Perfluoroalkyl and Polyfluoroalkyl Substances in Groundwater Used as a Source of Drinking Water in the Eastern United States

All samples with PFOA+PFOS concentrations greater than 70 ng/L are from public-supply wells.

“(all are from public-supply wells)”

ΣPFAS exhibit a significant positive Spearman correlation with the number of PFAS detected (rho = 0.91; p < 0.001).

“ΣPFAS exhibit a significant positive Spearman correlation with the number of PFAS detected in the samples (rho = 0.91; p < 0.001)”

In samples with both 3H data and PFAS detections (n = 136), 92% of the detections occur in modern water.

“In samples that have both 3H data and PFAS detections (n = 136), 92% of the detections occur in modern water”

At least two PFAS were detected in 53% of public-supply wells.

“At least two PFAS were detected in 53% of public-supply wells and 10% of domestic wells”

About 99% of PFAS detections occur in samples with at least some modern water (modern + mixed).

“about 99% occur in samples with at least some modern water (modern + mixed)”

At least one PFAS was detected in 54% of the 254 groundwater samples.

“At least one PFAS was detected in 54% of the samples (n = 254)”

Percent agricultural land within 500 m is significantly smaller for wells containing PFAS detections than for wells with no detections.

“there are significantly smaller percentages of agricultural and undeveloped lands within 500 m of wells that contain PFAS detections than near wells with no detections”

Eight of the 10 undetected PFAS are PFAA precursors (n = 5) or PFCA with 12+ carbon atoms (n = 3).

“Eight of the 10 undetected PFAS are PFAA precursors (n = 5) or PFCA with 12+ carbon atoms (n = 3)”

The dominant PFAS in mixtures vary between networks.

“but the dominant PFAS in mixtures vary between networks”

Only the shallowest network (NECBS), with the highest PFAS detection frequency, has 100% of its samples assigned to the modern age category.

“Only the shallowest network (NECBS), with the highest PFAS detection frequency (Figure 2B), has 100% of its samples assigned to the modern age category”

Percent urban land use within 500 m of wells is significantly higher for wells containing PFAS detections than for wells with no detections.

“There is a significantly larger percentage of urban land within 500 m of wells that contain PFAS detections than near wells with no detections”

• Also stated in: § Abstract · plain

  “Concentrations of tritium, chloride, sulfate, DOC, and manganese + iron; percent urban land use within 500 m of the wells; and VOC and pharmaceutical detection frequencies were significantly higher in samples containing PFAS detections than in samples with no detections.”

2.4% (n = 6) of samples have PFOA+PFOS concentrations greater than the 70 ng/L health advisory level.

“2.4% (n = 6) of the samples have PFOA+PFOS concentrations greater than the 70 ng/L health advisory level”

At least two PFAS were detected in 47% of the samples.

“≥2 PFAS were detected in 47% of the samples”

There is a significant positive correlation (rho = 0.86; p = 0.014) between PFAS detection frequency and ΣPFAS medians.

“there is a significant positive correlation (rho = 0.86; p = 0.014) between detection frequency and ΣPFAS medians”

Two other networks (NECBD; MIAM) have >95% of their samples assigned to the modern category.

“Two other networks (NECBD; MIAM) have >95% of their samples assigned to the modern category.”

At least two PFAS were detected in 10% of domestic wells.

“At least two PFAS were detected in 53% of public-supply wells and 10% of domestic wells”

Samples containing a PFAS detection have significantly higher 3H concentrations than samples with no detections.

“samples that contain a PFAS detection have significantly shallower well depths and higher 3H concentrations than samples with no detections”

• Also stated in: § Abstract · plain

  “Concentrations of tritium, chloride, sulfate, DOC, and manganese + iron; percent urban land use within 500 m of the wells; and VOC and pharmaceutical detection frequencies were significantly higher in samples containing PFAS detections than in samples with no detections.”

Networks NECBS, NECBD, and SURF have relatively large fractions of samples containing >6 PFAS (37 to 54%).

“Networks NECBS, NECBD, and SURF have relatively large fractions of samples containing >6 PFAS (37 to 54%)”

Modern samples are from wells with significantly shallower depths than premodern samples.

“modern samples are from wells with significantly shallower depths than premodern samples”

DOC concentrations are significantly higher in samples containing PFAS detections than in samples with no detections.

“Concentrations of DOC, Cl, SO4, Ca + Mg, and Mn + Fe are significantly higher in samples containing PFAS detections than in samples with no detections”

• Also stated in: § Abstract · plain

  “Concentrations of tritium, chloride, sulfate, DOC, and manganese + iron; percent urban land use within 500 m of the wells; and VOC and pharmaceutical detection frequencies were significantly higher in samples containing PFAS detections than in samples with no detections.”

