The uptake and depletion of fenitrothion in cattle, pasture and soil following spraying of pastures for locust control

Summary. Fenitrothion is an organophosphorus insecticide widely used for the control of locusts in Australia and overseas. It is sprayed on swarms and bands of locusts and on the pastures on which they feed. However, there is little Australian data on depletion rates of fenitrothion when used this way. Consequently, there has been concern that beef cattle producers may not be able to guarantee that their cattle meet legal requirements with respect to residue levels following grazing on sprayed pasture. This paper reports a study conducted in February 1998 in central western New South Wales on the rate of depletion of fenitrothion in cattle, pasture and soil after fenitrothion spraying. The cattle were 18-month-old heifers in forward store condition. Fenitrothion was detected in the fat of 7 of the 66 exposed cattle. Residues in 2 of these exceeded the Maximum Residue Limit of 0.05 mg/kg. No fenitrothion was detected in the fat of the 26 cattle slaughtered 14 days or later after treatment or in muscle and liver samples. The half life of fenitrothion was 2–3 days in the soil and 1–2 days in the pasture. We conclude that the 14-day slaughter withholding period currently approved by the National Registration Authority is appropriate.