Toxicity assessment of organic UV filters Benzophenone-3 (BP-3) and Enzacamene (4-MBC) using the freshwater planarian Girardia tigrina

UV filters are contaminants of emerging concern, acting as endocrine disruptors, and altering the normal development of living organisms. Due to their lipophilic properties, they accumulate in aquatic sediments, endangering epibenthic organisms such as planarians. We aimed to assess the sensitivity of Girardia tigrina to two organic UV filters, 2-hydroxy-4-methoxybenzophenone (BP-3, Benzophenone-3) and 4-methylbenzylidene camphor (4-MBC, Enzacamene), by evaluating mortality, behavioural activity, cephalic regeneration after decapitation, and biochemical endpoints. A 96-hour LC_{50 s} of 1483 µg/L and 1653 µg/L were estimated for BP-3 and 4-MBC, respectively. Sublethal concentrations of both compounds impaired planarian cephalic regeneration; BP-3 induced a delay in auricles regeneration, while 4-MBC delayed both photoreceptors and auricles regeneration. Locomotion significantly decreased in planarians exposed to 4-MBC, while BP-3 exposure did not induce locomotion alterations in G. tigrina. Moreover, induced phase II detoxifying enzyme (measured through Glutathione-S-transferase activity) was also observed in 4-MBC exposure, possibly mitigating oxidative damage, while BP-3 exposure caused oxidative damage (increased lipid peroxidation levels). Exposure to both compounds led to a reduction in acetylcholinesterase activity, showing evidence of neurotoxicity. Even though this study reported deleterious effects in exposed G. tigrina, the concentrations at which effects were reported are still higher than those usually reported in the freshwater environment. However, we would like to emphasise the importance of such studies in supporting the regulation and environmentally safe use of sunscreen products.