Changes to the Withholding Period on Labels of Products Containing Bromoxynil
October 2009
Bromoxynil is the active constituent in a number of herbicide products commonly used to control a wide range of weeds in pastures and food and fodder crops.
In connection with a use extension application, the APVMA assessed new data and released a Trade Advice Notice in May 2008 (PDF, 226kb).
The assessment of the new data and other related information essentially showed that bromoxynil residues were more readily transferred to animals consuming treated food crops, pastures and fodder crops than previously understood.
In light of this new information, the withholding period (14 days for grazing and for cutting for stockfood) specified on the current product labels is no longer adequate for some products as they could present an unacceptable risk to (i) human health, as the National Estimated Daily Intake (NEDI) exceeds the Acceptable Daily Intake (ADI) and (ii) trade, as residues may occur in export hay and in animals consuming treated feeds at levels above those allowed in major markets for these commodities.
Approved label rates for application of bromoxynil to cereals and/or pastures fall into the following 3 broad groups, and are largely dependant on a co-formulate or tank-mix partner(s) and target weed.
- Less than 300 g bromoxynil/ha
- Between 400 and 420 g bromoxynil/ha
- Greater than 560 g bromoxynil/ha
Based on the data available to the APVMA the highest pasture residue observed at 14 days after application at 300 – 313g bromoxynil/ha was <0.1 mg/kg on a fresh weight basis. This is equivalent to <0.5 ppm on a dry weight basis.
The previously proposed entry in Table 4 of the MRL Standard was T1 mg/kg for Primary Feed Commodities. Residues at 14 days after application at 300 g ai/ha are 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 g bromoxynil/ha and observing an 8-week grazing withholding period. That livestock burden formed the basis of proposed animal commodity MRLs. It is considered that residues arising from a livestock burden equivalent to <0.5 ppm would be within the proposed animal commodity MRLs.
Therefore products for which the application rates to cereals and/or pastures are 300 g bromoxynil/ha or less do not require any changes to be made to the current 14-day withholding period for cutting or grazing.
In relation to application rates of 400 to 420 g bromoxynil/ha, a high residue equivalent to 15 ppm dry weight occurs at 14 days after application and of 1.5 ppm occurs at 42 days after application of 400 g bromoxynil/ha. At 42 days, residues expected after an application rate of 560 g bromoxynil/ha are expected to be similar to those observed after application of 400 g bromoxynil/ha.
On the basis of the information made available to the APVMA, the same residue management strategies should apply to products with a maximum application rate of about 400 g bromoxynil/ha as those with a maximum application rate of 560 g bromoxynil/ha.
On this basis:
- the currently approved withholding period for grazing and cutting for stock food of 14 days remains appropriate for products used at rates of 300 g bromoxynil/ha or less on pastures and/or cereal crops.
- a withholding period for grazing and cutting for stock food of 8 weeks is necessary to manage residues of bromoxynil when used on cereals and/or pastures at rates of 400 g bromoxynil/ha or higher.
Therefore, the currently approved labels need to be amended for bromoxynil products used on cereals and/or pastures at rates of 400 g bromoxynil/ha or higher. The APVMA has written to all registrants of bromoxynil products, asking registrants with products for which application rates exceed 300 g bromoxynil/ha to effect the label amendments. It is anticipated that the label amendments would be completed by end of November 2009.
Other relevant matters
Registrants have been advised that further residue data (as outlined in section 6 of Bromoxynil Residues Assessment) would allow refinement of the MRLs and WHPs and can be submitted for consideration by the APVMA through normal registration processes.