wall support

Hello, I was replacing the existing drywall in my dining room and when I took the old drywall off i noticed that an interior wall (between the dinning room and the kitchen) had all 2x4 studs set 16 on center but then there was a 4x4 in the wall as well. I dont know if this 4x4 is pressure treated. I was wondering if it is pressure treated is there any health concerns with leaving it in the wall seeing how there will be drywall on top of it.

any input would be greatly appreciated.
-Srobmo