In milk samples taken 2 days after spraying, 2.8 p. p. m. of DDT was found. This amount gradually dropped to 0.6 p. p. m. in 21 days. The amount of dieldrin found was approximately twice that of DDT. The maximum contamination from Dilan was one-fourth and from methoxychlor and Perthane one-seventh that of DDT. Less than 0.1 p. p. m. of malathion was found in milk samples taken 5 hours after spraying with emulsion sprays. Only traces were present in the milk 24 hours after spraying. All subsequent samples were free of contamination. Malathion suspensions caused slightly higher residues than emulsions.

STUDIES have been made on the storage of insecticides in the fat of beef cattle following ingestion of feed artificially contaminated with the insecticides to simulate residues on hay and forage crops. The first tests were made at concentrations thought likely to exceed field contamination. If insecticide storage seemed excessive, further experiments were made at progressively lower dosages until minimum field residues were studied. The first studies covered feeding periods of 4 weeks. Later the feeding time was extended to 8 weeks and finally to 16 weeks, which was the feeding period used in most of these studies.

The test animals, cattle and sheep, were maintained under the supervision of the cooperating veterinarians, who were responsible for all details of the feeding and the collection of the fat samples. Each feeding was weighed and the insecticide added in acetone solution to the feed at the time of weighing. The feed consisted of ground corn and oats, cottonseed meal, and chopped alfalfa hay.

Fat samples were taken by omentectomy before starting the feeding, at 4-week intervals during the feeding time and at intervals after the feeding of the insecticides ceased to determine the duration of contamination.

The insecticides studied include aldrin, BHC, chlordane, DDT, dieldrin, endrin, heptachlor, methoxychlor, and toxaphene. Some of the materials were fed at several dosage levels.

Methoxychlor showed less tendency to be stored in the body fat than any of the insecticides studied. There was no detectable accumulation of methoxychlor in the fat after feeding 25 p. p. m. in all items of the diet for 16 weeks.

Technical aldrin, dieldrin, endrin, and heptachlor fed at dosages of 2.5 p. p. m. for 16 weeks were stored in the fat at rates of 5.2, 14.3, 0.8, and 0.2 p. p. m., respectively, in cattle, and 4.5, 10.5, 1.4, and 2.1 p. p. m. in sheep.

Toxaphene fed at 25 P. p. m. for 16 weeks resulted in the storage of 12 p. p. m. in the fat of cattle and 8 p. p. m. in the fat of sheep.

Dieldrin resulted in the greatest storage of any of the insecticides studied. A dosage of the 1.0 p. p. m. in the diet for 16 weeks resulted in a storage of 2.2 p. p. m. in the fat of both cattle and sheep.

DDT residues on corn plants that had been treated for control of European corn borer averaged 23 P. P. m. when beef cattle were placed in the field. After 2 months on the stover range, the DDT content of their fat was 4.1 to 5.8 p. p. m. Three months after discontinuance of feeding on the contaminated forage, DDT was not detected in the fat.

Thus the insecticides can be arranged in the approximate order of their tendency toward storage as follows: Dieldrin, aldrin, BHC, DDT, endrin, chlordane, heptachlor, toxaphene, and methoxychlor. The insecticides having the greatest tendency toward storage in the fat were also the ones most slowly eliminated from the fat after feeding of the insecticides ceased.

Studies were made on the storage of insecticides in the fat of beef cattle resulting from spray treatments with practical concentrations of DDT, methoxychlor, lindane, chlordane, gamma chlordane, heptachlor, toxaphene, malathion, and TDE (the common name for the technical product dichloro-diphenyl-dichloroethane).

The storage of insecticides in the fat of beef cattle 3 weeks after a single spray treatment with 0.5 percent DDT, TDE, and methoxychlor was 11.2, 11.0, and 2.8 p. p. m., respectively. The residue of methoxychlor had been eliminated 8 weeks later, but small residues of DDT and TDE were still present in the fat 27 weeks after spraying. Six repeated spray applications with these insecticides at 3-week intervals resulted in storage in the fat in the following. amounts: DDT, 35 P. P. m.; TDE, 28 P. p. m.; and methoxychlor, 2.4 P. p. m. Detectable residues of DDT and TDE were still present 36 weeks after the last spraying had been made.

Detectable amounts of lindane were not found in fat of cattle sprayed six times at 3-week intervals with 0.03 percent lindane. A method sensitive to 2.5 P. p. m. was used.

There was no detectable storage in the fat of cattle sprayed 16 times at weekly intervals with 0.5 percent malathion. The fat samples were taken 2 weeks after the last spraying and were analyzed by a method that was sensitive to 0.5 p. P. m.

Samples of fat taken from cattle 2 weeks after the last of six spray treatments at 2-week intervals with 0.5 percent heptachlor, chlordane, and gamma chlordane contained residues of 19, 21, and 24 P. P. m., respectively. The residues had dropped to 2, 4, and 0.3 P. P. m. 14 weeks later.

When cattle were sprayed 12 times at 2-week intervals with 0.5 percent toxaphene, analysis for organically bound chlorine indicated 14 P. P. m. of the insecticide to be present in the fat. The method used for this experiment was sensitive to only 4.0 P. P. m., however.

In conclusion) then, recommendations for the application of insecticides to forage crops and to farm animals must take into consideration the possibility that the chemicals may contaminate milk and meat products.

ROSCOE H. CARTER, a chemist in the Entomology Research Branch, Agricultural Research Service, is a graduate of Morningside College and the State University of Iowa. He has been employed by the Department of Agriculture since 1927 in insecticide investigations.

H. V. CLABORN is chemist in charge of Pesticide Chemicals Research Section of Entomology Research Branch at Kerrville, Tex. Since entering the Department of Agriculture in 1927, he has worked in the Bureau of Chemistry and Soils, Bureau of Entomology and Plant Quarantine, the research laboratories of the Bureau of Dairy Industry, and the Food and Drug Administration.

G. T. WOODARD is assistant veterinarian in charge of the Animal Disease and Parasite Research Section at Kerrville, Tex. He is a graduate of the Texas Agricultural and Mechanical College. Since 1952 he has been engaged in work on the problems of insecticide toxicology.

RAY E. ELY is animal nutritionist in the Experiment Stations Division of the Department of Agriculture. He is a graduate of Michigan State College and the University of Missouri. Formerly he was employed by the Nutrition and Physiology Section of the Dairy Husbandry Research Branch at Beltsville.