Per- and Polyfluoroalkyl Substances (PFAS) in the United States

PFAS were first recognized as a potential chemical of concern in the United States in 1966 (Hayes and Faber, 2019) according to a response memo from the Food and Drug Administration that rejected PFAS as a food additive, citing liver studies. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are probably the most studied PFAS chemicals in terms of toxicology and epidemiologic evaluations (Agency for Toxic Substances and Disease Registry [ATSDR], 2021, 2023). These compounds and other PFAS are potentially persistent in the human body, and some have been detected in the blood (and breastmilk) of almost all U.S. residents tested (Calafat and others, 2007; Zheng and others, 2021), and the longer-fluorinated carbon chain compounds and some emerging PFAS have been shown to bioaccumulate and biomagnify in humans and animals (Conder and others, 2008; Munoz and others, 2019). PFOA and PFOS have caused tumors in animals and have been linked to low birth weights, and disruption of the immune system and thyroid hormones (ATSDR, 2021; Panieri and others, 2022). These compounds have also been associated with nonalcoholic fatty liver disease (Costello and others, 2022).

Consumption of contaminated drinking water is one of many exposure pathways for PFAS in the general population (Sunderland and others, 2019). PFAS are persistent in both surface-water and groundwater environments owing to their high solubility, limited ability to bind to organic carbon, and resistance to biodegradation (Post and others, 2012). PFOA, PFOS, and other PFAS have been detected in finished drinking water and drinking-water sources affected by releases from many sources, including but not limited to industrial facilities and wastewater treatment plants, as well as in waters with no known point sources (Post and others, 2009; Hu and others, 2016; Andrews and Naidenko, 2020; Andrews and others, 2021). Through the third Unregulated Contaminant Monitoring Rule, the EPA conducted a nationwide reconnaissance of selected U.S. systems and collected samples from 4,920 drinking-water systems, detecting PFAS in more than 100 of the systems, including at least one system in Illinois that had detectable concentrations of PFOA (EPA, 2017). A spatial analysis of the third Unregulated Contaminant Monitoring Rule data indicated that the number of industrial sites, fire training areas, and wastewater treatments plants were predictors of PFAS-detection frequencies (Hu and others, 2016). Boone and others (2019) tested the untreated and treated water at 25 drinking-water treatment plants in the United States where PFAS were suspected to be present and detected PFAS in all samples; one location had PFOA and PFOS concentrations that exceeded the EPA’s previous health-advisory level (HAL) of 70 nanograms per liter (ng/L). In addition, Boone and others (2019) determined that only 5 of the 25 locations had statistically significant differences between the source and treated water, indicating that typical water-treatment techniques may be ineffective for PFAS. Hu and others (2016) also suggested two primary actions that would aid in the identification of PFAS contamination sources: (1) lowering the analytical reporting limits, and (2) additional sampling of private supply wells and smaller community water supplies serving populations less than (<) 10,000.

Although PFAS have been recognized since the 1960s as harmful to humans and the environment, changes in manufacturing processes and nationwide regulations limiting PFAS use have been minimal until the last decade (Interstate Technology Regulatory Council, 2020). The enactment of Section 7321 of the National Defense Authorization Act of 2020, an EPA program to track and learn about toxic chemical releases that may pose a threat to human health and the environment, added selected PFAS to the Toxic Release Inventory (EPA, 2021a, 2021b, 2022b). The National Defense Authorization Act of 2020 created a specific charge to the Department of Defense to create a PFAS-free alternative to firefighting foam by October 2024 (Simba, 2021). This follows the passage of the Federal Aviation Administration Reauthorization Act of 2018 (Public law 115-254, 132 Stat. 3186) that no longer required U.S. airports to use PFAS-based firefighting foams (Simba, 2021). The EPA released draft aquatic life criteria for PFOA and PFOS in April 2022 (EPA, 2022c).