PFAS detection frequencies range from 3.7% (MISE) to 92.9% (NECBS) among well networks.

“PFAS detection frequencies range from 3.7 (MISE network) to 92.9% (NECBS)”

Samples containing a PFAS detection have significantly shallower well depths than samples with no detections.

“samples that contain a PFAS detection have significantly shallower well depths and higher 3H concentrations than samples with no detections”

Sulfate concentrations are significantly higher in samples containing PFAS detections than in samples with no detections.

“Concentrations of DOC, Cl, SO4, Ca + Mg, and Mn + Fe are significantly higher in samples containing PFAS detections than in samples with no detections”

• Also stated in: § Abstract · plain

  “Concentrations of tritium, chloride, sulfate, DOC, and manganese + iron; percent urban land use within 500 m of the wells; and VOC and pharmaceutical detection frequencies were significantly higher in samples containing PFAS detections than in samples with no detections.”

pH is not significantly different between samples containing PFAS detections and samples with no detections.

“however, pH is not significantly different between the two PFAS groups”

Overall, three PFAS occur in ≥80% of the mixtures (PFOA > PFBS > PFOS).

“Overall, three PFAS occur in ≥80% of the mixtures (PFOA > PFBS > PFOS)”

Ca+Mg concentrations are significantly higher in samples containing PFAS detections than in samples with no detections.

“Concentrations of DOC, Cl, SO4, Ca + Mg, and Mn + Fe are significantly higher in samples containing PFAS detections than in samples with no detections”

Percent undeveloped land within 500 m is significantly smaller for wells containing PFAS detections than for wells with no detections.

“there are significantly smaller percentages of agricultural and undeveloped lands within 500 m of wells that contain PFAS detections than near wells with no detections”

PFAS were detected in 60% of public-supply wells.

“PFAS were detected in 60% of public-supply wells and 20% of domestic wells”

• Also stated in: § Abstract · plain

  “60 and 20% of public-supply and domestic wells, respectively, containing at least one PFAS detection”

PFOA and PFOS are two of the three most frequently detected PFAS.

“PFOA and PFOS represent two of the three most frequently detected PFAS”

Mn+Fe concentrations are significantly higher in samples containing PFAS detections than in samples with no detections.

“Concentrations of DOC, Cl, SO4, Ca + Mg, and Mn + Fe are significantly higher in samples containing PFAS detections than in samples with no detections”

• Also stated in: § Abstract · plain

  “Concentrations of tritium, chloride, sulfate, DOC, and manganese + iron; percent urban land use within 500 m of the wells; and VOC and pharmaceutical detection frequencies were significantly higher in samples containing PFAS detections than in samples with no detections.”

Fourteen of the 24 analyzed PFAS were detected at least once in groundwater samples.

“Fourteen of the 24 PFAS were detected in groundwater”

• Also stated in: § PFAS Occurrence in Groundwater · plain

  “Fourteen of the 24 analyzed PFAS were detected at least once in groundwater samples”

PFAS were detected in 20% of domestic wells.

“PFAS were detected in 60% of public-supply wells and 20% of domestic wells”

• Also stated in: § Abstract · plain

  “60 and 20% of public-supply and domestic wells, respectively, containing at least one PFAS detection”

In NECBS, 68% of samples contain combinations of two or more PFAS that are unique to that sample.

“In NECBS, 68% of the samples contain combinations of two or more PFAS that are unique to that sample.”

Network NECBS has three PFAS that occur in ≥80% of the mixtures (PFOA > PFOS > PFBS).

“Network NECBS has three PFAS that occur in ≥80% of the mixtures (PFOA > PFOS > PFBS)”

Chloride concentrations are significantly higher in samples containing PFAS detections than in samples with no detections.

“Concentrations of DOC, Cl, SO4, Ca + Mg, and Mn + Fe are significantly higher in samples containing PFAS detections than in samples with no detections”

• Also stated in: § Abstract · plain

  “Concentrations of tritium, chloride, sulfate, DOC, and manganese + iron; percent urban land use within 500 m of the wells; and VOC and pharmaceutical detection frequencies were significantly higher in samples containing PFAS detections than in samples with no detections.”

The highest ΣPFAS (1645 ng/L) occurs in a public-supply well from STRV.

“The highest ΣPFAS (1645 ng/L) occurs in a public-supply well from STRV.”

There are significant differences in well depths between the networks, with median depths ranging from 7.7 m (NECBS) to 88.4 m (MISE).

“There are significant differences in well depths between the networks (Figure S3A), with median depths ranging from 7.7 (NECBS) to 88.4 m (MISE).”

