Article pubs.acs.org/est
Compositional Effects on Leaching of Stain-Guarded (Perfluoroalkyl and Polyfluoroalkyl Substance-Treated) Carpet in Landfill Leachate Minhee Kim,† Loretta Y. Li,*,† John R. Grace,‡ Jonathan P. Benskin,§ and Michael G. Ikonomou§ †
Department of Civil Engineering, University of British Columbia, 6250 Applied Science Lane, Vancouver, British Columbia, Canada V6T 1Z4 ‡ Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, British Columbia, Canada V6T 1Z3 § Institute of Ocean Sciences, Fisheries and Oceans Canada (DFO), 9860 West Saanich Road, Sidney, British Columbia, Canada V8L 4B2 S Supporting Information *
ABSTRACT: Perfluoroalkyl and polyfluoroalkyl substances (PFASs) from stain-guard treated carpets in landfills continue to be released into the environment. To understand the leaching of PFASs from carpets to landfill leachate as a function of environmental factors, leaching concentrations of ten perfluoroalkyl carboxylic acids and four perfluoroalkyl sulfonic acids were quantified for different pHs, contact times, mixing speeds, and temperatures. Partitioning from carpet to leachate and distilled water at different pHs showed negligible differences. The total concentration of leaching PFASs in distilled water was approximately 1 ng L−1 higher than in landfill leachate, indicating that the presence of multivalent cations in leachate could have a negative effect on leaching of PFASs. For all PFASs monitored, leaching increased with increasing contact time and temperature. Perfluorohexanoic and perfluoroheptanoic acids experienced the largest increases with contact time and temperature. Gibbs free energy (ΔG > 0), enthalpy (ΔH > 0), and entropy energy (ΔS < 0) indicated that PFAS leaching from carpet was dominantly controlled by entropy-driven processes and did not differ significantly among individual PFASs. PFAS concentrations in leachate with rotation of an end-over-end contactor were higher than under static conditions, but otherwise, varying the rotation speed had negligible influence. The results provide useful information for management of discarded stainguard carpets in landfills.
■
INTRODUCTION Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been detected over the past decades in many environmental and biological compartments. Perfluoroalkyl acids (PFAAs) are among the most commonly detected PFASs in the environment, and some of them have the potential to bioaccumulate.1−3 These substances are of increasing concern due to their persistence4 and potential adverse health effects.5 Perfluorooctanesulfonate (PFOS), its salts, and perfluorooctane sulfonyl fluoride (PFOSF) were added to Annex B of the Stockholm convention on persistent organic pollutants (POPs) in May 2009, resulting in global restrictions on the application and production of these compounds.6,7 However, PFASs have already been incorporated in consumer products for six decades due to the unique structure of the extremely strong carbon− fluorine bond, contributing to excellent thermal and chemical stability in a wide range of products, including stain- and waterrepellent coatings on carpets, paper and textiles, grease-resistant food packaging and paper, fire-resistant cables, fire-fighting foams, surfactants in cleaners, medical equipment, motor oil additives, and insecticides.8−10 Of the 96 000 tons of these industrial and consumer products between 1970 and 2002, © 2015 American Chemical Society
stain-guard carpets comprised approximately 50% of estimated total global historical perfluorooctane sulfonyl fluoride (POSF) production and use.11 In Canada, 58% of total perfluoroalkyl sulfonic acids (PFSAs) were applied to fabric and carpet between 1997 and 2000.12 Carpets and carpet treatment products contained perfluoroalkyl carboxylic acids (PFCAs) in levels13 from 0.04 to 14 100 ng g−1. The 3M Company estimated that nearly 53% of the initial concentration of fluorochemical-treated carpet remained before disposal.14 Dinglasan-Panlilio and Mabury15 also documented 0.04−3.8% polyfluorinated telomer alcohols (FTOHs) residual to dry mass for carpet protection products. Releases from landfilled carpets to the environment occur from residual PFCAs, PFSAs, or fluorotelomer-based and perfluoroalkyl sulfonyl-based precursors which can be degraded to PFCAs and PFASs.16−20 PFASs are still being released into the environment from stain-guard treated carpets in landfills, even from those no longer being Received: Revised: Accepted: Published: 6564
October 31, 2014 April 13, 2015 May 1, 2015 May 19, 2015 DOI: 10.1021/es505333y Environ. Sci. Technol. 2015, 49, 6564−6573
Article
Environmental Science & Technology
