Safety evaluation for human and aquatic environment of physical and chemical UV-filters used in cosmetics

Sunscreens play a fundamental role in the prevention of ultraviolet-induced skin damage and skin cancer, yet growing attention has been directed toward the environmental fate of UV filters released into aquatic ecosystems during product use. Among these, titanium dioxide (TiO2) is widely employed as an inorganic UV filter in both micro-sized and nano-sized forms, particularly in modern broad-spectrum sunscreen formulations. Despite its extensive use, the environmental behaviour and ecotoxicological implications of TiO2 remain insufficiently understood, especially when assessed in the context of complete formulations rather than as isolated raw materials. The aim of this study was to evaluate the environmental release and ecotoxicological effects of TiO2-based sunscreen systems using a formulation-aware approach designed to better approximate realistic wash-off scenarios. Both micro-TiO2 and nano-TiO2 were investigated as isolated active ingredients and as components of finished sunscreen formulations. Leachate-based exposure methods were applied to simulate product release into aquatic media, and ecotoxicological responses were assessed using a multi-species test battery representative of different trophic levels and biological functions. Physicochemical characterisation and titanium quantification were integrated with biological testing in order to support interpretation of the observed effects. The results indicate that the environmental behaviour of TiO2-based sunscreen systems is strongly influenced by formulation context, particle characteristics, and exposure medium. Differences between micro- and nano-sized materials were not determined exclusively by nominal particle size, but also by aggregation behaviour, matrix interactions, and environmental conditions. Moreover, the ecotoxicological profile of formulation-derived leachates differed from that of isolated TiO2 active ingredients, underscoring the limitations of substance-only testing for the environmental assessment of sunscreen products. Overall, this study demonstrates that realistic ecotoxicological evaluation of TiO2-based sunscreens requires a combined consideration of particle physicochemistry, formulation architecture, and biologically relevant exposure conditions. These findings contribute to the development of more robust environmental risk assessment strategies and support the design of sunscreen products that better reconcile effective human photoprotection with reduced ecological impact. Keywords: sunscreen; titanium dioxide; TiO2; nanoparticles; inorganic UV filters; ecotoxicology; environmental risk; leachates; formulation science; aquatic toxicity.