This subject has come up many times before. Those beach-cleaners don't pick up small ring & coin sized object. The rake-mechanisms only pick up bottles, cans, McDonalds bags, etc....
*HOWEVER*, there are different varying brands/models of beach cleaners. And one of them *IS* capable of picking up items as small a coins & rings . It has some sort of sieve/ screen system of sorting. And it's adjustable on the hole/screen sizes, such that the operator can set it to smaller versus larger.
And the smaller , more scrutinous you set the controls for, the slower it will go, and the more "drag" you put on the engines to drive it, etc.... And ..... no doubt, would end up picking up seashells, pebbles, and other stuff that is NOT trash. But I heard a funny story that operators of this particular machine, on a certain beach, would PURPOSEFULLY set it to that level, and PURPOSEFULLY work overtime off-the-clock on their own time.
Fortunately .... that particular brand of machine is not widely sold or used anywhere. And none of the beach cleaner machines work on the wet sand anyhow.
So the bottom line is: None of the beaches where you see those machines used, are any threat to us.