(SPMDs) as Passive Air Samplers for Persistent Organic Polluta

between sites. High amounts were sequestered in. SPMDs at sites where previous active monitoring has indicated relatively high atmospheric concentrati...
0 downloads 17 Views 102KB Size
Download PDF
Environ. Sci. Technol. 2001, 35, 2576-2582

Further Developments in the Use of Semipermeable Membrane Devices (SPMDs) as Passive Air Samplers for Persistent Organic Pollutants: Field Application in a Spatial Survey of PCDD/Fs and PAHs RAINER LOHMANN,† BRIAN P. CORRIGAN, MIKE HOWSAM,‡ KEVIN C. JONES,* AND WENDY A. OCKENDEN Environmental Science Department, Lancaster University, Lancaster, LA1 4YQ U.K.

Semipermeable membrane devices (SPMDs) were deployed at 19 sites in northwest England to test their efficacy as passive atmospheric samplers for polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs). SPMDs were found to be efficient samplers for vapor phase species in the atmosphere, with good reproducibility between samplers. Species which are partially or completely particle associated under ambient U.K. conditions were also sampled by the SPMDs but with poorer reproducibility. It is suggested that SPMDs could be used to indicate “hotspots” of particulate associated species, however. Differences in absolute and relative concentrations of all PCDD/Fs and PAHs sequestered by the SPMDs were observed between sites. High amounts were sequestered in SPMDs at sites where previous active monitoring has indicated relatively high atmospheric concentrations, confirming the potential of SPMDs as a tool for semiquantitative spatial monitoring of atmospheric species. SPMDs also respond to differences in the mixture of compounds present in the atmosphere, thereby aiding source apportionment studies.

Introduction Persistent organic pollutants (POPs) are conventionally monitored in the atmosphere using high volume (HiVol) air samplers. Major disadvantages of this technique are the cost of apparatus and the need for electrical supply. The scale of studies can thereby be restricted. Passive sampling technologies could alleviate these problems. In particular, such technologies would be useful for spatial studies, for example around (suspected) point sources or as a monitoring tool. In order for passive samplers to be viable, reproducibility between samplers needs to be good, to ensure that any * Corresponding author phone: +44-1524-593972; fax: +44-1524593985; e-mail: [email protected]. † Present address: Ralph M. Parsons Laboratory, 48-336, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. ‡ Present address: Institute of Ecological Sciences, Department of Animal Ecology, Vrije Universieit, De Boelelaan 1087, 1081 HV, Amsterdam, The Netherlands. 2576

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 12, 2001

intersite variation that may occur can be distinguished from intrasite variations. Ideally information would be available on uptake kinetics by a sampler, so that sampled concentrations can be converted to atmospheric concentrations, allowing quantitative data interpretation. In the absence of this information, as long as it could be assumed that the uptake kinetics at each site had been the same, differences in sequestered amounts and profiles could be used in a semiquantitative manner to discern spatial differences. Temperature and/or wind-speed are likely to be the principal factors controlling the uptake kinetics of a sampler. Deployment equipment can be designed to minimize the effects of wind-speed differences between sites. Finally, information needs to be available on the length of time required for exposure. This is to ensure that sequestered concentrations of target analytes are sufficiently above instrument and method quantitation limits for detection to be reliable. Passive sampling of POPs is complicated by the vaporparticle partitioning of many of these compounds at ambient temperatures. This partitioning behavior is dependent on the ambient temperature, the amount and nature of particles in the atmosphere, and on the physical-chemical properties of individual compounds. It is important to realize whether a passive sampler only samples vapor phase constituents, particulate phase constituents, or a mixture of both. Semipermeable membrane devices (SPMDs) have been successfully tested as passive air samplers for POPs which predominantly occur in the vapor phase, such as polychlorinated biphenyls (PCBs), hexachlorobenzene, DDE, and hexachlorocyclohexanes (e.g. refs 1-4). The SPMDs that were used in these previous studies consist of a low-density lay flat polyethylene tubing containing a thin film of the synthetic lipid triolein (5). Vapor-phase constituents of the atmosphere permeate through the membrane of the SPMD and concentrate in the lipid. During exposure, some methyl oleate and oleic acid (triolein’s primary lipid impurities) may seep out through the membrane, creating a sticky surface on the exterior of the sampler, to which particles may adhere. It has been suggested that it is possible that compounds associated with the particles that stick to the surface of SPMDs during exposure may be sampled by the SPMD (1). This could either be achieved through desorption from the particles into the sequestering lipid or simply the fact that compounds associated with particles adhered to the SPMD surface are extracted during sample preparation. The purpose of this study was to carry out field deployments to investigate the effectiveness of SPMDs as samplers for POPs that are either partially or completely particle associated in the atmosphere. Polychlorinated dibenzo-pdioxins and -furans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) were used as test analytes. Reproducibility of SPMDs was investigated. The sensitivity of SPMDs to spatial differences in atmospheric concentrations and profiles was also explored across an area where some background information on typical atmospheric concentrations of PCDD/Fs and PAHs was available. Finally, a first attempt was made to estimate sampling rates of these compounds by SPMDs.

