Organophosphorus residues in wool grease resulting from specified on-farm lice and flystrike control treatments

OBJECTIVE: To investigate wool organophosphorus concentrations resulting from a range of farm pesticide application methods. DESIGN: Random sampling of wool for pesticide residues and on-farm interviews to determine associated treatments. PROCEDURE: Tasmanian fleece wool lots were sampled at random and tested for organophosphorus residues. The grower was identified and the pesticide treatments applied to the sheep were ascertained by on-farm interview. RESULTS: The residue concentrations showed a large variation that was not accounted for by differences in treatments by growers. Organophosphorus concentrations were proportional to the number of treatments applied, and inversely related to the time between pesticide application and the subsequent shearing, and were significantly influenced by the method of application. After allowing for the time of application, plunge dipping resulted in pesticide residue concentrations 2 to 2.5 times greater than shower dipping, using spray races or hand jetting, and the use of these methods caused larger residues than the use of jetting races. CONCLUSIONS: We recommend that plunge or shower dipping should not be used more than 7 weeks after shearing, nor at higher concentration than the standard dose rate used for lice control, whereas jetting may be satisfactory for up to 7 months after shearing, provided only one application is administered.