In the last decade, beach cleanups have grown into a global phenomenon, with volunteers gathering at regular intervals for the Sisyphean task of cleaning up plastic trash. Now, new research on a remote Australian island chain suggests that beach cleanups can inadvertently mask the full scale of plastic pollution, much of which lies below the sand’s surface.

The look at isolated islands also provides a disturbing glimpse of what beaches in populated places might look like if they were never cleaned up and plastic simply accumulated year upon year, breaking down ultimately into smaller and smaller pieces: microplastics.

What that trash collection can’t retrieve, however, are the microplastics in the sand beneath the surface. No one is sure how