Measurement of Novel, Drinking Water-Associated PFAS in Blood from Adults and Children in Wilmington, North Carolina
2020; National Institute of Environmental Health Sciences; Volume: 128; Issue: 7 Linguagem: Inglês
10.1289/ehp6837
ISSN1552-9924
AutoresNadine Kotlarz, James McCord, David N. Collier, C. Suzanne Lea, Mark J. Strynar, Andrew B. Lindstrom, Adrien A. Wilkie, Jessica Y. Islam, Katelyn Matney, Phillip Tarte, M.E. Polera, Kemp Burdette, Jamie C. DeWitt, Katlyn May, Robert C. Smart, Detlef R.U. Knappe, Jane A. Hoppin,
Tópico(s)Quantum Electrodynamics and Casimir Effect
ResumoVol. 128, No. 7 ResearchOpen AccessMeasurement of Novel, Drinking Water-Associated PFAS in Blood from Adults and Children in Wilmington, North Carolinais corrected byErratum: "Measurement of Novel, Drinking Water-Associated PFAS in Blood from Adults and Children in Wilmington, North Carolina" Nadine Kotlarz, James McCord, David Collier, C. Suzanne Lea, Mark Strynar, Andrew B. Lindstrom, Adrien A. Wilkie, Jessica Y. Islam, Katelyn Matney, Phillip Tarte, M.E. Polera, Kemp Burdette, Jamie DeWitt, Katlyn May, Robert C. Smart, Detlef R.U. Knappe, and Jane A. Hoppin Nadine Kotlarz Department of Civil, Construction, and Environmental Engineering, North Carolina State University (NCSU), Raleigh, North Carolina, USA Department of Biological Sciences, NCSU, Raleigh, North Carolina, USA Center for Human Health and the Environment, NCSU, Raleigh, North Carolina, USA , James McCord Center for Environmental Measurement and Modeling, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA , David Collier Center for Human Health and the Environment, NCSU, Raleigh, North Carolina, USA Department of Pediatrics, Brody School of Medicine, East Carolina University (ECU), Greenville, North Carolina, USA , C. Suzanne Lea Center for Human Health and the Environment, NCSU, Raleigh, North Carolina, USA Department of Public Health, ECU, Greenville, North Carolina, USA , Mark Strynar Center for Environmental Measurement and Modeling, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA , Andrew B. Lindstrom Center for Environmental Measurement and Modeling, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA , Adrien A. Wilkie Department of Biological Sciences, NCSU, Raleigh, North Carolina, USA Department of Epidemiology, UNC Gillings School of Global Public Health, Chapel Hill, North Carolina, USA , Jessica Y. Islam Department of Biological Sciences, NCSU, Raleigh, North Carolina, USA Department of Epidemiology, UNC Gillings School of Global Public Health, Chapel Hill, North Carolina, USA , Katelyn Matney New Hanover County Health Department, Wilmington, North Carolina, USA , Phillip Tarte New Hanover County Health Department, Wilmington, North Carolina, USA , M.E. Polera Cape Fear River Watch, Wilmington, North Carolina, USA , Kemp Burdette Cape Fear River Watch, Wilmington, North Carolina, USA , Jamie DeWitt Center for Human Health and the Environment, NCSU, Raleigh, North Carolina, USA Department of Pharmacology and Toxicology, ECU, Greenville, North Carolina, USA , Katlyn May Center for Human Health and the Environment, NCSU, Raleigh, North Carolina, USA , Robert C. Smart Department of Biological Sciences, NCSU, Raleigh, North Carolina, USA Center for Human Health and the Environment, NCSU, Raleigh, North Carolina, USA , Detlef R.U. Knappe Department of Civil, Construction, and Environmental Engineering, North Carolina State University (NCSU), Raleigh, North Carolina, USA Center for Human Health and the Environment, NCSU, Raleigh, North Carolina, USA , and Jane A. Hoppin Address correspondence to Jane A. Hoppin, Department of Biological Sciences, Campus Box 7633, NC State University, Raleigh, NC 27695-7633 USA. Telephone: (919) 515-2918. Email: E-mail Address: [email protected] Department of Biological Sciences, NCSU, Raleigh, North Carolina, USA Center for Human Health and the Environment, NCSU, Raleigh, North Carolina, USA Published:22 July 2020CID: 077005https://doi.org/10.1289/EHP6837Cited by:26AboutSectionsPDF Supplemental Materials ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail AbstractBackground:From 1980 to 2017, a fluorochemical manufacturing facility discharged