Methods SPMDs. Standard SPMDs as designed by the U.S. Geological Survey (5) (80-90 cm × 2 cm, 75 µm membrane, 1 mL (0.915 g) triolein) were obtained from Environmental Sampling Technologies, St. Joseph, MO. SPMDs were deployed in fivesided metal boxes, with the open side pointing downward. The deployment box was designed not only to protect the 10.1021/es0001862 CCC: $20.00

 2001 American Chemical Society Published on Web 05/11/2001

FIGURE 1. Simplified diagram of deployment apparatus for SPMDs.

FIGURE 2. Location of sample sites. SPMDs from direct sunlight, rain, and direct deposition but also to allow movement of air under and around the SPMDs. Boxes measured 110 mm (h) × 220 mm (l) × 65 mm (d). SPMDs were wound around rods within the box, ensuring that the SPMD did not touch itself (Figure 1). Two SPMDs were deployed in each box, such that the two SPMDs would be combined at the extraction stage to make one sample. Based on data for uptake rates of PCBs by SPMDs (1) and typical atmospheric concentrations of PAHs and PCDD/Fs (6-8), it was estimated that target analytes should be readily detectable in the SPMDs after a 6-week exposure. SPMDs were deployed at 19 sites (site locations detailed below) in November/December 1999. Differences in deployment and subsequent collection times were minimized in order to ensure, as far as possible, that samples were exposed over the same time period. Actual deployment time varied from 42 to 45 days, with deployment/collection not differing by more than 3 days. The average temperature during the deployment period was 6 °C, with temperatures ranging between -5 and + 12 °C at one site where detailed meteorological information was recorded. On collection, samples were stored in sealed, solvent-cleaned cans at -17 °C until required for extraction. Sample Sites. SPMDs were deployed at 19 sites in northwest England (Figure 2). Sites were chosen and samples deployed to test reproducibility, uptake, and sensitivity to spatial differences in atmospheric PCDD/Fs and PAHs concentrations and profiles. Reproducibility. Two samples (two SPMDs each) were deployed at site A, Lancaster University’s field station, where reproducibility was to be tested. Sensitivity to Spatial Differences. Eighteen of the SPMDdeployment sites were chosen to cover a range of different environmental conditions around the urban conurbation of Lancaster. It was suspected that there would therefore be

