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Researchers Explore Emerging Pollutants’ Photochemical Behavior in Natural Waters Using Quantum Chemical Calculations

Organic sunscreens released from sea-bathing or wastewater discharges are emerging pollutants frequently detected in natural waters, and draw extensive concerns due to potential ecological risks. Photochemical transformation of organic sunscreens in surface waters may influence their environmental fate and ecological risk. The latest researches on the photochemical behavior of organic sunscreens were summarized in a paper entitled.

"Aquatic environmental photochemical behavior of organic sunscreens" (Chinese Science Bulletin 2013, Vol 58(30), 2989), wrote by Dr. Siyu Zhang from the research group of Professor Jingwen Chen at the Dalian University of Technology, China.

As excellent sunlight absorbers, organic sunscreens potentially undergo photochemical transformation directly by absorbing ultraviolet emission of sunlight. Natural water constituents may influence the photochemical behavior. This paper summarized the photochemical behavior of organic sunscreens reported so far, including photolytic rates, effects of water constituents, products and toxicity. They found that photolysis half-lives of different organic sunscreens range from several hours to a month, related to molecular structures, seasons, latitude, properties of waters. Dissolved oxygen, pH, dissolved organic matters (DOM), chloride, nitrate, carbonate/bicarbonate, and metal ions may influence photochemical transformation rate or products of organic sunscreens, with the effects varied with properties of organic sunscreens. The photochemical transformation of some organic sunscreens may lead to formation of toxic products, e.g. reactive oxygen species, endocrine disruptors, cytotoxic substances. Chen's group has worked on environmental photochemical behavior of organic pollutants for over ten years. Besides organic sunscreens, they found that photochemical transformation of other emerging pollutants also varies significantly with molecular structures and water constituents. In one of their articles, progress in studies on aqueous environmental photochemical behavior of antibiotics was summarized (SCIENTIA SINICA Chimica, 2010, 40(2), 124).

"Photochemical transformation is important in determining the fate of organic pollutants in the environment, and there are many pollutants for which the photochemical behavior is not well understood, so we attempted to develop methods to predict environmental photochemical behavior of pollutants" said Dr. Chen.

They employed quantum chemical calculations based on density functional theory (DFT) or time-dependent DFT (TD-DFT), and quantitative structure-activity relationship (QSAR) to explore the dependence of environmental photochemical behavior on molecular structures and water constituents. In their recent works, the environmental photochemical transformation for several kinds of emerging pollutants was investigated, including sunscreens, antibiotics, and polybrominated diphenyl ethers. The pH-dependent photolytic mechanisms of ciprofloxacin (ES&T 2013, 47, 4284), hydroxyl radical induced photooxidation mechanisms and kinetics of BDE-15 (ES&T, 2011, 45, 4839) were elucidated. A DFT approach for evaluating effects of dissolved oxygen, DOM and Cl- on photochemical behavior of emerging pollutants was developed (ES&T, 2010, 44, 7484).


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