wastewater containing poorly understood per- and polyfluoroalkyl substances (PFAS) to the Cape Fear River, the primary drinking water source for Wilmington, North Carolina, residents. Those PFAS included several fluoroethers including HFPO-DA also known as GenX. Little is known about the bioaccumulation potential of these fluoroethers.Objective:We determined levels of fluoroethers and legacy PFAS in serum samples from Wilmington residents.Methods:In November 2017 and May 2018, we enrolled 344 Wilmington residents ≥6 years of age into the GenX Exposure Study and collected blood samples. Repeated blood samples were collected from 44 participants 6 months after enrollment. We analyzed serum for 10 fluoroethers and 10 legacy PFAS using liquid chromatography–high-resolution mass spectrometry.Results:Participants' ages ranged from 6 to 86 y, and they lived in the lower Cape Fear Region for 20 y on average (standard deviation: 16 y). Six fluoroethers were detected in serum; Nafion by-product 2, PFO4DA, and PFO5DoA were detected in >85% of participants. PFO3OA and NVHOS were infrequently detected. Hydro-EVE was present in a subset of samples, but we could not quantify it. GenX was not detected above our analytical method reporting limit (2 ng/mL). In participants with repeated samples, the median decrease in fluoroether levels ranged from 28% for PFO5DoA to 65% for PFO4DA in 6 months due to wastewater discharge control. Four legacy PFAS (PFHxS, PFOA, PFOS, PFNA) were detected in most (≥97%) participants; these levels were higher than U.S. national levels for the 2015–2016 National Health and Nutrition Examination Survey. The sum concentration of fluoroethers contributed 24% to participants' total serum PFAS (median: 25.3 ng/mL).Conclusion:Poorly understood fluoroethers released into the Cape Fear River by a fluorochemical manufacturing facility were detected in blood samples from Wilmington, North Carolina, residents. Health implications of exposure to these novel PFAS have not been well characterized. https://doi.org/10.1289/EHP6837IntroductionPer- and polyfluoroalkyl substances (PFAS) are a broad class of synthetic chemicals used to manufacture fluoropolymers, stain repellents, paper coatings, and fire-fighting foams (Kissa 2001). In addition to the PFAS produced for commercial purposes, other PFAS can be formed as by-products or impurities of fluorochemical production (Dinglasan et al. 2004; James and Franklin 1966; Liang et al. 1998; Moore et al. 1966). Many PFAS have high aqueous solubility and are persistent in the environment. As a result, PFAS are stable in water and can travel over long distances in freshwater and marine ecosystems (Banzhaf et al. 2017; Möller et al. 2010). PFAS releases into the environment can therefore impact drinking water sources both near and far from the source of contamination (Hu et al. 2016; Ingelido et al. 2018; Mak et al. 2009; Pan et al. 2018; Sharma et al. 2016; Sun et al. 2016).PFAS are not substantially removed by most conventional drinking-water treatment processes, including coagulation, flocculation, sedimentation, filtration, and disinfection (Rahman et al. 2014). Elevated concentrations of PFAS have been reported in the finished drinking water of community water systems that source water from areas with industrial facilities producing or using PFAS (Graber et al. 2019; Hu et al. 2016). Notably, perfluorooctanoic acid (PFOA) releases from a fluorochemical plant near Parkersburg, West Virginia, resulted in parts-per-billion levels of PFOA in drinking water sourced from contaminated wells; in the community, tap water consumption was a significant predictor of serum PFOA levels (Emmett et al. 2006; Hoffman et al. 2011). Human exposure to PFAS [PFOA and perfluorooctane sulfonate (PFOS) are the most studied to date] has been associated with thyroid disease, ulcerative colitis, elevated cholesterol levels, developmental delays, liver disease, kidney and testicular cancer, and immunosuppression (ATSDR 2018; DeWitt et al. 2009; Steenland et al. 2010; Sunderland et al. 2019).In North Carolina, a 2,150-acre fluorochemical manufacturing facility (i.e., Fayetteville Works) (Figure 1) discharged process