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in dioxane solution was investigated under xenon lamp irradiation. The quantum yields (b2) for direct photodegradation of these TCDDs were 1.009x10-3, 2.798 X103, and 1.990x10-2mol einstein-1, respectively, at 313 nm, which is a wavelength usually used in determining the quantum yield of a test compound. However, the quantum yields of these TCDDs at wavelengths of the maximal photodegradation peak at more than 295nm were 2.133X103, 3.020x10-3, and 3.283X10-2, respectively, at their maximal photodegradation peaks, and were higher than those at 313 nm. Based on these quantum yields and the measured absorption spectra together with the solar intensity data available in the literature, we estimated the direct sunlight first-order photodegradation rate constants of these TCDDs under conditions of variable sunlight intensities on the surface of water bodies during various seasons at 40N latitude. Also determined were the corresponding half-life times.

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The photodegradation of 3, 3-diindolylmethane(DIM), which has the antifungal activity against Xanthomonas campestris pv. oryzae, Cochliobolus miyabeanus and Pyricularia oryzae, was investigated under xenon lamp irradiation. The maximal degradation of DIM in 12.5 ppm methanol solution was observed in the UV range of 280 nm to 290 nm. The range of wavelengths for the maximal degradation shifted to longer wavelengths as DIM concentration in methanol solution increased. For example, the range shifted from 280-290nm in 12.5ppm solution to 320-330nm in 200ppm solution. Nine compounds were detected as the photodegradation products of DIM and their structures were tentatively determined by gas chromatography-mass spectrometry as 3-formylindole, indole, 2-aminophenol, indole-2, 3-dione, methyl 2-aminobenzoate, indole-2-one, 3-methoxymethylindole, methyl 2-ethylaminobenzoate, and 1-(2-dimethylaminophenyl)ethanone, respectively.