My best guess is that the GP is referring to the concentration of PFOAs in the test setup. It is possible that a technology that is good at reducing higher concentrations of PFOAs is not good at further reducing PFOAs concentration at lower concentrations.
However, from the link to the paper in another comment (note that this is from the introduction; I don't have permission to view the full paper):
> After finding the best operating condition, the effects of solution parameters such as initial pH, DO, temperature, PFOA concentration, and electrolyte concentration in broad ranges were determined. PFOA concentration and sulfate dosage were chosen to be representative of different aqueous environments (e.g., natural waters and brine solutions).
So I'm not sure where GP gets that this 200 PPB number is the case for all of the tests.
However, from the link to the paper in another comment (note that this is from the introduction; I don't have permission to view the full paper):
> After finding the best operating condition, the effects of solution parameters such as initial pH, DO, temperature, PFOA concentration, and electrolyte concentration in broad ranges were determined. PFOA concentration and sulfate dosage were chosen to be representative of different aqueous environments (e.g., natural waters and brine solutions).
So I'm not sure where GP gets that this 200 PPB number is the case for all of the tests.