out of the ground. There were oil slicks on the creek near my home. They were all natural seeps. The Chumash Indians in the area used the tar like oil that seeped out of the ground to waterproof baskets and other objects.
Of course, we've managed to go get lots of oil and use it in lots of ways, thereby polluting much more area. We're good at that. Lots of metals are poisonous to living things. Copper, lead, antimony, and many others. They occur in nature. We've exploited those deposits for our technology, some of which I am using to write this post on DU.
Technology can move poisons from one place to another and create some real problems. However, the lead used in bullets, shotgun shot, and fishing sinkers is one of the less problematic metals, since the lead is in its metallic form. It's still an issue, but there is more lead in all those cars driving around spewing other pollutants than in all the bullets you can imagine. From the car's battery to the weights used to balance your tires and the solder used in its wiring, it's a much more dangerous source of lead. Water soluble compounds of lead are formed inside your car's battery. That's why there are battery recycling programs out there. It used to be that they were just dumped in landfills, where that lead compound leached out.
There are many reasons to restrict firearms ownership. Lead pollution is not one of them. It's a very tiny part of the lead put into the environment by technology. Up until recent years, just about all the paint used on everything had lead in it. Why? Because lead oxide is a great white pigment, one that has never been equaled. Lead makes great bullets and fishing sinkers, too. It's cheap and heavy, the two primary requirements.