differences in atmospheric concentrations and profiles between sites. For a contrast of potential pollutant sources, SPMDs were also deployed in the city center of Manchester. Site descriptions are given in Table 1. Extraction and Cleanup. Prior to extraction, SPMDs were spiked with a recovery standard containing a mixture of deuterated PAHs (anthracene, pyrene, p-tertiaryphenyl, benzo[a]pyrene, benzo[ghi]perylene), all 17 13C12-2,3,7,8substituted PCDD/Fs congeners, 13C12-2,8-Cl2DF, 13C12-2,7Cl2DD, and 13C12-2,3,7-Cl3DD. SPMDs were dialyzed for 2 × 24 h in hexane. After dialysis, the two SPMD extracts from each sample site were combined to make one sample per site (except site A, where the four SPMDs were combined making two samples). Extracts were cleaned up through a mixed silica gel/alumina column (silica gel grade 60 from Merck, neutral alumina, Brockman grade 1 from Merck; 20 mm diameter column containing from top 10 g silica gel (3% deactivated) and 15 g alumina (6% deactivated); sample eluted with 175 mL of dichloromethane (DCM)/hexane (50: 50, v:v)). Extracts were further cleaned up by gel-permeation chromatography (25 mm diameter column containing 12 g S-X3 biobeads from BDH, preswollen and sample eluted with DCM/hexane (50:50, v:v); first 33 mL eluent discarded, 3480 mL eluent collected). Samples were solvent exchanged to isooctane and deuterated PAH GC internal injection standards added (phenanthrene, fluoranthene, benzo[a]anthracene, perylene, and 1,3,5-triphenylbenzene). Samples from sites A (1 sample), C, D, E, J, K, L, N, O, Q, and R were analyzed for PAHs by GC-MS (HP-5890 series II, 30 m DB5MS column), according to a method described elsewhere (9). The following PAHs were analyzed in this study: phenanthrene (Phen), anthracene (Anth), 1-methylphenanthrene (1-mPhen), fluoranthene (Fluo), pyrene (Py), benzo[a]anthracene (BaA), chrysene (Chry), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[e]pyrene (BeP), benzo[a]pyrene (BaP), perylene (Per), indeno[123-cd]pyrene (IP), dibenzo[ah]anthracene (DahA), and benzo[ghi]perylene (BghiP). After PAH analysis, samples from all sites were further cleaned-up using a mixed silica gel column (silica gel from Merck, grade 60; 2 cm diameter column containing, from the bottom upward, anhydrous sodium sulfate, 2.5 g activated silica gel, 2.5 g basic silica gel (1 M 33% NaOH), 2.5 g activated silica gel, 5 g acid silica gel (44% H2SO4), 2.5 g activated silica gel and anhydrous sodium sulfate). Extracts were eluted with 110 mL of hexane. Extracts were then fractionated on a basic alumina column (Super alumina 1 B (basic alumina) from ICN; 1 cm diameter column 4.5 g basic alumina). Samples were eluted with 10 mL of DCM/hexane (7:93 v:v) (F1), 6 mL of toluene (F2), and then 20 mL of DCM/hexane (50:50, v:v) (F3 - contains PCDD/Fs). F3 was concentrated to a final volume of ca. 20 µL in nonane. Immediately prior to quantitation, 37Cl4-labeled 2,3,7,8-Cl4DD was added as a retention index and GC internal injection standard. All samples were analyzed by HRGC-HRMS using an HP 6890 and Micromass Autospec Ultima at a resolving power of 10 000, according to a method described elsewhere (10). Total PCDD/F homologues were quantified on a 30 m DB5-MS column, and the 2,3,7,8-PCDD/Fs were quantified on a 60 m SP2331 using the isotope dilution method. QA/QC. SPMD field blanks (SPMDs which were not exposed) and solvent/laboratory blanks each had an inclusion rate of 10%. Detection limits and quantification limits were calculated from the blanks (detection limit as mean plus 3 times the standard deviation of the blank and quantitation limit as mean plus 10 times the standard deviation of the blank). For PAHs, concentrations of all analytes were calculated relative to the GC internal injection standards. Recoveries of the deuterated PAHs added prior to extraction varied from 50 to 120%. Results were not corrected for VOL. 35, NO. 12, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

2577

TABLE 1. Description of Sample Sites site

description

comment

A

field station, semirural

B C D E F G H I J K L M N O P Q R S

urban, industrial - Manchester city center coastal (Morecambe Bay/Irish Sea), near Blackpool coastal (Morecambe Bay/Irish Sea), near Blackpool small village on River Lune down-wind motorway up-wind motorway coastal (Morecambe Bay), mouth of River Lune industrial - effluent treatment works, on River Lune rural rural, mushroom farm in area city residential area industrial coastal (Morecambe Bay), industrial harbor city residential area, incinerator coastal (Morecambe Bay), village residential area coastal (Irish Sea), small village coastal (Morecambe Bay) rural, village residential area, domestic coal and wood burning

four SPMDs exposed (two samples) - reproducibility; typical PAH and PCDD/F concentrations known typical PAH and PCDD/F concentrations known less than 1 km from site D less than 1 km from site C

PCDD/F concentrations in sludge known

typical PCDD/F concentrations known

recovery of these compounds. They were used as a method check. For PCDD/Fs the recovery of all 13C12- labeled internal standards was calculated relative to the GC internal injection standard. Recoveries of the 13C12-PCDD/Fs standards added prior to extraction ranged from 62 to 88%. The isotope dilution method corrects for recoveries of these compounds.

Results and Discussion General Comments on Compounds Detected. Table 2 shows sequestered amounts of PCDD/Fs and PAHs for all samples in the study. Perylene was below limits of quantitation in all samples, and dibenz[ah]anthracene could not be detected in > 50% of samples. All other PAHs analyzed were routinely detected in the SPMDs. Cl7DFs and Cl8DF were generally below limits of detection. 1,2,3,7,8,9-Cl6DF was never detected, and 1,2,3,4,7,8,9-Cl7DF was detected in < 50% of the SPMDs. The other 2,3,7,8-substituted PCDD/Fs congeners and other homologue groups were routinely detected in the SPMD samples. Vapor-Particle Issues. Vapor-particle partitioning in the atmosphere can be approximated from a compounds subcooled liquid vapor pressure (PL) and/or its octanol-air partition coefficient (KOA). Compounds with PL greater than ca. 0.01 Pa (log KOA < 10) are vapor phase constituents; compounds with PL less than ca. 0.000001 Pa (log KOA > 12) are almost entirely particle associated, and compounds with PL (log KOA) between these values can be considered as mixed phase atmospheric constituents (11, 12). The majority of PAHs analyzed in this study and PCDD/Fs with three or more chlorines are at least partially particle associated in the atmosphere under typical U.K. conditions. In ambient U.K. conditions benzo[e]pyrene, benzo[a]pyrene, indeno[123-cd]pyrene, and benzo[ghi]perylene are typically > 95% associated with particulate species (8) and Cl6-8-DFs and Cl7-8DDs are typically > 85 and 95% particle associated, respectively (13). All these compounds were routinely detected in the SPMDs in this study (Table 2). It is likely, therefore, that SPMDs do sample particulate species. The data from this study, however, cannot fully support this hypothesis. Figure 3 shows amounts of (a) PCDD/F homologue groups and (b) PAHs sequestered by the SPMDs at site A. The mean concentrations of these compounds in the vapor and particulate phases of the atmosphere at this site from February to October 1999 are also shown. It is evident from Figure 3 that SPMDs were able to sample greater masses of 2578

