Aquatic photochemistry of diclofenac in the presence of natural dissolved organic chromophoric material and nitrate

作者：Peuravuori Juhani^*

来源：International Journal of Environmental Analytical Chemistry, 2012, 92(13): 1470-1492.

DOI：10.1080/03067319.2010.534159

• diclofenac
• photochemical transformation
• inner filter effect
• natural humic water
• nitrate
• phototransformation products

Photolysis experiments with diclofenac (DCF) in aqueous solutions under different artificial irradiations were performed to characterise the influence of natural chromophoric dissolved organic material (CDOM) and nitrate ions (NO3-) on the transformation rate of DCF. The irradiations were carried out by a low-energy UVA-vis (315-400-800 nm) and powerful UVB-uva (280-315-400 nm) lights simulating natural conditions. Alterations of molecular size distributions and optical properties of CDOM after different irradiation intervals were also detected. The kinetic measurements and principal structural determinations of the transformation products were performed by a GC-EI-MS (gas chromatography electron impact mass spectrometry) technique. The capacity of the CDOM for production of (OH)-O-center dot radicals or/and different reactive transient oxidants was not enough powerful to initiate the indirect photolysis of the DCF even assisted by NO3- ions. As a consequence, the CDOM acts as a quencher reducing the photochemical transformation rate of DCF, and in the applied conditions the phototransformation of DCF takes place alone through direct photolysis even under the UVB-uva radiation. Likewise, the action of NO3- ions as photoinductors under the applied conditions was not so significant as usually expected. The kinetic half-life for the phototransformation of DCF was at the best less than one hour corresponding to an apparent quantum yield of 0.097. Structural compositions of detected transformation products were analogous with the conventional ones. The only exception was the formation of a quite UV-resistant carbazole-dione derivative. Irradiation of DCF in pure laboratory water generated practically generated this carbazole-dione derivative solely, thus confirming the photocyclisation as the main phototransformation pathway. However, in the presence of CDOM the main phototransformation pathways were photocyclisation, dehydration, and decarboxylation. It may be that CDOM does not necessarily stimulate pathways but rather decreases the importance of photocyclisation in front of dehydration and decarboxylation competitive pathways. The main photoproducts in the presence of CDOM were: a carbazole-dione derivative, carbazole-1-acetic acid, 1-(2,6-dichlorophenyl)indolin-2-one, and 2-2-(chlorophenylamino)benzaldehyde.

• 出版日期2012