Environ. Sci. Technol. 2010, 44, 5534–5539
Global Pilot Study of Legacy and Emerging Persistent Organic Pollutants using Sorbent-Impregnated Polyurethane Foam Disk Passive Air Samplers SUSIE GENUALDI, SUM CHI LEE, MAHIBA SHOEIB, ANYA GAWOR, LUTZ AHRENS, AND TOM HARNER* Environment Canada, Science and Technology Branch, 4905 Dufferin Street, Toronto, Ontario M3H 5T4
Received March 26, 2010. Revised manuscript received June 9, 2010. Accepted June 18, 2010.
Sorbent-impregnated polyurethane foam (SIP) disk passive air samplers were deployed alongside polyurethane foam (PUF) disk samplers at 20 sites during the 2009 spring sampling period of the Global Atmospheric Passive Sampling (GAPS) Network. The SIP disk samplers consisted of PUF disks impregnated with finely ground XAD-4 resin. The addition of XAD-4 greatly improves the sorptive capacity of the PUF disk samplers for more volatile and polar chemicals, and allows for linear-phase sampling over several weeks for these compounds. The SIP and PUF disks were analyzed for polychlorinated biphenyls (PCBs), neutral polyfluoroalkyl compounds (PFCs), and ionic PFCs. Correlations between sampler-derived air concentrations for PCBs in the PUF and SIP disks samplers were significant (p < 0.05). The SIP disks effectively captured 4-50% more of the low molecular weight PCBs than the PUF disks samplers, and the PUF disks also had limitations for timeweighted passive sampling of neutral PFCs in air. Theoretical uptake curves for PUF disks showed rapid equilibration occurring in just hours for 8:2 FTOH and in a few days for MeFOSE, while theoretical curves for SIP disks showed superior sampling profiles for the neutral PFCs. PFCs were measured on SIP disks at all sites with 8:2 FTOH being the dominant compound detected and urban centers (n ) 3) having the highest total neutral PFC concentrations ranging from 51.7 to 248 pg/m3. A positive correlation was found between the FTOHs and FOSAs/ FOSEs (p < 0.001, Pearson correlation) indicating similar contamination sources. The SIP disk appears to be a promising passive air sampler for measuring both emerging and legacy POPs on a global scale. They can also be used as a complement to the PUF disk sampler for capturing broader classes of compounds, or as a replacement for PUF disks entirely, especially when longer than quarterly deployment periods are desired.
Introduction The Global Atmospheric Passive Sampling (GAPS) study has been measuring persistent organic pollutants (POPs) worldwide on both spatial and temporal scales since 2005 (1-3). The GAPS Network currently has 55 sites, mainly remote * Corresponding author e-mail:
[email protected]; phone: 416739-4837; fax: 416-739-4281. 5534
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background locations with a few urban and agricultural sites. POPs are of global concern because of their environmental persistence, toxicity, and potential to bioaccumulate (4). They also have the ability to undergo long-range atmospheric transport and accumulate in remote locations such as the Arctic (4). The Stockholm Convention on POPs under the United Nations Environment Programme (UNEP) identified a group of POPs termed the “dirty dozen” to be removed from the global environment (5). These POPs include organochlorine pesticides (OCPs), industrial chemicals such as polychlorinated biphenyls (PCBs), and their byproducts, mainly dioxins and furans (5). Recently in 2009, nine additional POPs were added to the Stockholm convention, including OCPs, polychlorinated diphenyl ethers (PBDEs), perfluorooctane sulfonate (PFOS), and perfluorooctane sulfonyl fluoride (PFOS-F) (6). Polyfluoroalkyl compounds (PFCs) including PFOS and perfluorooctanoate (PFOA) have been measured in biota in remote regions (7-10). It is thought these ionic compounds are a result of more volatile precursor compounds (neutral PFCs) that are reaching these regions by either long-range atmospheric transport followed by degradation to ionic PFCs such as PFOS and PFOA or by direct transport through ocean currents (11-19). To monitor the new compounds in air, which is one of the two core media for monitoring POPs under the Global Monitoring Plan of the Stockholm Convention (20), a new type of passive air sampler that can measure PFOS and its volatile precursors (e.g., fluorotelomer alcohols (FTOHs), perfluorooctane sulfonamides (FOSAs), and sulfonamidoethanols (FOSEs)) is necessary. The sorbent-impregnated polyurethane foam disk (SIP) sampler has been shown to have a much higher sorptive capacity (∼2 orders of magnitude for the FTOHs) than the polyurethane foam (PUF) disk sampler for the measurement of FTOHs and FOSAs and FOSEs (21). This sampler was effective at measuring concentrations of FTOHs, FOSAs, and FOSEs in indoor air in Canada, which typically have much higher concentrations than those observed in outdoor air (21). SIP disk samplers appear to be a promising complement or alternative to the PUF disk sampler currently being used in the GAPS Network. The objectives of this research were to compare the performance of the SIP disk to the PUF disk sampler under field conditions to effectively sample POPs, and to assess the ability of the SIP disk sampler to capture a wider range of target compounds including FTOHs, FOSAs, and FOSEs.