wastewater to the Cape Fear River as early as 1980 (Wagner and Buckland 2017). Several poorly understood PFAS, including hexafluoropropylene oxide dimer acid (HFPO-DA or GenX), have been detected in water samples collected downriver of the facility's effluent discharge point (Hopkins et al. 2018; McCord and Strynar 2019; McCord et al. 2018; Strynar et al. 2015; Sun et al. 2016; Zhang et al. 2019). These PFAS are collectively referred to as fluoroethers because they have the traditional perfluoroalkyl carbon chains characteristic of legacy PFAS, such as PFOA, but the chains are interrupted by ether oxygen(s) (see Figure S1) (Strynar et al. 2015). The released fluoroethers, including GenX, were generated as by-products of fluoropolymer production at Fayetteville Works facility (Hopkins et al. 2018; McCord and Strynar 2019). Human exposure to by-products of fluorochemical manufacturing has not been studied to date.Figure 1. Cape Fear River Basin, North Carolina, United States. Note: PFAS, per- and polyfluoroalkyl substances.Approximately 80 miles downriver of Fayetteville Works is the raw water intake for the Cape Fear Public Utility Authority (CFPUA), which provides drinking water to approximately 200,000 people in New Hanover County, home to Wilmington, North Carolina. Raw water concentrations of the fluoroethers were similar to treated water concentrations because the fluoroethers were not measurably removed by CFPUA's water treatment processes, which included several advanced steps (i.e., raw and settled water ozonation, biofiltration, and ultraviolet light disinfection) (Hopkins et al. 2018). In early June 2017, the public became aware of the presence of GenX in their drinking water (Hagerty 2017). Community concern and subsequent action by the North Carolina Department of Environmental Quality (NC DEQ) resulted in the fluorochemical manufacturer reducing its wastewater discharges to the Cape Fear River on 21 June 2017, and by September 2017, the facility stopped discharging process wastewater containing PFAS into the Cape Fear River (NC DEQ 2017). As a result, the GenX concentration in Wilmington's drinking water source dropped from approximately 700 ng/L before discharge control to approximately 100 ng/L 1 week later (Hopkins et al. 2018; Sun et al. 2016; Zhang et al. 2019).We initiated The GenX Exposure Study in November 2017 to answer community members' questions about their exposure to GenX and other PFAS. We included in our analysis fluoroethers that were by-products of fluorochemical manufacturing at Fayetteville Works as well as legacy PFAS historically used throughout the Cape Fear River Basin. We report here the initial findings for serum PFAS levels measured in a Wilmington, North Carolina, population.MethodsStudy PopulationIn November 2017 and May 2018, we recruited individuals from New Hanover County, North Carolina, to participate in the GenX Exposure Study. We partnered with Cape Fear River Watch, a local nongovernmental organization focusing on water quality in the region; the New Hanover County Health Department; the New Hanover County NAACP; and informal community partners to inform the public about the study. Press releases, news stories, public service announcements, recruitment flyers, social media platforms, and the study website ( https://genxstudy.ncsu.edu/) were used to promote the study.CFPUA distributes drinking water to the City of Wilmington and unincorporated areas of New Hanover County not served by privately owned systems. CFPUA operates three treatment plants with separate distribution systems: One plant sources water from the lower Cape Fear River, and the other two from various groundwater sources (CFPUA 2020b). Most (153,200 or 80%) of the 190,500 people served by CFPUA receive water from the lower Cape Fear River (NC Drinking Water Watch 2020). The Richardson and Monterey Heights groundwater treatment plants serve 37,250 people collectively.Study participants were required to be current residents of New Hanover County, ≥6 years of age, and to have lived in a home served with CFPUA drinking water for at least 12 months prior to November 2017 (the start of enrollment). Up to four individuals per household