Wood that has water sitting on for an extended period or repeatedly will often turn black. A professional way to take the black out is to use denatured alcohol applied with a piece of 0000 steel wool. (Thanks to Bob Arth, furniture repairer, 763-571-5044, for this tip.) The alcohol will open the pores of the wood so that it can dry out. The steel wool is better than a cloth because it won't absorb the alcohol. 0000 grain is generally too fine to scratch the wood. But certainly test in a small inconspicuous area before doing a whole project.
A client showed me this. It's not super eco-friendly but it works and it's good in a pinch. Use Comet on tile bathroom floors to brighten it up. I think it's the bleach in the Comet that makes it work so well. Of course, test a small area first.
When you think of plastics polluting the ocean and waterways, the image of plastic bottles floating in the water might come to mind. But there is another problem also now being reported by scientists: invisible microfibers, mainly from synthetic clothing, being eaten by plankton and other small creatures and causing harm and disease all the way through the food chain.
As a cleaner I use microfiber cleaning cloths. In fact, this has been a revolution in the cleaning industry since these cloths are so effective at picking up dirt and germs. Having just learned about this problem, however, I will need to reconsider my use of them.