# PFAS: The Journey from Wonder Chemicals to Environmental Nightmares and the Search for Solutions
## 2 Applications and Environmental Ubiquity of PFAS
### Environmental Exposure and Ubiquity  
The strong C-F bond in PFAS, due to the small size and high electronegativity of fluorine, makes PFAS chemically inert, with low molecular polarity, amphiphilicity and high stability against thermal, chemical, oxidative and reductive degradation [44; 45]. Depending on the carbon chain length, volatility, water-solubility, and the headgroup functionality make a significant impact on their distribution in the environment. The short-chain PFAS molecules are more volatile and have a high mobility. Hence, they can travel via the atmosphere and can enter water cycles even located far from the areas of direct exposure. Meanwhile, long-chain PFAS molecules are less volatile and more hydrophobic. Hence, they are more easily bound to solid matrices like soil. Table 3 shows how the unique properties of PFAS contributed to specific industrial applications. The two sources of release of PFAS into the environment are point sources and non-point sources. Point sources are discrete and stationary meanwhile non-point sources are diffuse sources of unknown origin or location. Industrial/manufacturing facilities, firefighting training sites, wastewater treatment plants (WWTPs), and landfills are typically categorized as point sources and atmospheric transport of volatile PFAS, consumer products breakdown, surface runoff, and precipitation can be categorized as non-point sources [51; 52]. One primary point source of PFAS contamination of surface and ground water is the AFFF used in firefighting training exercises. Since the US military has been the largest consumer of AFFFs for firefighting training exercises, PFAS contamination in water due to AFFF has been widely documented. The US Air Force has identified nearly 200 Department of Defense (DoD) installations where AFFF has been used [53] in firefighting foam and the foam can be washed away to the nearby water resources and soil. Per-fluoroethylcyclohexanesulfonate (PFECHS) is used in aircraft hydraulic fluid as an erosion inhibitor and in 2011, it was identified in a predatory fish in the Great Lakes and the surface water of the lakes [54; 55; 56; 57; 58]. Surface water and groundwater play a vital role in societal demands such as drinking water, water transport, and irrigation [59]. However, both surface water and ground water are severely polluted with organic waste and suspended solids [60; 61]. Moreover, it has \begin{table}
\begin{tabular}{c c} \hline
**Unique Properties of PFAS** & **Resulting Industrial Applications** \\ \hline Chemically Inert & Chemical-resistant coating (gasket and seals), Non-stick cookware coating (Teflon pans) [6; 46] \\ \hline Low Molecular Polarity & Hydrophobic coatings (textile, paper), Stain repellents (Carpets) [6] \\ \hline Amphiphilicity & Surfactants in fire-fighting foams (AFFF), emulsifiers in cosmetics and pharmaceuticals [37] \\ \hline Thermal Stability & Aerospace applications, High-temperature lubricants, Insulating materials in electronics (printed circuit boards) [24; 47] \\ \hline Chemically Stability & Long-lasting coatings, corrosion-resistant materials [24] \\ \hline Electrical Insulation & Insulation for wiring and electronics [24; 48] \\ \hline Lipophilicity & Oil and grease repellent in food packaging [48; 49] \\ \hline Low Surface Energy & Anti-sticking applications [24; 37] \\ \hline High Density & Medical imaging applications [24; 50] \\ \hline Water Repellency & Outdoor gear, Waterproof clothing [24] \\ \hline Chemical Resistance & Reactive substance containers, Harsh chemical environments, Protective gloves [6] \\ \hline \end{tabular}
\end{table} 
Table 3: Unique Properties of PFAS and Resulting Industrial Applications. been identified that unlike other organic pollutants, perfluoroalkyl acids (PFAAs) are water soluble and have been detected in both surface water including lakes, rivers, and tributaries, and in ground water in similar concentrations in the range of 1-1000 ng/L [62].