, but complied with Irish and New Zealand GAP. Pre-slaughter intervals are 14 days in the UK and Ireland, and 21 days in New Zealand. The maximum, median and mean residues after 14 days were 1.3, 1.1 and 1.1 mg/kg in omental fat and 4.3, 1.3 and 2.3 mg/kg in subcutaneous fat, in which the three individual residues were 4.3, 1.4 and 1.3 mg/kg. After 21 days the maximum, median and mean residues were 1.2, 0.75 and 0.8 mg/kg in omental fat and 1.4, 1.0 and 1.2 mg/kg in subcutaneous fat, in which these were also the individual residues.

A comparison of the residues of 4.3, 1.3 and 1.4 mg/kg in subcutaneous fat at 14 days and consideration of the relation between 14- and 21-day residues in both omental and subcutaneous fat led the Meeting to conclude that 4.3 mg/kg was probably aberrant. It is not consistent with the other results, except to the extent that higher residues in subcutaneous fat than in other fats are not unexpected.

In summary, from the available data the maximum and median residues to be expected in sheep from single dipping according to GAP would be as follows.

	Residue, mg/kg
	Maximum	Median
milk	0.02	0.02
muscle	0.03	0.02
liver	0.01	<0.01
kidney	0.02	0.02
kidney fat	0.7	0.7
omental fat	1.3	1.1
subcutaneous fat	1.4	1.4

From the available information on residues in individual sheep the Meeting concluded that a level of 2 mg/kg would be required to cover residues in sheep fat arising from single dipping according to GAP. Although this is greater than the current CXL of 0.7 mg/kg, several trials according to GAP show that residues above 0.7 mg/kg are likely to occur. A pre-slaughter interval of 35 days would appear to be required to reduce fat residues to the CXL. The Meeting noted that the most reliable sheep dipping trials which complied with GAP were with single dips, although GAP in most countries allows multiple dipping. This emphasises the need for a higher limit than 0.7 mg/kg. Additional trials meeting current standards and including multiple dips according to GAP are highly desirable, as are monitoring data on sheep fat, especially from sheep known to have received dip or spray applications at maximum GAP rates.

Cattle spraying. Thirteen trials were reported, but the Meeting did not review one from 1972 which was available only in Russian. Six of the remaining 12 were very old studies (1962-7), not meeting current reporting standards and often with outdated analytical methods. The Meeting placed little emphasis on these in estimating maximum residue levels in cattle, but considered 5 of the remaining 6 studies to be at least marginally acceptable to varying degrees. It was recognized that they were all with single applications, although GAP generally permits more than one spray. Four of them were concerned with residues in milk and two with residues in fat or tissues.

Residues in milk. A fairly well described 1971 Swiss trial was not fully acceptable to the Meeting, but was of particular interest because it involved multiple applications in accordance with current GAP. However, because of the obsolete analytical method (autoanalyser) and inadequate reporting of certain details, some uncertainty remains on the validity of the results. The mean diazinon residues in the milk did not exceed 0.02 mg/kg (maximum 0.03 mg/kg) 4 days (the GAP withdrawal interval) after the 3rd spraying (the maximum GAP number). All residues were <0.02 mg/kg after 6 days and mean residues 0.03 mg/kg after 3 days, which is the GAP withdrawal period in other countries.

In a fairly well described Australian study in 1974 the mean diazinon residues in the milk from 5 cows from a herd treated according to GAP were 0.02 mg/kg (maximum 0.05 mg/kg) 5 days after treatment compared to 3- or 4-day GAP withdrawal intervals. This is consistent with the 1971 study. The residues were 0.05 mg/kg in a composite sample of butter and the mean residues in composited skim milk were about 1/3rd to 1/6th of the level in the whole milk, confirming the affinity of diazinon with fat. The study clearly demonstrates that the residues in milk from individual cows are significantly reduced when bulked with milk from other members of a treated herd.

In a 1986 Australian trial the mean diazinon residues in milk were <0.01 mg/kg 70 hours (2.9 days) after a single spray at 1.2 times the GAP concentration compared to the Australian pre-slaughter interval of 3 days and the milk withdrawal intervals of 3 or 4 days in other countries.

A 1994 Egyptian trial was at the concentration of Egyptian GAP, but with a single application whereas 3 are permitted. The highest diazinon residue in the milk was 0.3 mg/kg 6 hours after application, but decreased to <0.005 mg/kg after 36 hours, half the 3-day Egyptian GAP withdrawal interval. Some details were not reported.

