DDT Residues on Alfalfa1

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Abstract
Previous work on toxicity of DDT to warm-blooded animals is reviewed. One, 2, and 3 treatments of alfalfa with 3% DDT dusts were made at 10-day intervals on wet and dry foliage at the rates of 15 and 30 lb. per acre. Samples of foliage were collected immediately after the last application and at 10-day intervals thereafter for 40 days. The DDT residues were detd. on oven-dried samples by the Stiff and Castillo xanthydrol-pyridine colorimetric method. The maximum amt. found was 162 ppm. on hay harvested immediately after the 3d dusting at the rate of 30 lb. per acre. The minimum amt. of 10 ppm. was on foliage collected 40 days after receiving a single application of dust at the rate of 15 lb. per acre. The amt. of residue increased with the number of dustings, then decreased over a 40-day period following the final treatment and tended to become equal on all plots dusted at the same rate, regardless of the number of applications at that rate. More residue persisted on foliage dusted while wet than on that treated while dry, but again there was a tendency toward equalization after 40 days of weathering. The effect of feeding DDT residues to animals over a period of yrs. has not been detd.