ΣPFAS medians range from 2.2 ng/L (MISE) to 40.0 ng/L (SURF) among well networks.

“ΣPFAS medians range from 2.2 (MISE) to 40.0 ng/L (SURF)”

There are significant differences in 3H concentrations between the well networks, with median concentrations ranging from 0.1 TU (MISE) to 4.7 TU (STRV).

“There are also significant differences in 3H concentrations between the well networks (Figure S3B), with median concentrations ranging from 0.1 tritium units (TU) (MISE) to 4.7 TU (STRV).”

Ca+Mg/SO4 ratios are significantly lower in samples that contain PFAS detections than in samples with no detections.

“Ca + Mg/Cl and Ca + Mg/SO4 ratios are significantly lower in samples that contain PFAS detections than in samples with no detections”

Ca+Mg/Cl ratios are significantly lower in samples that contain PFAS detections than in samples with no detections.

“Ca + Mg/Cl and Ca + Mg/SO4 ratios are significantly lower in samples that contain PFAS detections than in samples with no detections”

The cumulative number of potential PFAS sources <5 km from the sampled wells is significantly higher for wells containing PFAS detections than for wells with no detections.

“Moreover, the cumulative number of potential PFAS sources <5 km from the sampled wells is significantly higher for wells containing PFAS detections than for wells with no detections.”

There is a significant inverse correlation (p < 0.001) between well depth and Mn.

“there is a significant inverse correlation (p < 0.001) between well depth and Mn (but not Fe)”

VOC detection frequencies are significantly higher in samples containing PFAS detections than in samples with no detections.

“VOC and pharmaceutical detection frequencies were significantly higher in samples containing PFAS detections than in samples with no detections”

The most common co-occurring pharmaceuticals include carbamazepine > gabapentin > meprobamate.

“The most common co-occurring pharmaceuticals include carbamazepine > gabapentin > meprobamate (Figure S6B).”

NECBD has a larger fraction of samples with unique PFAS mixtures than SURF.

“NECBD has a larger fraction of samples with unique PFAS mixtures than SURF (Figure S2B), even though SURF (86%) has a larger fraction of urban land within 500 m of its wells than NECBD (74%).”

The number of potential PFAS sources within 5 km of NECBD wells is significantly higher than the number within 5 km of SURF wells.

“The number of potential PFAS sources within 5 km of NECBD wells is significantly higher than the number within 5 km of SURF wells (Figure S5A).”

NECBD and SURF appear to have similar numbers of septic systems in 500 m buffers around their wells.

“NECBD and SURF appear to have similar numbers of septic systems in 500 m buffers around their wells (Figure S5B), based on estimates of N input to septic systems in the United States,51 which is used here as a proxy for septic-system density.”

• cites [51] LaMotte, 2018Not checked yet

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VOC and pharmaceutical detection frequencies are substantially higher in samples that contain PFAS detections (62 and 33%, respectively) than in samples with no detections (21 and 2%, respectively).

“VOC and pharmaceutical detection frequencies are substantially higher in samples that contain PFAS detections (62 and 33%, respectively) than in samples with no detections (21 and 2%, respectively) (Table S12).”

There is no significant correlation between well depth and Fe.

“there is a significant inverse correlation (p < 0.001) between well depth and Mn (but not Fe)”

Pharmaceutical detection frequencies are significantly higher in samples containing PFAS detections than in samples with no detections.

“VOC and pharmaceutical detection frequencies were significantly higher in samples containing PFAS detections than in samples with no detections”

Boosted regression tree models that consider 57 chemical and land-use variables show that tritium concentration, distance to the nearest fire-training area, percentage of urban land use, and DOC and VOC concentrations are the top five predictors of PFAS detections.

“Boosted regression tree models that consider 57 chemical and land-use variables show that tritium concentration, distance to the nearest fire-training area, percentage of urban land use, and DOC and VOC concentrations are the top five predictors of PFAS detections”

SURF has a larger fraction of urban land within 500 m of its wells (86%) than NECBD (74%).

“NECBD has a larger fraction of samples with unique PFAS mixtures than SURF (Figure S2B), even though SURF (86%) has a larger fraction of urban land within 500 m of its wells than NECBD (74%).”

These source categories and most others listed in Table S8 are significantly closer to wells that contain PFAS detections than to wells with no detections.

“These source categories and most others listed in Table S8 are significantly closer to wells that contain PFAS detections than to wells with no detections (Table S13).”

The top five predictors of PFAS detection are 3H concentration, distance to the nearest fire-training area, DOC concentration, percentage of urban land use, and ΣVOC.

