AFAIK, none.
HBN is low toxicity unless inhaled (sub micron particles can get deep in the lungs). Even with a fragmenting bullet scattering through tissue (maximum HBN dispersion) the amount on a bullet is miniscule. Lead itself is a far greater risk - and it is very low.
The version I use is 2.5 Micron - not as small or costly as some (0.5 micron) - but excellent results as noted by others in this thread. Search Amzn for "Microlubrol 4oz 2.5 micron" HBN. Curren cost $45.
Clean barrels to bare metal, swab with 99% isopropyl / HBN slurry, dry overnight & push a cple clean patches to remove loose material. Vibratory tumble bullets 30 min to an hour in a dedicated clean medium to large pill bottle with a quarter to half Tsp powder, no BB's or SS balls, just the bullets. TAPE THE LID SHUT. Painter's tape is fine.
Pour 'em onto a micro fiber cloth, pick up the four corners & roll around. Bullets will have a slightly frosted or cloudy appearance - not solid white - & are noticably slippery when trying to pick one up.
Note that most aoutomotive oil filters are rated as 5.0 micron, meaning they allow smaller particles through. I think 0.5 micron products are marketing & a way to maximize profits. You do you.
The 2.5 micron HBN wafts out of the container as a superfine powder with the slighest disturbance so I wear a USA-made (Armbrust) KN-95 when working with it.
At this point I intend to continue using it on every jacketed or mono rifle bullet I load. Handguns I shoot mostly polycoated lead & haven't gotten a round tuit for HBN.
HTH.