Here is a story that caught my interest about the ingredients in sunscreens harming ocean life. It turns out that the active ingredients in mineral sunblocks, Titanium Dioxide (TiO2) and Zinc Oxide (ZnO), undergo a chemical reaction that produces hydrogen peroxide.
The way it works is that when a photon hits the molecule it is converted to heat and a free electron. The free electron reacts with Oxygen to produce an oxygen radical which reacts with free hydrogen which then combines with another to form hydrogen peroxide.
Anyway, this increased level of hydrogen peroxide in the ocean water can kill off some of the marine phytoplankton. This is a significant food source for larger sea creatures so when phytoplankton is reduced it has devastating effects on other animals.
This just makes me think of the advice that is given by organizations like the Environmental Working Group (EWG). They do an annual recommendation for sunscreens and always choose TiO2 and ZnO based products as the “safest” choice for consumers. There is no good evidence that organic sunscreen ingredients like Oxybenzone or Octinoxate are dangerous for people but that doesn’t stop the EWG from suggesting they are.
As this story about the effect of TiO2 on aquatic life demonstrates, there may be unintended consequences to what you think is good advice. If you care about the environment it is probably better for you to use sunscreens based on different UV filters that don’t include mineral sunscreens.