Mineral UV filters and their effects on Pocillopora damicornis metabolome

The rising use of sunscreens and cosmetics containing ultraviolet (UV) filters has increased their presence in marine ecosystems. UV filters encompass a wide range of organic and mineral compounds with diverse behaviors and properties in aquatic environments. The mineral filters titanium dioxide (TiO₂) and zinc oxide (ZnO) are commonly found in cosmetic products as particles or nanoparticles (NPs) and are increasingly used as alternatives to organic UV filters. In this study, the effects of a coated form of TiO₂ (Solaveil™ XTP₁, 60 nm, hydrophobic) and uncoated ZnO particles from two different sizes (Zano®10 and Zano®M, 60 and 250 nm, hydrophilic) were assessed on the symbiotic tropical coral Pocillopora damicornis using an untargeted metabolomic approach. Corals were exposed for seven days to environmentally relevant particle concentrations (5 to 1000 μg.L^-1), and their metabolomes were analyzed using UHPLC-HRMS/MS. While TiO₂ exposure did not induce significant metabolomic changes, both sizes of ZnO particles caused shifts in the metabolome of the coral's symbiotic dinoflagellates, leading to a noticeable decrease in the relative concentrations of symbiont lipids and pigments. A size-dependent toxicity of ZnO was observed: ZnO NPs triggered signs of bleaching at concentrations as low as 300 μg.L^-1, whereas larger ZnO particles exhibited only mild effects at the highest concentration tested (1000 μg.L^-1). This underscores the critical role of particle size in determining toxicity. This research highlights the contrasting effects of different mineral UV filters on symbiotic corals and aims to inform cosmetic companies in selecting mineral filters that minimize harmful impacts on coral reefs.