PFAS-water-index

PFAS in water: origin, risks, standards, and treatment

PFAS are a vast family of per- and polyfluoroalkyl substances used for several decades for their non-stick, waterproofing, and grease- and heat-resistant properties. Their extremely high persistence and mobility have led to widespread contamination of surface water, groundwater, and certain drinking water resources. Regulations are evolving rapidly, with European standards applicable since January 2026 and very low limits for certain PFAS in the United States.

Family: Organofluorine substances
Major property: Very high persistence
EU Sum: 100 ng/L
Total PFAS EU: 500 ng/L

What are PFAS in water?

PFAS, or per- and polyfluoroalkyl substances, constitute a vast family of synthetic organofluorine compounds. They are characterized by the presence of carbon-fluorine bonds that are particularly stable, which explains their persistence in the environment.

This family includes several thousand substances with very different properties. The most studied include PFOA, PFOS, PFHxS, PFNA, PFBS, and HFPO-DA, often called GenX.

PFAS have been used in many industrial and consumer products for their non-stick, waterproofing, stain-resistant, heat-resistant, grease-resistant, and chemical-resistant properties.

Keep in mind: PFAS do not refer to a single contaminant, but a very large family. Their mobility, persistence, toxicity, and elimination vary greatly depending on the chain length and chemical structure.

Why are PFAS so persistent?

The carbon-fluorine bond is one of the strongest in organic chemistry. It resists many natural thermal, chemical, and biological degradation processes.

Property	Environmental consequence
Very stable C–F bonds	Slow or very limited natural degradation.
Polar head and fluorinated chain	Surfactant behavior and complex interactions with water and surfaces.
Variable solubility	Different mobility depending on structure and chain length.
Low volatility of many ionic PFAS	Persistence in water and soil.
Transformable precursors	Gradual formation of persistent terminal PFAS.

How can PFAS be classified?

PFAS can be classified according to their structure, functional group, and the length of their carbon chain.

Perfluorinated carboxylic acids

This family includes PFOA, PFNA, PFHxA, and PFBA.

Perfluorinated sulfonic acids

This includes PFOS, PFHxS, PFBS, and PFDS.

Fluorinated ethers

Some recent substitutes, such as HFPO-DA, belong to this category.

Precursors

Compounds such as certain fluorotelomer alcohols can transform in the environment into persistent perfluorinated acids.

Fluorinated polymers

They have different properties than non-polymeric PFAS, but their manufacturing, additives, and degradation can be associated with PFAS emissions.

Which main PFAS are monitored in water?

Abbreviation	Name	General characteristic
PFOA	Perfluorooctanoic acid	Historical, persistent, and widely studied PFAS.
PFOS	Perfluorooctanesulfonic acid	Former component of firefighting foams and surface treatments.
PFHxS	Perfluorohexanesulfonic acid	Very persistent and bioaccumulative.
PFNA	Perfluorononanoic acid	Long-chain carboxylic acid.
PFBS	Perfluorobutanesulfonic acid	Shorter chain, generally more mobile in water.
HFPO-DA	Hexafluoropropylene oxide dimer acid	GenX-type substitute.
PFHxA	Perfluorohexanoic acid	Short-chain PFAS, mobile and difficult to adsorb.
PFBA	Perfluorobutanoic acid	Very mobile, less well retained by certain carbons.

Long-chain and short-chain PFAS

Chain length strongly influences mobility, bioaccumulation, and treatment effectiveness.

Category	General behavior	Consequence for treatment
Long-chain	Stronger adsorption on organic matter and proteins.	Often better retained by activated carbon and resins.
Short-chain	More mobile in water and less adsorbed on surfaces.	More difficult to remove by conventional adsorption.
Precursors	Can transform into terminal PFAS.	Targeted analysis may underestimate total load.