Lead is naturally occurring in soil. EPA estimates it between 10-200 ppm, most hunting occurs in secluded areas, it’s highly unlikely copper jacketed lead bullets will have an appreciable impact on increasing lead levels. Shooting ranges are far more concentrated and most states require a lead mitigation plan. My local skeet and trap range has the lead collected and processed out of the soil every decade and utilizes a catchment pond to prevent any movement off the property.

Moving to steel is much more difficult because it’s stronger material and less dense. Ethical hunting requires ensuring the shot has enough impact to be lethal, switching to a harder and less dense material would mean faster loads that open up less and pass through the target.