graphic) in order to maintain consistency in all experiments. To ensure homogeneity of the carpet samples, all carpet pieces were then divided into quarters, resulting in four separate portions, each of which was mixed thoroughly mechanically. Two pairs of the portions were then mixed together, and the resulting two “half-portions” were then combined and blended to form a single homogeneous matrix. This procedure was repeated 10 times for each type of carpet. PFASs from carpet samples were extracted in triplicate. Details of the collection and pretreatment of the carpets are provided in the Supporting Information. Composite carpet samples (5 g each) were next weighed and placed into a 50 mL polypropylene tube, then spiked with 22.5 ng of mass-labeled internal standards (13C4 PFBA, 13C2 PFHxA, 13C4 PFOA, 13C5 PFNA, 13C2 PFDA, and 13 C4 PFOS). Internal standards were applied to correct for the loss of analyte during sample preparation and account for matrix-induced ionization effects. The spiked carpets were allowed to sit for a few minutes until the solvent dried. The extraction was then carried out by adding 15 mL of methanol to the carpets five times. After each stage of extraction with methanol, the centrifuge tubes were shaken in a vortex shaker for ∼15 min. The extracts (∼75 mL total volume) were reduced under nitrogen to a final volume of 45 mL and then spiked with 22.5 ng recovery standard (500 μg of a 500 ppb standard). The solution was then vortex-mixed, and a portion of the extract was transferred to a 300 μL polypropylene microvial for analysis by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Collection, Handling and Analysis of Landfill Leachate. The leachate was collected from a Canadian urban landfill, which accepts municipal waste, as well as residuals and sludge from wastewater treatment plants. Under agreement with the landfill operator, we cannot divulge the location of the landfill. In order to minimize changes in leachate quality, samples were immediately stored in high-density polyethylene (HDPE) bottles at −20 ± 2 °C. Before contacting carpet samples with the leachate, the closed bottles were left in the room for 2 h to reach room temperature. Details of the collection and pretreatment of the landfill leachate are provided in the Supporting Information. The leachate was analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), total organic carbon (TOC), exchangeable cations (Ca2+, Mg2+, Na+, and K+) and metals (Al, Fe, Cd, Cu, Pb, Mn, and Zn). The TOC and metals of the leachate were characterized by USEPA Standard Methods 5310B (2000) and 3120 (1999), respectively.28 The PFAS extraction procedure from collected leachate was adopted from a previously developed USEPA method.29 Prior to extraction, the pH of each sample was checked. All samples and blanks were spiked with 2 ng of masslabeled internal standards. SPE cartridges (Oasis WAX 6 cm3, 500 mg, 30 μm) were conditioned with 5 mL of 0.3% ammonium hydroxide in methanol, 5 mL of 0.1 M formic acid, and 5 mL of reagent high-performance liquid chromatography (HPLC)-grade distilled water prior to loading. Samples were mixed, and then loaded dropwise (5 mL min−1) under vacuum. After loading, the cartridges were washed with 5 mL of 20% methanol and 80% of 0.1 M formic acid in reagent water. The cartridges were next dried under vacuum and eluted with 4 mL of 0.3% ammonium hydroxide in methanol. The extracted solution was spiked with recovery standard and a portion was transferred into a conical vial for analysis by HPLC-MS/MS. Experimental Procedure. The leaching experiments were conducted in a pilot-scale end-over-end contactor (See Abstract
manufactured, and this will continue in future years as carpets now in service or storage continue to be sent to landfills. Several studies on PFAS concentrations in leachate indicate PFOS and perfluorooctanoic acid (PFOA) concentrations up to 82 000 ng L−1 in landfills that received wastes from PFAS manufacturing.21,22 Recent studies have monitored the concentration range and various composition for PFASs in landfill sites in Canada (30−21 000 ng L−1 based on 13 PFASs),23,24 United States (2700−7400 ng L−1 based on 24 PFASs)25 and Germany (30−13 000 ng L−1 based on 43 PFASs).26 However, the leaching capacity of PFASs at landfill sites depends heavily on environmental factors such as pH, temperature, ionic strength of leachate and contact time. The leaching capacity and mechanisms of PFAS transfer from carpets to landfill leachate as a function of environmental factors have not been addressed. The objectives of this study were (i) to quantify the effect of environmental factors on the leaching of 14 PFASs encompassing ten PFCAs and four PFSAs from stain-guard carpet to landfill leachate under different pH, rotation speed, contact time and temperature conditions; and (ii) to estimate the leaching capacities and behavior for PFASs on carpets treated with stain-guard in leachate as a function of contact time and temperature. The results provide greater understanding of the parameters influencing the leaching of PFASs from stain-guard-covered carpet in landfills. In addition, these results provide useful information for regulators to contribute to best waste management practices and to decisions about appropriate ways to dispose of PFAS-containing waste and to regulations regarding PFASs in consumer products.
