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.

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Experiments were conducted to study quantitatively and qualitatively the penetration of ethyl parathion, diazinon, lindane, and aldrin from sand into the roots of peas and the translocation of these insecticides within the plant system. The effects of the detergent LAS on the uptake of these insecticides and on plant growth were also investigated. All the insecticides, with the exception of diazinon, accumulated within the roots of pea plants while growing in sand treated with insecticides at 5 p.p.m. LAS did not affect the penetration of lindane or aldrin into roots, but significantly reduced the amounts of parathion that penetrated the root system. Apparently, all the insecticides were translocated into the greens, yet the organophosphorus compounds were metabolized and detoxified. Lindane residues in the green plant part were the highest among the insecticides tested, though LAS reduced that translocation. Aldrin, after its penetration into the pea roots, was partially epoxidized into dieldrin which was then translocated to a small extent into the pea greens. Roots were most susceptible to both LAS and pesticide treatments.

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