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 12, 2001

FIGURE 3. Comparison between HiVol determined vapor and particulate concentrations (8) and amount of compound sequestered by the SPMD for (a) PCDD/F homologue groups and (b) PAH compounds at site A. compounds that were associated with the vapor phase of the atmosphere than they were compounds that were associated with the particulate phase of the atmospheresi.e. there was apparently preferential uptake of vapor phase species. It should also be noted that although it is suggested that SPMDs may be able to sample particle associated species from the atmosphere, it is not clear how these species would be sampled. It is not known whether compounds associated with the particles would desorb and permeate through the SPMD membrane, being truly sequestered by the sampler, or whether they would be merely extracted from the surface associated particles during dialysis. In this study, the exterior of the SPMD was not cleaned prior to extraction in order to ensure that all particles that were effectively “sampled” by the SPMD would be included in the extraction. Not cleaning

TABLE 2. Sequestered Amounts of PCDD/Fs and PAHs in Spatial Studya amount sequestered by SPMD (pg SPMD-1 for PCDD/Fs and ng SPMD-1 for PAHs)

VOL. 35, NO. 12, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9

2579

compound

A-1

A-2

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

exposure time (days) 2,3,7,8-Cl4DF 1,2,3,7,8-Cl5DF 2,3,4,7,8-Cl5DF 1,2,3,4,7,8-Cl6DF 1,2,3,6,7,8-Cl6DF 1,2,3,7,8,9-Cl6DF 2,3,4,6,7,8-Cl6DF 1,2,3,4,6,7,8-Cl7DF 1,2,3,4,7,8,9-Cl7DF 2,3,7,8-Cl4DD 1,2,3,7,8-Cl5DD 1,2,3,4,7,8-Cl6DD 1,2,3,6,7,8-Cl6DD 1,2,3,7,8,9-Cl6DD 1,2,3,4,6,7,8-Cl7DD Cl1DFs Cl2DFs Cl3DFs Cl4DFs Cl5DFs Cl6DFs Cl7DFs Cl8DF Cl2DDs Cl3DDs Cl4DDs Cl5DDs Cl6DDs Cl7DDs Cl8DD phenanthrene anthracene 1-methylphenanthrene fluoranthene pyrene benzo[a]anthracene chrysene benzo[b]fluoranthene benzo[k]fluoranthene benzo[e]pyrene benzo[a]pyrene perylene indeno[123-cd]pyrene dibenzo[ah]anthracene benzo[ghi]perylene

42 2.56 1.66 0.50 0.53 0.39 ND 0.25 NQ ND 0.19 0.64 0.27 0.32 0.35 2.91 810 22000 181 84 19 2.6 NQ NQ 216 43 60 22 5.4 6.1 NQ 1640 48 311 999 500 19 76 19 18 15 NQ NQ 4.0 ND 2.5

42 3.26 1.42 0.41 0.32 0.37 ND 0.24 NQ ND 0.11 0.40 1.92 NQ NQ NQ 845 22200 152 66 14 1.6 NQ NQ 208 40 67 17 4.7 NQ NQ

45 5.79 2.29 1.15 0.58 0.76 ND 0.65 2.65 ND ND 0.76 0.74 0.90 0.64 8.53 2020 3130 686 186 24 3.4 NQ NQ 305 105 162 41 6.8 8.7 39

43 2.01 1.21 0.44 0.25 0.35 ND ND 2.66 1.03 ND 0.47 NQ 0.34 0.26 5.02 893 34600 157 64 13 2.5 4 14 395 57 71 22 5.2 13 51 2520 86 738 1260 452 32 97 20 24 15 14 NQ 6.5 ND 3.0

43 2.31 1.34 0.74 0.54 0.45 ND 0.46 NQ ND ND 0.53 0.42 0.48 0.46 3.87 923 36600 179 67 13 2.2 NQ NQ 379 53 66 20 5.4 9.1 26 5440 278 718 5840 1140 56 129 35 37 26 16 NQ 18 1.0 13

