Environ. Sci. Technol. 2000, 34, 3137-3142
Polychlorinated Naphthalenes in the Atmosphere of the United Kingdom T O M H A R N E R , * ,† ROBERT G. M. LEE,‡ AND KEVIN C. JONES‡ Meteorological Service of Canada, Environment Canada, 4905 Dufferin Street, Downsview, Ontario, M3H 5T4 Canada, and Environmental Science, Lancaster University, Lancaster, LA1 4YQ U.K.
Archived extracts from two air sampling campaigns were used to investigate PCNs in the U.K. atmosphere. In the first study, daily air samples were collected at a semi-rural location (Hazelrigg) in northwest England in 1994. Air parcel back-trajectories were used to distinguish air masses that stemmed from distinct sectors, and 18 samples representing four regions (Arctic/Scandinavia; Atlantic; mainland Europe; U.K.) were selected for PCN analysis. The mean for all samples was ∑PCN ) 59 pg m-3 and ∑PCN/ ∑PCB ) 0.31 with a profile that was dominated by the 3-Cl and 4-Cl PCN homologue groups. Atmospheric concentrations of PCN and the ratio ∑PCN/∑PCB were lowest for samples that had trajectories that stemmed from the Arctic/Scandinavia sectors20 pg m-3 and 0.24, respectively. Highest values were observed for air that lingered over the U.K. before arriving at the sampling sites 108 pg m-3 and 0.41, respectively. These results are consistent with elevated PCN burdens in the eastern Arctic Ocean for air samples that stemmed from the U.K. region and suggest that the U.K. is a significant emission source of PCNs. On the basis of this study, we also conclude that a ∑PCN/∑PCB ratio of 0.2-0.25 is characteristic of background air resulting from diffuse emission sources and that a ratio much greater than 0.25 indicates an increasing contribution from “nondiffuse” or “point sources” of PCNs. In the second study, extracts were obtained for 1998-1999 from four stations operated under the TOMPS monitoring programsManchester (urban), Hazelrigg (semirural), Stoke Ferry (rural), and High Muffles (rural). PCN air burdens were highest at Manchester (138-160 pg m-3) and decreased to ∼22-35 pg m-3 at the rural sites.
Introduction The ubiquitous nature of polychlorinated naphthalenes (PCNs) is of concern because of their dioxin-like toxicity. Exposure to PCNs has been blamed for the death of two Britons in the 1940s (1, 2). Early studies reported high concentrations of ∑PCN in British birds of prey (3) and freshwater and marine biota in Sweden (4). More recently, they have been reported in human tissue (5) and a wide range of biological samples (6, 7) on a congener-specific basis. Several congeners exhibit high dioxin-like toxicity, and * Corresponding author phone: (416)739-4837; fax: (416)739-5708; e-mail:
[email protected]. † Environment Canada. ‡ Lancaster University. 10.1021/es000883u CCC: $19.00 Published on Web 06/21/2000
2000 American Chemical Society
FIGURE 1. Structure of polychlorinated naphthalenes showing the numbering of the chlorine substitution positions. Substitution in the r or peri positions leads to greater distortion of the molecule. 2,3,7,8,-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalents (TEFs) have been reported (8, 9) and are of similar magnitude to some of the coplanar PCBs (10). The use-history of PCNs has paralleled and preceded that of the PCBs. Produced by chlorination of molten naphthalene, PCNs exist as 75 possible congeners that contain one to eight chlorine atoms (Figure 1). They are structurally similar to the polychlorinated biphenyls (PCBs) and exhibit similar chemical and thermal stability. They were first used commercially in the early 1900s for wood, paper, and textile impregnation but were shortly thereafter replaced by PCBs after incidents of worker-related toxicity (11). Koppers Company (Pennsylvania) was one of the largest producers of technical PCN formulations (Halowaxes) until they voluntarily ceased production in 1977 (12). PCNs were produced in Europe under various names including Seekay Waxes (ICI, United Kingdom) and Nibren Waxes (Bayer, Germany) (12). Little is known of the production volumes and production history in the United Kingdom, and no studies of PCNs in the atmosphere have been