I am a total layman when it comes to this, but I would have a very very hard time believing that lead rifle rounds have any measurable affect on the environment. Whitetail hunters can go years without firing a shot. I hunted 13 years before I shot my first deer. I got two this year, and on the second the round didn't pass through the animal. So in my 13 total years of deer hunting I have put exactly 165 grains of bullet into the environment, a fraction of that being lead and the remainder being the copper jacket.

Also, waterfowl hunting puts a lot of shot into the water where it can contaminate the drinking supply, and animals that feed from the bottom can ingest them. A round fired at a deer will be lodged in the dirt, frequently in some wooded area where it will never harm anything.