“The relative importance of the model variables (Figure 4) indicates that the top five predictors of PFAS detection are 3H concentration, distance to the nearest fire-training area, DOC concentration, percentage of urban land use, and ΣVOC.”

The percentage of urban land use was also in the top 10 most influential predictor variables for all scenarios except for the model predicting PFOA, where it was number 11.

“The percentage of urban land use was also in the top 10 most influential predictor variables for all scenarios except for the model predicting PFOA, where it was number 11.”

Samples with co-occurring detections of PFAS and pharmaceuticals have significantly higher concentrations of B and total N than samples that do not have co-occurring PFAS and pharmaceutical detections.

“detections of PFAS and pharmaceuticals have significantly higher concentrations of B and total N than samples that do not have co-occurring PFAS and pharmaceutical detections (Figure S7).”

In all scenarios, 3H, DOC, and VOC concentrations and distance to the nearest fire-training area were in the top 10 most influential predictor variables.

“In all scenarios, 3H, DOC, and VOC concentrations and distance to the nearest fire-training area were in the top 10 most influential predictor variables (Table S10).”

CDFM concentrations in air-saturated water (0.0009 μg/L at 20 °C) are very low compared to the concentrations measured in this study.

“Atmospherically derived CDFM could enter groundwater in recharge that is unrelated to PFAS sources, although CDFM concentrations in air-saturated water (0.0009 μg/L at 20 °C)61 are very low compared to the concentrations measured in this study.”

• cites [61] Haase, 2014, Measurements of HFC-134a and HCFC-22 in groundwater and unsaturated-zone air: Implications for HFCs and HCFCs as dating tracers, Chem. Geol. sourceNot checked yet

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Nitrate and B concentrations, for the most part, are significantly higher in NECBD samples that contain PFAS or pharmaceutical detections than in samples with no detections.

“That network has a relatively high abundance of septic systems within 500 m of the wells (Figure S5B), and nitrate and B concentrations, for the most part, are significantly higher in NECBD samples that contain PFAS or pharmaceutical detections than in samples with no detections (Table S14).”

SURF samples with co-occurring PFAS and CDFM detections and samples with only CDFM detections do not have significantly higher B or total N concentrations than samples without those detections.

“SURF samples with co-occurring PFAS and CDFM detections and samples with only CDFM detections do not have significantly higher B or total N concentrations than samples without those detections (Figure S9), suggesting that the PFAS + CDFM co-occurrences are not associated with human-waste disposal.”

Variables potentially related to PFAS sorption (e.g., SO4 and Cl) are among the top 10 predictors.

“Variables potentially related to PFAS sorption (e.g., SO4 and Cl) are also among the top 10 predictors.”

NECBD has a relatively high abundance of septic systems within 500 m of the wells.

“That network has a relatively high abundance of septic systems within 500 m of the wells (Figure S5B), and nitrate and B concentrations, for the most part, are significantly higher in NECBD samples that contain PFAS or pharmaceutical detections than in samples with no detections (Table S14).”

PFAS detections co-occur in 90% of the samples that contain a CDFM detection.

“PFAS detections co-occur in 90% of the samples that contain a CDFM detection, and 96% of the samples with co-occurring CDFM and PFAS also contain PFOA and/or PFOS.”

In NECBD, 41% of the public-supply wells with PFAS detections also have at least one detection of a pharmaceutical.

“In NECBD, 41% of the public-supply wells with PFAS detections also have at least one detection of a pharmaceutical.”

96% of the samples with co-occurring CDFM and PFAS also contain PFOA and/or PFOS.

“PFAS detections co-occur in 90% of the samples that contain a CDFM detection, and 96% of the samples with co-occurring CDFM and PFAS also contain PFOA and/or PFOS.”

The probability of PFAS detection decreases with increasing distance from a fire-training area.

“Conversely, the probability of PFAS detection decreases with increasing distance from a fire-training area.”

Hydrologic position and groundwater age are controlling factors for PFAS occurrence in groundwater.

“consistent with the hydrologic position and groundwater age being controlling factors for PFAS occurrence in groundwater”

The likelihood of detecting PFAS in groundwater decreases with increasing well depth.

“The relations between depth, age categories, and onset of widespread PFAS use imply that the likelihood of detecting PFAS in groundwater decreases with increasing well depth.”

The large fractions of samples containing >6 PFAS in NECBS, NECBD, and SURF may be related to the large fractions of urban land use in 500 m buffers around those wells (74 to 92%).

“which may be related to the large fractions of urban land use in 500 m buffers around those wells (74 to 92%)”

Urban areas could be expected to have a greater density of potential PFAS sources compared to agricultural and undeveloped landscapes.