Residues in tissues. In a 1986 Australian trial a single spray at 1.2 times the GAP concentration gave maximum and mean/median diazinon residues of 0.7 and 0.6 mg/kg in kidney fat after 7 days, and 0.2 and 0.2 mg/kg in omental fat after 14 days. There were no data at the 3-day GAP pre-slaughter interval. Subcutaneous fat, which would be expected to have higher residues than other fats, was not analysed. After 7 days residues were <0.01 mg/kg in muscle, kidney and liver. In a 1996 Australian back spray trial a single GAP application gave diazinon residues in subcutaneous fat of <0.05 mg/kg in 5 animals and 0.08 mg/kg in one after 4 days. The residues in renal fat were <0.05 in 6 animals.

In summary the cattle spraying trials suggest that single spray applications according to GAP might produce the following results.

Sample	Residue, mg/kg			Pre-slaughter interval, days
	Max.	Median	Mean	In trial	GAP
Milk			0.02	3-5	3-4
Loin (subcutaneous) fat	0.08	0.05		4	3
Renal fat	0.7	0.6		7	3
Omental fat	0.2	0.2		14	3
Muscle, liver, kidney	0.01			7	3
	0.07			1	3
	0.031			31	3

¹ Estimated residue at GAP pre-slaughter interval. See discussion below.

Some of these residues may be lower than likely maximum levels. In particular, especially in view of the results of the sheep dipping trials, some qualification must attach to the residue in subcutaneous cattle fat in particular because no residues in subcutaneous fat were reported in the GAP trial which gave 0.7 mg/kg in renal fat after 7 days. Residues would have been be expected to be higher in subcutaneous fat, probably above 1 mg/kg. Similarly, even the 0.7 mg/kg in renal fat may be too low as a maximum residue level since it occurred after 7 days whereas the GAP withdrawal interval is 3 days, and residues in renal fat in 2 separate animals of the study after a 1-day withdrawal period were 1.3 and 2.9 mg/kg.

Special attention should also be given to the residues in muscle, kidney and liver since no results were available at the 3-day GAP pre-slaughter interval. The maximum and mean residues after 1 day were 0.06 and 0.06 mg/kg in muscle, 0.02 and 0.02 mg/kg in liver and 0.07 and 0.07 mg/kg in kidney. The Meeting concluded that although the residues would be lower after 3 days they would still exceed the 0.01 mg/kg found after 7 days, and estimated a maximum residue level of 0.03 mg/kg in muscle, liver and kidney from single spray applications to cattle according to GAP.

No conclusion could be drawn with confidence about the results of multiple GAP applications as only very old, inadequately reported, studies were available. Although one of these suggested that residues in omental fat might increase with multiple applications, there were no results at a GAP withdrawal interval, and no analyses of other (e.g. subcutaneous) fat or tissues. The Meeting therefore considered modem spray trials on cattle under maximum GAP conditions (which include multiple sprays) to be highly desirable. Analyses should preferably be for diazinon, diazoxon and hydroxydiazinon in milk, muscle, edible offal and fat (including kidney, omental and especially subcutaneous fat).

Sheep spraying. In a rather poorly reported Australian trial in 1971 with EC and WP formulations applied at twice the GAP concentration, diazinon residues did not exceed 0.16 mg/kg in fat or 0.09 mg/kg in muscle after the GAP pre-slaughter interval of 14 days. In a well-documented Swiss trial in 1994 residues in fat (from the base of the tail) were determined 28 days after a single spray at the GAP concentration. The Swiss withdrawal interval is 21 days. The maximum and median residues from each of three different EC formulations were 0.29 and 0.12 mg/kg, 0.24 and 0.16 mg/kg, and 0.22 and 0.11 mg/kg with an overall maximum and median of 0.29 and 0.14 mg/kg. The Meeting concluded that diazinon residues in sheep fat are unlikely to exceed 0.3 mg/kg after 28 days from a single spray application according to Swiss GAP. There was no information on multiple applications, for which data on residues in milk and tissues are desirable, nor on residues at the GAP withdrawal interval of 21 days.

Goat spraying. In a 1986 Australian trial with a single application approximating the GAP concentration, the residues in two goats after the 14-day Australian GAP pre-slaughter interval were <0.01 mg/kg in the muscle, liver and kidney of both animals, 0.02 and 0.01 mg/kg in kidney fat and 0.03 and 0.01 mg/kg in omental fat. Subcutaneous fat was not analysed. In a 1987 Australian trial the mean residues in milk were 0.02 mg/kg after 78 hours. The GAP withdrawal interval for milk is 3 or 4 days in other countries.

