Difference Between PFAS and PFOS

The key difference between PFAS and PFOS is that PFAS refers to a group of compounds having multiple fluorine atoms attached to an alkyl chain, whereas PFOS refers to a member of the PFAS group having a carbon chain containing 8 carbon atoms.

PFAS is a large group of man-made compounds including PFOS, PFOA, GenX, etc. The term PFAS stands for per- and poly-fluoroalkyl substances while the term PFOS stands for perfluorooctanesulfonic acid.

1. Overview and Key Difference
2. What is PFAS
3. What is PFOS
4. Side by Side Comparison – PFAS vs PFOS in Tabular Form
5. Summary

What is PFAS?

PFAS is per- and poly-fluoroalkyl substances that include man-made organofluorine substances. These chemical compounds have multiple fluorine atoms attached to an alkyl chain. The perfluoroalkyl moiety of these compounds is given as –C_nF_2n-. We can find more than 4000 members in this chemical group.

It also has a sub-group known as fluorosurfactants. These compounds contain a fluorinated tail and a hydrophilic head. This tail and head structure is the reason for naming them as surfactants. These surfactant molecules are very effective in reducing the surface tension of water than hydrocarbon surfactant molecules. Generally, a fluorosurfactant can reduce the surface tension to a value that is about half of what can be obtained using hydrocarbon surfactants.

Fluorocarbons are typically lipophilic. Therefore, these structures tend to concentrate at the liquid-air interface. Moreover, these molecules do not undergo London forces, which is a factor that is responsible for the lipophilicity of molecules. Due to the high electronegativity of the fluorine atoms, the polarizability of the surfactant surface is reduced.

Besides, PFAS has a major economic role regarding the polymer industry where companies such as DuPont, 3M, etc. has the most of its applications. These PFASs are used in polymer production based on emulsion polymerization.

What is PFOS?

PFOS is perfluorooctanesulfonic acid. It is a member of the PFAS group of chemical compounds. PFOS is considered as an anthropogenic fluorosurfactant as well as a global pollutant. We can produce this material via industrial synthesis, or it forms as a byproduct from the degradation of polymer materials. There are two major pathways for the production of this compound in industrial-scale: electrophilic fluorination and telomerization.

Figure 01: Structure of PFOS

The chemical formula of PFOS is C₈F₁₇O₃S. It is a hydrophobic and lipophobic compound similar to other fluorocarbon compounds. Further, its sulfonate group adds polarity to this molecule. We can observe that these compounds are exceptionally stable in industrial applications and also in the environment where it acts as a pollutant. Apart from that, PFOS can lower the surface tension of water when compared to hydrocarbon surfactants.

What is the Difference Between PFAS and PFOS?

The term PFAS stands for per- and poly-fluoroalkyl substances while the term PFOS stands for perfluorooctanesulfonic acid. The key difference between PFAS and PFOS is that PFAS refers to a group of compounds having multiple fluorine atoms attached to an alkyl chain whereas PFOS refers to a member of the PFAS group having a carbon chain containing 8 carbon atoms.

Moreover, the stability of PFAS varies depending on the chemical structure while PFOS is exceptionally stable. So, this is also a significant difference between PFAS and PFOS.

Below is a summary tabulation of the difference between PFAS and PFOS.

Summary – PFAS vs PFOS

Reference:

1. “Per- and Polyfluoroalkyl Substances.” Wikipedia, Wikimedia Foundation, 17 May 2020, Available here.
2. “Perfluorooctanesulfonic Acid.” Wikipedia, Wikimedia Foundation, 10 June 2020, Available here.