Absorption by sheep of dieldrin from contaminated soil.

Objective: To study the accumulation of dieldrin residues in sheep from ingestion of contaminated soils was studied in two experiments.

Design: A controlled feeding study of sheep fed contaminated soils of different type at varying intervals. ANIMALS AND PROCEDURE: Thirty-four 2-year-old wethers were divided into four groups (one control sheep only) and fed water-soluble dieldrin or soil contaminated with aldrin and dieldrin at varying intervals in the first study. In a second study 34 similar sheep were divided into four treatments with one being a control. Sheep were fed sandy, high clay or high organic matter soils with similar dieldrin and aldrin concentrations.

Results: In the first study the concentration of dieldrin in the body fat of sheep dosed with dieldrin-contaminated soil was about half that in the body fat of sheep dosed with an equivalent amount of water-soluble dieldrin. The concentration of dieldrin was almost the same in sheep fed 500 micrograms of total dieldrin per day as it was in sheep fed 5000 micrograms every tenth day, over a 50-day period. In the second experiment sheep accumulated nearly three times as much pesticide from a soil with a high organic matter content, and about four times as much from a soil with a high clay content, as from a sandy soil with the same dieldrin content, over a 100-day period. The half-life of dieldrin in the fat of all sheep varied between 96 and 116 days after sheep caused ingesting contaminated soil.

Conclusions: Dieldrin concentrations in the fat of sheep that consume dieldrin contaminated soil fall within 10 days of removal from the source of contamination. However, dieldrin accumulates in the wool of sheep that consume dieldrin contaminated soil.