were allowed to participate. We excluded pregnant women and people who were human immunodeficiency virus- or hepatitis C-positive. Individuals were recruited in both English and Spanish. The majority of our participants were recruited in November 2017, with a smaller, targeted recruitment in May 2018. In November, interested individuals contacted the study office to be screened for eligibility. Eligible individuals were scheduled for a clinic visit at the New Hanover County Health Department during the weekend of 10–12 November 2017. We conducted a second recruitment of participants in May 2018, aimed at increasing participation of African Americans. We joined the annual health fair at the MLK Center in Wilmington, hosted by the New Hanover County NAACP. Recruitment, enrollment, and biological sample collection took place at the MLK Center on 5 May 2018. We also scheduled repeat blood and urine collection from a random sample of the November 2017 participants.All study participants provided written informed consent to participate. All phases of the study were conducted in compliance with the North Carolina State University Institutional Review Board.Data CollectionDuring clinic visits, we consented participants, administered a questionnaire, collected biological samples (blood and urine), and measured height and weight. Study staff administered a questionnaire to each participant at the clinic visit to collect information on demographics, drinking water habits, residential history, health history, and PFAS exposures other than drinking water. Children completed a shortened version of the adult questionnaire. Parents provided the residential history for their children.Trained phlebotomists collected nonfasting blood samples from participants. For participants who were ≥11 years of age, four tubes of blood (two red-top tubes for serum, two ethylenediaminetetraacetic acid (EDTA) tubes for whole blood or plasma) were collected. For children 6–10 years of age, two red-top tubes for serum were collected. Serum tubes were spun at 1,300×g for 10 min in a Sorvall RT 600D centrifuge at room temperature. Serum was aliquoted into transfer tubes. One EDTA tube was processed for plasma; the remainder was saved as whole blood. Spot urine samples were provided by study participants during the clinic visit. Urine and blood samples were stored on dry ice and transported to East Carolina University (Greenville, NC) and stored at −80°C. A 2-mL aliquot of serum was shipped on dry ice to the U.S. Environmental Protection Agency (EPA) in Research Triangle Park, North Carolina, where they were stored at −80°C until analysis.PFAS Analysis in BloodAnalytical standards.Native standards for GenX, perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), PFOA, perfluorononanoic acid (PFNA), perfluorobutane sulfonic acid (PFBS), perfluorohexane sulfonic acid (PFHxS), PFOS, and 6:2 fluorotelomer sulfonate (6:2 FTS) and mass-labeled standards for GenX, PFBA, PFHxA, PFOA, PFNA, PFHxS, PFOS, and 6:2 FTS were purchased dissolved in methanol from Wellington Laboratories (see Table S1). Analytical standards for perfluoro-2-methoxyacetic acid (PFMOAA), perfluoro-2-methoxypropanoic acid, 2,3,3,3-tetrafluoro-2-(pentafluoroethoxy)propanoic acid, perfluoro-2-ethoxypropanoic acid (PEPA), perfluoro-3,5-dioxahexanoic acid (PFO2HxA), perfluoro-3,5,7-trioxaoctanoic acid (PFO3OA), perfluoro-3,5,7,9-tetraoxadecanoic acid (PFO4DA), perfluoro-3,5,7,9,11-pentaoxadodecanoic acid (PFO5DoA), and 1,1,2,2-tetrafluoro-2-(1,2,2,2-tetrafluoroethoxy)ethanesulfonic acid (NVHOS) and for perfluoro-3,6-dioxa-4-methyl-7-octene-1-sulfonic acid (Nafion by-product 1), and perfluoro-2-{[perfluoro-3-(perfluoroethoxy)-2-proanyl]oxy}ethanesulfonic acid (Nafion by-product 2) were acquired as aqueous solutions (1,000 ng/μL) from the Chemours Company because there were no commercial sources. The identity of each standard was confirmed by high-resolution mass spectrometry (HRMS). A mixed PFAS standard stock solution was prepared in methanol at 0.1 ng/μL.Sample preparation.Fifty microliters of serum was transferred into 2-mL polypropylene tubes and 100μL0.1M formic acid containing mass-labeled standards (6.25 