43 3.19 2.06 0.92 0.74 0.59 ND 0.49 1.59 NQ 0.21 0.50 0.28 0.76 0.35 3.55 1510 79000 254 72 23 3.8 NQ NQ 259 45 65 20 7.6 8.8 14 4200 430 700 2420 1380 68 145 28 27 20 13 NQ 8.5 ND 7.0

43 1.09 0.86 0.40 0.26 0.21 ND 0.23 NQ ND 0.17 0.22 ND ND ND 3.09 1010 9070 91 34 8.9 2.6 NQ ND 110 20 25 8.0 5.0 7.1 13

42 1.01 0.90 0.41 0.41 0.26 ND 0.39 NQ ND NQ 0.41 0.40 0.40 0.33 2.59 760 15500 73 34 8.2 3.2 NQ NQ 113 16 20 6.9 2.9 6 14

43 7.02 3.50 1.95 1.35 0.95 ND 0.62 3.40 0.99 0.32 0.89 0.53 0.59 0.57 6.56 3750 143000 696 242 45 9.1 6.3 NQ 410 103 105 30 8.7 13.9 37

43 1.03 0.49 0.18 0.14 0.14 ND ND NQ ND 0.12 0.22 ND ND ND ND 3590 444000 83 33 5.2 NQ NQ ND 230 22 29 12 3.7 NQ NQ

43 3.67 2.56 1.02 0.72 0.66 ND 0.67 1.56 NQ 0.25 0.94 0.57 0.65 0.49 3.96 774 13300 216 103 27 4.6 NQ NQ 231 49 73 30 10 9.1 NQ 1860 65 332 1320 639 31 112 37 33 24 16 NQ 17 0.5 11

43 2.40 1.69 0.76 0.49 0.43 ND 0.50 NQ ND 0.21 0.72 ND 0.47 0.38 3.11 868 8970 153 66 19 3.2 NQ NQ 170 28 42 17 6.1 6.5 13 2100 175 309 1040 637 29 64 16 15 NQ NQ NQ 2.5 ND 1.5

43 1.67 0.87 0.34 ND 0.24 ND ND NQ ND NQ 0.25 0.29 ND 0.36 NQ 624 20500 113 49 11 1.9 NQ ND 185 25 36 13 3.5 4.8 NQ 1310 90 234 717 467 27 53 17 17 14 14 NQ 5.5 ND 3.5

43 2.79 2.23 1.25 1.24 1.01 ND 0.79 2.73 0.60 0.16 0.91 0.74 1.02 0.71 7.25 746 33300 138 73 23 5.1 4.9 NQ 223 40 73 40 18 16 51

43 2.30 1.29 0.52 0.40 0.41 ND 0.25 ND ND ND 0.31 0.27 0.39 0.32 3.72 1120 77700 140 63 15 NQ ND ND 336 33 48 17 6.0 7.8 13 1750 32 588 1050 483 24 116 38 35 25 NQ NQ 23 1.5 14

43 1.71 1.31 0.54 0.39 0.36 ND 0.30 1.72 ND 0.12 0.33 ND 0.28 NQ 3.58 741 17900 108 54 15 1.2 NQ NQ 146 24 36 8.3 4.9 7.7 14 1530 68 223 679 474 22 49 18 15 14 NQ NQ 5.0 ND 3.5

43 0.63 0.24 NQ NQ 0.15 ND ND ND ND 0.11 NQ NQ ND ND 3.18 655 10700 39 14 4.2 2.3 NQ NQ 79 10 13 1.4 2.8 6.6 12

43 4.33 1.89 0.88 0.70 0.47 ND 0.47 NQ NQ 0.24 0.41 NQ 0.34 0.37 3.44 1180 12500 281 108 21 4.1 NQ ND 338 36 40 14 3.8 7.7 17 2295 79 443 1180 384 29 87 28 26 20 NQ NQ 14 1.0 8.5

43 2.45 1.37 0.57 0.32 0.39 ND 0.29 NQ NQ 0.11 0.49 0.26 0.40 0.29 2.26 623 16700 152 43 14 2.5 NQ ND 227 29 36 13 5.0 NQ NQ 894 12 189 650 320 8.5 61 21 18 15 15 NQ 7.5 0.5 3.5

42 2.00 1.02 0.42 0.27 0.22 ND 0.22 ND ND NQ 0.25 1.56 ND ND 2.63 1180 2970 115 41 7.9 NQ NQ NQ 115 20 24 9.3 3.9 5.9 11

a

NQ - not quantified (QA/QC rejected); ND - not detected in sample.

FIGURE 4. SPMD reproducibility for PCDD/Fs homologue groups.