In March of 2021, the EPA announced that it will develop national primary drinking-water standards and wastewater effluent standards for PFOA and PFOS (EPA, 2021a, 2021c). In the interim, the EPA issued updated PFOA and PFOS HALs of 0.004 and 0.02 ng/L, respectively, and added HALs for perfluorobutanesulfonic acid (PFBS) and hexafluoropropylene oxide dimer acid (HFPO–DA) and its ammonium salt (together referred to as “GenX chemicals”) (EPA, 2022d; table 2). GenX chemicals include a variety of recently developed compounds intended to replace PFOA and PFOS. The interim HALs provide guidelines for States and public water suppliers until the national primary drinking-water standards are established. Regional screening levels (RSLs) were also released in May 2022 (EPA, 2022e). RSLs are used to characterize the nature and magnitude of risks to human health and ecological health (EPA, 2022e). The EPA also proposed maximum contaminant levels for six PFAS in drinking water (PFOA [4 ng/L]; PFOS [4 ng/L]; perfluorononanoic acid, perfluorohexanesulfonic acid [PFHxS], PFBS, HFPO–DA [Hazard Index 1.0]) in March of 2023 (EPA, 2023). To support and inform potential State-specific standards, some States are undertaking studies to determine the prevalence of PFAS in drinking-water supplies within their borders (Safer States, 2023).

Per- and Polyfluoroalkyl Substances in Illinois

According to the Illinois Environmental Council and the Environmental Working Group, PFAS have been detected in eight drinking-water systems in Illinois (Simba, 2021; Environmental Working Group, 2022). The IEPA (2022a) currently applies preliminary health-based guidance levels (HBGLs) for seven of the most widely used PFAS, whereas the EPA has applied HALs for four PFAS and applies risk-based RSLs for additional PFAS, primarily for children (ingestion and dermal) (table 2) (EPA, 2022d, 2022e). The IEPA is planning to set a statewide minimum threshold to help guide public health officials in responding to PFAS contamination. The current study could be used to help determine the next steps for setting a statewide maximum contaminant level in Illinois. Information on the creation of a statewide maximum contaminant level for PFAS in Illinois can be accessed on the IEPA web page (IEPA, 2022b; IEPA, 2023).

Purpose and Scope

This report summarizes the occurrence and distribution of PFAS from samples collected by IEPA in CWS systems across Illinois. Data are available from either Illinois EPA’s Drinking Water Watch system (IEPA, 2022c) or Illinois EPA’s PFAS Sampling Network (IEPA, 2022d). The results from the initial samples, confirmation, and secondary confirmation samples were provided to the USGS in a spreadsheet. The data from this spreadsheet were used to statistically evaluate the occurrence and distribution of PFAS. Results are presented in various graphs illustrating the range, frequency, and the distribution of the types of PFAS detected in the drinking-water sources are presented on maps.

Sampling Plan and Sample Analysis

The initial goal of the sampling plan was to collect samples from finished water at 1,456 entry points to the distribution system representing 1,749 CWS systems across Illinois for the analysis of PFAS. However, only active entry points were sampled (that is, CWS systems that were actively treating source water and then supplying drinking water directly to the population or to other CWS systems for redistribution). A CWS system could have multiple supply wells, surface-water intakes, and entry points into the CWS distribution system. All active entry points at each CWS system were sampled and each entry point is distinguished with a unique identification number. Initial samples represent the first sample collected at each entry point of a CWS. If the initial sample results had any detectable PFAS, a confirmation sample was collected at those same entry points to verify the presence of that detected PFAS from the initial sampling event. If the confirmation sample did not confirm the initial detection, a secondary confirmation sample was collected. The results of the third sample helped determine whether PFAS was confirmed at that sample location. The type of PFAS detected at or above the HBGL were also considered for additional confirmation sampling. For example, PFOA has an HBGL of 2 ng/L, which is equal to the MRL and was initially detected in 9 samples but was not detected in the confirmation sample or secondary confirmation sample; and therefore, not confirmed. There were instances in which confirmation samples were collected to confirm the presence of other PFAS detected in the initial sample and PFOA was detected for the first time. In these instances, because PFOA is of particular concern due to a low HBGL at the MRL, a secondary confirmation sample was collected, and the results helped determine whether PFOA was confirmed in that sample. One or more of the same PFAS repeatedly detected in at least two sampling events indicated the sample site and water system both were categorized as confirmed detections. Ultimately, the IEPA collected 1,711 unfiltered field samples (includes quality-control samples) of finished water at active entry points (that is, water entering the system of pipes used to distribute drinking water to the customer) between September 2020 and December 2021 at 1,017 Illinois CWS systems (fig. 1) for the analysis of PFAS. Of the 1,711 total samples collected, 1,428 were initial field samples, 164 samples were confirmation samples, 33 were secondary confirmation samples, and the remainder were duplicate samples. The median length of time between the initial and confirmation collection dates was 28 days and the secondary confirmation-sample median length of time between the first and third collection dates was 56 days.