“Urban areas could be expected to have a greater density of potential PFAS sources compared to agricultural and undeveloped landscapes, although biosolids are recognized as a potential PFAS source on agricultural lands.50”

• cites [50] Sepulvado, 2011, Occurrence and fate of perfluorochemicals in soil following the land application of municipal biosolids, Environ. Sci. Technol. sourceNot checked yet

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PFAS and pharmaceuticals are known to co-occur in sources associated with human-waste disposal (e.g., septic-system/landfill leachate and wastewater treatment plants).

“PFAS and pharmaceuticals, however, are known to co-occur in sources associated with human-waste disposal (e.g., septic-system/landfill leachate and wastewater treatment plants).10,54−56”

• cites [10] Hu, 2016, Drinking water linked to industrial sites, military fire training areas, and wastewater treatments plants, Environ. Sci. Technol. Lett. sourceNot checked yet

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• cites [54] Benskin, 2012, Per- and polyfluoroalkyl substances in landfill leachate: Patterns, time trends, and sources, Environ. Sci. Technol. sourceNot checked yet

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• cites [55] Schaider, 2014, Pharmaceuticals, perfluorosurfactants, and other organic wastewater compounds in public drinking water wells in a shallow sand and gravel aquifer, Sci. Total Environ. sourceNot checked yet

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• cites [56] Bradley, 2016, Pre/post-closure assessment of groundwater pharmaceutical fate in a wastewater-facility-impacted stream reach, Sci. Total Environ. sourceNot checked yet

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The relation between PFAS and urbanization implies that the risk of PFAS contamination of groundwater could increase as urbanization encroaches on agricultural and undeveloped land.

“The relation between PFAS and urbanization is important because it implies that the risk of PFAS contamination of groundwater could increase as urbanization encroaches on the agricultural and undeveloped land.”

The co-occurrence of PFAS with other chemicals does not necessarily indicate that they are from the same source, particularly in urban areas where independent sources could coexist in proximity to each other.

“The co-occurrence of PFAS with other chemicals does not necessarily indicate that they are from the same source, particularly in urban areas where independent sources could coexist in proximity to each other.”

PFAS persist in the environment.

“PFAS persist in the environment,5−8”

• cites [5] Prevedouros, 2006, Sources, fate, and transport of perfluorocarboxylates, Environ. Sci. Technol. sourceNot checked yet

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• cites [6] Wang, 2011, 6:2 fluorotelomer sulfonate aerobic biotransformation in activated sludge of waste water treatment plants, Chemosphere sourceNot checked yet

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• cites [7] Weber, 2017, Geochemical and hydrologic factors controlling subsurface transport of poly- and perfluoroalkyl substances, Cape Cod, Massachusetts, Environ. Sci. Technol. sourceNot checked yet

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• cites [8] Newell, 2020, Comparing PFAS to other groundwater contaminants: Implications for remediation, Remediation sourceNot checked yet

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Elevated DOC concentrations could promote PFAS mobility through electrostatic or hydrophobic interactions in the dissolved phase or by competing with PFAS for sorption sites.

“Higher DOC concentrations in samples containing PFAS detections are consistent with previous studies indicating that elevated DOC concentrations could promote PFAS mobility through electrostatic or hydrophobic interactions in the dissolved phase or by competing with PFAS for sorption sites.48,49”

• cites [48] Du, 2014, Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents – A review, J. Hazard Mater. sourceNot checked yet

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• cites [49] Kothawala, 2017, Influence of dissolved organic matter concentration and composition on the removal efficiency of perfluoroalkyl substances (PFASs) during drinking water treatment, Water Res. sourceNot checked yet

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Field replicates and laboratory matrix spike duplicates indicated low variability in PFAS detection and/or concentration.

“Field replicates and laboratory matrix spike duplicates indicated low variability in PFAS detection and (or) concentration.”

Hydrologic position, geochemistry, and land use are important controls on PFAS occurrence in groundwater.

“consistent with the hydrologic position, geochemistry, and land use being important controls on PFAS occurrence in groundwater”

The presence of VOCs and pharmaceuticals indicates that the chemical inventory in groundwater contaminated with PFAS is complex.

“ΣVOCs (median = 0.07 μg/L) and Σpharmaceuticals (median = 0.025 μg/L) are low, but their presence indicates that the chemical inventory in groundwater contaminated with PFAS is complex.”

PFAS in the unsaturated zone can be sources to underlying groundwater systems for decades.