Experimental Section Sample Collection. SIP and PUF disk samplers were concurrently deployed at 20 sites during the 2009 spring sampling period (April to June) of the Global Atmospheric Passive Sampling (GAPS) Network (Figure SI.1 and Table SI.1 in the Supporting Information). The sampling locations consisted of 12 background, 4 polar, 3 urban, and 1 agricultural site. Individual sites were chosen based on the interests of Canada’s Chemical Management Plan (North America) and also on potential source regions. The climate classification of the sites chosen for the pilot study were temperate, cold, polar, and dry regions, but there were no sites representative of the tropical region. Previous studies of PUF disk samplers deployed in the tropical regions (1, 3, 22) have shown they are effective at sampling POPs under these conditions. However, further studies are necessary to verify the performance of the SIP disk sampler under tropical conditions. The PUF and SIP disks were individually housed inside 10.1021/es1009696
2010 American Chemical Society
Published on Web 06/25/2010
prewashed, presolvent rinsed stainless steel chambers. Details on the sampling apparatus have been previously provided (22). Sample Preparation. PUF disks (14 cm diameter ×1.35 cm thick; surface area 365 cm2, mass 4.40 g, volume 207 cm3, Tisch Environmental, Cleves, OH) were precleaned by first washing in water followed by Soxhlet extraction for 24 h with acetone followed by another 24 h with petroleum ether. The PUF disks were then dried in a desiccator for ∼24 h and placed in clean, solvent-rinsed glass jars. Details on the preparation of SIP disk samplers have been previously reported (21). Briefly, XAD-4 (Supelco, Bellefonte, PA) was cleaned using successive sonications with methanol, dichloromethane, and hexane and then finely ground using a ball mill to a particle size of ∼0.75 µm. The ground XAD was further Soxhlet extracted for 30 h using methanol, dichloromethane, and hexane. SIP disks were prepared by consecutively dipping precleaned PUF disks in an XAD-4/hexane (6.4 g/L) slurry and were uniformly coated with an average XAD-4 mass of 435 ( 68 mg per disk (n ) 75) (21). In comparison to the XAD-2 resin based passive air sampler, which uses ∼20 g of XAD-2 resin (spheres) (23), only 0.5 g of finely ground XAD-4 is impregnated onto a PUF disk (in making a SIP disk) to increase its capacity to measure volatile compounds. Finely ground XAD has a higher sorptive capacity compared to the XAD spheres (of the same mass) and is also easier to clean/extract which helps to maintain lower blanks levels (21). Prior to deployment, PUF disks were spiked with 250-500 ng per disk of each of the following depuration compounds (DCs): 13C12 PCB 3, 13C12 PCB 9, 13C12 PCB 15, 13 C12 PCB 32, PCB 30, PCB 107, PCB 198, and d6 γ-HCH. These compounds consist of labeled and unlabeled PCBs not typically found in air, and range in log KOA values from 6.57 to 10.86 (24). SIPs were not spiked with depuration compounds in this study and were assumed to have the same sampling rates as the PUF disk codeployed at each location, given their identical geometry and that uptake is air-side controlled (25). Details on the sample extraction and quantification can be found in the Supporting Information. QA/QC. Field blanks were collected at all 20 sites for both PUF and SIP disk samples. The blank values for PCBs were below the limit of quantification (LOQ) for all congeners except PCB 8. In all cases where blanks had values of PCB 8 above the LOQ, measurements of PCB 8 in the corresponding samples were all below the LOQ. Therefore no blank correction was necessary. The SIP disk blanks were below the LOQ for all compounds except 8:2 FTOH and 10:2 FTOH and the concentration of the blanks ranged from 2 to 30% of the concentrations measured in the samples. For each site, the blank value was used as the new LOQ for that site and only samples with values greater than the LOQ were reported. Estimated method detection limits (EDLs) were calculated using EPA method 8280A and ranged from 0.41 to 1.2 pg/m3 for PCBs, 0.43 to 1.1 pg/m3 for the neutral PFCs, and 0.0087 to 0.18 pg/m3 for the ionic PFCs. All SIP and PUF disk samples were recovery corrected for neutral and ionic PFCs using the surrogate