You test it with animals.
It's inorganic, has simple structure and contains only non-toxic compounds, so there is no reason to be worried.
If you want to worry, direct your attention towards Vantablack and other carbon nanotubes. It has specific target organ toxicity from single exposure and while it does not appear to be carcinogenic it needs more testing.
yttrium and indium are both suspected to be toxic, manganese can certainly be toxic. no idea about the relative doses, I suspect that the chemists certainly thought about this etc, so I'm not trying to say YInMn is toxic, but "inorganic, has simple structure" doesn't mean anything, as it also describes Cobalt Blue, which is definitely toxic.
> It's inorganic, has simple structure and contains only non-toxic compounds, so there is no reason to be worried.
So is asbestos...
I knew that someone would reply with asbestos when I wrote that. "simple structure" is there to exclude asbestos.
Asbestos is dangerous because it's a tiny spike that sticks into cell. Just like nanotube of similar length.
I'm calling a big old [citation needed] on a compound that's only existed for a decade. It might not be acutely toxic, but recently we seem to be finding all sorts of subtle effects from compounds that've been in common use for decades.
How does one establish non-toxicity?