■
MATERIALS AND METHODS Experimental Approach. PFASs constitute a very diverse class of substances which includes PFAAs, low-molecularweight precursors and high-molecular-weight fluoropolymers. As a result of this chemical diversity, the occurrence of PFAAs in leachate can arise via three major pathways: (i) direct partitioning of residual PFAAs from the carpet to leachate; (ii) partitioning and subsequent transformation of low-molecularweight PFAA-precursors; and (iii) degradation of fluoropolymers to release low molecular weight precursors, which partition to leachate and subsequently degrade to PFAAs. In the present work we hypothesized that the first process ((i) direct partitioning of PFAAs) would be much faster than chemical or biological transformation of either low or highmolecular weight precursors, based on negligible difference between PFAA concentrations in landfill leachate during a period of 24 h under the same testing conditions, using landfill leachate only (without added carpet) (see Figure S1 in Supporting Information). Nonetheless, it is important to consider that the results in the present work represent a “lower-bounds estimate” of PFAA leaching which does not include contributions from precursors which may occur over longer time periods. Collection, Handling and Analysis of Carpet. Used carpets were collected from offices and warehouses in Canada, all with date of manufacture before 2005. These carpets were characterized for PFASs. PFASs from carpet samples were extracted by the method described by L’Empereur et al.,27 with all carpet samples extracted in triplicate. Carpet fibers were simply separated by cutting them from their attached backings. All carpets were cut into 20 × 20 mm squares (see Abstract 6565
DOI: 10.1021/es505333y Environ. Sci. Technol. 2015, 49, 6564−6573
Article
Environmental Science & Technology Table 1. Physicochemical Properties of PFASs Analysed in This Study group
CAS
acronym
molecular structure
MM (g mol−1)
perfluoroalkyl carboxylic acid (PFCAs, F(CF2)nCOOH)
375−22−4 2706−90−3 307−24−4 375−85−9 335−67−1 375−95−1 335−76−2 2058−94−8 307−55−1 376−06−7
PFBA PFPeA PFHxA PFHpA PFOA PFNA PFDA PFUnA PFDoA PFTA
C3F7COOH C4F9COOH C5F11COOH C6F13COOH C7F15COOH C8F17COOH C9F19COOH C10F21COOH C11F23COOH C13F27COOH
214 264 314 364 414 464 514 564 614 714
0.37 0.40 0.42 0.47 0.50 0.52 0.52 0.52 0.52 0.52
1.0 1.0 2.6 5.8 1.3 3.0 6.7 1.6 4.1 2.6
× × × × × × × × × ×
103 103 102 10 10 10° 10−1 10−1 10−2 10−3
−0.36 0.64 1.23 1.96 2.69 3.42 4.15 4.88 5.61 7.07
perfluoroalkyl sulfonate (PFSAs, F(CF2)nSO3H)
375−73−5 355−46−4 1763−23−1 335−77−3
PFBS PFHxS PFOS PFDS
C4F9SO3H C6F13SO3H C8F17SO3H C10F21SO3H
300 400 500 600
−3.57 −3.34 −3.27 −3.26
1.0 1.5 7.5 4.2
× × × ×
103 102 10° 10−1
−1.81 −0.45 1.01 2.47
pKaa
SW,A− (g L−1)b KOW, A−c
a Acid dissociation constant (from SciFinder Scholar). bAqueous solubility of anionic species (from SciFinder Scholar). cOctanol/water partition coefficient of anionic species (from SciFinder Scholar).
pH was checked in the distilled water after contact with carpet. Separation of floating carpet fibers from the liquid was achieved by passing a 45 mL aliquot of each sample through a 200 μm stainless steel mesh and collected in a 50 mL polypropylene tube. In addition to the above tests, an operational blank test was carried out in the contacting device to determine the degree of cross-contamination from sampling containers or tubes, sample handling and transportation. Method detection limits (MDL) were defined as the quantity of a given analyte in 50 mL of leachate producing a signal-to-noise ratio of 3. MDL of 14 PFASs are provided in Table S4 of the Supporting Information. Measurement of PFAS Concentrations. The concentrations of PFASs were analyzed by the Department of Fisheries and Oceans Canada Institute of Ocean Sciences (DFO-IOS) in Sidney, BC. A Dionex P680 HPLC equipped with a Waters XTerra C18 (5 μm, 4.6 mm × 30 mm) reversedphase column and a Waters Opti-Guard C18 1-mm guard cartridge were utilized to separate the target analytes. In addition, PFASs in the pump were separated from PFASs in the samples by two Waters Xterra C18 (5 μm, 4.6 mm × 30 mm) columns, linked in series and placed upstream of the injector. In the initial conditions, the mobile phase consisted of 10% solvent A (100% methanol) and 90% solvent B (0.1% ammonium hydroxide/0.1% ammonium acetate). The gradient elution program was: 0−1 min, 90% B; decrease to 0% B for 8 min; maintain at 0% B until 12 min; return to starting conditions by 12.1 min; equilibrate for 4 min. The flow rate was then held constant at 250 μL min−1. Analysis of the samples was performed by an API 5000Q triple-quadrupole mass spectrometer (AB Sciex, Concord, ON, Canada) operating in negative ion Multiple Reaction Monitoring (MRM) mode. For the first 4.0 min of each run, the flow was diverted from the mass spectrometer by a Vici Valco diverter valve. The source temperature was 400 °C. Analyst v. 1.5.1 software was used to target and quantify the analytes. Assessments of method accuracy, recovery and QA/QC are provided in the Supporting Information. The PFASs analyzed in this study were perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid
graphic), following a method similar to the Toxicity Characteristic Leaching Procedure (TCLP) under USEPA SW846 Method 1311 (1992).28 Details of the design and operation of the pilot-scale end-over-end contactor were provided by Danon-Schaffer et al.30 The device simultaneously contacted carpet with liquid in five separate parallel stainless steel vessels. Each vessel has an inside diameter of 76 mm, an inside length of 914 mm and a capacity of 5.0 L. Prior to the experiments, each of the five stainless steel vessels in parallel in the end-overend contactor were triple-solvent-washed (acetone, toluene, and hexane), then air-dried, to remove possible PFAS contamination. 100 g of carpet composite samples were added to each vessel, together with 4 L of leachate. A headspace of ∼20% (i.e., ∼1 L) of the total vessel volume was provided in each test. The baseline experiment was carried out for a contact time of 6 h at pH 6, temperature 288 K and rotation speed of 8 rpm under aerobic condition. In order to explore the effects of contact time, pH, temperature and rotation speed on leaching rates of various PFASs, the experimental conditions were varied around the baseline conditions. The leachate pH was changed over the range of 5−8. The temperature was varied from 278 to 308 K, a range which is similar to the range of seasonal temperature of municipal solid waste landfills in British Columbia. 31 Composite carpets were contacted with leachate samples for 1, 2, 6, and 24 h. Sáez et al.32 indicated that biodegradation of PFASs as a result of biological activity under aerobic conditions was not significant over a period of up to 9 weeks. Hence we assume that biological activity had negligible effect during our experiments. Further experiments over a longer time frame are required to investigate the contribution of precursors to levels in leachate. Tests were conducted at three rotation speeds: 0 (static), 4 and 8 rpm. PFAS leaching rates were also explored in the absence of other agents (e.g., organic and inorganic matter, metals, etc.) to shed light on how PFASs enter the aqueous media. In these tests, similar to the above experiment, 100 g of carpet composite samples were added to each vessel, together with 4 L of distilled water. HPLC grade distilled water was used in these experiments to minimize cross-contamination. The pH of the distilled water was adjusted to 5, 6, 7, and 8 using reagent grade glacial acetic acid and sodium hydroxide. A pretest was carried out to maintain the pH of the distilled water, and the 6566
DOI: 10.1021/es505333y Environ. Sci. Technol. 2015, 49, 6564−6573
Article
Environmental Science & Technology Table 2. PFAS Concentrations (ng g−1) of Composite Carpeta before Leaching Test acronym
PFBA
PFPeA
PFHxA
PFHpA
PFOA
PFNA
PFDA
PFUnA
PFDoA
PFTA
PFBS
PFHxS
PFOS
PFDS
Conc.
5.6 × 10° 1.2 × 10°
7.7 × 10 6.2 × 10°
1.0 × 102
1.4 × 102
1.0 × 102
2.9 × 10 2.6 × 10°
5.0 × 10 1.3 × 10
7.4 × 10 1.8 × 10
1.3 × 10°
1.0 × 10°
3.0 × 10−1
2.5 × 10 4.6 × 10°
3.0 × 10−1
1.9 × 10
9.7 × 10 8.9 × 10°
8.0 × 10−1
1.1 × 10
4.7 × 10 4.7 × 10°
SDb a
5.9 × 10°
2.0 × 10−1
Carpets collected from offices and warehouses in Canada. bStandard deviations, n = 3.
Table 3. Properties and PFAS Concentrations (ng L−1) in Landfill Leachate before Leaching Test metals (mg L−1) −1
property
pH
PFASs
7.03 PFBA
1392 PFPeA
674 PFHxA
Conc.
Compositional Effects on Leaching of Stain-Guarded (Perfluoroalkyl and Polyfluoroalkyl Substance-Treated) Carpet in Landfill Leachate Minhee Kim,† Loretta Y. Li,*,† John R. Grace,‡ Jonathan P. Benskin,§ and Michael G. Ikonomou§ †
Department of Civil Engineering, University of British Columbia, 6250 Applied Science Lane, Vancouver, British Columbia, Canada V6T 1Z4 ‡ Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, British Columbia, Canada V6T 1Z3 § Institute of Ocean Sciences, Fisheries and Oceans Canada (DFO), 9860 West Saanich Road, Sidney, British Columbia, Canada V8L 4B2 S Supporting Information *
ABSTRACT: Perfluoroalkyl and polyfluoroalkyl substances (PFASs) from stain-guard treated carpets in landfills continue to be released into the environment. To understand the leaching of PFASs from carpets to landfill leachate as a function of environmental factors, leaching concentrations of ten perfluoroalkyl carboxylic acids and four perfluoroalkyl sulfonic acids were quantified for different pHs, contact times, mixing speeds, and temperatures. Partitioning from carpet to leachate and distilled water at different pHs showed negligible differences. The total concentration of leaching PFASs in distilled water was approximately 1 ng L−1 higher than in landfill leachate, indicating that the presence of multivalent cations in leachate could have a negative effect on leaching of PFASs. For all PFASs monitored, leaching increased with increasing contact time and temperature. Perfluorohexanoic and perfluoroheptanoic acids experienced the largest increases with contact time and temperature. Gibbs free energy (ΔG > 0), enthalpy (ΔH > 0), and entropy energy (ΔS < 0) indicated that PFAS leaching from carpet was dominantly controlled by entropy-driven processes and did not differ significantly among individual PFASs. PFAS concentrations in leachate with rotation of an end-over-end contactor were higher than under static conditions, but otherwise, varying the rotation speed had negligible influence. The results provide useful information for management of discarded stainguard carpets in landfills.
■
INTRODUCTION Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been detected over the past decades in many environmental and biological compartments. Perfluoroalkyl acids (PFAAs) are among the most commonly detected PFASs in the environment, and some of them have the potential to bioaccumulate.1−3 These substances are of increasing concern due to their persistence4 and potential adverse health effects.5 Perfluorooctanesulfonate (PFOS), its salts, and perfluorooctane sulfonyl fluoride (PFOSF) were added to Annex B of the Stockholm convention on persistent organic pollutants (POPs) in May 2009, resulting in global restrictions on the application and production of these compounds.6,7 However, PFASs have already been incorporated in consumer products for six decades due to the unique structure of the extremely strong carbon− fluorine bond, contributing to excellent thermal and chemical stability in a wide range of products, including stain- and waterrepellent coatings on carpets, paper and textiles, grease-resistant food packaging and paper, fire-resistant cables, fire-fighting foams, surfactants in cleaners, medical equipment, motor oil additives, and insecticides.8−10 Of the 96 000 tons of these industrial and consumer products between 1970 and 2002, © 2015 American Chemical Society
stain-guard carpets comprised approximately 50% of estimated total global historical perfluorooctane sulfonyl fluoride (POSF) production and use.11 In Canada, 58% of total perfluoroalkyl sulfonic acids (PFSAs) were applied to fabric and carpet between 1997 and 2000.12 Carpets and carpet treatment products contained perfluoroalkyl carboxylic acids (PFCAs) in levels13 from 0.04 to 14 100 ng g−1. The 3M Company estimated that nearly 53% of the initial concentration of fluorochemical-treated carpet remained before disposal.14 Dinglasan-Panlilio and Mabury15 also documented 0.04−3.8% polyfluorinated telomer alcohols (FTOHs) residual to dry mass for carpet protection products. Releases from landfilled carpets to the environment occur from residual PFCAs, PFSAs, or fluorotelomer-based and perfluoroalkyl sulfonyl-based precursors which can be degraded to PFCAs and PFASs.16−20 PFASs are still being released into the environment from stain-guard treated carpets in landfills, even from those no longer being Received: Revised: Accepted: Published: 6564
October 31, 2014 April 13, 2015 May 1, 2015 May 19, 2015 DOI: 10.1021/es505333y Environ. Sci. Technol. 2015, 49, 6564−6573
Article
Environmental Science & Technology
