This is a wrong choice. You use this word in sentences like this:
Der Kellner bedient die Gäste.
The waiter serves the guests.
This means: The guests are talking with each others and having fun, while the waiter is working. The waiter is bringing drinks and food to the guests.
If you say:
Als der Abteilungsleiter bediene ich 10 Mitarbeiter.
Then you express this:
I am the boss of the department, and as this boss it is my job to bring my employees drinks and food and to carry away used dishes.
This is probably not exactly what you did mean. (Btw: Your sentence is grammatically absolutely correct, but the meaning is weird.)
für jemanden verantwortlich sein
This means »to be responsible for somebody«
Als Abteilungsleiter bin ich verantwortlich für 10 Mitarbeiter.
This is also grammatically correct, and it has an understandable meaning. In this context it means:
I am the boss of this department, and I have to take care for my employees. Because if some of them is doing something wrong, it will be me who gets blamed for it.
But there is even a better version:
Ich leite eine Abteilung mit zehn Mitarbeitern.
I manage/direct a department with 10 employees.
The wording is different, because you don't manage or direct employees, but you manage a department. And the former used word »Abteilungsleiter« (i.e. »department manager« or »department director«) was split up into its components, of which one is the verb »leiten« (to guide, to manage). So there is no need to use the word »Abteilungsleiter« in this sentence.
Those sentences have the same meaning:
Ich leite eine Abteilung.
Ich bin (ein) Abteilungsleiter.