standards; further details on the surrogates chosen for each native compound have been previously reported (21). Method recovery values for the neutral PFCs, ionic PFCs, and PCBs ranged 29-134%, 14-89%, and 73-123%, respectively. Due to the high percent recovery for PCBs, it was not necessary to recovery correct the PCB concentrations. Sample Volumes derived from Depuration Compounds. Site-specific sampling rates were calculated for each site based on the loss of depuration compounds (DCs) added to the PUF disks prior to deployment. Only DCs having retention percentages less than 60% were used in this calculation, which ensures the loss of the DCs was due to depletion and not analytical variability (3). The percentage of depuration
compounds present on the PUF disk at the end of the deployment period was greater than 7% at every site. If a depuration compound is completely lost at the end of the deployment period, that compound is not included in the calculation. DCs were not added to SIP disks since most would not meet this retention percentage due to the increased sorptive capacity of the SIP disk sampler. The high molecular weight depuration compounds (PCB-107 and PCB-198) are expected to have ∼100% recovery due their high KOA values (10.73 and 11.87, respectively), as demonstrated in previous studies (1, 2, 22). To account for loss during the analytical method, depuration compounds are normalized to PCB-198. Previous studies indicate that the recovery of PCB-198 from the PUF disk samples prior to correction agrees well with the method recovery values (22). In this study, the method recovery of PCBs was 103 ( 19%, which is close to the average recovery of 83 ( 15% for PCB-198 before correction. For the PUF disks, each PCB congener was adjusted for the volume of air (Vair) sampled during the deployment time based on the KPSMAIR partition coefficient between the passive sampling medium (PSM) and air of each congener using eq 1 (22). Vair ) (K′PSM-A) × (VPSM) ×
{
[
1 - exp -
kA K′PSM-A
×
]}
1 t Dfilm
(1)
Where K′PSM-A is equal to KPSM-AIR multiplied by the density of the passive sampling medium (DPSM in g/m3), VPSM is the volume of the passive sampling medium (m3), kA is the airside mass transfer coefficient (m/day), Dfilm is the effective film thickness (m), and t is time (days). Site-specific kA values were derived from the loss of DCs at each sampling location. Sampling rates R (m3/day) were calculated by multiplying the kA values by the surface area of the PUF disk sampler and can be found in Table SI.1 in the Supporting Information. The same R values are applied to the SIP disks since they have the same geometry as the PUF disk sampler, which implies the uptake rate (kinetics) of contaminants into the sampler is the same. This surrogate approach is required because SIP disks have a much greater sorptive capacity (equilibrium phase) and retain DCs more strongly. Losses of DCs from the SIP disks over the 3-month deployment period are not sufficient for deriving R. Further details on these calculations and previous uptake study results involving both the SIP and PUF disk samplers for PCBs and neutral PFCs have been described elsewhere (1, 3, 21, 22, 26). For the SIP disk samplers, for all PCB congeners, site-specific sampling rates determined using the PUF disk samplers were applied, assuming mass transfer is air-side controlled. SIP disks were also not expected to reach equilibrium for PCBs based on their greater sorptive capacity (21). The average site-specific sampling rates during this study ranged from 6.34 ( 4.03 m3/day. For the ionic PFCs, an average sampling rate of 4 m3/day was used. This is the average gas-phase sampling rate observed under the GAPS Network for the same sampler geometry (3) and is consistent with results from an unpublished uptake study for PFOS and PFOA, conducted in our laboratory. Further calibration studies are necessary to accurately calculate the sampling rate for these compounds. The air concentrations given for ionic PFCs represent results from gas-phase sampling only. Because many of these compounds are found in the particle phase (27),which has a lower sampling rate compared to the gas phase (28), the derived air concentrations are likely to be underestimating the true air concentrations.
