Looks like it's something disintegrating up under the sink...is there anything black up there? Sometimes the underside of sinks is covered in something black (older sinks I've had in my houses). Not sure what it is, but maybe it's getting old and just dropping little bits off? Maybe a black rubber fitting on something?

Is that a pull out shelf? Is something tall that's usually kept on the shelf scraping the bottom of the sink above when it's pulled in and out?

its the bottom of the bathroom cabinet, there is one sink with a drawer on either side. most of the black stuff is under the sink but there is some along the edges inside as well. my fear is roach droppings.

We don’t use this bathroom often at all, this cabinet has only been opened a handful of times in the past couple of months. The spray bottles don’t seem to have anything on top so it seems everything in there is from before I placed the bottles there.

Well, I'd just vacuum it up and see if it reappears. I did notice that the bottles seemed to be dust free. Maybe something the previous owner or tenant had in there that sloughed off some black dust.

If you think it could possibly be roach droppings put a couple of sticky traps down. If there’s any bugs at all you’ll find out.

Oh, jeez, roaches aren't a problem here, so I would never have thought of something like that :-(

I hope it’s not, I’m just really scared of having roaches so anytime I see black specks or something I get worried that’s what it is. Hopefully it is just corrosion from the sink/drawers...