Obviously you should use food rated argon if you want to be safe. It's just going to be more expensive and harder to source.

My sense is that I'd be better off avoiding all plastics (not feasible in this world) than waiting for food-grade argon. But yes, this is a decision each person should make.

Ah yes, the common problem all of us face in our daily lives.

“If you want to be safe” doesn’t really jive with “extremely limited risk.”

Of course it does. To put it bluntly, it is extremely likely that any bottle of industrial argon is actually food safe because it's produced in basically the same condition that food safe argon. The main impurity while producing argon is oxygen. The main difference between industrial and food safe argon will be how their container is handled but argon as an environment is not really suited to bacterial development.

If you don't feel okay taking this risk, you can buy food grade argon which, well, is guaranteed to be food safe.

Also, don't get me wrong, I'm specifically talking about argon there. I would never use industrial distilled water or ethanol with food for example. That would be risky. I have heard of people using industrial CO2 to carbonate beverage. That makes me uneasy because CO2 is a good solvent.