Results and Discussion PCB Concentrations. To compare the performance of the SIP disk sampler to that of the PUF disk sampler to capture VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Comparison between SIP and PUF disk samplers using linear regressions of PCBs measured as (A) pg/sampler and (B) air concentrations in pg/m3. The dashed lines represent a 1:1 relationship between PUF and SIP disk samplers.
FIGURE 2. Polychlorinated biphenyl (PCB) concentrations (pg/m3) measured in air using (A) PUF disk and (B) SIP disk air samplers. Starred sampling locations (*) indicate urban sites. legacy POPs, the PCBs accumulated in the PUF and SIP disks were compared using linear regressions. Three separate regressions were performed between the two samplers for low (di-, tri-), medium (tetra-, penta-), and high (hepta-, octa-, nona-, deca-) molecular weight PCBs. In Figure 1A, PCBs are compared between the two samplers in units of pg/sampler, while in Figure 1B the PCBs have been converted to air concentrations (pg/m3) using site-specific sampling rates and an additional correction was made for the PUF disks for the volume of air sampled based on the KPSM-AIR partition coefficient for each congener. In Figure 1A and B, r2 is close to unity (0.94, 0.99, respectively) in the regressions for the high molecular weight PCB congeners compared to the r2 of the regressions for the low molecular weight congeners (0.84, 0.91, respectively). From previous calibration studies, it is expected that the high molecular weight PCBs will remain in the linear sampling phase for the entire deployment period in both the PUF and SIP disk samplers, while some of the low molecular weight PCBs have the potential to reach equilibrium in the PUF disks before the 5536
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end of the deployment (1, 25). When the amount of PCBs accumulated in the PUF and SIP disks was converted from pg/sampler (Figure 1A) to pg/m3 (Figure 1B), the slope of each of the regressions became close to 1: di- and tri- (0.50 to 0.53), tetra- and penta- (0.78 to 0.85) and hepta-, octa-, nona-, deca- (0.91 to 1). This correction more accurately calculates the sampler-derived air concentrations for PCBs in the PUF disk samplers, and also confirms the ability of the SIP disk to effectively capture PCBs as well as the PUF disk air sampler. The concentrations of PCBs measured in air using PUF and SIP disk samplers on a spatial scale can be seen in Figure 2A and B and Tables SI.3 and SI.4 in the Supporting Information. The air concentrations (pg/m3) compare quite well between the two samplers for the higher molecular weight PCBs with a percent difference of 5.5-11% for the penta- through hepta- congers and 28-70% for the di- to tetra- congeners. The SIP disk samplers show concentrations of the di-, tri-, and tetra- PCBs measured on the west coast of North America (sampling sites 4, 13, 17) that are 4-50%
FIGURE 3. (A) Neutral polyfluoroalkyl compounds (PFCs) and (B) ionic PFCs measured in air (pg/m3) using SIP disk air samplers. Starred sampling locations (*) indicate urban sites.
FIGURE 4. Theoretical uptake profiles for MeFOSE and 8:2 FTOH in (A) PUF disk and (B) SIP disk samplers at the Toronto, Ontario sampling location. Stars indicate the volume of air sampled at the end of the deployment period (90 days). higher than those measured by the PUF disk samplers, due to the higher sorptive capacity of the SIP disks to capture chemicals with lower log KOA values. Using a two sample t-test, the mean concentrations of PCBs measured at all sites were compared between the SIP and PUF samplers for the following congener groups: di- and tri- chlorobiphenyls (p ) 0.18), tetra- and penta- chlorobiphenyls (p ) 0.56), and hexa- to nona- chlorobiphenyls (p ) 0.95). The two-sided p-values were all much greater than 0.05, indicating that there is no statistically significant difference between the means of each group. The SIP disks compare well to the PUF disks under field conditions for the measurement of legacy POPs, and appear to be a promising sampler for the measurement of the more volatile PCB congeners. PFC Concentrations. Concentrations of PFCs in air were measured globally using SIP disk air samplers (Figure 3, Table SI.5). The dominant neutral PFC measured at all sites was 8:2 FTOH. The three urban sites in Toronto, ON Canada, Paris, France, and Sydney, FL (Figure 3, starred 6, 11, 18) had some of the highest concentrations with the sums of all neutral PFCs ranging from 51.7 to 248 pg/m3. A positive correlation was found between the neutral PFC classes FTOHs and FOSAs/FOSEs (p < 0.001, Pearson Correlation, SPSS version 16) indicating common contamination sources. Seven ionic PFCs (C4, C6, C8 PFSAs, C8-C11 PFCAs) were detected, with PFOS as the dominant compound. The highest sum of ionic PFC concentrations was also observed at the urban site Paris, France with a total concentration of 245 pg/m3. The PFCAs (C8-C11) were detected only at the Paris site, with concentrations ranging from 0.296 to 4.49 pg/m3 (Table SI.5).
