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The distribution and fate of three 14C radiolabeled diphenyl ether herbicides, nitrofen (2,4‐dichlorophenyl 4′‐nitrophenyl ether), X‐52 or methoxy‐nitrofen (2,4‐dichlorophenyl 3′‐methoxy‐4′‐nitrophenyl ether), and bifenox (2,4‐dichlorophenyl 3′‐carbomethoxy‐4′‐nitrophenyl ether), were evaluated in a laboratory rice (Oryza sativa L., Taichung Native No. 1) paddy model ecosystem. Nitrofen was relatively stable under model ecosystem conditions and was bioconcentrated and stored over a 33‐day period in tissues of alga (Oedogonium cardiacum Wittrock), snail (Physa sp.), mosquito (Culex pipiens quinquefasciatus Say), and fish (Gambusia affinis Baird & Girard). The carbomethoxy group of bifenox served as an effective degradophore and tissue storage of the parent compound was minimal. The methoxy group of the methoxynitrofen was not an effective degradophore. The laboratory rice paddy model ecosystem is a useful tool for evaluating the environmental effects and fate of pesticides to be used in rice culture.

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Structure‐activity relationships were examined in toxicological studies with DDT‐type insecticides. The Taft σ* parameter for the electronegative character of substituents correlated well with the uptake of the analogs through insect tarsi and with acute oral toxicities to mice. Substituent groups with stronger electron‐withdrawing capacities penetrated more slowly through the insect cuticle and were markedly more toxic to mice. A nuclear magnetic resonance method was utilized to obtain estimated σ* values for use in the correlations.

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