Phototoxicity of Sunscreens to Sea Anemones and Corals [electronic resource]

다국어 초록 (Multilingual Abstract)

Most coral reefs, an invaluable ecological resource, are endangered from human activity. Although much of the threat is from global factors driven by rising atmospheric carbon dioxide concentrations, local factors can exacerbate them. One such factor, sunscreen use, may be of particular concern, as some estimates suggest that up to 6000 tons of sunscreens are released into reef environments every year, where they can bioaccumulate in coral tissue and may cause toxicity, including death, according to lab studies. One study observed concentrations of oxybenzone sunscreen as high as 1.4 mg/L at a reef in the US Virgin Islands and death at 10-fold lower concentrations to coral larvae in the lab. Exacerbation of coral declines by sunscreens emitted by tourists would be particularly ironic considering the importance of ecotourism for promoting coral reef conservation. These findings prompted quick legislative action on several sunscreen ingredients including oxybenzone in jurisdictions with reefs, such as Hawaii, the US Virgin Islands and Palau. The bans are considered controversial, however, as the sunscreen toxicity mechanisms are not understood and there may not be sufficient evidence either that the banned ingredients are toxic to reefs or that their alternatives are safer.The studies in this dissertation demonstrate that phototoxicity from sunscreens or their metabolites is a dominant toxicity pathway in sea anemones, a model organism for corals. The first study finds that oxybenzone, although a sunscreen in vitro, is metabolized into phototoxic glucoside conjugates both in the anemones and in a mushroom coral. This suggests that sunscreen developers may need to avoid similar structures to design reef-safe products. The second study shows that 3 other typically non-banned sunscreen ingredients (avobenzone, dioxybenzone, and homosalate) are also phototoxic to anemones, whereas two commonly banned ingredients (octinoxate and octocrylene) are not. This suggests that by not considering phototoxicity, regulators may not be targeting the right sunscreen ingredients for protecting reefs. Both studies find that the sunscreens are significantly more toxic to anemones without their algal symbionts, as the algae provide partial protection to the animals by sequestering the photoxins. This suggests that "bleached" corals that have expelled their algae in response to global stressors would be particularly vulnerable to phototoxicity from sunscreens. Taken together, these results suggest that phototoxicity of both the sunscreen ingredient and its metabolic products needs to be considered in research, regulation, and design of sunscreens safer for coral reefs.