My bf is a born and raised Floridian and gun owner. But thinks my Kimber 10mm auto pisses off the environment. Is he trolling me or is this real?

I dont know if he’s born and raised Floridian redneck (he is) or just trolling me but I’ve been carrying my kimber 10mm auto outside of work or in the car and he thinks it’s making the environment worse bc of the lead. He wants me to carry a glock or get a 9mm handgun with copper bullets so he can feel better about the environment. I wasn’t aware that lead pisses off the environment and at this point I just want to know if this is real or if bf is trolling me. He’s been a gun owner 100x longer than me and I know he’s conservative republican so it’s weird to hear this. I always thought it was the calibers that made a difference in the environment. Not the rounds or bullet type.