“PFAS in the unsaturated zone can be sources to underlying groundwater systems for decades,7,14”

• cites [7] Weber, 2017, Geochemical and hydrologic factors controlling subsurface transport of poly- and perfluoroalkyl substances, Cape Cod, Massachusetts, Environ. Sci. Technol. sourceNot checked yet

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• cites [14] Guo, 2019, A mathematical model for the release, transport, and retention of per- and polyfluoroalkyl substances (PFAS) in the vadose zone, Water Resour. Res. sourceNot checked yet

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The results are consistent with the conceptual model of PFAS concentrations in groundwater increasing with decreasing distance to PFAS sources and increasing density of PFAS sources.

“nevertheless, the results are consistent with the conceptual model of PFAS concentrations in groundwater increasing with decreasing distance to PFAS sources and increasing density of PFAS sources.”

• AssumptionRests on an assumption: The potential PFAS source categories in the geospatial databases are sources of PFAS to groundwater.

The co-occurrence of CDFM and 1,1-dichloroethane with PFAS was also noted in the UCMR3 dataset.

“The co-occurrence of CDFM and 1,1-dichloroethane with PFAS was also noted in the UCMR3 dataset.3”

• cites [3] Guelfo, 2018, Evaluation of a national data set for insights into sources, composition, and concentrations of per- and polyfluoroalkyl substances (PFAS) in U.S. drinking water, Environ. Pollut. sourceNot checked yet

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Laboratory-blank results prompted censoring of reported detections for PFBA in 15 groundwater samples in two analytical batches and for a detection of 6:2 FTS in one groundwater sample in a separate batch.

“Laboratory-blank results prompted censoring of reported detections for PFBA in 15 groundwater samples in two analytical batches and for a detection of 6:2 FTS in one groundwater sample in a separate batch.”

No PFAS detections were reported for any blank types collected in the field, with the exception of one PFBA detection in a field blank.

“No PFAS detections were reported for any blank types collected in the field, with the exception of one perfluorobutanoate (PFBA) detection reported for a field blank”

The relation between PFAS detections and Mn+Fe is consistent with reductive dissolution of Mn and Fe oxides in anoxic groundwater that could reduce the sorption capacity of solids or mobilize PFAS already adsorbed to those solids.

“The relation between PFAS detections and Mn + Fe is consistent with reductive dissolution of Mn and Fe oxides in anoxic groundwater that could reduce the sorption capacity of solids or mobilize PFAS already adsorbed to those solids.”

Model results indicate that it may be possible to predict PFAS detections in groundwater using existing data sources.

“Model results indicate that it may be possible to predict PFAS detections in groundwater using existing data sources.”

Examination of data for routine laboratory reagent spikes and matrix spikes indicated little bias, with all median recovery values for PFAS between 85 and 103%.

“Examination of data for routine laboratory reagent spikes and matrix spikes indicated little bias (all median recovery values for PFAS between 85 and 103%); reagent spikes exhibited low variability in recovery.”

Competition for sorption sites between negatively charged PFAS and inorganic anions could help explain the higher Cl and SO4 concentrations in samples containing PFAS detections.

“Competition for sorption sites between negatively charged PFAS and inorganic anions could also help explain the higher Cl and SO4 concentrations in samples containing PFAS detections.47,48”

• cites [47] Lyu, 2019, Transport and retention of perfluorooctanoic acid (PFOA) in natural soils: Importance of soil organic matter and mineral contents, and solution ionic strength, J. Contam. Hydrol. sourceNot checked yet

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• cites [48] Du, 2014, Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents – A review, J. Hazard Mater. sourceNot checked yet

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The relation between PFAS detections and Ca+Mg appears more consistent with previous studies when Ca+Mg concentrations are normalized to Cl or SO4 concentrations.

“The relation between PFAS detections and Ca + Mg appears to be more consistent with previous studies when Ca + Mg concentrations are normalized to Cl or SO4 concentrations.”

Some PFAS are known or suspected to be associated with adverse human-health effects.

“some PFAS are known or suspected to be associated with adverse human-health effects.11−13”

• cites [11] 2016Not checked yet

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• cites [12] 2016Not checked yet

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• cites [13] Sunderland, 2019, A review of the pathways of human exposure to poly- and perfluoroalkyl substances (PFAS) and present understanding of health effects, J. Expo. Sci. Environ. Epidemiol. sourceNot checked yet

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Historically, the polymerization process used PFOA and PFOS as emulsifiers.

“Historically, the polymerization process used PFOA and PFOS as emulsifiers.60”

• cites [60] Dams, 2017, Chapter 1. Industrial Aspects of Fluorinated Oligomers and PolymersNot checked yet

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The three sources could produce similar chemical patterns with respect to PFAS, pharmaceuticals, B, and total N.

