Photodegradation with sunlight

Studies have appeared where photolysis in natural bodies of water under normal sunlight conditions has been examined. For example, metolachlor was slowly photodegraded by sunlight in lake water, with a half-life of 22 days in summer and 205 days in winter (28). Addition of a 5% solution of dissolved organic matter to the water extended the half-Hves two to three times longer, depending on the season (see PHOTOCHEMICAL TECHNOLOGY, photocatalysis). ... 

Surface water photodegradable with 8 hours of sunlight in water with t,/2 = 44 d, t,/2 = 15-28 d in lake and river water, and t,/2 < 2 d on soil surface (Hartley Kidd 1987) ... 

Parathion binds tightly to soil particles and has little or no potential for groundwater contamination. Residues of parathion may persist for days or weeks. Parathion readily undergoes photodegradation and sunlight can convert parathion into paraoxon. The breakdown of parathion in soil or water increases with alkalinity. Parathion residues on crops typically decay with a half-life of 1 day. 

An estimated vapor pressure of 4.7 x lO mmHg indicates DeBDE will exist solely in the particulate phase in the ambient atmosphere. Particulate-phase DeBDE will be removed from the atmosphere by wet and dry deposition. Direct photodegradation may be fairly rapid based upon studies with sunlight irradiation. If released into soil, DeBDE is expected to be immobile based upon an estimated Kqc of 692 000. Volatilization from moist soil surfaces is not expected to be an important fate process based upon an estimated Henry s law constant of 1.2 x lO atm mmol. No data were located showing the... 

The a- and [3-isomers of endosulfan undergo photolysis in laboratory tests after irradiation in polar solvents and upon exposure to sunlight on plant leaves. The a-isomer also undergoes isomerization to the P-isomer, which is relatively more stable (Dureja and Mukerjee 1982). A photolytic half-life of about 7 days was reported for endosulfan by EPA (1982c). The primary photolysis product is endosulfan diol, which is subsequently photodegraded to endosulfan a-hydroxyether. Endosulfan sulfate is stable to direct photolysis at light wavelengths of >300 nm however, the compound reacts with hydroxy radicals, with an estimated atmospheric half-life of 1.23 hours (HSDB 1999). 

Photolysis photodegradation of 5 ppm initial concentration in methanol-water (3 7, v/v) by high pressure mercury lamp or sunlight with a rate constant k = 1.84 x 1CL3 mur1 and t, 2 = 6.27 h (Wang et al. 1991) the... 

Ephedrine (17) was known to give coloured products on exposure to sunlight. When a 1 % solution was irradiated with UV light from a 30 W tube the solution became coloured and colourless needle-shaped crystals separated. With prolonged exposure, the crystals redissolved as the solution darkened to an intense brown. On analysis, the crystalline compound was identified as the oxazolidine (18). This compound was known to be formed by reaction between ephedrine and benzaldehyde, so it was assumed that the primary photodegradation product of the drug was benzaldehyde [27]. 

There appear to be no reports of photodegradation of the hypnotic, methaqua-lone (323), but two of its metabolites are photolabile. The main metabolite, the A1-oxide (324), was photolysed at 366 nm or in sunlight to the oxaziridine (325) which could be isolated with care [184], Further degradation, either thermal or photochemical, gave the more readily isolated products (326) to (329). A mechanistic explanation for these observations was offered [185]. A solid second metabolite (330) rapidly turned maroon on exposure to laboratory light and an alcoholic solution became intensely coloured under a medium-pressure... 

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