Hi Lina,
I believe this is a repeated question filter a sharepoint list.
Anyway here you have mijn twee centen.
Try adding a tasks web part in your page and add a column "Department" to this tasks web part and enter some value, say 'IT'. Then add a UserContextFilter web part to same page. Configure it so that it sends "Department" user profile value to Tasks web part. At this point, when you try to connect usercontextfilter wp to tasks wp, you won't be able to see "Department" in drop down list. Beacuse this drop down list values are populated based on of tasks web part.