Photochemistry of halogenated benzene derivatives. Part IX. environmental aquatic phototransformation of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile)     

Jan Kochany  Ghulum Ghaus Choudhry  G. R. Barrie Webster 《Pest management science》1990,28(1):69-81

Photochemistry of the herbicide 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) (I) was investigated by irradiating at approximately 313 nm. Aqueous phase photoreactions of 0.078–7.800 × 10^?5m solutions of I were carried out at different pH values. Quantum yields for the loss of I in buffered solutions were 0.008 (±0.0004), 0.048 (±0.0024), and 0.044 (±0.0022) at pH 2.6, 7.0, and 11.0, respectively. In neutral and basic conditions, I absorbed more strongly at wavelengths > 290 nm, an environmentally significant region. Phototransformation of I was monitored by HPLC and UV-VIS spectrometry. All photoreactions of I gave rise to the generation of two products, 3-bromo-4-hydroxybenzonitrile and 4-hydroxybenzonitrile. The former photoproduct was tentatively identified from its mass spectral data. The photoproducts can be accounted for with a proposed mechanism involving free radicals.  相似文献   

Physical and hydraulic properties of synthetic envelopes for subsurface drainage in Pakistan     

M. Rafiq Choudhry  Abdul Khaliq  W. F. Vlotman  Habib-Ur-Rehman 《Irrigation and Drainage Systems》1995,9(1):73-84

Three imported and four local synthetic envelope materials were tested in the laboratory with upward flow permeameters to determine their physical properties and hydraulic performance. The base soil was taken from the site of the Fourth Drainage Project, Faisalabad, Pakistan. The performance parameters included ratios of gradient and hydraulic conductivity of the interface of envelope material and base soil and the discharge through the permeameter, which were evaluated against established particle-retention and filter criteria.The study concluded that each of the tested materials satisfied the particle-retention criteria because the ratio of characteristic diameters of envelope (O₉₀) and soil (d₉₀) remained less than 2.5. The filter criteria, however, could not be met satisfactorily, particularly during receding hydraulic gradients, when the ratio of envelope and base soil hydraulic conductivities (Ke/Ks) dropped below 1, except in the case of one imported material. Blocking of the soil-envelope interface occurred due to the internal movement of soil particles, particularly during receding gradients.  相似文献