ng/mL) was added to denature serum proteins. Each sample was then vortex mixed and 450μL cold (−20°C) acetonitrile was added to precipitate proteins. The sample was vortex mixed again and centrifuged at 12,500×g for 5 min in an IEC CL31R Multispeed Centrifuge (Thermo Scientific) at room temperature. Finally, a 100-μL aliquot of the acetonitrile supernatant was placed into a liquid chromatography (LC) vial with 100μL0.4 mM ammonium formate buffer (1:1 mixture).Sample analysis.Measurements for 20 PFAS, 10 fluoroethers, and 10 legacy PFAS (Table 1) in serum were conducted using LC-HRMS. Each serum sample was analyzed using a Thermo Vanquish ultra-performance liquid chromatograph coupled to a Thermo Orbitrap Fusion mass spectrometer. Using a 25-μL injection volume, PFAS were separated on an Accucore Vanquish C18+LC column (100×2.1mm, 1.5μL particle diameter). The mobile phases were 95:5% vol/vol water:acetonitrile with 0.4 mM ammonium formate (Eluent A) and 5:95% vol/vol water:acetonitrile with 0.4 mM ammonium formate (Eluent B), with a flow rate of 300μL/min. The LC method used a 3-min pre-equilibration time at 10% B followed by a linear gradient from 10% to 100% over 10 min with a 3-min hold at 100% B. The mass spectrometer was run in full scan mode with a mass range of 100–700 Da and 120,000 resolving power at m/z 200.Table 1 Ten fluoroethers and 10 legacy PFAS measured for in serum samples in the GenX exposure study.Table 1 has eight columns, namely, Short name, U.S. EPA registry name, Formula, CAS number (hyperlinked to U.S. EPA Chemicals Dashboard superscript a), DTXSID superscript b, Monoisotopic mass, deprotonated, number of fluorinated carbons, and Chain length superscript c.Short nameU.S. EPA registry nameFormulaCASN (hyperlinked to U.S. EPA Chemicals Dashboarda)DTXSIDbMonoisotopic mass, deprotonated# of fluorinated carbonsChain lengthcFluoroethers HFPO-DA (GenX)Hexafluoropropylene oxide dimer acidC6HF11O3 13252-13-670880215328.967757 PMPAPerfluoro-2-methoxypropanoic acidC4HF7O3 13140-29-980528474228.974135 PEPAPerfluoro-2-ethoxypropanoic acidC5HF9O3 267239-61-260896486278.970946 PFO2HxAPerfluoro-3,5-dioxahexanoic acidC4HF7O4 39492-88-150892351244.969136 PFO3OAPerfluoro-3,5,7-trioxaoctanoic acidC5HF9O5 39492-89-220892348310.960848 PFO4DAPerfluoro-3,5,7,9-tetraoxadecanoic acidC6HF11O6 39492-90-590723993376.9525510 PFO5DoAPerfluoro-3,5,7,9,11-pentaoxadodecanoic acidC7HF13O7 39492-91-650723994442.9442612 NVHOS1,1,2,2-Tetrafluoro-2-(1,2,2,2-tetrafluoroethoxy)ethanesulfonic acidC4H2F8O4S 801209-99-480904754296.947346 Nafion by-product 1Perfluoro-3,6-dioxa-4-methyl-7-octene-1-sulfonic acidC7HF13SO5 29311-67-930892354442.9264710 Nafion by-product 2Perfluoro-2-{[perfluoro-3-(perfluoroethoxy)-2-propanyl]oxy}ethanesulfonic acidC7H2F14SO5 749836-20-210892352462.9327710Legacy PFAS PFBAPerfluorobutanoic acidC4HF7O2 375-22-44059916212.979234 PFPeAPerfluoropentanoic acidC5HF9O2 2706-90-36062599262.976045 PFHxAPerfluorohexanoic acidC6HF11O2 307-24-43031862312.972856 PFHpAPerfluoroheptanoic acidC7HF13O2 375-85-91037303362.969667 PFOAPerfluorooctanoic acidC8HF15O2 335-67-18031865412.966478 PFNAPerfluorononanoic acidC9HF17O2 375-95-18031863462.963289 PFBSPerfluorobutane sulfonic acidC4HF9SO3 375-73-55030030298.942945 PFHxSPerfluorohexane sulfonic acidC6HF13SO3 355-46-47040150398.936667 PFOSPerfluorooctane sulfonic acidC8HF17SO3 1763-23-13031864498.930289 6:2 FTS6:2 fluorotelomer sulfonateC8H5F13SO3 27619-97-26067331426.967969Note: CASN, Chemical Abstracts Services Number; EPA, Environmental Protection Agency; GenX, hexafluoropropylene oxide dimer acid.aU.S. EPA CompTox Chemistry Dashboard ( https://comptox.epa.gov/dashboard).bDTXSID is a unique substance identifier used in the U.S. EPA CompTox Chemistry Dashboard (Williams et al. 2017).cIncludes carbon, oxygen, and sulfur atoms in the fluoroalkyl chain but does not include oxygen atoms in the anionic group (i.e., does not include O in carboxylic acid).Extracted ion chromatograms for 6:2 FTS (426.9679±5 ppm) yielded a doublet peak that was selected for follow-up MS/MS investigation with higher-energy C-trap dissociation (HCD) normalized collision energy of 45. Standards of 6:2 FTS (Schultz et al. 