Revit Material Definition

I've received files exported from Revit to DWG - to be included in a Microstation model.

They all have long lists of RevitMaterialDefinitions as shown below. As far as I can tell, they're neither attached nor assigned to any geometry in the files, so I'd like to remove them.

If I select them all and hit delete, Microstation crashes.

It takes several minutes to delete each one at a time (there are hundreds).

Does anyone know how to remove them all at once?

I've tried going back and forth between DGN and DWG, with no luck.

Thanks,

Max

Connect - 10.12.00.40

v8i - 08.11.09.829