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A study was made of the extent to which insecticides may be absorbed and translocated from contaminated soils into plant tissues and the relationships among absorbance of insecticidal residues, soil types, and crops. Lindane, DDT, and aldrin were absorbed into crops, the degree being dependent on the crop, the soil type in which the crop had grown, the insecticide, and its concentration within the soil. Carrots not only absorbed more Procedure Soil Treatment and Sampling. In May 1954, a sandy loam, Miami silt loam, and muck soil were treated with DDT at 10, 100, and 1000 pounds per acre, lindane at 1, 10, and 100 pounds per acre, and aldrin at 2, 20, and 200 pounds per acre.

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A steady decrease of extractable [14C] parathion residues in soils over a 1-month incubation period was accompanied by an increase of unextractable, bound 14C-labeled residues, resulting finally in total recoveries of extracted plus bound residues of 80 to 87 percent of the applied radiocarbon. Soils containing bound residues were nontoxic to fruit flies. Binding of 14C-labeled residues was related to the activity of soil microorganisms; soil sterilization resulted in a reduction of binding by 58 to 84 percent. Under flooded (anaerobic) conditions, the binding of compounds labeled with 14C doubled, and parathion was reduced to aminoparathion. Reinoculation of sterilized flooded soil fully reinstated the binding capacity. [14C] Aminoparathion was preferentially bound to soil, since its binding within 2 hours was 30 times greater than that of [14C] parathion. Because of the existence of formerly "unseen," unextractable residues, the concept of "persistent" and "nonpersistent" pesticide residues might have to be reconsidered.