Introduction

Per- and polyfluoroalkyl substances (collectively known as PFAS) are man-made chemicals that have been manufactured since the 1940s. These substances have been used in the United States for decades in many consumer and industrial products such as nonstick, stain-resisting, water-repelling agents, and in firefighting foams. PFAS are persistent in the environment and are known to have adverse effects on the health of humans and animals. Reduction in the manufacture and use of certain PFAS began in the late 1990s, and countries around the world have been working to both control PFAS in the environment and reduce human exposure pathways. PFAS have been detected throughout the world, with higher concentrations near areas where they are either manufactured or used (such as fire-training areas), and in wastewater and sewage sludge (biosolids). PFAS are resistant to degradation and are known to migrate away from sources in groundwater and surface water, threatening human exposure through contaminated drinking water. Recent studies of PFAS in wastewater discharges to streams have shown decreases over time; however, wastewater discharges, biosolids disposal, and industrial sources continue to be a concern for drinking-water contamination (U.S. Environmental Protection Agency, 2022; Hu and others, 2016; Wang and others, 2017; Sunderland and others, 2018).

The areal extent, presence and magnitude of PFAS concentrations in Massachusetts rivers and streams from point and nonpoint sources is unknown. Thus, a baseline characterization of those factors is needed so that PFAS in rivers and streams can be better quantified, and their sources and pathways managed. In 2020, the U.S. Geological Survey (USGS), in cooperation with the Massachusetts Department of Environmental Protection (MassDEP), conducted three sampling rounds at 64 sites on 27 rivers and streams across the Commonwealth. Water samples were collected upstream and downstream from 25 municipal wastewater treatment facilities (only downstream at one facility) that discharge to rivers, many of which are upstream from intakes for public drinking-water supplies. Samples also were collected from an additional 15 sites to represent nonmunicipal, wastewater-affected streams with other suspected nonpoint sources or where no upstream sources were suspected. Locations of the sampled stream sites are shown in figure 1.

The information obtained from this study will provide MassDEP recent, comparable, and reliable data on concentrations of PFAS in rivers and streams in Massachusetts and will also help resource managers prioritize and better quantify the extent of PFAS concerns associated with wastewater treatment facilities that are upstream of intakes for public drinking-water supplies. Additionally, data from stream sites that were not known to be affected by wastewater discharges will fill spatial gaps in statewide characterization. This report describes the sample collection and analytical methods used in the study, provides a summary of the field and laboratory quality-assurance information collected, briefly describes the frequency of occurrence and magnitude of PFAS concentrations measured, and describes the publicly available results and metadata from this study and how to access them.

Study Design

Water samples were collected from August 17 through November 9, 2020, upstream and downstream from 25 wastewater treatment facilities (except at site number 33 [fig. 1], where only downstream samples were collected) and at 15 river or stream sites that were not associated with wastewater discharges (table 1, in back of report). Samples were collected at each site three times over nearly 4 months, with the period between sampling rounds generally lasting 3 to 4 weeks. To ensure that the samples were representative of base-flow concentrations, thereby minimizing PFAS input or dilution from stormwater runoff and overland flow, samples were collected when the streams were at base-flow conditions. For this study, base-flow conditions were defined as those following three or more consecutive days of declining flow and an instantaneous flow less than the 25th percentile of annual daily mean flow (Rantz and others, 1982a, b).

The sampling sites included existing MassDEP monitoring sites, wastewater treatment facility ambient monitoring sites, USGS monitoring sites, and several new sites established for this project. All the sampling sites were assigned USGS station numbers and names. The sites were chosen so that they were only minimally affected by contributions from joining tributaries between the sample sites and the wastewater treatment facilities. Distances upstream and downstream from the wastewater treatment facility discharge points were generally less than (<) 1 mile. In some rivers, however, such as the Merrimack, downstream sampling sites were nearly 8 miles downstream from the discharge point owing to access limitations.

Flow conditions during sample collection were determined from the USGS WaterWatch website, which displays current streamflow conditions relative to the annual daily mean for a site and period of record (https://waterwatch.usgs.gov/?m=real&r=ma&w=map). The 64 sampling sites were spatially associated with an active USGS continuous streamgage (table 2, in back of report; fig. 1). In some cases, several PFAS sampling stations were associated with a single USGS streamgage, such as that on the Assabet River. The USGS streamgages were used as index stations to determine if streams met the sampling criteria for base-flow conditions defined previously.

