by Brian Horton, University of Tasmania
Woolgrowers rely on chemical applications to manage sheep lice and blowfly strike. A consequence of chemical use on sheep is the possible presence of pesticide residues in their body tissues and wool. The presence of residues from lice and flystrike control treatments pose a number of issues.
Wool rehandling period is the period between treatment and when the wool or treated sheep can be safely handled without the need for protective clothing. Some products can pose health risks to those handling the sheep for some time after treatment or to those handling the wool shorn from recently treated sheep. If a wool-rehandling period is given on the label, this must be observed to protect those handling the sheep or wool, but may also be required for other wool residue issues.
Wool harvesting interval (WHI) (equivalent to wool withholding period) is the period between treatment and when wool can be harvested to satisfy Australian environmental requirements.
Most chemicals used to treat external parasites bind to the wool grease rather than the fibre itself. The scouring process removes wool grease and most contaminants at the same time, resulting in contaminated scour effluent and lanolin.
In Australia, most scour plants send sludge to landfill and the liquid effluent goes into ocean outlets, sewerage systems or evaporation ponds. However, most wool is scoured overseas where scour plants often discharge effluent into inland waterways, where there are stricter standards for scour effluent.
Meat withholding period (WHP) is the time from chemical application to when an animal may be slaughtered for the domestic market. The WHP is mandatory for domestic slaughter and is always on the label.
Export slaughter interval (ESI) is the time from chemical application to when an animal may be slaughtered for export. The ESI may not be on the label, but is required by any abattoir that may export meat. The ESI can be found in the Products list in LiceBoss Tools, on the current version of the National Sheep Vendor Declaration or on the APVMA website.
The products for lice control are applied to the skin or wool of the sheep, but there is some absorption through the skin, or in the case of jetting or dipping, ingestion or inhalation of small amounts of the chemical. Therefore, the specified periods are required to ensure that no detectable levels of these chemicals are left in muscle, fat or other tissues. Some products have a relatively long WHP or ESI and care must be taken when treating lambs to ensure that this will not delay their planned sale.
Wool has a marketing advantage over synthetic fibres because it is a natural product, produced from a renewable resource in an environmentally sustainable way. Although the final woollen article is free of pesticides, there are concerns that pesticide residues on greasy wool could harm the ‘clean and green’ image of wool. Producers who use registered products according to label directions satisfy the legal requirements to offer wool for sale, but guidelines that are more stringent exist for producers targeting the European Eco-label for Textiles market.
The European Eco-label for Textiles enables consumers to recognize garments that are made from raw wool (i.e. unscoured or ‘greasy’ wool) that meets residue specifications currently deemed acceptable in terms of environmental impact.
The pesticide limits for greasy wool to meet European Eco-label requirements are:
(triflumuron, diflubenzuron and dicyclanil)
Cyromazine, macrocylic lactones (e.g. ivermectin, abamectin), neonicotinamides (e.g. imidicloprid) and magnesium fluorosilicate are not restricted provided the normal wool withholding periods are observed for these products.
Farmers can meet Eco-label wool requirements without drastic changes to flock management provided certain pesticides are avoided, as their use, even according to the label, will exceed the limits shown above: