## 3 Aqueous Film Forming Foam (AFFF)
### Current AFFF Detection Efforts  
[PERSON] et al., (2019) examined the contamination at a Norwegian firefighting training facility, 15 years after the use of PFOS-based AFFF products had ceased [70]. In the soil, PFOS made up 96% of the total PFAS concentration and varied from 0.3 to 6500 \(\upmu\)g/kg. To determine how much PFOS was still present in the source zone and if it could form a long-term source contaminating the site's groundwater, they performed unsaturated column studies with pristine soil similar to that found at the site and the same PFOS containing AFFF. Using both a high and low water infiltration rate (9.7 and 4.9 mm/day for 7 and 14 weeks, respectively) to change aqueous saturation of the soil columns, [PERSON] et al., were able to model the contaminating effects of PFOS. The low infiltration rate represented 2 years of snow melt, and the high infiltration rate represented extra water added in areas of firefighting training. Utilizing LC/MS-MS, PFOS was detectable in the leachate of the higher infiltration experiment after 14 days where the concentration increased from 20 to 2200 ng/L after 49 days. Soils were also tested at various depths for PFOS detection and found that contamination reached as far as the groundwater level at 4 m below the surface. These results concluded that PFAS leaching from highly contaminated areas poses a long-term risk for contamination of local groundwater and consequently transport to neighboring surface water. [PERSON] et al., (2017), investigated the concentration of 10 perfluoroalkyl acids (PFAAs) in various environmental and biological samples including: water, soil, grass, chicken egg yolk, serums of horses, cattle, sheep, and humans to determine the extent of PFAAs leaching from a fire-fighting training area into an aquifer [68]. This study sought to expand upon the usage of both abiotic and biotic sampling introduced by [PERSON] et al., to not only quantify PFAA contamination but also investigate the spread of the contamination into terrestrial ecosystems [62]. Sample analysis was completed using LC/MS-MS in conjunction with isotopic dilution mass spectrometry to determine individual concentrations. PFOS in water samples ranged from 0.17 to 14 \(\upmu\)g/L, and perfluorohexaneculphonic acid (PFHxS) between 0.07 to 6.0 \(\upmu\)g/L. PFOS concentrations in human serum were 38 to 381 \(\upmu\)g/L, while PFHxS ranged from 39 to 214 \(\upmu\)g/L. Statistical significance was shown between cattle in the contamination zone compared to outside of the zone (\(p<0.01\)) in measuring PFOS and PFHxS concentrations. The highest PFOS concentration found in human serum was 30 times higher compared to the general Australian population. Their efforts concluded that insufficiently remediated sources of PFAAs further spread and contaminate terrestrial ecosystems which expose increasingly more individuals. [PERSON] et al., (2016) utilized a unique approach to indirectly measure the total concentration of PFAA precursors as well as directly measure twenty specific PFAS analytes in wastewater samples from 8 wastewater treatment plants (WWTPs) that discharge into San Francisco Bay [67]. The most prevalent of these PFAS analytes include: perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), fluorotelomer sulfonate (FtS), and perfluoropentanoic acid (PFPeA). Indirect measurement was accomplished utilizing a previously developed assay that uses hydroxyl radicals to oxidize precursors into perfluorinated carboxylates which are easily identifiable using LC/MS-MS [64; 107]. Six of the WWTPs contained similar amounts of total PFASs with the following median amounts: PFHxA (24 ng/L), PFOA (23 ng/L), PFBA (19 ng/L), and PFOS (15 ng/L). The remaining two plants contained significantly higher concentrations of PFASs with one having a PFOS of 420 ng/L and another plant having PFOS of 560 ng/L, 390 ng/L 6:2 FtS, 570 ng/L PFPeA, and 500 ng/L PFHxA.