[Inkscape-user] Removing unused gradients

I'm drawing a set of icons, all on the same canvas but on different layers, with most layers off at any given time. Now, I don't remember which gradients are used by a single icon, and which I used for more than one, etc. So what I did was just to be sure I duplicated a lot of gradients so I don't accidentaly change anything in another icon.

And now I have a long long list of similar gradients and I would like to get rid of anything I don't use anynore. Any way to do this?

Michael