In connection with a use extension application, the APVMA assessed new data and issued a Trade Advice Notice in May 2008.
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 was previously understood.
In light of this new information, the withholding period specified on the current product labels (14 days for grazing or cutting for stockfood) is no longer adequate for some products, as they could present an unacceptable risk to:
- human health, because the national estimated daily intake exceeds 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.
Approved label rates for application of bromoxynil to cereals and pastures fall into the following three broad groups, and are 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 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 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 is 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 are 300 grams bromoxynil per hectare or less do not require any changes to be made to the current 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 occurs at 14 days after application and 1.5 parts per million occurs at 42 days after application of 400 grams bromoxynil per hectare. At 42 days, residues after an application rate of grams bromoxynil per hectare are 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, 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 this basis:
- the currently approved withholding period for grazing and cutting for stockfood of 14 days remains 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 is necessary to manage residues of bromoxynil when it is used on cereals and pastures at rates of 400 grams bromoxynil per hectare or higher.