FIGURE 5. SPMD reproducibility for PAHs (SPMDs deployed for 6 weeks in summer 1999).

the exterior of the SPMDs also ensured that direct exposure to laboratory air was kept to a minimum. This reduced risk of contamination of samples and blanks. The interior of each SPMD was spiked with a recovery standard prior to extraction to ensure that the methyl oleate/oleic acid film on the surface of the SPMD did not interfere with extraction efficiency. Recoveries of these standards were good, and it was decided that lack of surface cleaning was not problematic. All results will be referred to as “sequestered”, although it is not known whether compounds were truly sequestered or remained associated with particles adhered to the SPMD surface. In addition, it should be noted that as SPMDs are not designed as samplers for particulate species they are unlikely to sample particles in a quantitative manner. It is therefore likely to be difficult to convert sequestered amounts of particle-associated pollutants into true atmospheric concentrations, in a mass pollutant per volume of air basis. An abnormally high sequestered concentration of particle associated species from a site, however, may suggest that it warrants further investigation. SPMDs could therefore be used as an initial screening tool for particulate species. Further investigation of the ability of SPMDs to sample particulate species is therefore required. Reproducibility. Figure 4 shows sequestered amounts of PCDD/Fs homologue groups for the two samples at site A. The data for the two samples were very similar, although it is obviously not possible to do rigorous statistical testing on just two samples. The results are particularly encouraging, suggesting that SPMDs can be reliably used to sample PCDD/ Fs from the vapor phase of the atmosphere. Differences between the two samples increased slightly with increasing chlorination. This is perhaps not surprising, as these heavier compounds would have been largely particle associated and amounts per SPMD were low, adding to relative quantification errors. In this study, only one sample from site A was analyzed for PAHs. As part of a separate study, two SPMD samples were deployed simultaneously at site A for 6 weeks in the summer of 1999. Data for sequestered PAH amounts in these samples are shown in Figure 5. Again, it is not possible to perform statistical analysis on two samples to statistically test method reproducibility, but it would appear that there was good reproducibility between sequestered PAH amounts, with best reproducibility for the lighter, predominantly vapor phase species. In summary, SPMDs exhibited good reproducibility for sequestering vapor-phase PCDD/Fs and PAHs from the atmosphere. Reproducibility for the particulate species was less good, but data obtained suggest that SPMDs could be used to indicate “hot-spots” of particulate associated species. Sensitivity to Spatial Differences. PCDD/Fs. Data for sequestered amounts at all sites are given in Table 2. SPMDs were dominated by vapor phase associated PCDD/Fs. The dioxin profiles of all samples were dominated by Cl2DDs (46-78% (mean 63%) of PCDDs) and the furan profiles by

the Cl2DFs (52-99% (mean 91%) of PCDFs). A dominance of lighter congeners in atmospheric samples has also been detected by HiVol samplers (8, 10, 13). Of the 2,3,7,8substituted congeners, 1,2,3,4,6,7,8-Cl7DD dominated the dioxin profile in the majority of samples (58-97% (mean 71%)), and 2,3,7,8-Cl4DF dominated the furan profile in all samples (22-61% (mean 41%)). A previous study at site A has shown that ambient concentrations of Cl2DFs are greatest when air masses come from the westsi.e. over the Irish Sea and Morecambe Bay (10). A separate study analyzed sewage sludge collected at site I (14). High concentrations of Cl2DD/Fs were detected in the sludge compared with sludges collected from other sewage treatment works in northwest England. The data from these previous studies are supported by the SPMD data here. There were very high concentrations of the vapor phase furans (Cl1-3DF) in the SPMD sample at site I, for example. The effluent treatment works, site I, is situated on the River Lune (Figure 2). It would also appear that this sewage works is affecting downstream areassfor example, high concentrations of Cl2DFs were observed at site E, a small village on the River Lune, and high concentrations of all PCDD/Fs were seen at site H (mouth of the River Lune). A rough transect can be drawn from Morecambe Bay, through sites H, E, A, J to site S (sites F, G, and K are ignored, as they are relatively sheltered from the direction of the predominant westerly winds). Concentrations of Cl2DFs were observed to decrease along this transect from west to east. Sites around south Morecambe Bay (C, D, H, M, and N) and along the River Lune (sites E, H, and I) also exhibited high Cl2DF concentrations compared with the more inland Lancaster area sites (A, F, G, J, K, L, O, and S), north Morecambe Bay sites (P, Q, and R) and the Manchester site (B). This suggests that Morecambe Bay/River Lune may be local sources of these compounds, rather than the Irish Sea or beyond. These data support those of Lohmann et al. (10). Differences in sequestered profiles were also evident between sites. For example, the ratio of Cl1DF:Cl2DF was much greater at sites B (0.65) and S (0.40) than at the other sites (0.01-0.11, mean 0.04). Site B also had a greater Cl3DF:Cl2DF ratio than the other sites (0.22 at site B compared with 0.0002-0.0389 (mean 0.009) at the other sites). PAHs. Samples from 11 of the sites were analyzed for PAHs. Data for PAHs sequestered by SPMDs at each site are given in Table 2. The PAHs that are associated with the vapor phase of the atmosphere (i.e. 3- and 4-ring PAHs) dominated all samples. Phenanthrene was the predominant PAH sequestered in the majority of samples, in all cases constituting > 40% of the total PAH. Phenanthrene, fluoranthene, pyrene, and 1-methylphenanthrene made up > 92% of PAHs analyzed in all samples. These compounds are typically dominant in HiVol determined air samples (6, 8). As with the PCDD/Fs, the SPMDs deployed in this study were able to discern differences in atmospheric concentrations and profiles of PAHs between sites. Sites D and E showed

