Citation problems, in supporting general information, what kind of paper should I cite? A country implements the most stringent environmental regulations in a
  region.


For a general statement/common knowledge like this, I cited a peer-reviewed journal paper, which has a similar claim in their introduction. However, the problem is neither this claim is the main findings of the journal paper, nor the paper provides any secondary citation. So it is a general claim made by the authors. 

Can I cite the paper? or must I cite all the related environmental standards of all the countries from the region? I really think it is unnecessary, however, there is no such review in this region and in this subject.
If you want to use a fact, either prove it yourself or cite a reliable source. If that paper does not provide a source for that fact then it’s not good enough in my opinion, but standards across fields vary.