Correction - Residues in milk and body fat of cattle grazed on pastures treated with dieldrin

Residues of dieldrin in the milk and body fat of cattle grazed on pastures sprayed or dusted with 1 lb dieldrin an acre were determined. Cattle were grazed on treated pastures immediately or three weeks after dieldrin was applied. Grazing was either continuous or restricted to two hours a day. Samples of milk for analysis of dieldrin were taken at weekly intervals for 3-4 months after treatment of pastures. Composite samples from the renal, omental, and subcutaneous fat of cattle were analyzed for dieldrin 9-13 weeks after the commencement of grazing on treated pastures. Dieldrin in milk and body fat was analyzed by modifying the colorimetric method of Cueto. Samples were saponified with ethanol and potassium hydroxide, the unsaponified matter extracted into petroleum ether and the whole sample chromatographed on an alumina column. Colour estimations were made with a recording spectrophotometer and the absorbances obtained, converted to �g dieldrin. The method detected at least 20 �g pure dieldrin. Dieldrin was found in milk and body fat regardless of the grazing practice or the formulation of dieldrin used. Residues were low when cattle were restricted to two hours grazing a day beginning three weeks after the application of dieldrin and were lower with dieldrin applied as a dust than as a spray.