Sunscreen ingredients may not be as harmful to freshwater organisms as previously thought due to their adaptive abilities, according to a recent study at the University of Alberta.
Researchers exposed a species of water flea called Daphnia magna to common chemicals found in sunscreen that block ultraviolet (UV) light. Although the first generations of water fleas died off quickly, the organisms largely adapted to the presence of the chemicals after three months.
“People are concerned that when they go swimming, a lot of the sunscreen that’s on their skin is going to leech off into the water that they’re swimming in. That’s where a lot of the environmental contamination comes from,” Aaron Boyd said, the study’s lead author and a PhD candidate in the department of biological sciences.
The purpose of the research was to determine whether common sunscreen chemicals responsible for blocking harmful UV rays, called UV filters, are toxic to aquatic invertebrate organisms. A previous study, supervised by assistant professor Tamzin Blewett from the department of biological sciences, had shown that some popular UV filters were very toxic to a species of water flea over two weeks of exposure.
In the follow-up study, the researchers wanted to see the long-term effects, so they monitored how the water fleas adapted over five generations. According to Boyd, the water fleas were exposed continuously for almost 100 days.
“For this particular study we wanted to go beyond what we would consider to be standardized lab testing … there’s a big difference between what happens in the environment and those very standardized test conditions.”
According to Boyd, the first two generations showed high death rates, indicating toxicity. However, by the fifth generation, there was little evidence of toxicity, even though the water was equally contaminated with UV filters the entire time. This meant that the water fleas adapted to the chemicals.
The researchers speculated that the fleas may have been more resistant to the chemicals in later generations due to exposure before birth, triggering a process phenotypic plasticity that turns certain genes off or on.
Whatever the mechanism, if Daphnia magna can adapt after a few generations, Boyd thinks other aquatic organisms can likely adapt too. His team’s findings suggest that the results from short-term studies may not accurately reflect what happens in the natural environment.
“One thing that society is excellent at is pumping chemicals into the environment faster than we can test them. There are a lot of different things we need to be working on, but we have very limited resources,” Boyd said. “These chemicals should be monitored as a potential future concern, but currently they’re not something that I think should be our primary focus.”
The study only looked at three UV filters — oxybenzone, avobenzone, and octocrylene — but Boyd noted that there are dozens of different chemicals and many types of UV filters. His team hopes to investigate some of the other chemicals they haven’t tested yet, including solvents and fragrances frequently found in sunscreen.
As for this summer, Boyd urges people to keep wearing sunscreen to protect themselves when they go outside.
“I don’t think that people need to be particularly concerned this summer when they’re going swimming, and it’s more important to be wearing sunscreen to protect yourself from skin cancer,” Boyd said. “That is much more severe than any harm that they would be causing to the environment directly.”