You would think something so small to pass through on-board filters would just burn int he can instead of lodging and disturbing the peace inside the FCUs. Must be some pretty tenacious stuff, surely there is other material that can be used as a filtering medium?
The stuff is all sizes and only partially dissolved depending on pressure, temp etc.. A very small amount may get through the last chance filter and afterwards morph into a minute egg with a hard enough shell to jam a valve.
FADECs are not prepared for sticky valves.
It's certainly not everyday stuff.