A critical examination of data, assumptions and statistical approaches for previously published QSARs for the octanol-water and soil-water partition coefficients (K
OW and K
OC) of polychlorinated ...biphenyl (PCBP) congeners identified a number of error sources. A variety of new QSARs were developed based on weighted homogeneity of slopes models. The best type of models used the degree of chlorination in the orthoposition of the PCB molecule as predictor variable together with either the calculated molecular total surface area (TSA) or the gas chromatographic relative retention times (RRT). Prediction of logK
OW and logK
OC for all 209 PCB congeners were based on 53 and 48 experimental data points, respectively. The predicted values were compared to test data sets of 12 and 27 experimental data points, respectively. The QSAR models gave predictions in good agreement with experimental test data.
The soil sorption of six chlorobenzenes and 20 PCB congeners was studied by allowing aqueous trace solutions (ppb) of transformer fluids to equilibrate with 3-6 different soils. Linear relations were ...found between distribution constants and soil organic carbon content. Sorption was favored by a high degree of chlorination and the absence of ortho-substitution in the biphenyl. Sorption kinetics seemed to be first-order controlled (two steps) with rate constants in the order of many hours. We present correlations between sorption data and published physical data, which will be useful for modeling the transport and the fate of PCBs and chlorobenzenes in the environment.
Upon irradiation in air-saturated aqueous solution, naphthalene is mainly converted into 7-hydroxy-1,4-naphthoquinone, 2-formylcinnamaldehyde and 2-carboxycinnamaldehyde. The quantum yield of ...photolysis is equal to 0.0025±0.0005. Naphthalene is likely to be phototransformed via monophotonic ionization that occurs with a quantum yield equal to 0.02. The radical cations formed after the electron ejection can deprotonate or react with water yielding radicals that are oxidized by molecular oxygen. Finally, 2-formylcinnamaldehyde and 2-carboxycinnamaldehyde are yielded. The production of 7-hydroxy-1,4-naphthoquinone is consistent with the intermediary formation of photolabile 1,4-naphtoquinone.
Phototransformation of Propiconazole In Aqueous Media Vialaton, Delphine; Pilichowski, Jean-François; Baglio, Daniela ...
Journal of agricultural and food chemistry,
11/2001, Letnik:
49, Številka:
11
Journal Article
Recenzirano
The photolysis of propiconazole in pure water, in water containing humic substances, and in natural water was investigated. The reaction rates were determined, and the main photoproducts were ...identified with the help of HPLC−mass spectrometry and by NMR. The quantum yield for direct photolysis was 0.11 ± 0.01 at the maximum of absorption (269 nm). Photocyclization after HCl elimination and photohydrolysis of the cyclized intermediate were the main reaction pathways at 254 nm. By contrast, oxidation prevailed over dechlorination in simulated or natural solar light. Humic substances (10 mg·L-1) and naturally occurring chromophores contained in natural water enhanced the rate of propiconazole photodegradation in solar light. Half-life in June in Clermont-Ferrand (latitude 46°N) was found to be 85 ± 10 h in pure water and 60 ± 10 h in natural water; showing that photodegradation of propiconazole in natural waters involves both direct photolysis and photoinduced reactions. Keywords: Propiconazole; direct photolysis; photoinduced transformation; humic substances; natural water; solar light
The phototransformation of 4-chloro-2-methylphenol was studied in distilled, natural or humic substances containing waters. Samples were irradiated under different conditions: in monochromatic light ...at 280
nm, in polychromatic light with lamps emitting within the wavelength ranges 290–350
nm and 300–450
nm and in solar-light. When 4-chloro-2-methylphenol is irradiated in pure water, dechlorination occurs with a good efficiency (Φ
=
0.66). Methylbenzoquinone is the main primary photoproduct in oxygenated solution; methylhydroquinone and methylhydroxybenzoquinone are produced via secondary photolysis of methylbenzoquinone, especially in polychromatic light. Humic substances enhance significantly the rate of photodegradation of 4-chloro-2-methylphenol at
λ
>
300
nm. The photoinduced reaction yields 3-chloro-
trans–
trans- and 3-chloro-
cis–
trans-1-methyl-1-one-2,4-hexadienoic acids. The opening of the aromatic ring is explained by the abstraction of the phenolic hydrogen atom by reactive species produced by excitation of the humic substances followed by the reaction of the 4-chloro-2-methylphenoxyl radical with HO
2
·/O
2
−· radicals. When 4-chloro-2-methylphenol is dissolved in natural waters and exposed to solar-light, dechlorinated and ring opening products are produced. It is deduced that under environmental conditions 4-chloro-2-methylphenol can be phototransformed by both direct and photoinduced processes.