Discrete measurements of water temperature, specific conductance, pH, and dissolved-oxygen concentration were made in-place and across the stream channel (with YSI 6920 V2-1 multiparameter probes) and the medians of these measurements were applied to the environmental samples. Turbidity also was measured (with a Hach 2100P turbidity meter), either in a grab sample collected from the river center or in the composited sample from a churn splitter. Depending on the width of the river, the USGS standard isokinetic, depth-integrated sampling method, or a modified version, was used to collect the samples (USGS, variously dated). At sites at which the water was shallow enough to wade, samples were collected using a DH-81 depth-integrated hand sampler. At sites that were too deep to wade, samples were collected from bridges using either a DH-95 sampler that was lowered to the stream using a bridge board or by hand, or when flows were <1.5 feet per second (ft/s), samples were collected using a weighted-bottle sampler. If a bridge was not present at the site (such as the Taunton River), samples were collected from a boat using a weighted-bottle sampler. For sites with a cross-sectional width of <30 feet (ft) a single vertical, depth-integrated sample was collected using the DH-81 sampler (or weighted-bottle sampler if flows were <1.5 ft/s) at the center of the river. The sample water was then decanted directly into the sample bottles for analysis at the laboratory. At sites with cross-sectional widths ranging from 30 to 60 ft, three multivertical, depth-integrated subsamples were collected, one each at the center of the channel and at points equidistant from the center and the left and right banks; these subsamples were then decanted into a 4-liter polyethylene churn splitter, which is a compositing container. Sample bottles were filled directly from the churn while the composited sample was being mixed by the churn plunger. At sites where the channel was greater than (>) 60 ft wide, 10 equal-width increment samples were collected using the DH-95 and composited into an 8-liter polyethylene churn splitter, except at Deerfield River (station number 01170006) and Chicopee River (station number 01177000); at those sites, 10 equal-width transect multiple-vertical samples were collected using a weighted-bottle sampler instead of the DH-95 sampler because flows were <1.5 ft/s. At stations on the Nashua River (station number 01095920) and the Assabet River (station number 01097390), the only safe sample-collection locations were from the riverbank (by wading in near the edge) or from a dock. The sampling methods used at each site for the three sampling rounds are shown in table 2 (in back of report).

Results of Analyses of Environmental and Quality-Control Samples

A total of 192 discrete environmental water samples and 53 field QC samples were collected for the 64 sites during the study period (August to November 2020). The water-quality data for the environmental samples are available to the public online from the USGS National Water Information System (NWIS) web interface (USGS, 2020). The data for the environmental samples and the associated field and laboratory QC samples are available in a data release (Savoie and Argue, 2022).

Measurable concentrations of PFAS were detected in samples from all 27 rivers and streams; however, the number of different substances and their concentrations varied across the State and site types. Nineteen of the 24 PFAS for which samples were analyzed were detected at least once. Five PFAS: fluorotelomersulfonate (8:2 FTS), fluorotelomersulfonate (4:2 FTS), perfluorodecanesulfonate (PFDS), perfluorononanesulfonate (PFNS), and perfluorooctanesulfonamide (PFOSA, also called FOSA) were not detected in any of the samples. A statistical summary of PFAS detected in samples collected from August to November 2020 at 64 sites (192 samples) is shown in table 4. Summary statistics for the minimum, median, mean, and maximum concentrations of each analyte do not include the results that were reported as less than the reporting limit (table 1).

The number of PFAS detected in each sample ranged from a low of one substance, measured in samples from Wright Brook, to a high of 16 PFAS, measured in samples from the Shawsheen River. Concentrations of individual PFAS ranged from estimated concentrations that were greater than the method detection limit (MDL) and less than the reporting limit (RL) to 109 ng/L. Six PFAS were detected in 90 percent or more of the samples analyzed; these included the substances perfluorooctanoate (PFOA), perfluorooctanesulfonate (PFOS), perfluoroheptanoate (PFHpA), perfluoropentanoate (PFPeA), perfluorobutanoate (PFBA), and perfluorobutanesulfonate (PFBS). PFPeA and perfluorohexanoate (PFHxA) had the highest overall median concentrations, at 10.9 and 10.7 ng/L, respectively. The highest maximum concentrations reported were for PFPeA and PFBS, at 106 and 109 ng/L, respectively. The highest maximum concentrations of PFOA, PFHpA, PFBA, and PFBS (42, 19, 54, and 109 ng/L, respectively) were measured in samples from the North Nashua River. The highest PFOS concentration (55 ng/L) was measured in the Shawsheen River and the highest PFPeA concentration (106 ng/L) was measured in Sawmill Brook (table 4). Concentrations typically increased from sampling sites upstream to sites downstream from the wastewater treatment facilities, although at some downstream sites concentrations decreased. At sampling sites with associated wastewater treatment facilities, more PFAS were detected and at higher concentrations than at sampling sites on rivers without wastewater treatment facilities.