made. However, some insight to the historical inputs of PCNs to the U.K. environment has been gained through analysis of a rural freshwater sediment core (13), which shows peak inputs of PCNs ca. 1960 at ∼20% of the value of the peak for PCBs that occurred ca. 1978. Beland and Greer (14) estimate that the global cumulative PCN production represents ∼10% of the PCB value. Although the use of PCNs has declined in the past few decades, they are not prohibited in most countries and still occur in many PCB-like applications such as capacitor fluids, engine oil additives, and electrical insulators (12) and as contaminants in commercial PCB fluids (15). PCNs have also been found in incinerator emissions (16) and are believed to be formed by combustion of PAHs by a “de novo” synthesis pathway (17). Recent atmospheric concentrations of PCNs have been reported in Germany (18), urban Chicago (19), Sweden (20), and the eastern Arctic Ocean and land-based Arctic monitoring stations (21). Back-trajectory analysis for the eastern Arctic Ocean samples has related episodes of elevated PCN and PCB concentrations to air trajectories that stem from the United Kingdom and other European regions in the 5-day period prior to their collection, implicating these regions as potential sources. Here we investigate the assertion that the U.K. is a significant “source” of PCNs. PCNs are analyzed in archived samples from two intensive studies. In the first study, air samples were collected at a semi-rural location in northwest England in 1994 over the course of several months VOL. 34, NO. 15, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Comparison of Recent Measurements (pg m-3) of Polychlorinated Naphthalenes and Polychlorinated Biphenyls in Air
a
location
type
∑PCN
∑PCB
Augsburg, Germany, 1992-1993 Augsburg, Germany, 1992-1993 Chicago, IL, 1995 Downsview, Canada, 1995 Barents Sea, 1996 E. Arctic Ocean, 1996 Norwegian Sea, 1996 Alert, Canada, 1993-1994 Dunai, Russia, 1993 Lancaster, U.K., 1995b Lancaster, U.K., 1994 Manchester, U.K., 1998-1999
urban rural urban urban remote remote remote remote remote semi-rural semi-rural urban
60 24 68 17 40 12 7.1 3.5 0.8 152 66 149
nra nr 350 nr 126 24 75 38 30 471 163 381
nr, not reported.
b
∑PCN/∑PCB
ref 18 18 19 19 19 19 19 19 19 24, 25 this study, 22 this study, 22
0.19 0.32 0.50 0.09 0.09 0.03 0.32 0.40 0.39
Diurnal sampling study conducted during stable atmospheric conditions.
TABLE 2. Sampling Information, ∑PCN and ∑PCB Concentrations, and ∑PCN/∑PCB Ratios for Air Samples Collected in 1994 at Hazelrigg, a Semi-Rural Site in Northwest Englanda sector
sample no.
date (m/d-m/d)
air vol (m3)
∑PCN
∑PCB
∑PCN/∑PCB
Arctic/Scandinavia Arctic/Scandinavia Arctic/Scandinavia Arctic/Scandinavia Arctic/Scandinavia Arctic/Scandinavia Arctic/Scandinavia
s66 s56 s57 s64 s50 s170 s171
5/27-5/28 5/19-5/20 5/20-5/21 5/25-5/26 5/15-5/16 10/3-10/4 10/4-10/5
302 384 503 351 344 385 399
46 12 15 35 10 10 14
89 58 109 181 64 57 54
0.52 0.21 0.14 0.19 0.16 0.18 0.26
mean ( SD Europe Europe Europe
s47 s48 s70
5/11-5/12 5/12-5/13 6/1-6/2
409 352 390
20 ( 13 22 35 166
87 ( 46 165 196 261
0.24 ( 0.13 0.13 0.18 0.64
mean ( SD Atlantic Atlantic Atlantic
s75 s80 s81
6/6-6/7 6/11-6/12 6/12-6/13
383 323 360
74 ( 65 71 55 29
207 ( 49 263 124 145
0.32 ( 0.28 0.27 0.44 0.20
mean ( SD U.K. U.K. U.K. U.K. U.K.
s176 s177 s178 s179 s180
10/10-10/11 10/11-10/12 10/12-10/13 10/13-10/14 10/14-10/15
378 393 381 376 440
52 ( 17 41 47 34 83 336
177 ( 61 141 172 192 243 347
0.30 ( 0.12 0.29 0.27 0.18 0.34 0.97
mean ( SD
108 ( 115
219 ( 81
0.41 ( 0.32
mean for all samples (n ) 18)
59 ( 78
159 ( 83
0.31 ( 0.21
a
Samples are divided into sectors of air mass origin based on air back-trajectory analysis.
(22). The second set of extracts was selected from recently archived samples from four sites routinely monitored in the TOMPS air sampling program (23). Extracts represent the last quarter of 1998 and the first quarter of 1999 (i.e., n ) 8). The relative importance of the U.K. as an emission source of PCNs is assessed with the use of 5-day air parcel backtrajectories, and atmospheric burdens are compared to PCBs.