Sample collection methods followed the SOP contained in the IEPA QAPP (Dulka and Rousey, 2020; IEPA, 2020). According to the SOP and QAPP, each sample set from a unique entry point consisted of a minimum of an unfiltered field sample (two 250-milliliter polypropylene bottles) and a field reagent blank (FRB) (one bottle). Precision and bias were measured by collecting additional samples for field duplicates and laboratory fortified sample matrix (LFSM)/LFSM duplicate (LFSMD) per batch of 20 field sample sets. A total of 86 field duplicate samples and 75 LFSM/LFSMD samples were collected in this study. The LFSM is an aliquot of field sample to which known quantities of the method compounds (18 PFAS) are added. The LFSM is processed and analyzed exactly like a sample, and its purpose is to determine whether the sample matrix contributes bias to the analytical results. The LFSMD is a duplicate field sample used to prepare the LFSM, which is fortified, extracted, and analyzed identically to the LFSM. The LFSMD is used to evaluate the precision associated with any potential matrix effects observed from the LFSM sample.

At the time the finished water samples were collected, information regarding the drinking-water source was recorded for each sampling site—groundwater (GW), surface water, (SW), or mixed sources of surface water and groundwater (MX) according to the type of water entering the distribution system from the entry point sampled. The source water designations are based on IEPA CWS system records. Groundwater is sourced from supply wells extracting water from one or more aquifers. Surface water is sourced water from intakes situated within a river, lake, or reservoir. Mixed water is sourced from water that is either combined at the water system from both groundwater and surface water prior to the treatment and sampling, or from groundwater wells that are under the influence of surface water. CWS systems may have groundwater wells, surface water intakes, or a combination of both. These CWS systems may combine the water prior to treatment, or they may have separate treatment points. Additionally, some parts of the treatment and distribution system may service different geographical areas. Most CWS systems will fit within the GW, SW, and MX categories of source-water type identified at the sampling points, but there are several CWS systems that do not fit into these general categories. These CWS systems have source water from groundwater and surface water sources but are not mixed. Therefore, discussions or interpretation of PFAS distribution among the GW, SW, or MX sources may have additional considerations not presented in this study.

Samples were submitted to Eurofins Eaton Analytical, LLC, in South Bend, Indiana—a National Environmental Laboratory Accreditation Conference-certified laboratory—for analysis of a suite of 18 PFAS (table 1) using the EPA Method 537.1 (Shoemaker and Tettenhorst, 2018). The MRL is established in the laboratory method, represents the minimum concentration that may be reported by a laboratory as a quantified value, and is no lower than the lowest concentration MRLs. The lowest concentration MRL is the lowest true concentration for which a future recovery is expected to be between 50 and 150 percent with a 99-percent confidence level (Shoemaker and Tettenhorst, 2018). The laboratory lowest concentration MRLs were used to set the MRLs in this study—the MRL for all PFAS in this study is 2 ng/L. Although not required by the EPA Method 537.1, the detection limit is a threshold below which measured values are not considered significantly different from a blank signal (Helsel, 2012; Shoemaker and Tettenhorst, 2018). Concentrations above the instrument’s detection limit and below the MRL are possible; however, only results greater than or equal to the MRL (2 ng/L) were reported to the USGS. Any detections reported below the 2.0 ng/L MRL were considered not detected by IEPA. Laboratory analytical results are stored and available in the IEPA Safe Drinking Water Information System through Drinking Water Watch, which is a publicly available database (IEPA, 2022c; https://water.epa.state.il.us/dww/index.jsp). The data also can be viewed at the IEPA designated PFAS ArcGIS web page (IEPA, 2022d; https://illinois-epa.maps.arcgis.com/apps/dashboards/bd611162a7f74cfe88b6928c926416c3). The IEPA PFAS Dashboard displays all PFAS detections from the 2020–21 sampling effort, including the duplicate samples. Based on the results from separate sampling events at each entry point, categories are provided for Not Detected, Confirmed Detections (with a minimum of two detections of the same PFAS at or above the MRL), and Unconfirmed Detections (with only a single detection of a PFAS from all samples). The IEPA Dashboard also displays all the results from the initial, confirmation, and secondary confirmation samples at each site along with the duplicate samples that had detections not reported in the associated field sample.

