We're part of nature and so everything we do is occurring there. Is the real distinction things that wouldn't exist without human intervention? So, like Teflon and plumcots wouldn't be natural but water and plutonium are.
Things that aren't naturally occurring would be supernatural, no?
That's the original meaning of "artificial", something that occurs through art or skill. Humans have always distinguished themselves from the rest of nature, it's part of that. It's not a useless distinction, but it breaks down when 'natural' is considered healthy or otherwise good, and 'artificial' unhealthy or otherwise bad, when that's a non-sequitur.
Now we're arguing semantics. "Naturally occuring" in English means not synthetically produced / found naturally in the environment outside of human influences.
Things that aren't naturally occurring would be supernatural, no?