Bromoxynil

Update of withholding period for bromoxynil products

In September 2018, the Australian Pesticides and Veterinary Medicines Authority (APVMA) received residue trial data for a bromoxynil product, Jaguar Selective Herbicide, under section 161 of the Agricultural and Veterinary Chemicals Code scheduled to the Agricultural and Veterinary Chemicals Code Act 1994.

Evaluation of this data indicated that residues of bromoxynil in cereal forage after application of the product at the maximum label rate (275 grams bromoxynil/hectare) would not comply with the bromoxynil Temporary Primary Feed Commodities MRL of 1 mg/kg in the Agricultural and Veterinary Chemicals Code (MRL Standard) Instrument 2019 when assessed after a 14 day grazing withholding period, current on the label at that time, or even after a withholding period of six weeks.

Based on the levels of residues in forage, it estimated that residues in animal commodities would also be above current MRLs.

It was considered that this data is relevant to other registered bromoxynil products. As a result, the APVMA has required bromoxynil product labels with grazing withholding periods of 14 days or six weeks, to be updated with an eight week grazing withholding period.

The section 161 data provided to the APVMA in September 2018 included trials on a second bromoxynil product, Velocity Selective Herbicide. An outcome of the evaluation of this data was that no changes were required to the label of Velocity Selective Herbicide, which retains the grazing withholding period of six weeks.

Previous action on bromoxynil (2008)

In May 2008, in connection with a use extension application, the APVMA assessed new data and issued a Trade Advice Notice.

The assessment of the new data and other related information showed that bromoxynil residues were more readily transferred to animals consuming treated food crops, pastures and fodder crops than was previously understood.

In light of this information, the withholding period specified on product labels at that time (14 days for grazing or cutting for stockfood) was considered no longer adequate for some products, as they could present an unacceptable risk to:

  • human health, because the national estimated daily intake exceeded the acceptable daily intake
  • trade, because residues may occur in export hay and in animals consuming treated feeds at levels above those allowed in major markets for those commodities.

At the time of this assessment, the approved label rates for application of bromoxynil to cereals and pastures fell into the following three broad groups, largely dependent on a co-formulate or tank-mix partner(s) and the target weed:

  • less than 300 grams of bromoxynil per hectare
  • 400–420 grams of bromoxynil per hectare
  • more than 560 grams of bromoxynil per hectare.

Based on the data available to the APVMA, the highest pasture residue observed at 14 days after application at 300–313 grams of bromoxynil per hectare was less than 0.1 milligrams per kilogram on a fresh-weight basis. This is equivalent to less than 0.5 parts per million on a dry-weight basis.

The previously proposed entry in Table 4 of the MRL standard was T1 milligrams per kilogram for primary feed commodities. Residues at 14 days after application at 300 grams bromoxynil per hectare were expected to comply with that proposed standard.

A livestock burden of 0.35 ppm was estimated in the previous residues assessment following treatment of pastures at 560 grams bromoxynil per hectare and observing an eight-week grazing withholding period. That livestock burden formed the basis of proposed animal commodity maximum residue limits (MRLs). It was considered that residues arising from a livestock burden equivalent to less than 0.5 parts per million would be within the proposed animal commodity MRLs.

Therefore, products for which the application rates to cereals or pastures were 300 grams bromoxynil per hectare or less were not considered to require any changes to be made to the 14-day withholding period for cutting or grazing.

For application rates of 400–420 grams bromoxynil per hectare, a high residue equivalent to 15 parts per million dry weight occurred at 14 days after application and 1.5 parts per million occurred at 42 days after application of 400 grams bromoxynil per hectare. At 42 days, residues after an application rate of grams bromoxynil per hectare were expected to be similar to those observed after application of 400 grams bromoxynil per hectare.

 On the basis of the information made available to the APVMA in 2008, the same residue management strategies should apply to products with a maximum application rate of about 400 grams bromoxynil per hectare as those with a maximum application rate of 560 grams bromoxynil per hectare.

On that basis:

  • the then currently approved withholding period for grazing and cutting for stockfood of 14 days was considered to remain appropriate for products used at rates of 300 grams bromoxynil per hectare or less on pastures and cereal crops
  • a withholding period for grazing and cutting for stockfood of eight weeks was considered necessary to manage residues of bromoxynil when it is used on cereals and pastures at rates of 400 grams bromoxynil per hectare or higher.

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