LOL KG, I'll bet this is going to come up again and again as it already has...<sigh>
NEWSFLASH if nickel causes cancer so dies TITANIUM keep reading...
Based on what the EPA says, nickel carbonyl and nickel refinery dust (includes subsulfides) are carcinogens, not nickel itself.
Nickle Compounds | Technology Transfer Network Air Toxics Web site | US EPA
How nickel carbonyl is formed:
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Composition of nickel refinery dust:
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The EPA says "Nickel occurs naturally in the environment at low levels. Nickel is an essential element in some animal species, and it has been suggested it may be essential for human nutrition."
The EPA recommends that drinking water levels for nickel should not be more than 0.1 mg per liter (nickel itself is insoluble so must be a compound). The OSHA has set an enforceable limit of 1.0 mg nickel/m3 for metallic nickel and nickel compounds in workroom air to protect workers during an 8-hour shift over a 40-hour work week.
ATSDR - Toxicological Profile: Nickel
So based on the above if we include compounds then might as well say Titanium is a carcinogen as well:
CCOHS: What's New Archive
And lets not forget nickel allergy, guess what so is titanium:
Titanium | MELISA Medica Foundation
So until I see mass spec data of vapor from my Ni200 atty, I believe I am far closer to inhaling TiO2 than nickel refinery dust or nickel carbonyl. Use detergents with whiteners? Use paper? Breathe in a room with white walls? Yep, yep and yep. And I'm not worried about that either.
Sleep tight
Out of all the affordable and reasonably nonreactive at lower temperatures metals, Nickel is an excellent choice.