I shoot bullseye pistol in competition, and between matches and practice I'm often in the range 2 or 3 nights a week. In between, I practice with an air pistol in my basement.
A few years ago, I was diagnosed with elevated lead and started wearing a respirator in the regular indoor range. I didn't wear the respirator in my basement airgun range. After a couple years, my blood lead level came back into, and has since stayed within, the normal range. Based on that experience, I think that you need not be concerned with lead contamination in your indoor airgun range. My understanding is that most of the airborne lead in shooting ranges comes from the lead styphnate priming compound and not the bullets. Obviously, the priming compound is not an issue with airguns.
NRA Benefactor Life Member
NRA Certified Pistol Instructor
Pemigewasset Valley Fish & Game Club