It should be quite clear to you that on this Earth, at the level of the biosphere, there is nothing except humans that produce radioactive waste. We are the only species that does something so dangerous. It's a problem because it contaminates and destroys the biosphere if it's not handled extremely carefully and there are no organisms which can compost such waste in any useful way. So it's unnatural.

Plastic is another unbelievably horrible man made concoction which is absolutely destroying the natural world due to poor handling.

Since plastic waste and nuclear waste aren't food for other organisms, or don't naturally break down, they're not materials that belong in the natural environment. The is the same environment from which you come from, owe everything too, and which you're still totally and utterly dependent on for your survival.

Hopefully that's a good answer...

By the way, I used to share your beliefs, that it's all the same, it's all "natural", but I just can't keep up the mental charades anymore. Our intellect and creativity is an important part of our short-term survival, but thus far it's been massively destructive and I can't see that changing anytime soon.