2004) and a polyfluoroalkyl ether carboxylic acid 2,2,3,3-tetrafluoro-3-((1,1,1,2,3,3-hexafluoro-3-(1,2,2,2-tetrafluoroethoxy)propan-2-yl)oxy)propanoic acid (known as Hydro-EVE) (Chemical Abstracts Services Number 773804-62-9) (U.S. EPA 2020) were prepared and analyzed by LC-HRMS/MS; annotated MS/MS spectra were compared with spectra collected from 10 serum samples randomly selected from our Wilmington cohort samples.Calibration standards ranging in concentration from 0.1 ng/mL to 25 ng/mL were prepared in newborn calf serum (ThermoFisher Scientific) by spiking PFAS standard stock solution into the serum; calibration standards were processed using the protocol for human serum samples described above. Compounds were quantified using a relative response ratio of the native standard and isotopically labeled internal standard; the [M-H]− or [M-H-CO2]− ions were used. Integration of PFAS isomers was consistent with U.S. EPA Method 537.1 (U.S. EPA 2018); that is, for compounds with branched and linear isomers (PFOA, PFOS, PFHxS), peaks for the branched and linear isomers were integrated together to report total concentration.Serum samples were run in batches of approximately 50 samples. Each batch contained in-house spiked newborn calf serum samples for continuing calibration checks. National Institutes of Standards and Technology (NIST) standard reference material (SRM) 1957 human serum was analyzed for calibration verification (acceptance criteria were ≤30% difference from consensus value). Mean concentrations of legacy PFAS (PFHpA, PFHxS, PFOA, PFOS, and PFNA) in SRM 1957 were within 10% difference of reference values determined by an interlaboratory analysis (see Table S2). We calculated the precision between replicate analyses by taking the difference divided by the average. Intrarun replicate analysis precision for duplicate analyses was less than 30% for most PFAS (see Table S3). As expected, lower replicate precision was observed at lower concentrations.The study sera were run in batches across eight analytical runs. Each analyte was assigned a batch-specific method reporting limit (MRL) defined as the first point of the standard curve for which the regression equation yielded a calculated value within 30% of the true value. For analytes with significant background signal in calf serum blanks, the MRL was designated as three times the maximum response in newborn calf serum blanks (i.e., in the 0-ng/mL standard), if higher than the MRL from the calibration curve. Higher instrument background levels for PFPeA, PFO2HxA, and GenX were observed on some analytical runs and resulted in higher batch-specific MRLs for those PFAS (see Table S4). In addition, the mass spectrometer had a high background response for the mass corresponding to PFMOAA, making it difficult to distinguish PFMOAA standards. We prioritized the method development for PFAS with longer alkyl (ether) chain length (e.g., PFO5DoA), which we suspected were more likely to be detected in blood (Ng and Hungerbühler 2014). Thus, we moved forward without measuring samples for PFMOAA.Statistical MethodsTo calculate summary statistics, we used the first blood sample collected from each participant (i.e., the blood sample collected when the participant was enrolled; that is, the November 2017 sample for most participants and the May 2018 sample for new enrollees in May). We present results for PFAS detected in 60% or more of 344 serum samples. For samples analyzed in duplicate, average values were used in the analyses. Sample results below the MRL were assigned a fill value of the MRL divided by the square root of 2 (Calafat et al. 2007; Daly et al. 2018). However, when we summed the mass concentration of all detectable PFAS to determine total PFAS in serum, we added 0 to the total for PFAS that were below the MRL so that we did not bias the sum upward because of multiple nondetected chemicals. We assessed correlation of PFAS serum concentrations using Spearman correlation coefficients; values greater than or equal to 0.70 were considered highly correlated.To compare differences between participants served with treated Cape Fear River water or another drinking water source, we used a