Chlorofluorooctane sulfanate (ClFOS or Cl-PFOS) : metabolites or by-product during the production of perfluorooctane sulfanate?

Researchers from the National Research Centre for Environmental Toxicology of Australia used liquid chromatography quadrupole time-of-flight tandem mass spectrometry found some novel fluorinated surfactants in firefighters. The study was published this week at Environmental Science and Technology.

One of the novel chemicals is chlorofluorooctane sulfanate (ClFOS or Cl-PFOS), or one F atom in PFOS get replaced with Cl.

One hypothesis for the origin of Cl-PFOS is due to metabolism of PFOS-related compounds in human body.

On the other hand,  I think it is plausible that the novel chlorofluorooctane sulfanate is a by-product during the production of PFOS.  Check the analysis of chemical reactions during the production of PFOS: