As ammunition is currently loaded, the places where possible contaminants occur are in the projectile (lead) and as a result of combustion of the primer and powder.  Outdoors, in any kind of breeze, the toxic effects of gun gas (combusted powder and primer) are quickly dissipated and are not harmful.  The only problem area for the gun gas is on indoor ranges.  Gun gas accumulation is hazardous -- it can be flammable and toxic in high concentrations and is certainly not pleasant to breathe -- so that's why indoor ranges have positive air pressure ventilating systems.  The positive air pressure moves the gun gas and lead particulate outside.

 

Back in my Navy days, I had a good chance to get a real dose of the stuff when we fired the 5"/38 guns on the destroyers.  The 5"/38 (single or twin) was a very popular and efficient gun used by the Navy from the 1930's to the  1980's.  It shot a 55 or 70 pound projectile, using a 38 pound, cased powder charge, to a maximum range of 13 miles.  The gun was semi-automatic and required a well-trained crew to get the maximum rate of fire which was about 25 rounds per minute per barrel.  Now, the Navy is well aware of the flammability and toxicity of gun gas.  The 5"/38 was equipped with a high pressure air system that blew into the chamber to blow gun gas out the muzzle each time the breech block came down as a result of firing.  Nonetheless, there was a lot of gas still in the fired case that got into the gun house after each shot that was not blown-out by the gas ejection system.  When we were shooting AA practice on towed target sleeves, we'd leave both side doors open for ventilation and I'd be standing in the open hatch at the back of the gun house as a safety observer.  The hot case man's job was to grab the fired case and throw it out the case ejection holes at the back of the gun house (if the ejected case did not exit by itself).  After firing as fast as we could load the tray, the gun gas was so thick inside the interior that all you could see was the oval hatch opening as a white, hazy hole!  Talk about fouled air!  This was not under wartime conditions.  Under wartime conditions, the gun house entry doors are supposed to be closed and dogged tight.