Occurrence of twelve UV filters and evidence of cis-octinoxate formation in Adriatic coastal waters: Environmental implications

UV filters used in personal care products are increasingly recognised as emerging contaminants due to their persistence and ecological risks. Detected in aquatic systems at concentrations from ng L^-1 to μg L^-1, their monitoring is essential for environmental risk assessment but challenging because of their diverse physicochemical properties, requiring sensitive analytical methods. This study optimised a solid-phase extraction gas chromatography-tandem mass spectrometry (SPE-GC-MS/MS) method for the simultaneous determination of twelve UV filters in marine waters. The method showed suitable linearity, precision, and recoveries, with detection limits below 1 ng L^-1. Seawater samples collected along the Adriatic coast (Rimini and Riccione, Italy) during peak recreational activity were analysed. All twelve UV filters were detected, with octocrylene (up to 23,100 ng L^-1), homosalate (up to 16,400 ng L^-1), and ethylhexyl salicylate (up to 10,900 ng L^-1) being most abundant. Trans-2-Ethylhexyl methoxycinnamate (E-EHMC, the trans isomer of octinoxate, 13-1474 ng L^-1) occurred consistently with its isomer Z-EHMC (cis-octinoxate), contributing 18-64 % of total (E + Z)-EHMC, suggesting in situ photochemical conversion, since the cis form is negligible in cosmetic products. Benzophenone, ethylhexyl dimethyl PABA, 4-methylbenzylidene camphor, benzyl salicylate, and isoamyl methoxycinnamate were found at lower yet relevant concentrations. UV filters banned under European regulations, such as menthyl anthranilate and etocrylene, were absent or barely detected. This work provides the first data on sunscreen UV filters in Adriatic coastal waters and the first quantitative evidence of Z-EHMC in environmental waters, highlighting its in situ formation and contributing to understanding their environmental fate and risks.