Unless you use an impervious substance to line the pots, you cannot prevent any contamination that may occur. I'm sure that you realize that anything that is porous just won't, can't do what you wish.

Think about it: if you pour water into a burlap bag, what will happen?

To achieve the results that you're looking for, you need to use something that will create an impervious barrier against liquids and gases (oxygen, etc.).

I doubt the cheap US made pots are any safer that the cheap pots made in China. You don't know what they are made of either. Maybe you can find some organic approved plastic pots somewhere that you are comfortable using. Do some research and let us know what you come up with.