graphic) in order to maintain consistency in all experiments. To ensure homogeneity of the carpet samples, all carpet pieces were then divided into quarters, resulting in four separate portions, each of which was mixed thoroughly mechanically. Two pairs of the portions were then mixed together, and the resulting two “half-portions” were then combined and blended to form a single homogeneous matrix. This procedure was repeated 10 times for each type of carpet. PFASs from carpet samples were extracted in triplicate. Details of the collection and pretreatment of the carpets are provided in the Supporting Information. Composite carpet samples (5 g each) were next weighed and placed into a 50 mL polypropylene tube, then spiked with 22.5 ng of mass-labeled internal standards (13C4 PFBA, 13C2 PFHxA, 13C4 PFOA, 13C5 PFNA, 13C2 PFDA, and 13 C4 PFOS). Internal standards were applied to correct for the loss of analyte during sample preparation and account for matrix-induced ionization effects. The spiked carpets were allowed to sit for a few minutes until the solvent dried. The extraction was then carried out by adding 15 mL of methanol to the carpets five times. After each stage of extraction with methanol, the centrifuge tubes were shaken in a vortex shaker for ∼15 min. The extracts (∼75 mL total volume) were reduced under nitrogen to a final volume of 45 mL and then spiked with 22.5 ng recovery standard (500 μg of a 500 ppb standard). The solution was then vortex-mixed, and a portion of the extract was transferred to a 300 μL polypropylene microvial for analysis by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Collection, Handling and Analysis of Landfill Leachate. The leachate was collected from a Canadian urban landfill, which accepts municipal waste, as well as residuals and sludge from wastewater treatment plants. Under agreement with the landfill operator, we cannot divulge the location of the landfill. In order to minimize changes in leachate quality, samples were immediately stored in high-density polyethylene (HDPE) bottles at −20 ± 2 °C. Before contacting carpet samples with the leachate, the closed bottles were left in the room for 2 h to reach room temperature. Details of the collection and pretreatment of the landfill leachate are provided in the Supporting Information. The leachate was analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), total organic carbon (TOC), exchangeable cations (Ca2+, Mg2+, Na+, and K+) and metals (Al, Fe, Cd, Cu, Pb, Mn, and Zn). The TOC and metals of the leachate were characterized by USEPA Standard Methods 5310B (2000) and 3120 (1999), respectively.28 The PFAS extraction procedure from collected leachate was adopted from a previously developed USEPA method.29 Prior to extraction, the pH of each sample was checked. All samples and blanks were spiked with 2 ng of masslabeled internal standards. SPE cartridges (Oasis WAX 6 cm3, 500 mg, 30 μm) were conditioned with 5 mL of 0.3% ammonium hydroxide in methanol, 5 mL of 0.1 M formic acid, and 5 mL of reagent high-performance liquid chromatography (HPLC)-grade distilled water prior to loading. Samples were mixed, and then loaded dropwise (5 mL min−1) under vacuum. After loading, the cartridges were washed with 5 mL of 20% methanol and 80% of 0.1 M formic acid in reagent water. The cartridges were next dried under vacuum and eluted with 4 mL of 0.3% ammonium hydroxide in methanol. The extracted solution was spiked with recovery standard and a portion was transferred into a conical vial for analysis by HPLC-MS/MS. Experimental Procedure. The leaching experiments were conducted in a pilot-scale end-over-end contactor (See Abstract
manufactured, and this will continue in future years as carpets now in service or storage continue to be sent to landfills. Several studies on PFAS concentrations in leachate indicate PFOS and perfluorooctanoic acid (PFOA) concentrations up to 82 000 ng L−1 in landfills that received wastes from PFAS manufacturing.21,22 Recent studies have monitored the concentration range and various composition for PFASs in landfill sites in Canada (30−21 000 ng L−1 based on 13 PFASs),23,24 United States (2700−7400 ng L−1 based on 24 PFASs)25 and Germany (30−13 000 ng L−1 based on 43 PFASs).26 However, the leaching capacity of PFASs at landfill sites depends heavily on environmental factors such as pH, temperature, ionic strength of leachate and contact time. The leaching capacity and mechanisms of PFAS transfer from carpets to landfill leachate as a function of environmental factors have not been addressed. The objectives of this study were (i) to quantify the effect of environmental factors on the leaching of 14 PFASs encompassing ten PFCAs and four PFSAs from stain-guard carpet to landfill leachate under different pH, rotation speed, contact time and temperature conditions; and (ii) to estimate the leaching capacities and behavior for PFASs on carpets treated with stain-guard in leachate as a function of contact time and temperature. The results provide greater understanding of the parameters influencing the leaching of PFASs from stain-guard-covered carpet in landfills. In addition, these results provide useful information for regulators to contribute to best waste management practices and to decisions about appropriate ways to dispose of PFAS-containing waste and to regulations regarding PFASs in consumer products.
