https://www.wired.com/story/ocean-plastics-bacteria/

This planet has a problem with plastic. Not just the big masses of it accumulating in the Pacific, but with the tiny bits that are blowing into pristine mountaintop habitats. The flecks showing up in a range of sea creatures. The specks materializing even in human feces.

Now scientists have exposed a potential new consequence of the plastic menace: The toxins the material leaches into seawater inhibit the growth and photosynthetic efficiency of the bacteria Prochlorococcus, which is responsible for producing an estimated 20 percent of the oxygen we breathe. That means Prochlorococcus is also responsible for 20 percent of carbon capture on this planet (one molecule of carbon goes in, one molecule of oxygen goes out), theoretically spelling trouble for humanity’s quest to keep CO2 out of the atmosphere. This is early research, though, and comes with several big caveats. Indeed, it exposes the challenges of studying a threat as new and omnipresent as plastic pollution.