Photodecomposition of several pesticide chemicals exposed to sunlight on silica gel chromatoplates is accelerated by photosensitizing agents, including some other pesticide chemicals. The following two surveys were made by a simple procedure involving exposure to sunlight for up to 1 hr: 28 candidate sensitizers of known triplet-energy values were tested individually for activity in sensitizing the photodegradation of each of 23 radio-labeled pesticide chemicals; 175 unlabeled pesticides were screened for photosensitizing activity against each of six C14labeled insecticide chemicals. The conversion of aldrin, dieldrin, and endrin to photoisomeric derivatives is accelerated by many compounds of high triplet-energy state. Some aromatic amines sensitize the photodecomposition of DDT and several chlorinated cyclodienes, possibly by formation of charge transfer complexes. Anthraquinone shows the broadest spectrum of activity of the sensitizers tested in combination with organophosphorus compounds, methylcarbamates, pyrethroids, rotenone, dinitrophenol derivatives, piperonyl butoxide, and 2,4-D. There is a possibility of a photosensitizing pesticide chemical markedly altering the persistence of another pesticide chemical, but these interactions of a photosensitizing nature occur with only a few combinations of pesticides studied.

Rotenone and some related substituted-4-chromanones act as photosensitizers to accelerate the photoalteration of chlorinated cyclodiene insecticide chemicals exposed to sunlight on bean leaves. The

When applied at low concentrations to plant foliage, rotenone catalyzes the photoisomerization of dieldrin and other cyclodiene insecticide chemical residues. This finding of a new type of interaction between pesticide chemicals suggests the possibility of controlling the persistence of residues on plants by use of certain pesticide-photosensitizer combinations and application sequences.

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