■
MATERIALS AND METHODS Experimental Approach. PFASs constitute a very diverse class of substances which includes PFAAs, low-molecularweight precursors and high-molecular-weight fluoropolymers. As a result of this chemical diversity, the occurrence of PFAAs in leachate can arise via three major pathways: (i) direct partitioning of residual PFAAs from the carpet to leachate; (ii) partitioning and subsequent transformation of low-molecularweight PFAA-precursors; and (iii) degradation of fluoropolymers to release low molecular weight precursors, which partition to leachate and subsequently degrade to PFAAs. In the present work we hypothesized that the first process ((i) direct partitioning of PFAAs) would be much faster than chemical or biological transformation of either low or highmolecular weight precursors, based on negligible difference between PFAA concentrations in landfill leachate during a period of 24 h under the same testing conditions, using landfill leachate only (without added carpet) (see Figure S1 in Supporting Information). Nonetheless, it is important to consider that the results in the present work represent a “lower-bounds estimate” of PFAA leaching which does not include contributions from precursors which may occur over longer time periods. Collection, Handling and Analysis of Carpet. Used carpets were collected from offices and warehouses in Canada, all with date of manufacture before 2005. These carpets were characterized for PFASs. PFASs from carpet samples were extracted by the method described by L’Empereur et al.,27 with all carpet samples extracted in triplicate. Carpet fibers were simply separated by cutting them from their attached backings. All carpets were cut into 20 × 20 mm squares (see Abstract 6565
DOI: 10.1021/es505333y Environ. Sci. Technol. 2015, 49, 6564−6573
Article
Environmental Science & Technology Table 1. Physicochemical Properties of PFASs Analysed in This Study group
CAS
acronym
molecular structure
MM (g mol−1)
perfluoroalkyl carboxylic acid (PFCAs, F(CF2)nCOOH)
375−22−4 2706−90−3 307−24−4 375−85−9 335−67−1 375−95−1 335−76−2 2058−94−8 307−55−1 376−06−7
PFBA PFPeA PFHxA PFHpA PFOA PFNA PFDA PFUnA PFDoA PFTA
C3F7COOH C4F9COOH C5F11COOH C6F13COOH C7F15COOH C8F17COOH C9F19COOH C10F21COOH C11F23COOH C13F27COOH
214 264 314 364 414 464 514 564 614 714
0.37 0.40 0.42 0.47 0.50 0.52 0.52 0.52 0.52 0.52
1.0 1.0 2.6 5.8 1.3 3.0 6.7 1.6 4.1 2.6
× × × × × × × × × ×
103 103 102 10 10 10° 10−1 10−1 10−2 10−3
−0.36 0.64 1.23 1.96 2.69 3.42 4.15 4.88 5.61 7.07
perfluoroalkyl sulfonate (PFSAs, F(CF2)nSO3H)
375−73−5 355−46−4 1763−23−1 335−77−3
PFBS PFHxS PFOS PFDS
C4F9SO3H C6F13SO3H C8F17SO3H C10F21SO3H
300 400 500 600
−3.57 −3.34 −3.27 −3.26
1.0 1.5 7.5 4.2
× × × ×
103 102 10° 10−1
−1.81 −0.45 1.01 2.47
pKaa
SW,A− (g L−1)b KOW, A−c
a Acid dissociation constant (from SciFinder Scholar). bAqueous solubility of anionic species (from SciFinder Scholar). cOctanol/water partition coefficient of anionic species (from SciFinder Scholar).
