Photolysis of mixtures of UV filters octocrylene and ethylhexyl methoxycinnamate leads to formation of mixed transformation products and different kinetics.

The treatment with ultraviolet (UV) light is a well-known technique for water disinfection. Photodegradation by UV light is in discussion as measure for advanced water treatment that could provide a potential removal option for micropollutants. Micropollutants such as ingredients from personal care products are also present in grey water. Grey water gets increasingly attention as a source for water reuse. For that purpose it has to be treated. UV-treatment is an option. However, the knowledge on the fate of micropollutants within such a treatment is little. Therefore, we investigated the fate of the UV filters ethylhexyl methoxycinnamate (EHMC), and octocrylene (OCR) as for both UV filters the presence in grey water was reported. OCR as a single compound was investigated with regard to its degradation kinetics and possible photo-transformation products (photo-TPs). These results were compared with those of EHMC previously reported in literature. The mixture of the two UV filters was also investigated to reveal if mixture effects occur regarding the elimination of the UV filters and the formation of TPs. A medium pressure mercury vapor lamp (200-400 nm) was employed for photolysis. This study shows that OCR itself was eliminated below the limit of detection after 256 min and that photo-TPs were formed. The photolysis of the mixture demonstrated alterations of the degradation rates and patterns. Additional TPs were formed by the reaction of the UV filters or TPs with each other. The study shows that more attention should be paid to mixture-effects and mixture-TPs that may cause further follow-up effects.

Photodegradation of the UV filter ethylhexyl methoxycinnamate under ultraviolet light: Identification and in silico assessment of photo-transformation products in the context of grey water reuse.

To prevent water shortages in the future and to reduce domestic water consumption, decentralized grey water (GW) reuse has become increasingly important. This water has, however, to be free of pollutants. Conventional treatment of GW does not fully eliminate micropollutants such as the UV filter substance ethylhexyl methoxycinnamate (EHMC). EHMC, which is commonly used in sunscreens and personal care products, is an endocrine disruptor and shows potential to bioaccumulation, which is also reflected in its low water solubility. Photolysis has been proposed as an alternative treatment method for other micropollutants, but it is not clear yet whether it can also be used to eliminate EHMC. One goal of this study was to better understand the basic pathways involved in this process. It aimed to identify photo-transformation products (photo-TPs) by using, in the test conditions, an initial concentration of EHMC higher than those expected in the environment. Acetonitrile (ACN) was added in low concentrations to the aqueous solution to overcome the low aquatic solubility of EHMC. The influence of this co-solvent on the degradation kinetics was studied. The photolysis experiments were carried out using a medium pressure mercury lamp, which emits UV light in the range of 200-400nm. The quantum yield of the photolysis of EHMC was 0.0042 and 0.0023mol·Einstein-1 (for 0.2 and 0.5% ACN (v/v), respectively), and the relative and absolute UV photon fluxes were determined. HPLC was used to monitor the elimination kinetics of EHMC, which followed first-order kinetics. The results of LC-MSn analyses revealed that beside others, several oxidized and hydroxylized EHMC isomers were formed as photo-TPs in aqueous solution. Using a set of in silico quantitative structure-activity relationship (QSAR) models, this study also offered new insights concerning the environmental fate and toxicity of the TPs of EHMC.