2580

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 12, 2001

elevated amounts of the vapor phase PAHs. Sites D, E, J, and N showed relatively high amounts of the 5- and 6-ring PAHs. Site D showed a fluoranthene:phenanthrene ratio that was noticeably different from the other sites. Based on sequestered amounts, at site D the ratio of fluoranthene:phenanthrene was 1.07. The fluoranthene:phenanthrene ratio ranged from 0.45 to 0.73 (mean 0.57) at all other sites. It is clear from the PAH data that atmospheric PAH concentrations/mixtures are extremely heterogeneous, even on a local scale as small as the one studied here. This is to be expected from the numerous and varied PAH sources that exist in urban and rural environments. Sites C and D are less than 1 km apart, for example. With the exceptions of 1-methylphenanthrene and benzo[a]pyrene, all PAH compounds measured in the sample from site D were 1.3-4.5 times higher than those measured in the sample from site C. At site C, fluoranthene constituted 24% of the total measured PAHs, compared with 43% at site D. The difference in concentrations between sites C and D indicates an extremely important caveat for spatial studies: namely that proximity to any possible source must be considered in experimental design, especially when dealing with POPs, such as PAHs, that have many diffuse primary emission sources. Comparison of the data in this study with literature data for actively measured air concentrations of pollutants allows a crude estimation of SPMD sampling rates (m3/day). Data are available for HiVol determined atmospheric concentrations of PCDD/Fs at sites A, B, and S (7, 8) and PAHs at site A (8). Assuming linear uptake, which seems reasonable for a 6-week exposure period (1, 2), SPMD sampling rates (RS, m3/day) can be estimated using

RS ) mSPMD/(t /Cair)

(1)

where mSPMD is the mass sequestered by the SPMD after time t (days) and Cair is the atmospheric concentration (mass/ m3). It should be noted that there are artifacts with the determination of atmospheric partitioning with HiVol samples. For example, gas-phase compounds can absorb to the filter and be miscounted as particle-associated species. Conversely, particle associated species can desorb from the particles collected on the filter and be falsely interpreted as being vapor phase components. This can lead to errors in the calculation of SPMD sampling rates using eq 1. However this approach is reasonable for calculating SPMD sampling rates based on real-world samples. At site A, from February to October 1999 mean atmospheric concentrations (vapor plus particle) of Phen, BkF, IP, and BghiP were 4, 0.3, 0.2, and 0.2 ng/m3, respectively (8). Using eq 1, SPMD sampling rates of these groups of compounds are approximately 9, 1, 0.4, and 0.3 m3/day/ SPMD, respectively. If it is assumed that only the vapor phase is sampled, sampling rates equate to approximately 9, 43, 16, and 7 m3/day/SPMD for Phen, BkF, IP, and BghiP, respectively. It must be stressed that as active sampling was not carried out concurrently with the SPMD deployment, these calculations are made utilizing literature data. Therefore, these are only very crude estimates of atmospheric sampling rates of PAHs by SPMDs, but to the authors knowledge, these are the first approximations for atmospheric PAH sampling rates by SPMDs. Mean atmospheric concentrations of Cl4DDs (vapor plus particulate) measured at site A from February to October 1999 and sites B and S in February 1998 were 0.1, 0.7, and 0.1 pg/m3, respectively (7, 8). SPMD sampling rates of Cl4DDs are estimated at approximately 24, 5, and 7 m3/day/ SPMD at sites A, B, and S, assuming uptake of vapor plus particles and at approximately 26, 9, and 13 m3/day/SPMD assuming uptake of vapor phase only. Mean vapor plus particulate atmospheric concentrations of Cl7DDs at site A