Field replicate samples were collected at sites that included a wide range of PFAS concentrations, from less than the RL to more than 100 ng/L. The relative percent difference for the field replicate samples was <20 percent for all substances. The relative percent difference between laboratory control sample pairs was <30 percent for all pairs except for Fluorotelomersulfonate (6:2 FTS) in work group WG1414858. The laboratory control sample pair in work group WG1414858 (WG1414858-3 and WG1414858-2) differed by 46 percent, however 6:2 FTS was not detected in the environmental samples analyzed in work group WG1414858. The percent recovery of all the matrix spike samples fell within the set recovery limits for each analyte measured. Data from field and laboratory quality control samples are included as tables in the accompanying data release (Savoie and Argue, 2022).

Perfluorohexanoate (PFHxA) was detected frequently in the QC samples at concentrations greater than the MDL and less than the RL and ranged from 0.305 to 0.513 ng/L. The QC samples with detections of PFHxA included three field source-solution blanks, 80 percent of the field blank samples, two of three deionized water blanks, and 44 percent of the laboratory method blanks. In response to the frequent detection of PFHxA in both field and laboratory blanks, two measures were employed to identify and describe the observed low-level systematic bias for PFHxA results. First, all detections greater than the MDL and less than the RL were reported as less than the RL. Second, a subset of environmental results was qualified with a “V” remark code, indicating that the concentrations may be affected by contamination. Environmental results less than or equal to 10 times the 95-percent upper confidence limit for the 95th percentile of the PFHxA concentrations measured in blanks (Mueller and others, 2015) were qualified with a “V” remark code. The 95-percent upper confidence limit of the 95th percentile of PFHxA concentrations measured in blank samples was 0.513 ng/L. Therefore, all environmental and replicate samples with concentrations of PFHxA reported above the RL and below 5.13 ng/L were qualified with a “V” remark code. The rationale was that potential contamination for this subset of samples could be as great as 10 percent of the measured value; thus, the effect of the contamination bias on the environmental value may be of significance for the measured PFHxA concentrations in these samples. For concentrations in environmental samples >5.13 ng/L, the potential contamination bias would be <10 percent of the reported concentration and is less significant to the environmental values; thus, these values were not qualified with a “V” remark code but were flagged with value qualifier “v” in NWIS, indicating that PFHxA was detected in the laboratory method blank. The PFHxA contamination bias resulted in 36 samples (29 environmental and 7 replicate samples) with PFHxA concentrations greater than the RL and <5.13 ng/L qualified with a “V” remark code.

Selected additional results were also qualified with a “V” remark code because the laboratory method blank completed during the analysis had one or more detections of PFAS. Perfluorononanoate (PFNA) concentrations for six environmental samples (L2046360-01, -02, -03, -06, -08, and -09) were qualified with a “V” remark code because the laboratory method blank in the work group WG1429821 had an estimated PFNA concentration (E1.2 ng/L) that was nearly equal to values reported in the environmental samples. Perfluorohexanesulfonic acid (PFHxS) and PFOS were detected in the laboratory method blank associated with work group WG1432858. PFHxS concentration values for four environmental samples (L2048824-01, -02, -04, and -05) were qualified with a “V” remark code because the environmental sample concentrations were nearly four times the concentration detected in the laboratory method blank (E0.728 ng/L). The PFOS concentration values for the environmental samples in WG1432858 were greater than 10 times the concentration in the laboratory method blank and therefore were not qualified with a remark code but were flagged with value qualifier “v” in NWIS, indicating that PFOS was detected in the laboratory method blank. The PFOS concentration in the field blank in WG1432858 (L2048824-03) was also qualified with a “V” remark code because the field blank concentration was similar to the concentration in the laboratory method blank (E0.728 ng/L). The PFOS concentrations for the environmental samples in WG1432858 were greater than 10 times the concentration in the laboratory method blank and therefore were not qualified with a remark code but were flagged with value qualifier “v” in NWIS, indicating that PFOS was detected in the laboratory method blank.