Statistical analyses of PFAS-sampling results were applied using the R statistical computing environment, version 2022.07.2 (R Core Team, 2022). Censored data—that is, concentrations below the MRL—were analyzed using the maximum likelihood estimation (Helsel, 2012; Lee and Helsel, 2022). The Kruskal-Wallis rank sum test (Kruskal and Wallis, 1952), a nonparametric statistical equation, was applied to test for differences among PFAS (includes censored and detections above MRL) in groundwater, surface water, and mixed drinking-water sources (Hollander and Wolfe, 1973; Helsel and others, 2020). The null hypothesis for the Kruskal-Wallis rank sum test is that the mean ranks of the values are equal among the three drinking-water sources. Probability values (p-values) of <0.05 (p-value<0.05) rejects the null hypothesis of equal mean rank among the drinking-water sources.

Quality-Assurance and Quality-Control Analysis and Results

Instrument and field sampling precision is assessed from repeated measurements of the same PFAS in duplicate samples from the same source. A total of 86 duplicate samples were collected during the 2020–21 PFAS sampling period. The initial sampling event included 72 duplicate samples for PFAS analysis. PFAS were detected in 14 of the 72 initial field duplicate samples. Fourteen additional duplicate samples were collected during the confirmation sampling events at CWS locations where PFAS were detected above the MRL in the initial field samples. No site had more than one duplicate sample collected, and no duplicate samples were collected during the secondary confirmation sampling. Detected PFAS concentrations in the associated field sample were compared to the duplicate sample results. The relative percent difference, calculated as the absolute difference in the field sample and duplicate sample concentrations divided by the mean of the two concentrations, was generally less than 10 percent for most of the results, with a few exceptions (table 3). One confirmation sample and associated duplicate sample from a CWS (IL1115700) had consistent differences between concentrations of PFBS (15 percent), PFHxA (23 percent), and PFOA (10 percent). There were no indications of any sample integrity issues for this sample noted in the dataset provided to the USGS. These larger percent differences may be from low concentrations of PFAS that are close to the detection limits (MRLs) using EPA Method 537.1. Additionally, there were five total instances where a PFAS was detected in either the sample or the duplicate but not in both; however, subsequent confirmation sampling at the locations of earlier sampling events ultimately confirmed the detection (table 3). When PFAS were detected in the field sample, the associated FRBs were analyzed by the laboratory and the results were reported to IEPA. According to IEPA, the FRB results were less than the MRL (Michelle Rousey, IEPA, written commun., June 2, 2022). The results from the duplicate and FRB sample analyses were generally of acceptable precision and no indication of cross-contamination instances were evident.

The LFSM/LFSMD are sampled and analyzed exactly like a field sample and are used to identify whether background characteristics of the water samples being analyzed (in this case, components that are not the 18 PFAS in EPA Method 537.1 [Shoemaker and Tettenhorst, 2018]) are interfering with the measurement of the target compounds—PFAS. The laboratory spikes (that is, adds) a known concentration of the 18 PFAS to the LFSM and LFSMD samples and then analyzes the samples. The laboratory subtracts the unspiked sample concentration (field sample) from the known spiked sample concentration (LFSM/LFSMD), and then divides by the spike concentration; this is multiplied by 100 to calculate the percent recovery. Of the 75 LFSM/LFSMD samples collected, 7 sample sets exceeded the spike percent recovery upper limit of 150 percent (Michelle Rousey, IEPA Bureau of Water – Quality Control Officer, written commun., February 2022). In each instance, the exceedance in percent recovery was due to concentrations of PFAS in the associated field sample below the MRL (2 ng/L) but high enough to bias the LFSM/LFSMD result. These instances did not affect or further qualify the field sample results because the source of the high recovery was not related to matrix enhancement; rather, the high recovery was due to the native concentration of PFAS in the parent (field) sample.