science

Here's one: https://www.publichealthontario.ca/-/media/documents/l/2014/lead-among-shooters.pdf

Lots of relevant links to other studies in the References section. A couple relevant paragraphs from the link PDF:

A health care practitioner notified a local health unit after seeing an asymptomatic 70 year old male patient with a blood lead level (BLL) of 12 μg/dL (0.61 μmol/L1). The patient reported that he shoots twice weekly at an indoor firing range operated by volunteers. Public Health Ontario (PHO) was asked to “review the patient’s BLL and provide advice on the significance of the results relative to expected background levels”. As a result of this advice, a lead exposure assessment of the firing range was initiated by the health unit.

Results from the exposure assessment found that four of the five breathing zone samples performed on shooters [task-based time-weighted average (TWA) lead concentrations ranged from 3–147 μg/m3 over the sampling periods (19–47 minutes)] exceeded Ontario’s occupational exposure limit of 50 μg/m3 (8 hr TWA). This indicated the inadequacy of the existing ventilation system to reduce inhalable airborne lead generated during shooting. Wipe and vacuum samples showed the presence of lead on eight of the nine surfaces tested. Lead dust on surfaces inside a firing range can be easily transferred to hands, which can result in ingestion of lead through hand-to-mouth contact.

A good gun range should have ventilation systems that filter air from the range itself and prevent any lead particles from migrating into the non-range areas (lounge / weapons-maintenance areas, any attached ammo shop, bathrooms, etc.). The highest-risk area is where the targets sit. The amount of lead particulate at the shooting bays will vary depending on the type of ammo (copper jacketed bullets would likely generate less lead particulate, plain lead wadcutter would likely generate more), but any ammo type is going to get smashed into bits when it hits the backstop behind the target. The ventilation system needs to pull air at the targets, and pull it away from people. I'm sure many ranges have less-than-adequate ventilation systems. Shooters should still wash their face and everything south of their elbows really well after using the range, even if the range has great ventilation, because the amount of lead exposure in recreational shooting will always be non-zero.

There is non-lead ammunition, particularly bismuth. Similar density to lead but non-toxic. (Edit: also tungsten ammo, but I believe tungsten has similar toxicity issues to lead). Lead ammunition has been outright banned for waterfowl hunting in some areas, because lead pellets would inevitably wide up in the environment and leach into the wetlands. Lead is still the overall most common ammo type, because it's the cheapest material for the purpose.