“All three sources can have elevated B and total N concentrations,55,58,59 so they could produce similar chemical patterns with respect to PFAS, pharmaceuticals, B, and total N.”

All three sources (septic/landfill leachate, wastewater effluent, stormwater runoff) can have elevated B and total N concentrations.

“All three sources can have elevated B and total N concentrations,55,58,59 so they could produce similar chemical patterns with respect to PFAS, pharmaceuticals, B, and total N.”

• cites [55] Schaider, 2014, Pharmaceuticals, perfluorosurfactants, and other organic wastewater compounds in public drinking water wells in a shallow sand and gravel aquifer, Sci. Total Environ. sourceNot checked yet

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• cites [58] Cozzarelli, 2011, Biogeochemical evolution of a landfill leachate plume, Norman, Oklahoma, Ground Water sourceNot checked yet

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• cites [59] Vengosh, 1994, Boron isotope application for tracing sources of contamination in groundwater, Environ. Sci. Technol. sourceNot checked yet

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Urban areas have been associated with PFAS occurrence.

“Higher 3H concentrations are indicative of more modern water, urban areas have been associated with PFAS occurrence, and fire-training areas are known point sources of PFAS.7,17,63”

• cites [7] Weber, 2017, Geochemical and hydrologic factors controlling subsurface transport of poly- and perfluoroalkyl substances, Cape Cod, Massachusetts, Environ. Sci. Technol. sourceNot checked yet

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• cites [17] McGuire, 2014, Evidence of remediation-induced alteration of subsurface poly- and perfluoroalkyl substance distribution at a former firefighter training area, Environ. Sci. Technol. sourceNot checked yet

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• cites [63] Sardiña, 2019, Emerging and legacy contaminants across land-use gradients and the risk to aquatic ecosystems, Sci. Total Environ. sourceNot checked yet

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Many water-treatment processes do not effectively remove PFAS.

“Nevertheless, many water-treatment processes do not effectively remove PFAS.41,42”

• cites [41] Bradley, 2021, Public and private tapwater: Comparative analysis of contaminant exposure and potential risk, Cape Cod, Massachusetts, USA, Environ. Int. sourceNot checked yet

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• cites [42] Boone, 2019, Per- and polyfluoroalkyl substances in source and treated drinking waters of the United States, Sci. Total Environ. sourceNot checked yet

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Co-occurrences of CDFM, PFOA, and PFOS in groundwater could indicate that some of the PFAS are from fluoropolymer manufacturing.

“Thus, co-occurrences of CDFM, PFOA, and PFOS in groundwater could indicate that some of the PFAS are from fluoropolymer manufacturing.”

The PFAS + CDFM co-occurrences are not associated with human-waste disposal.

“SURF samples with co-occurring PFAS and CDFM detections and samples with only CDFM detections do not have significantly higher B or total N concentrations than samples without those detections (Figure S9), suggesting that the PFAS + CDFM co-occurrences are not associated with human-waste disposal.”

The model performance is excellent.

“The accuracy, sensitivity, specificity, and ROC were 0.91, 0.93, 0.89, and 0.97 for the training data and 0.84, 0.96, 0.72, and 0.90 for the holdout data, respectively, indicating excellent model performance (Table S9).”

The chemical and spatial data are consistent with at least some of the PFAS in samples with co-occurring CDFM and PFAS detections being sourced from chemical manufacturing.

“We do not know if PFAS and CDFM were used or released to the environment at those facilities, but the chemical and spatial data are consistent with at least some of the PFAS in samples with co-occurring CDFM and PFAS detections being sourced from chemical manufacturing.”

The model results are consistent with hydrologic position, groundwater geochemistry, and land use being important controls on PFAS occurrence in groundwater.

“Overall, the model results are consistent with the hydrologic position, groundwater geochemistry, and land use being important controls on PFAS occurrence in groundwater.”

Higher 3H concentrations are indicative of more modern water.

“Higher 3H concentrations are indicative of more modern water, urban areas have been associated with PFAS occurrence, and fire-training areas are known point sources of PFAS.7,17,63”

• cites [7] Weber, 2017, Geochemical and hydrologic factors controlling subsurface transport of poly- and perfluoroalkyl substances, Cape Cod, Massachusetts, Environ. Sci. Technol. sourceNot checked yet

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• cites [17] McGuire, 2014, Evidence of remediation-induced alteration of subsurface poly- and perfluoroalkyl substance distribution at a former firefighter training area, Environ. Sci. Technol. sourceNot checked yet

  Not checked in the free run.

