I can’t see anyone adding it, but who knows? (Not me!) As for natural sources, I’d rather have a little arsenic in my well than, say, lead. That’ll make ya crazy!
You have just given me a perfect answer to my brand of crazy....I can blame it on lead...now I just need to find the company that makes it so I can sue them...oh wait, that would be mother nature, :O( cannot sue her, she can be a bitch at times, tornados, hurricanes, snow storms...etc. Best to leave her alone.....:O)