from February to October 1999 and sites B and S in February 1998 were 0.2, 0.8, and 0.3 pg/m3 at sites A, B, and S (7, 8), giving rise to sampling rates of approximately 1, 0.2, and 0.5 m3/day/SPMD (vapor plus particle sampling) and 13, 10, and 27 m3/day/SPMD (vapor sampling). As with PAHs, it must be stressed that these are only approximate sampling rates and should be utilized with extreme caution for estimating atmospheric concentrations. Again, they are the first approximations for atmospheric PCDD/Fs sampling rates by SPMDs. It is interesting to note that there were differences in sampling rates of PAHs and PCDD/Fs between sites. At one site, SPMD sampling rates of PCBs were found to be greater in winter than in summer (1). Although differences in temperature were thought to be the principal reason for this, the affect of differences in wind-speed on sampling rates could not be ruled out. It is therefore also not possible to state whether it was only differences in temperature between sites that caused the differences in sampling rates observed here or whether wind-speed would have also played a part. It is suggested that as with uptake of PCBs by SPMDs (1), there was a general increase in sampling rate with increasing SPMD-air partition coefficient. This, however, was coupled with limitations to uptake caused by association of compounds with particles, as discussed above. Increasing orthosubstitution for the same level of chlorination has been found to result in decreasing sampling rate for PCBs (1, 15). This suggests that although most resistance to uptake/mass transfer is likely to be in the air-boundary layer, steric hindrance (and membrane resistance) have an affect on sampling rate. With PAHs and PCDD/Fs, this could result in a decrease in sampling rate for the heavier more aromatic/ chlorinated analytes. It is therefore suggested that it may not be possible to calculate a simple relationship between sampling rate and compound based solely on chemical properties of the compound. Full calibration studies are needed to investigate the importance of air-boundary layer and membrane resistance further. In summary, these data suggest that SPMDs can be used to semiquantitatively detect PAHs and PCDD/Fs in the atmosphere. Without more rigorous testing, they cannot be used to give true quantitative data. However, we have shown that SPMDs can be used in cost-effective monitoring or spatial studies. In the absence of true calibration data, the data produced by SPMDs would highlight sites where further, quantitative studies may be required.

Acknowledgments We are grateful to the U.K. Environment Agency, the U.K. Department of the Environment Transport and the Regions, and the U.K. Natural Environment Research Council for funding Lancaster University’s research into POPs in the atmosphere and research on SPMDs as passive air samplers. We are also grateful to the three anonymous reviewers for their careful and constructive review of the manuscript.

Literature Cited (1) Ockenden, W. A.; Prest, H. F.; Thomas, G. O.; Sweetman, A.; Jones, K. C. Environ. Sci. Technol. 1998, 32, 1538-1543. (2) Ockenden, W. A.; Sweetman, A.; Prest, H. F.; Steinnes, E.; Jones, K. C. Environ. Sci. Technol. 1998, 32, 2795-2803. (3) Prest, H. F.; Jacobson, L. A.; Huckins, J. N. Chemosphere 1995, 30, 1351-1361. (4) Petty, J. D.; Zajicek, J. L.; Huckins, J. N. Chemosphere 1993, 27 1609-1624. (5) Huckins, J. N.; Tubergen, M. W.; Manuweera, G. K. Chemosphere 1990, 20 533-552. (6) Coleman, P. J.; Lee, R. G. M.; Alcock, R. E.; Jones, K. C. Environ. Sci. Technol. 1997, 31, 2120-2124. (7) Lohmann, R.; Northcott, G. N.; Jones, K. C. Environ. Sci. Technol. 2000, 34, 2892-2899. VOL. 35, NO. 12, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

2581

(8) Ockenden, W. A.; Corrigan, B. P.; Howsam, M.; Harner, T.; Lohmann, R.; Jones, K. C. Lancaster University. Unpublished data. (9) Howsam, M.; Jones, K. C.; Ineson, P. Environ. Pollut. 2000, 108, 413-424. (10) Lohmann, R.; Green, N. J. L.; Jones, K. C. Environ. Sci. Technol. 1999, 33, 4440-4447. (11) Eisenreich, S. J.; Looney, B. B.; Thornton, J. D. Environ. Sci. Technol. 1981, 15, 30-38. (12) Harner, T.; Green, N. J. L.; Jones, K. C. Environ. Sci. Technol. 2000, 34, 3109-3114. (13) Lohmann, R.; Lee, R. G. M.; Green, N. J. L.; Jones, K. C. Atmos. Environ. 2000, 34, 2539-2547.

2582

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 12, 2001

(14) Stevens, J. L.; Green, N. J. L.; Jones, K. C. Chemosphere 2001, In press. (15) Huckins, J. N.; Petty, J. D.; Orazio, C. E.; Zajicek, J. L.; Gibson, V. L.; Clark, R. C.; Echols, D. R. Abstracts of 15th Annual SETAC Meeting SETAC, Denver, CO. November 1994; SETAC: 1994; Paper MB01, p 106.

Received for review August 14, 2000. Revised manuscript received March 17, 2001. Accepted March 29, 2001. ES0001862