That suggests zinc oxide particles are leading to degradants whose introduction to aquatic ecosystems is environmentally hazardous." "Also, the zinc-oxide-induced photodegradation products caused significant increases in defects to the zebrafish we used to test toxicity. "With either size of particle, zinc oxide degraded the organic mixture and caused a greater than 80% loss in organic filter protection against ultraviolet-A rays, which make up 95% of the UV radiation that reaches the Earth," Santillan said. "Our findings suggest that commercially available small-molecule-based formulas, which were the basis for the formulas we studied, can be combined in different ingredient ratios that minimize photodegradation."īut scientists saw big differences in photostability and phototoxicity when zinc oxide particles were added-either nanoparticles or the larger microparticles. "There have been several studies that showed sunscreens can quickly react under UV exposure-the specifically intended setting for their use-so it's pretty surprising how little toxicity testing has been done on the photodegradation products," Truong said. The scientists also looked at whether the UV radiation had caused any of the mixtures to become toxic to zebrafish, a widely used model organism that goes from egg to swimming in five days, and found that the UV-exposed mixture without zinc oxide did not cause any significant changes in the fish. The researchers then exposed the mixtures to ultraviolet radiation for two hours and used spectroscopy to check their photostability-i.e., what did sunlight do to the compounds in the mixtures and their UV-protective capabilities? They also made additional mixtures with the same ingredients, plus zinc oxide at the lower end of the commercially recommended amount. Scientists including the University of Oregon's James Hutchinson and Aurora Ginzburg and the University of Leeds' Richard Blackburn made five mixtures containing the UV filters-the active ingredients in sunscreens-from different products available in the United States and Europe. "And sunscreens containing inorganic compounds like zinc oxide or titanium dioxide, that block UV rays, are being marketed more and more heavily as safe alternatives to the organic small-molecule compounds that absorb the rays," Tanguay said. For example, oxybenzone has effectively been discontinued because of concerns that it harms coral reefs. What the public thinks about sunscreen safety has caused manufacturers, often based on limited data, to use lots of some ingredients while limiting others, she said. "Sunscreens are important consumer products that help to reduce UV exposures and thus skin cancer, but we do not know if the use of some sunscreen formulations may have unintended toxicity because of interactions between some ingredients and UV light," said Tanguay, an OSU distinguished professor and an international expert in toxicology. The questions: How stable, safe, and effective are sunscreen ingredients in combination rather than as individual compounds-which is how they are considered for Food and Drug Administration approval-and what about the safety of any chemical products that result from reactions caused by exposure to sunlight? The research team, which included College of Agriculture Sciences faculty Robyn Tanguay and Lisa Truong and graduate fellow Claudia Santillan, sought to answer important but largely neglected questions regarding the massive global sunscreen market, predicted by market data firm Statista to be worth more than $24 billion by the end of the decade. The toxicity analysis involved zebrafish, which share a remarkable similarity to humans at the molecular, genetic and cellular levels, meaning many zebrafish studies are immediately relevant to people.įindings were published today in Photochemical & Photobiological Sciences.
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