Methodology Sample Collection: Hazelrigg 1994 Study and TOMPS Samples. High-volume air samples were collected daily over the period March-October and December in 1994 at Hazelrigg, a semi-rural location just outside of Lancaster (population 70 000), about 5 km inland from the northwest coast of England. Analytical details and results for PCBs and PAHs are presented elsewhere (22). Five-day air parcel backtrajectories were determined at the Hazelrigg site for all samples collected in 1994. Samples that had trajectories stemming from distinct regions were then selected from the archive for PCN analysis. 3138
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The Toxic Organic Micropollutants Survey (TOMPS) has been operating in the U.K. since 1992. It has established ambient levels of PCBs, PAHs, and PCDD/Fs at selected urban and rural sites by taking 2-week-long samples consecutively throughout the year; at the present, samples are bulked to obtain quarterly data. PCB and PCN analyses are undertaken on a fraction of the bulked quarterly extract that is equivalent to 200-300 m3 of ambient air depending on the site. This sampling program has provided long-term concentration data principally for urban sites. In both studies, high-volume air samples were collected using a General Metalworks GPS1 PUF/pesticide sampler. Glass fiber filters were used for collecting the particulate phase, and polyurethane foam plugs were used for the gas phase. All samples were extracted by Soxhlet, and extracts were reduced in volume and fractionated using florisil. More details are presented elsewhere (22). The F1 portions from florisil were further fractionated on mini carbon columns in order to separate the PCNs from the bulk of the PCB congeners and to allow further reduction in volume for samples
FIGURE 2. PCN homologue concentrations/distributions for air arriving at the sampling location from different sectors. The U.K. sector refers to air that spent a significant portion of its 5-day history over the U.K. Mean concentrations of PCNs and PCBs for all samples (n ) 18) are shown.
FIGURE 3. Five-day air parcel back-trajectories (925 hPa) for Lancaster at the time of collection of the air sample having the highest and the lowest concentration of ∑PCN. stored in dodecane. These columns contained AX-21 activated carbon mixed 1:20 with silicic acid. The carbon-silicic acid mix (100 mg) was sandwiched between 50-mg layers of silicic acid. The column was prewashed with 5 mL of toluene followed by 5 mL of 30% DCM in cyclohexane. The first
fraction (F1-1) was eluted with 5 mL of 30% dichloromethane in cyclohexane and contained the multi-ortho- and a portion of the mono-ortho-PCBs. The second fraction (F1-2) was eluted using 5 mL of toluene and contained PCNs, nonorthoPCBs, and the remainder of the mono-ortho congeners. PCB VOL. 34, NO. 15, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 4. Correlation of ∑PCN versus ∑PCB for air samples from Hazelrigg. Samples are grouped according sectors of air mass origin.
FIGURE 5. Homologue contributions for 3-5 Cl PCNs at urban and semi-rural TOMPS sites in the U.K. for fourth quarter of 1998 and first quarter of 1999.
TABLE 3. PCN and PCB Concentrations at TOMPs Sites for Last Quarter 1998 (Q4-98) and First Quarter 1999 (Q1-99) Q4-98
Q1-99
TOMPS sites
∑PCN
∑PCBa
∑PCN/∑PCB
∑PCN
∑PCBa
∑PCN/∑PCB
High Muffles (rural) Manchester (urban) Stoke Ferry (rural) Hazelrigg (semi-rural)
22 160 35 40
57 555 82 99
0.39 0.29 0.43 0.40
31 138 27 37
72 206 66 88
0.43 0.67 0.41 0.42
a ∑PCB represents a corrected concentration-based measurement of 11 PCB congeners that are known to contribute to ∼68% of ∑PCB in the U.K.
congeners 208 and 209 in dodecane were added as internal standards for volume correction. Fraction F1-2 was volume reduced to 25 µL using a gentle stream of nitrogen. PCNs were determined by gas chromatography electron impact mass spectrometry (GC-EIMS, Fisons MD-800) in SIM using a 30-m DB-5MS column (0.25 mm i.d., 0.25 µm film). Peaks were quantified against Halowax 1014, a commercial mixture of 2-Cl to 8-Cl PCNs. All results have been blank and recovery corrected. Recoveries for the 3-Cl to 4-Cl were ∼90-100% 3140
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but dropped off for the higher molecular weight homologues (5-Cl, ∼25-95%; 6-Cl to 8-Cl, 0-90%). The poor recoveries of the 6-Cl to 8-Cl congeners were attributed to these congeners being retained more strongly by florisil since recovery tests on the carbon column step showed no significant losses. Because most of the toxicity is associated with the 6-Cl congeners, toxic equivalents (TEQs) will not be determined from these data. However, overall concentrations of PCNs are obtainable since typically >95% of the atmo-
spheric burden is associated with the 3-5-Cl congeners (the 3-Cl and 4-Cl congeners accounting for about 90% of this total) (21).
Results and Discussion Recent Measurements of PCNs in the Atmosphere. Table 1 outlines atmospheric burdens of PCNs at different sampling locations reported in the literature. In general, PCN burdens are high in urban areas (∼60-150 pg m-3) as compared to remote locations such the Arctic (