Wilcoxon rank sum test. Two study participants who were enrolled in the early stages of the recruitment effort and who shared the same residence did not meet the study eligibility criterion of residing in the CFPUA service area. Their residence, however, was in Wilmington, and their drinking water source was not the Cape Fear River. Therefore, we included these two participants as part of the group with drinking water not sourced from the Cape Fear River.For participants who provided repeat samples, we calculated percentage change over time using serum PFAS concentrations in November 2017 and May 2018. Percentage change was calculated as ConcentrationNovember 2017−ConcentrationMay 2018ConcentrationNovember 2017×100% [1] We also used a Wilcoxon test for paired samples to evaluate differences in serum PFAS concentrations between November 2017 and May 2018. All statistical analyses were conducted in R (version 3.5.1; R Development Core Team). The significance level for all statistical analyses was p 10y. In 75 of the 231 participating households (32%), at least 2 household members participated in the study. Most participants (97%) had drinking water sourced from the lower Cape Fear River, but 9 participants had another drinking water source.Table 2 Demographic characteristics of the 344 Wilmington, North Carolina, GenX exposure study participants.Table 2 has four columns, namely, Characteristic, November 2017 (n equals 310) (n, percentage), November 2017 Resampled May 2018 (n equals 44) (n, percentage), and May 2018 (n equals 34) (n, percentage).CharacteristicNovember 2017 (n=310) [n (%)]November 2017 (resampled May 2018) (n=44) [n (%)]May 2018 (n=34) [n (%)]Adult/child Adult (≥18y)256 (82.6)42 (95.5)33 (97.1) Child54 (17.4)2 (4.6)1 (2.94)Age group (y)a 6–1754 (17.5)2 (4.6)1 (3.1) 18–2912 (3.9)1 (2.3)2 (6.3) 30–3937 (12.0)4 (9.1)2 (6.3) 40–4957 (18.4)10 (22.7)2 (6.3) 50–5951 (16.5)9 (20.5)4 (12.5) 60–6962 (20.1)9 (20.5)13 (40.6) 70–8636 (11.7)9 (20.5)8 (25.0)Gender Female189 (61.0)28 (63.6)27 (79.4) Male120 (38.7)16 (36.4)7 (20.6) Transgender1 (0.3)00Race/ethnicityb Black, non–Hispanic8 (2.6)027 (79.4) Hispanic, regardless of race33 (10.7)3 (7.0)0 White, non–Hispanic261 (84.7)40 (93.0)4 (11.8) Otherc6 (2.0)03 Spanish speaker17 (5.5)00Residence in lower Cape Fear Region (y)d 1–988 (28.5)10 (22.7)6 (18.8) 10–19112 (36.3)18 (40.9)7 (21.9) 20–3976 (24.6)6 (13.6)6 (18.8) 40–4916 (5.2)5 (11.4)3 (9.4) 50–7317 (5.5)5 (11.4)10 (31.3)Drinking water sourcee CFPUA groundwater5 (1.6)1 (2.3)2 (5.9) CFPUA Cape Fear River301 (97.7)42 (97.7)32 (94.1) Not served by CFPUA2 (0.7)00Number of households2013530Participants per household 1130 (64.7)28 (80.0)26 (86.7) 246 (22.9)6 (17.4)4 (13.3) 312 (6.0)00 413 (6.5)1 (2.9)0Note: CFPUA, Cape Fear Public Utility Authority; GenX, hexafluoropropylene oxide dimer acid.aMissing age for three participants.bMissing race/ethnicity for two participants.cOther includes mixed-race individuals Native American/Pacific Islander, black or African American and Native American/Pacific Islander and white and other, Native American/Pacific Islander and white. May 2018: Other includes: American Indian/Alaska Native and Black or African American, black or African American and Native American/Pacific Islander and white, black or African American and white.dMissing years lived in lower Cape Fear River Region for 1 participant for the November 2017/May 2018 repeaters and 2 participants for the May 2018 new participants.eCFPUA distributes drinking water to New Hanover County, home of the City of Wilmington. Missing water source for 2 participants for November 2017, 1 participant for May 2018 repeaters.Figure 2. Study enrollment and blood sample collection in the GenX Exposure Study: Wilmington, North Carolina. Note: GenX, hexafluoropropylene oxide dimer acid.PFAS Analysis in BloodOur analytical method was developed to determine concentrations of 10 fluoroethers and 10 legacy PFAS (Table 1; see also Table S1) in the serum of all participants. The choice of which PFAS to include in our analytical method was informed by which PFAS had been reported in the lower Cape Fear River (Strynar et
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