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last updated: 6 September 2004

This Animal Residue Data Sheet provides information on the potential residues of dicamba in animal commodities and animal feed commodities when dicamba products are used according to Australian good agricultural practice. However, inadequate data are available to allow the provision of full information. If further residues data become available, this Animal Residue Data Sheet will be revised.

Currently, there are a number of registered products containing dicamba; a majority of products are registered for use in non-food producing situations (mainly lawn, turf and recreational areas). Other products are registered for use in food producing crops (barley, rye, oats, triticale, wheat, grass pastures, grain sorghum, maize, rice, sugarcane and potato). Although products containing only dicamba are currently registered, most available products are combinations of dicamba with either MCPA or bromoxynil.

Details of the registered use patterns can be found on the approved labels of registered products containing dicamba as an active constituent.

1.1 Current MRLs
The Australian MRLs for dicamba in food and animal feed commodities, as listed in Table 1 and Table 4 of the MRL Standard (as at September 2004) are shown below. The residue definition for dicamba is dicamba per se.

1.2 Summary of maximum feeding levels and livestock dietary intakes

Data indicating the magnitude of dicamba residues in crops were located in APVMA archives and the open scientific literature. No data were available to be able to establish the magnitude of expected residues in possible animal feeds following application of dicamba as per proposed use pattern.

Several studies were located examining the metabolism and residues of dicamba in cattle and chickens. These are summarised below.

Oehler D.D., and Ivie G.W., Metabolic Fate of the Herbicide Dicamba in a Lactating Cow, 1980, Vol 28 No. 4, J. Agric. Food Chem.

A lactating Jersey cow (411 kg) was administered 450 mg 14C Dicamba at 12 hourly intervals over 5 days (11 doses). This equated to an exposure of 2.2 mg/kg bw/day or 60 ppm in the diet (assuming 3-4% consumption).

Urine, faeces and milk were collected during the trial. Six hours following withdrawal from dosing the animal was slaughtered and various tissues were taken for analysis. The highest residues detected (total 14C) were in kidney (2.59 mg/kg eq.). Only low residue levels were found in the remaining edible tissues (liver, tongue, muscle, fat, heart and brain; range 0.3 – 0.02 mg/kg eq.).

Residue levels in excreta plateau after three days and after this period, the dose intake matched excretion. Overall 90.5% of the administered dose was lost in either urine (89%) or faeces (1.5%). Only 0.02% of the administered dose was present in milk (max. at 2.5 days was 0.04 ppm). Metabolites were monitored in all tissues and unmetabolised dicamba accounted for 0, 51 and 70% of total radioactive residues (TRR) in milk, liver and kidney, respectively.

Dicamba feeding study: Chickens
Groups of chickens were fed a diet fortified with dicamba (0.5, 1.5 and 5 ppm) for 28 days. Eggs were sampled on days 7, 14, 21 and 28. Chickens were slaughtered on days 14, 21 and 28. Samples of breast muscle, fat, liver, kidney and leg muscle were taken and immediately frozen for further analysis. Only samples from the 5 mg/kg feeding group were assayed. No residues of dicamba or its metabolites (5-hydroxy dicamba and 3,5- dicamba) were detected in tissues or eggs following feeding for 28 days, or up to 14 days following cessation of feeding.

Dicamba feeding study: Dairy Cattle
Nine lactating dairy cattle were capsule dosed every 12 hours, the dietary equivalent of 40, 120 or 400 ppm dicamba in the feed (based on 15 kg feed/day). Following 30 days of dosing, two animals from each group were slaughtered; the remaining animals were slaughtered 14 days after withdrawal from dosing. In all instances samples of kidney, liver, muscle and fat were taken for analysis. The results are tabulated below.

Table 1. Dicamba residues in tissues of cattle following 30 days continuous dosing

Milk was sampled throughout the study and up to 14 days following cessation of dosing. The highest residues and the day on which these occurred are tabulated following.

Following the maxima, residues levels in milk plateaued until cessation of the study. Elimination is rapid and residues in milk were nondetectable at 1, 4 and 8 days following withdrawal in the 40, 120 and 400 ppm study groups, respectively. It must be noted that the analytical method used in this study involved an oxidisation step, making dicamba and its metabolite, dichlorosalicylic acid (DCSA), unresolvable. Given the cattle metabolism study indicated that only dicamba metabolites were present in milk, the milk residues detected in this study are expected to be predominantly DSCA also.

The following data are required to fully assess residues of dicamba in animals and animal feeds:

• Residue studies for relevant animal feeds from trials conducted according to Australian Good Agricultural Practice, particularly for pastures and cereal crops.