pH was checked in the distilled water after contact with carpet. Separation of floating carpet fibers from the liquid was achieved by passing a 45 mL aliquot of each sample through a 200 μm stainless steel mesh and collected in a 50 mL polypropylene tube. In addition to the above tests, an operational blank test was carried out in the contacting device to determine the degree of cross-contamination from sampling containers or tubes, sample handling and transportation. Method detection limits (MDL) were defined as the quantity of a given analyte in 50 mL of leachate producing a signal-to-noise ratio of 3. MDL of 14 PFASs are provided in Table S4 of the Supporting Information. Measurement of PFAS Concentrations. The concentrations of PFASs were analyzed by the Department of Fisheries and Oceans Canada Institute of Ocean Sciences (DFO-IOS) in Sidney, BC. A Dionex P680 HPLC equipped with a Waters XTerra C18 (5 μm, 4.6 mm × 30 mm) reversedphase column and a Waters Opti-Guard C18 1-mm guard cartridge were utilized to separate the target analytes. In addition, PFASs in the pump were separated from PFASs in the samples by two Waters Xterra C18 (5 μm, 4.6 mm × 30 mm) columns, linked in series and placed upstream of the injector. In the initial conditions, the mobile phase consisted of 10% solvent A (100% methanol) and 90% solvent B (0.1% ammonium hydroxide/0.1% ammonium acetate). The gradient elution program was: 0−1 min, 90% B; decrease to 0% B for 8 min; maintain at 0% B until 12 min; return to starting conditions by 12.1 min; equilibrate for 4 min. The flow rate was then held constant at 250 μL min−1. Analysis of the samples was performed by an API 5000Q triple-quadrupole mass spectrometer (AB Sciex, Concord, ON, Canada) operating in negative ion Multiple Reaction Monitoring (MRM) mode. For the first 4.0 min of each run, the flow was diverted from the mass spectrometer by a Vici Valco diverter valve. The source temperature was 400 °C. Analyst v. 1.5.1 software was used to target and quantify the analytes. Assessments of method accuracy, recovery and QA/QC are provided in the Supporting Information. The PFASs analyzed in this study were perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid
graphic), following a method similar to the Toxicity Characteristic Leaching Procedure (TCLP) under USEPA SW846 Method 1311 (1992).28 Details of the design and operation of the pilot-scale end-over-end contactor were provided by Danon-Schaffer et al.30 The device simultaneously contacted carpet with liquid in five separate parallel stainless steel vessels. Each vessel has an inside diameter of 76 mm, an inside length of 914 mm and a capacity of 5.0 L. Prior to the experiments, each of the five stainless steel vessels in parallel in the end-overend contactor were triple-solvent-washed (acetone, toluene, and hexane), then air-dried, to remove possible PFAS contamination. 100 g of carpet composite samples were added to each vessel, together with 4 L of leachate. A headspace of ∼20% (i.e., ∼1 L) of the total vessel volume was provided in each test. The baseline experiment was carried out for a contact time of 6 h at pH 6, temperature 288 K and rotation speed of 8 rpm under aerobic condition. In order to explore the effects of contact time, pH, temperature and rotation speed on leaching rates of various PFASs, the experimental conditions were varied around the baseline conditions. The leachate pH was changed over the range of 5−8. The temperature was varied from 278 to 308 K, a range which is similar to the range of seasonal temperature of municipal solid waste landfills in British Columbia. 31 Composite carpets were contacted with leachate samples for 1, 2, 6, and 24 h. Sáez et al.32 indicated that biodegradation of PFASs as a result of biological activity under aerobic conditions was not significant over a period of up to 9 weeks. Hence we assume that biological activity had negligible effect during our experiments. Further experiments over a longer time frame are required to investigate the contribution of precursors to levels in leachate. Tests were conducted at three rotation speeds: 0 (static), 4 and 8 rpm. PFAS leaching rates were also explored in the absence of other agents (e.g., organic and inorganic matter, metals, etc.) to shed light on how PFASs enter the aqueous media. In these tests, similar to the above experiment, 100 g of carpet composite samples were added to each vessel, together with 4 L of distilled water. HPLC grade distilled water was used in these experiments to minimize cross-contamination. The pH of the distilled water was adjusted to 5, 6, 7, and 8 using reagent grade glacial acetic acid and sodium hydroxide. A pretest was carried out to maintain the pH of the distilled water, and the 6566
DOI: 10.1021/es505333y Environ. Sci. Technol. 2015, 49, 6564−6573
Article
Environmental Science & Technology Table 2. PFAS Concentrations (ng g−1) of Composite Carpeta before Leaching Test acronym
PFBA
PFPeA
PFHxA
PFHpA
PFOA
PFNA
PFDA
PFUnA
PFDoA
PFTA
PFBS
PFHxS
PFOS
PFDS
Conc.
5.6 × 10° 1.2 × 10°
7.7 × 10 6.2 × 10°
1.0 × 102
1.4 × 102
1.0 × 102
2.9 × 10 2.6 × 10°
5.0 × 10 1.3 × 10
7.4 × 10 1.8 × 10
1.3 × 10°
1.0 × 10°
3.0 × 10−1
2.5 × 10 4.6 × 10°
3.0 × 10−1
1.9 × 10
9.7 × 10 8.9 × 10°
8.0 × 10−1
1.1 × 10
4.7 × 10 4.7 × 10°
SDb a
5.9 × 10°
2.0 × 10−1
Carpets collected from offices and warehouses in Canada. bStandard deviations, n = 3.
Table 3. Properties and PFAS Concentrations (ng L−1) in Landfill Leachate before Leaching Test metals (mg L−1) −1
property
pH
PFASs
7.03 PFBA
1392 PFPeA
674 PFHxA
Conc.
