Analyses of turnip tops, sprayed three times with malathion at the rates of 10.1, 20.2 and 30.3 ounces active ingredient per acre per application, showed initial deposits of 1.3, 2.1 and 4.5 p.p.m., respectively. Collards sprayed twice with malathion at 16 ounces active ingredient per acre, showed residues no greater than 3.9 p.p.m. 3 days after the last application. Two applications of DDT at 16 ounces active ingredient per acre, left residues of 31.6 and 18.4 p.p.m. on collards and lettuce, respectively. The DDT residue on collards dissipated rapidly, find, by the 14th day, was below the federal tolerance of 7.0 p.p.m. The DDT residue Oil lettuce declined at the rate of approximately 1.0 p.p.m. per day and was also below tolerance at the end of 14 days. Snap beans sprayed twice with DDT at 12 active ingredient per acre, showed an average residue of 0.8 p.p.m. 1 day after the last application.
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Waites et al. (1958) studied this question.