Previous studies have shown that air masses associated with urban centers are sources of PFCs (29-31). A fourth background site in Groton, CT (Figure 3, 20), located in the Northeastern U.S., also had high concentrations of neutral PFCs with a sum of 107 pg/m3. Models created from emissions associated with the manufacture, use, and disposal of DuPont fluorotelomer-based products have also shown that the Northeastern United States has the highest ground level air concentrations of 8:2 FTOH (32). PFOS was found frequently in the SIP disk samplers, whereas C8-C11 PFCAs were only detected at the Paris site. The ionic PFCs could be originating from either fine particles collected with the SIP disk samplers (28) and/or degradation of neutral PFCs (FTOHs, FOSAs, FOSEs) to the ionic PFCs during the sampling period of ∼90 days (33). Ionic PFCs are typically found in the particulate phase of air samples (34). Levels of PFSAs in this study are similar to those reported in the particulate phase from Northern Europe, and levels of PFCAs at the Paris site are similar to those found in the particulate phase in Kjeller (Norway), Manchester (UK), and Mace Head (Ireland) (30). Lower PFOS levels of 0.1-2.5 pg/ m3 were found in the particulate phase from a latitudinal gradient in the marine atmosphere between Germany and South Africa in the Atlantic Ocean (34). More work is required to investigate the partitioning of neutral and ionic PFCs in the gaseous and particulate phases, and also their potential to degrade on the SIP disk sampler. Uptake of PFCs in PUF and SIP Disk Samplers. PFCs accumulated in PUF disk samplers were quite low and only detected at eight sampling locations: Groton, CT; Paris, VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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France; Whistler, BC, Canada; Barrow, AK; Toronto, ON, Canada; Storhofdi, Iceland; Malin Head, Ireland; and Sydney, FL (Table SI.6). PFOS was the only ionic PFC detected in the PUF disk samplers, while two neutral PFCs (MeFOSE and 8:2 FTOH) dominated and both were measured at the Toronto, ON site. To compare the effectiveness of the SIP disk sampler over the PUF disk sampler to collect PFCs, theoretical uptake profiles were created for MeFOSE and 8:2 FTOH for the Toronto, ON sampling location (Figure 4). These curves were generated using the site specific kA value and KPSM-AIR partition coefficients previously determined from an uptake study (21). During the deployment period, the effective volume of air sampled in the PUF disk sampler was 0.940 m3 for 8:2 FTOH and 43.8 m3 for MeFOSE, while the SIP disk sampler was able to sample the equivalent of about 107 m3 for 8:2 FTOH and 282 m3 for MeFOSE. The SIP disk sampler sampled in the linear range for the entire sampling period for MeFOSE and ∼60 days for 8:2 FTOH, which is much longer than the PUF disk sampler which reached equilibrium within hours for 8:2 FTOH and in ∼50 days for MeFOSE. Longer linear-phase sampling periods are desirable for passive samples so that a more accurate, time-weighted air concentration is derived. Implications. The SIP disk passive air sampler is effective at collecting the more volatile chemicals such as FTOHs, FOSAs, and FOSEs, and has derived air concentrations comparable to that of the PUF disk sampler for legacy POPs. This sampler appears to be a promising alternative to the traditional PUF disk samplers deployed worldwide in the GAPS Network. The use of SIP disk samplers would allow for a wider range of chemicals to be measured and monitored over time, which would support the Global Monitoring Plan of the Stockholm Convention on POPs.
Acknowledgments We thank all of the partners under the GAPS network who participated in the pilot study, and also Christine Spencer for help with the analysis of the ionic PFCs. Funding was provided by the Chemicals Management Plan, Pesticide Science Fund, and the Northern Contaminants Program.
Supporting Information Available Additional details on sampling sites and PCB and PFC concentrations. This information is available free of charge via the Internet at http://pubs.acs.org.
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