Pig spraying. In a fairly well documented 1974 Swiss trial diazinon residues were 0.01 mg/kg in muscle and 0.01 mg/kg in liver, kidney, unspecified fat and skin 28 days after one or two sprays at the GAP concentration. The Swiss pre-slaughter interval is 21 days. Even at twice the GAP concentration the residues were all 0.01 mg/kg except one residue of 0.04 mg/kg in muscle. The samples were also analysed for hydroxydiazinon, the pyrimidinol G 27550 and diazoxon, but the only measurable residue was 0.02 mg/kg of hydroxydiazinon in a single fat sample at the GAP spray concentration. The Meeting concluded that diazinon residues would be unlikely to exceed 0.01 mg/kg in pig tissues from Swiss GAP. For risk assessment purposes the figure would be 0.03 mg/kg.

Estimates of STMR levels

Because the number of trials of ectoparasite treatments were limited and the residues would be from different populations depending on the animal and the type of treatment, the Meeting considered using recommended MRLs for the estimation of dietary intake. However, to conform to the general approach to such estimations, the Meeting estimated STMR levels for animal products.

Poultry. No diazinon (<0.01 mg/kg) was detected in any sample of skin, muscle, eggs, fat or liver after feeding diazinon at a level equivalent to 10 times the expected dietary intake. The Meeting therefore concluded that the effective STMR for poultry meat, poultry edible offal and eggs should be zero.

Milk. Because milk is normally bulked before distribution, the Meeting used mean values of the residues in milk from different animals in individual trials as the basis for STMR estimates. The mean residues in milk from GAP applications were 0.02 mg/kg in cattle and goats from spraying and in sheep from dipping, and 0.01 mg/kg in cattle from ear tags. The Meeting estimated 0.02 mg/kg as a maximum residue level and an STMR level for milk.

Meat (muscle). Although the maximum residue level for use as an MRL for meat is expressed on a fat basis, for dietary intake purposes the Meeting also estimated an STMR for whole muscle. The distribution of maximum residues (mg/kg) in the meat of the animals treated according to GAP, with the types of treatment, were goats <0.01 (spray), pigs 0.01 (spray), cattle 0.02 (ear tags), 0.03 (spray, extrapolated value), and sheep 0.03 (dip). The Meeting estimated an STMR level of 0.02 mg/kg for the meat (whole muscle) of cattle, pigs, sheep and goats.

Edible offal. The residues from applications according to GAP (mg/kg) were as follows. Liver: goats <0.01 (spray), pigs <0.01 (spray), cattle <0.01 (ear tag), sheep 0.01 (dip), cattle 0.03 (spray, extrapolated value). Kidney: goats <0.01 (spray), pigs <0.01 (spray), cattle <0.01 (ear tag), sheep 0.02 (dip), cattle 0.03 (spray, extrapolated value). Liver and kidney combined, in rank order: <0.01 (6), 0.01, 0.02, 0.03, 0.03.

The Meeting estimated an STMR of <0.01 mg/kg for the liver and kidney of cattle, goats, pigs and sheep.

Fat. An STMR was estimated on the basis of the residues in the fat of cattle, goats, pigs and sheep from different uses against ectoparasites according to GAP. Combining the data for these animals gave the following distribution of residues in rank order.

Omental fat:	0.03, 0.2, 1.3 mg/kg.
Renal fat:	0.02, 0.04, 0.3, 0.7, 0.7 mg/kg.
Loin (subcutaneous) fat:	<0.01, 0.05 0.08, 0.3, 0.7, 1.4 mg/kg (omitting an aberrant value of 4.3 mg/kg).
All fat:	<0.01, 0.02, 0.03, 0.04, 0.05, 0.08, 0.2, 0.3, 0.3, 0.7, 0.7, 0.7, 1.3, 1.4 mg/kg.

The Meeting estimated an STMR of 0.3 mg/kg.

General observations. As has been noted, the trials of diazinon for ectoparasite control range from very old studies, unusable by current standards, to a few relatively recent well-documented trials reported to be in accordance with GLP. The Meeting has tried to make the best use of the available studies that prudence allows. In many cases even where GAP concentrations have been applied results are lacking at GAP withholding periods. Another common observation is that most of the acceptable studies are with single applications rather than the multiple applications permitted by GAP. In some cases very similar trials have inexplicably produced inconsistent results and in others no data are available on residues in subcutaneous fat, which has been shown to have higher residues than other fat after dermal applications.

These factors have required the Meeting to exercise judgement in estimating maximum residue levels and have lead to some uncertainty as to whether the recommended MRLs are sufficiently high to cover all uses of diazinon as an ectoparasiticide according to GAP. It is also at least possible that in practice some animals might be exposed to more than one type of treatment (e.g. spraying or dipping as well as ear tags or wound dressings). For these reasons the Meeting concluded that additional modem trials with diazinon used for ectoparasite control at maximum GAP concentrations and with multiple dip and spray applications, conducted in accordance with GLP, are desirable in order to confirm the estimated maximum residue levels and STMR levels.