• cites [63] Sardiña, 2019, Emerging and legacy contaminants across land-use gradients and the risk to aquatic ecosystems, Sci. Total Environ. sourceNot checked yet

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The model developed here indicates that it may be possible to predict PFAS detections in drinking-water wells using data sources already available.

“The model developed here indicates that it may be possible to predict PFAS detections in drinking-water wells using data sources already available, consistent with another recent study that used statistical models to predict susceptibility of private wells to PFAS contamination.22”

• cites [22] Hu, 2021, A statistical approach for identifying private wells susceptible to perfluoroalkyl substances (PFAS) contamination, Environ. Sci. Technol. Lett. sourceNot checked yet

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Those types of sources could account for some of the PFAS in the 37% of PFAS-contaminated samples from public-supply wells that contain at least one pharmaceutical.

“Those types of sources could account for some of the PFAS in the 37% of PFAS-contaminated samples from public-supply wells that contain at least one pharmaceutical.”

Fuel hydrocarbons like benzene co-occur with PFAS in groundwater in some fire-training areas.

“Fuel hydrocarbons like benzene co-occur with PFAS in groundwater in some fire-training areas.17”

• cites [17] McGuire, 2014, Evidence of remediation-induced alteration of subsurface poly- and perfluoroalkyl substance distribution at a former firefighter training area, Environ. Sci. Technol. sourceNot checked yet

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These results indicate robustness of the model.

“These results indicate robustness of the model.”

The data represent a conservative estimate of human exposure to PFAS because samples were collected prior to treatment.

“The data represent a conservative estimate of human exposure to PFAS because samples were collected prior to treatment.”

CDFM is used to manufacture monomers like tetrafluoroethene, which is an important building block in fluoropolymer production.

“CDFM, the most common co-occurring VOC in our dataset, is used to manufacture monomers like tetrafluoroethene, which is an important building block in fluoropolymer production.”

• cites [60] Dams, 2017, Chapter 1. Industrial Aspects of Fluorinated Oligomers and PolymersNot checked yet

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Fire-training areas are known point sources of PFAS.

“Higher 3H concentrations are indicative of more modern water, urban areas have been associated with PFAS occurrence, and fire-training areas are known point sources of PFAS.7,17,63”

• cites [7] Weber, 2017, Geochemical and hydrologic factors controlling subsurface transport of poly- and perfluoroalkyl substances, Cape Cod, Massachusetts, Environ. Sci. Technol. sourceNot checked yet

  Not checked in the free run.

• cites [17] McGuire, 2014, Evidence of remediation-induced alteration of subsurface poly- and perfluoroalkyl substance distribution at a former firefighter training area, Environ. Sci. Technol. sourceNot checked yet

  Not checked in the free run.

• cites [63] Sardiña, 2019, Emerging and legacy contaminants across land-use gradients and the risk to aquatic ecosystems, Sci. Total Environ. sourceNot checked yet

  Not checked in the free run.

The 24 PFAS analyzed here may not represent the total PFAS inventory in groundwater, given the large number of PFAS reported in commercial use and the environment.

“Likewise, the 24 PFAS analyzed here may not represent the total PFAS inventory in groundwater, given the large number of PFAS reported in commercial use and the environment.9”

• cites [9] Buck, 2011, Perfluoroalkyl and polyfluoroalkyl substances in the environment: Terminology, classification, and origins, Integr. Environ. Assess. Manage. sourceNot checked yet

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Although the dataset represents a broad spectrum of hydrogeologic settings in the eastern United States, important aquifer systems like the Northern Atlantic Coastal Plain system and the fracture-flow dominated Floridan carbonate-rock and Piedmont crystalline-rock systems are not represented.

“Although the dataset represents a broad spectrum of hydrogeologic settings in the eastern United States, important aquifer systems like the Northern Atlantic Coastal Plain system and the fracture-flow dominated Floridan carbonate-rock and Piedmont crystalline-rock systems are not represented.”

BRT modeling indicates that it is possible to predict PFAS occurrence based on the explanatory variables investigated here.

“BRT modeling indicates that it is possible to predict PFAS occurrence based on the explanatory variables investigated here.”

The PFAS results are likely to be relevant to human exposure at the tap.

“Thus, the PFAS results are likely to be relevant to human exposure at the tap.”

• AssumptionRests on an assumption: Treatment is often absent for households that rely on private domestic wells as a source of drinking water.

Groundwater affected by modern anthropogenic activity appears to be associated with PFAS, given significant relations between PFAS detections and variables such as 3H, urban land use, VOCs, and pharmaceuticals.

“Broadly, groundwater affected by modern anthropogenic activity appears to be associated with PFAS, given significant relations between PFAS detections and variables such as 3H, urban land use, VOCs, and pharmaceuticals.”