Toxicity of the organic UV filter oxybenzone to the brown macroalga Hormosira banksii and the green macroalga Ulva lactuca.

Oxybenzone (BP-3), a common sunscreen ingredient, has been detected in marine ecosystems and shown to be toxic to various marine species, raising environmental concerns. However, its effects on macroalgae remain largely unknown. This study investigated the toxicity of BP-3 on two macroalgae species: Hormosira banksii and Ulva lactuca. A chronic germination-inhibition experiment with H. banksii and an acute study with mature U. lactuca were conducted using BP-3 concentrations ranging from 0.03 to 27 mg/L. Results revealed significant inhibition of H. banksii spore germination at 3, 9, and 27 mg/L BP-3 at 72 h, with a 10 % effect concentration of 0.363 mg/L (95 % confidence interval: 0.27-0.45 mg/L). For U. lactuca, relative growth rate decreased by 20-70 % compared to controls in treatments of 0.1, 3, 9, and 27 mg/L BP-3 after 72 h. Exposure to ≥0.3 mg/L BP-3 resulted in lower chlorophyll a and b concentrations and higher lipid peroxidation, with significant differences observed between the control and ≥9 mg/L BP-3 treatments. Exposure to 1 mg/L BP-3 induced significant alterations in several key metabolic pathways associated with stress response mechanisms, energy metabolism, and cellular signalling in U. lactuca. These findings suggest that BP-3 does not pose an acute risk to mature U. lactuca or a chronic risk to H. banksii at concentrations typically observed in the marine environment, as in both cases effect concentrations exceeded BP-3 concentrations typically observed in marine environmental water samples. However, further research is needed to assess potential risks associated with chronic exposure to environmentally relevant concentrations. These toxicity data contribute valuable information for future risk assessments of BP-3 and aid in setting water quality guidelines for this widely used organic UV filter.