Multi-Matrix Assessment of Organic UV-Filters in a Major Freshwater Recreational Ecosystem in Central Europe: Spatio-temporal Distribution and Environmental Risk Assessment

• A novel SPE–UHPLC–MS/MS method was validated for four freshwater matrices • First detection of DBT and EHT in a large recreational freshwater lake • In-season water concentrations reached up to 148 897 ng/L (octocrylene at Szigliget) • Seasonal UV-filter input into Lake Balaton was estimated at 51.1 tons/summer • High RQ values (up to 107.5) indicate potential ecological risks in peak season • Citizen science revealed critical sunscreen use patterns and reapplication gaps Organic UV-filters (OUVFs), key ingredients of sunscreens, are increasingly recognized as emerging anthropogenic contaminants; however, their occurrence, seasonal dynamics, and ecological risks in intensively used freshwater recreational lakes remain poorly characterized. By integrating advanced environmental analytics, ecological risk assessment, multiparametric emission modelling, and citizen-science data, we present the first multi-matrix assessment of five widely used OUVFs – avobenzone (AVO), octocrylene (OC), octinoxate (EHMC), iscotrizinol (DBT), and ethylhexyl triazone (EHT) – in Lake Balaton. The study area is the largest shallow freshwater lake in Central Europe and one of Europe’s most intensively used recreational water bodies. Most of the investigated compounds are widely used across Europe and/or included in the 5 th EU Watch List (2025) under the Water Framework Directive, underscoring their regulatory relevance. Our matrix-optimized SPE–UHPLC–MS/MS method enabled sensitive quantification across environmental compartments. Maximum concentrations reached up to 152,603 ng/L in surface water, 975 ng/g d.w. in sediment, 28,116 ng/g d.w. in periphyton, and 46,012 ng/g d.w. in biota. Risk quotient analysis revealed high acute environmental risk for four compounds (e.g., RQ_EHT = 107.5). A newly developed multiparametric emission model, which can be applied to any shallow lake to realistically estimate the load of OUVFs, further estimated that 4.8–284.1 tons of OUVFs may enter Lake Balaton during a 60-day bathing period via direct recreational inputs (medium-use scenario: approximately 65 tons). Our study provides the first comprehensive assessment of next-generation OUVFs in Lake Balaton and shows that shallow recreational lakes experience substantial contaminant pressure during peak tourist periods. The combined analytical, modelling, and citizen-science evidence identifies sunscreen-derived contamination in shallow recreational lakes as a recreational intensity-driven pathway, i.e. the dominant control variables remain the number of bathers and treated skin surface area. Our findings not only emphasize the urgent need to include OUVFs in monitoring programs but also highlight that the effective management of sunscreen-derived pollution for the long-term sustainability of freshwater lakes requires complementing compound-centered regulatory approaches with recreation-oriented intervention strategies.