Lead Styphnate residue is the source of water and readily acid-soluble lead compounds in firing residue. That's why the DDNP-based NT (non-toxic) primers were developed for indoor range ammo. We had a member on this board with a friend who tested for lead contamination professionally and who went over all his reloading and casting benches. He found nothing anywhere, not even on the casting bench that alarmed his testing lab with one exception: it registered toxic all over the floor where he separated his dry tumbling media from cases after cleaning. That was mainly primer residue dust.
I don't know that the main risk at an indoor range is how much primer residue you breath in. A well-ventilated range should prevent that pretty well. Rather, I suspect it is the lead dust that is everywhere in an indoor range and especially on the floor out in front of the firing points that could maybe clog the filters they have to put in those ventilators to avoid turning the place where the system exhausts into an EPA cleanup site.
That dust is mostly gas cut lead blown off bullet base edges as either a cast or swaged bullet clears the muzzle, uncorking high velocity gas venting. That dust would also be contaminated by the primer residue, so I wouldn't be surprised if it registered as bad news in a contamination test. And, even though metallic lead itself is not normally very toxic (you could swallow a cast bullet and pass it without your blood lead levels jumping through the roof), lead that is very fine dust has a very high surface area so that even the limited reactivity lead has with stomach acid could scrounge a blood level jump if you got enough of it regularly. At to it that there are lead styphnate combustion products mixed in with it and that it will get on things that people touch before handling food can make it a concern.
I made a front sight extension for my Ruger bull-barrel .22 target pistol decades ago. When I was still active in bull's eye competition, at least once or twice a year, when the mound of lead from that gas cut dust impacting it on its underside built up into an unsightly enough (pun intended) mound that I would spend some time shaving it off with a pocket knife. It stuck well.
Meanwhile, at the indoor range, I've participated in enough post-match clean-ups with a push broom to know the lead dust, contaminated by the styphnate residue is all over the place and blackens the soles of your shoes and anything that touches it and sticks pretty well. You don't want to track it through a house where children live. So maybe range employee safety is another consideration.