Abstract Organophosphate (OP) residues in wool from lambs dipped with coumaphos, diazinon, bromophos ethyl, propetamphos, or chlorfenvinphos to protect against flystrike were monitored on six farms on the east coast of the North Island over a 12-week period. Residues were generally higher, by a mean factor of 1.6, in wool samples from the shoulder than in wool from the crutch area, and by a mean factor of 4.6 in wool from lambs dipped early in the run compared with those dipped at the end. Initial OP levels in the wool were, on average, 2.6 times those in the dipping solution. The calculated half-life of the OPs, assuming a simple exponential decay model, varied from 8 to 23 days.
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