What is PFAS?
PFAS (Per- and Polyfluoroalkyl Substances) is a class of chemical compounds that include over 12,000 synthetic organic chemicals used since the 1940s that contain multiple Fluorine (F) atoms. The two most studied PFAS compounds are Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS).
PFAS in the Environment
Although these chemicals provide beneficial uses to industry, there are several human health and environmental challenges due to the creation and use of PFOA and PFOS, including:
- Water Solubility – able to enter into, and spread via, groundwater and surface water with high stability making them resistant to chemical and biological degradation
- Bioaccumulation – concentrations can increase 10,000 times in fish and aquatic organisms
- Binds to proteins in blood and is reabsorbed by the human kidney – stays in circulation and, due to inefficient elimination, has a half-life of 4-9 years
- High maternal transfer to fetus
Select Chemical Properties of PFAS and other Contaminants
PubChem and EPA
|
Property |
PFOA |
PFOS |
PFBS* |
PCB 1260 |
TCE** |
|---|---|---|---|---|---|
|
Water Solubility 25° C (mg/L) |
9500 |
680 |
344 |
0.0027 |
1100 |
|
Soil Absorption Factor (Log Koc) |
2.0 |
2.5 |
1.5 |
6 |
2.4 |
|
Bioconcentration Factor (BCF) |
3 |
1000 |
0.71 |
100.000 |
4 |
*Perfluorobutane Sulfonate
**Trichloroethylene
How is PFAS measured?
PFAS concentrations are reported in concentrations of “parts per trillion”, or “ppt”. A ppt is a measurement of the quantity of a substance in the air, water, or soil where there is one part of that substance for every one trillion parts of the medium it is contained in (a ratio of 1:1,000,000,000,000). One part per trillion is equivalent to one nanogram per liter of water. A nanogram is a unit of measurement that is equal to one billionth of a gram.
One way to visualize this amount is that a dollar bill weighs about 1 gram. To get 1 nanogram, the dollar bill would be cut into 1,000 pieces. Take one of those pieces and cut it into another 1,000 equal pieces. Then take one of those pieces and cut it into another 1,000 pieces. Each piece in this group will be a billionth of the original dollar and will weigh approximately 1 nanogram.
Other ways to conceptualize one ppt are one second in 32,000 years or one grain of sand in an Olympic-size swimming pool.