PFAS
A family of several thousand synthetic fluorinated compounds whose carbon–fluorine bonds make them exceptionally persistent. They are mobile in groundwater, resistant to conventional treatment, and now detectable at low concentrations across much of the developed world.
Key facts
- Contaminant group
- Emerging contaminant
- European Union — legal limit
- 100 ng/l for the sum of 20 PFAS; 500 ng/l for total PFASUnder the recast Drinking Water Directive.
- United States — legal limit
- 4 ng/l each for PFOA and PFOSSet in 2024, with additional limits for several other compounds and a hazard index for mixtures. Substantially stricter than the EU sum approach.
- United Kingdom — guideline
- 100 ng/l guideline for the sum of 48 PFASA DWI guideline tiered value triggering investigation and action, rather than a statutory limit.
Where it comes from
- Aqueous film-forming firefighting foam, particularly at airports and military sites — the dominant cause of severe local groundwater contamination
- Fluoropolymer and fluorochemical manufacturing
- Stain and water repellent treatments on textiles and paper
- Landfill leachate and wastewater treatment discharge, which concentrate rather than destroy PFAS
How it behaves in water
The shorter-chain compounds are extremely mobile and travel with groundwater almost unretarded. Longer-chain compounds sorb more strongly to organic matter. None break down appreciably in the environment on human timescales, which is the origin of the "forever chemicals" label.
How it is measured
Measured in nanograms per litre — parts per trillion — by LC-MS/MS. Analytical difficulty is real: laboratory background contamination from PTFE equipment is a genuine problem, and different jurisdictions count different numbers of compounds, so a "total PFAS" figure is only meaningful with its analyte list.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| European Union | 100 ng/l for the sum of 20 PFAS; 500 ng/l for total PFAS | legal limit | Under the recast Drinking Water Directive. |
| United States | 4 ng/l each for PFOA and PFOS | legal limit | Set in 2024, with additional limits for several other compounds and a hazard index for mixtures. Substantially stricter than the EU sum approach. |
| United Kingdom | 100 ng/l guideline for the sum of 48 PFAS | guideline | A DWI guideline tiered value triggering investigation and action, rather than a statutory limit. |
Table sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- European Commission — Drinking Water Directive (EU) 2020/2184 and reporting. Open — attribution required · European Commission reuse policy (Decision 2011/833/EU)
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- United States Environmental Protection Agency — Safe Drinking Water Information System. Open · US Government work — public domain
Health context
The European Food Safety Authority set a group tolerable weekly intake of 4.4 ng per kg of body weight for four PFAS in 2020, based on reduced vaccine response in children. Associations are also reported with elevated cholesterol, thyroid effects, and kidney and testicular cancer. The evidence base is evolving and limits have tightened repeatedly as a result.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Granular activated carbon, effective for long-chain compounds and much less so for short-chain | Boiling, which concentrates PFAS |
| 2 | Ion exchange with PFAS-selective resin | Conventional coagulation, sedimentation and sand filtration |
| 3 | Reverse osmosis and nanofiltration, the most reliable across the whole family | Chlorination, ozonation and UV disinfection |
| 4 | Destruction of the concentrated waste stream is a separate and unsolved problem | Biological treatment |
Occurrence
Systematic monitoring under the US Unregulated Contaminant Monitoring Rule provides the largest occurrence dataset, and detects PFAS in supplies serving a substantial share of the US population.
Relationships
Related intelligence
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- Peer-reviewed scientific literature — Open-access hydrology, water chemistry and water use research. Public but restricted · Publisher terms — public access, reuse not clearly granted