Toxicity of inorganic nanoparticles and commercial sunscreens on marine bacteria

The Balearic Islands, a top tourist destination for sunny beaches, face physical and chemical pressures from human activities, impacting keystone species like the endemic seagrass Posidonia oceanica and its associated microbiome. This study evaluated the effects of ZnO and TiO₂ nanoparticles and three commercial sunscreens with varying protection factors (50 or 90) and chemical complexities (1- SPF50_E "eco-friendly"; 2- SPF50 not "eco-friendly"; 3- SPF90 not "eco-friendly") on five heterotrophic bacteria (Pseudomonas azotifigens, Marinobacterium litorale, Thiothrix nivea, Sedimenticola thiotaurini and Cobetia sp) and two autotrophic cyanobacteria (Halothece sp. and Fischerella muscicola) associated to P. oceanica, as well as a natural leaf epiphytic community. Results indicated that TiO₂ affected all heterotrophic bacteria, while ZnO was toxic to only two species, while autotrophs were unaffected. Commercial sunscreens impacted three heterotrophs and the natural epiphytic community, while autotrophs were only affected by SPF50. SPF50_E reduced phosphorus uptake, and both SPF50 and SPF90 decreased alkaline phosphatase activity. Reactive oxygen species production was mainly induced by SPF90, followed by SPF50_E and SPF50. Generally, the smallest bacteria were most sensitive to UV-filters (UVFs). This study indicates that UVFs exposure may alter the epiphytic community structure of P. oceanica.