Many species are exposed to many stresses
Studies to date have provided compelling laboratory evidence that some UV filters can have toxic effects on aquatic species, including corals, anemones and zebrafish, that are exposed to the chemicals. These findings have raised concerns about sunscreens’ larger-scale impacts on biological communities and ecosystems.
But outcomes in the environment will differ depending on what compounds, ecosystems and local environmental conditions are involved. That’s especially true for coral reefs. The committee highlighted reefs because they are ecologically, economically and culturally valuable, and attract large numbers of tourists who use sunscreens.
Coral reefs are declining worldwide due to multiple human-induced disturbances. Some of these disturbances are global, such as ocean warming and acidification driven by climate change. Other stressors, such as coastal water quality, are more local.
Studying the effects of chemicals on corals and coral reefs is challenging because they are both complex systems. Reef-building corals are a combination of an animal, single-celled algae and rich populations of bacteria living and working together. Coral reefs are made up of thousands of interacting organisms.
Importantly, many stress responses in corals occur without causing outright death, but impair their health, growth, resilience and even ability to reproduce. Scientists need to know more about these responses to guide effective management responses and interventions.
After in-depth reviews of the existing data, our study committee recommended that the U.S. Environmental Protection Agency should undertake an ecological risk assessment of the 17 UV filters used in sunscreens sold in the U.S. Such a study would include a comparison of toxicity findings to relevant concentrations and exposure conditions.
For example, what happens to organisms exposed to these chemicals occasionally versus those exposed regularly, in calm bays or along open, wave-swept coasts? How do UV filters differ in whether they break down in water, or accumulate in sediments or the tissues of living organisms?
In our view, an ecological risk assessment would provide EPA and others the basis for sound and effective policy development. The sooner this happens and the results are applied to the regulatory process, the better for everyone who is affected, including future generations.
The challenge of understanding long-term effects on humans and the environment
The question of whether UV filters pose harm to the environment while helping to reduce skin damage and prevent skin cancer is a conundrum. It seemingly pits human and environmental health against each other head-to-head and asks policymakers, medical experts and the public to choose between them.
Humans need sunlight to live, but overexposure to the sun’s damaging rays – ultraviolet radiation – causes sunburn and wrinkles and is a risk factor for the development of skin cancers, including the most deadly type, melanoma. Routine use of broad-spectrum sunscreen with SPF 30+ when outdoors has been found to prevent skin damage and skin cancer. But sunscreens are most effective as part of a set of behaviors that also includes wearing hats and cover-up clothing and seeking shade.
Most people in the U.S. don’t practice these behaviors frequently or thoroughly enough. So it’s important to weigh very carefully the potential effects of restricting the choice of available sunscreens.
Some jurisdictions already restrict the sale of certain sunscreens because concerned advocates believe doing so will be good for the environment. In the U.S., they include Hawaii, the U.S Virgin Islands and the city of Key West, Florida. Our report doesn’t draw a definitive conclusion about whether these measures are scientifically justified or effective. Rather, it emphasizes analyzing whether and how they may affect human health as well as the
The study draws attention to the challenge of understanding risks from UV filters to aquatic environments under various conditions, and in the context of overarching environmental stressors such as rising sea temperatures. It’s important to understand that for both environmental and human health issues, laboratory studies don’t always match what happens in the environment.
Studies of model systems such as bacteria and yeast, and organisms such as fish embryos and insect larvae, can yield findings that do not hold up in studies of humans. For both the environment and humans, it may not be possible or ethical to conduct true experiments that test the long-term effects of chemicals in UV filters.
Members of our committee wrestled to interpret the available evidence, and also with the gaps in that evidence. Ultimately we concluded that the science is not settled, but that there is much to build on to advance understanding of this issue. Our conclusions are not a win/lose outcome for either the environment or humans. Rather, they point to a need to think both broadly and strategically for the benefit of people and the planet.