Selected additional results were “V” qualified because the field blank associated with the environmental sample had one or more detections of PFAS. The PFOA concentration for environmental sample L2039415-24 (7.34 ng/L) was qualified with a “V” remark code because the associated field blank (L2039415-23) had a detection of PFOA at a concentration of 3.54 ng/L. PFOA, PFOS, perfluorodecanoate (PFDA), and perfluorononanoate (PFNA) were detected in the field blank associated with environmental sample L2048824-02. The “V” remark code was applied to the environmental results for PFDA and PFNA for sample L2048824-02 because the concentrations in sample L2048824-02 were within 10 times the concentrations in the field blank. The PFOA and PFOS concentrations for sample L2048824-02 were greater than 10 times the concentrations in the field blank and therefore were not qualified. For samples that were assigned value qualifiers, result-level comments were also added in the NWIS database to indicate that concentrations were associated with detections in field or laboratory blanks. The other detections in the field or laboratory blanks (perfluorotridecanoate [PFTrDA], perfluoroundecanoate [PFUnA], and 6:2 fluorotelomersulfonate [6:2 FTS]) were not associated with detections in the environmental samples, and therefore the associated environmental samples were not qualified with remark or qualifier codes.

Overall, the field and laboratory QC data indicate that the environmental data collected and reported are of known and definable quality and suitable to meet the objectives of the project. The analytical results provided by Alpha Analytical, Inc. included data qualifiers related to the method sensitivity and performance for each sample and substance analyzed. The USGS used those data qualifiers related to the method sensitivity and performance, combined with the distribution and frequency of contamination, bias, and random error measured in the QC samples analyzed for this project, to describe the quality of the data. The USGS has many metadata tools available to describe the quality of data; for this dataset, however, remark codes and value qualifier codes defined by NWIS were used to describe the quality of the results. The Alpha Analytical, Inc. sample labeling convention and data qualifiers with corresponding USGS remark and value qualifiers codes are described in appendix 1. Although selected results were qualified or remark codes were added on the basis of field or laboratory quality-assurance information, all data are published and available. The USGS recommends that data users review and consider the assigned remark codes and value qualifier codes when interpreting these data.

Summary

Water samples collected during three sampling rounds at 64 sites in 27 rivers and streams in Massachusetts were analyzed to determine the occurrence and concentrations of 24 per- and polyfluoroalkyl substances (PFAS). The samples were collected when the instantaneous flow of the rivers and streams were at base-flow conditions (flow less than the 25th percentile of annual daily mean flow) to minimize PFAS input or dilution from stormwater runoff and overland flow. The data collected show that measurable concentrations of PFAS were observed in all rivers and streams sampled. The number of PFAS detected in each sample ranged from a low of 1 substance, measured in samples from Wright Brook, to a high of 16 PFAS, measured in samples from the Shawsheen River. The PFAS detected most frequently—in 90 percent or more of the samples analyzed—included perfluorooctanoate (PFOA), perfluorooctanesulfonate (PFOS), perfluoroheptanoate (PFHpA), perfluoropentanoate (PFPeA), perfluorobutanoate (PFBA), and perfluorobutanesulfonate (PFBS).

Concentrations of individual PFAS ranged from estimated levels that were greater than the method detection limit and less than the reporting limit to 109 nanograms per liter (ng/L). The highest maximum concentrations reported were measured in samples from the North Nashua River, Shawsheen River, and Sawmill Brook. Concentrations typically increased from sampling sites upstream to downstream of the wastewater treatment facilities, although at some sites downstream concentrations decreased. At sampling sites associated with wastewater treatment facilities, more PFAS were detected and at higher concentrations than at sampling sites on rivers without wastewater treatment facilities.

Quality-control data demonstrated that concentrations of perfluorohexanoate (PFHxA) less than 5.13 ng/L may have been affected by a systematic positive bias in the analytical method. The positive bias reduced the ability to characterize low concentrations (less than 5.13 ng/L) of PFHxA. However, the median concentration of PFHxA was 10.7 ng/L and the maximum value 91 ng/L, indicating that more than 50 percent of the distribution of concentrations was high enough to overcome the potential systematic bias. All data are published and available and users are advised to review and consider the assigned remark and value qualifier codes when interpreting the data.

The data collected in this study provide information on PFAS occurrence and concentrations in Massachusetts rivers and streams that receive wastewater discharge from wastewater treatment and industrial facilities, and those that have no known or suspected sources of PFAS. This information can be used for watershed planning and wastewater discharge permitting in Massachusetts, particularly at facilities that discharge upstream from public water supplies. The results of the study will provide the Massachusetts Department of Environmental Protection with documentation of baseline water-quality conditions with respect to PFAS, and will help the U.S. Geological Survey assess sources, transport, and delivery of PFAS in rivers and streams on a nationwide basis.