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Placental Transfer of DDT in Beef Cattle

U. S. Department of Agriculture, Beltsville, Maryland 20705 and Virginia Polytechnic Institute and State University Front Royal, Virginia 22630

Abstract

Two experiments were conducted to study the transfer of DDT residues across the placental barrier in beef cattle. In the first experiment, DDT residue concentration and distribution were determined in 22 stillborn calves from cows fed either apple pomace, corn silage or an equal mixture of pomace and corn silage. The concentrations of total residues in the depot fat of stillborn calves and their dams were similar but the depots of the stillborn calves contained a higher proportion of DDE and a lower proportion of DDT. Distribution of residues among organs, muscles and fat depots in stillborn calves was similar to the distribution in tissues of adult cattle. In the second experiment, four pregnant heifers were given intravenous injections of ¹⁴C-labeled DDT; serial blood samples, urine, and feces were collected up to 14 days after injection and analyzed for radioactivity. Viable fetuses were taken by cesarean section at 5 min., 3 hr., 6 hr. and 10 days after injection and analyzed. Immediately after injection, radioactivity moved rapidly from the blood and was detected in maternal fat within 10 min. after injection. Levels of radioactivity were greater in maternal blood compared to fetal blood until 6 hr. after injection. Radioactivity was not detected in fetal liver and fat at 5 min. after injection but was detected in these fetal tissues at 3 hours. The data indicated that over an extended period of maternal exposure to DDT, the maternal and fetal fat tissues approach an equal residue level. However, the rapid movement of DDT from the maternal blood into maternal fat tissues appeared to preclude a large portion of a single dose of DDT from crossing the placental barrier.

¹ ARS, Nutrition Institute, Ruminant Nutrition Laboratory, Beltsville, Maryland 20705.

² ARS, Physiology and Genetics Institute, Beltsville, Maryland 20705.

³ VPI, Division of Research, College of Agriculture and life Sciences, Front Royal, Virginia 22630.

⁴ ARS, Front Royal Research Station, Front Royal, Virginia 22630.