Polychlorinated Biphenyls in Arctic Air. 1. Temporal ... - ACS Publications

Environ. Sci. Technol. 1997, 31, 3619-3628

Polychlorinated Biphenyls in Arctic Air. 1. Temporal and Spatial Trends: 1992-1994 G . A . S T E R N , * ,† C . J . H A L S A L L , ‡ L. A. BARRIE,‡ D. C. G. MUIR,† P. FELLIN,§ B. ROSENBERG,† F. YA. ROVINSKY,| E. YA. KONONOV,| AND B. PASTUHOV| Freshwater Institute, Department of Fisheries and Oceans, 501 University Cres., Winnipeg Manitoba, Canada R3T 2N6, Environment Canada, 4905 Dufferin St., Toronto Ontario, Canada, M3H 5T9, BOVAR Environmental, 2 Tippett Rd., Toronto Ontario, Canada, M3H 2V2, and Institute for Global Climate and Ecology, 20-b Glebovskaya, Moscow, Russia

In 1992, a long term program was established to measure the airborne concentrations of persistent organic pollutants (POPs) in the Arctic. To maximize spatial variation over a wide geographical area, three Arctic locations were selected; two sites in Canada, Alert on Ellesmere Island and Tagish in the western Yukon, and one in Russia at Dunai Island in eastern Siberia. PCB data is presented here for the years 1992-1994. Mean ∑PCB concentrations for 1993, the year when all three sites were running simultaneously, were 27.4, 17.0, and 34.0 pg/m3 at the Alert, Tagish, and Dunai sites, respectively. With the exception of the Tagish site in 1993, where ∑PCB concentrations were found to be weakly correlated with mean monthly temperatures, no correlation with temperature was observed. However, changes in the homolog group profile with temperature were apparent. On an annual basis, the trichlorinated congeners made the largest single contribution to the atmospheric concentrations of ∑PCB, however, this contribution declined with the onset of warmer months. This temperature-dependent homolog pattern was most clearly evident at Dunai, where the contribution of the pentachlorinated congeners matched or exceeded that of the trichlorinated congeners during May, June, and July of 1993. It was also evident at Alert and Tagish, but not to the same degree. Spatial and year-to-year differences at these Arctic sites were attributed to both the site’s proximity to source areas (where different PCB mixtures and quantities have been used) and to the influence of air mass movement from these source regions.

Introduction In 1974, Rappe (1) postulated that persistent organic pollutants (POPs) migrate thousands of kilometers from their point of release through the atmosphere as gases and aerosols and condense in low-temperature regions. Warm temperatures favored volatilization from the Earth’s surface in tropical and subtropical regions, while cold temperatures at higher * To whom correspondence should be addressed. Fax: (204) 9842403. E-mail: [email protected]. † Freshwater Institute. ‡ Environment Canada. § BOVAR Environmental. | Institute for Global Climate and Ecology.

S0013-936X(97)00375-1 CCC: $14.00

 1997 American Chemical Society

FIGURE 1. Sampling sites. latitudes favor deposition from the atmosphere into water, snow, ice, soil, and water (2-5). POPs of different volatility migrate through the global atmosphere at different velocities. Highly volatile compounds tend to remain airborne for longer periods of time and thus migrate faster than the less volatile POPs. The resulting differences in contaminant mixtures along varying temperature or latitudinal gradients is known as global fractionation (6). To date, a number of studies dealing with the measurements of POPs in ambient air have been published (7-15). Few, however, have involved high temporal resolution data sets (weekly or subweekly samples) with sampling periods greater than a few months. Even fewer involved the collection of both gas (polyurethane foam plugs, PUF) and particulate (filter) data. Hoff et al. (7) published the results from the first high temporal resolution PCB data set (two-day cycle) obtained over an annual cycle at Egbert, Ontario, Canada (44°14′ N, 79°47′ W) (Figure 1). On the basis of data presented by Foreman and Bidleman (16), it was assumed that the predominance of the PCB sample mass would reside on the PUFs and not on the filters. Filters, therefore, were not examined, and the results presented corresponded to the minimum for the total air concentration of over 91 PCB congeners. Their results showed a strong seasonal variation with peak concentrations occurring in the warmer summer months which was attributed to volatilization of previously deposited material. More recently, Oehme et al. (12) published the results from a year-long study involving weekly ambient air measurements of polychlorinated compounds at Ny-A° lesund (78°55′ N, 11°56′ W), Svalbard, Norway (Figure 1) in 1993. This study reported the concentrations of ten PCBs which were routinely monitored in other matrices such as biota and sediment under the Arctic Monitoring and Assessment Programme (AMAP). In contrast to the findings of Hoff et al. (7), no seasonal change of PCB concentrations was observed. Oehme et al. attributed this difference between sites to the closer proximity of the southern Ontario site to source regions and the fact that the temperature for substantial volatilization was not reached. On the basis of the Egbert results, it was postulated that temperatures above 10 °C were required for a prolonged period of time for substantial volatilization to occur.

VOL. 31, NO. 12, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. Range and Mean Concentrations (pg/m3) of Total PCBs (PUFs + Filters) and a Subset of Ten Congeners in Alert, Tagish, and Dunai Air for the Annual, Cold and Warm Monitoring Periods (Table 2) total PCBsa

AMAP subsetb

year

sampling period

mean (SD)

range

mean (SD)

range

1992 1993 1993 1993 1994 1994 1994

Sept 14-Dec 28 Jan 5-Dec 27 Jan 5-Apr 26, Oct 4-Dec 27 (C) May 3-Sep 27 (W) Jan 3-Dec 26 Jan 3-Apr 25, Oct 3-Dec 26 (C) May 2-Sep 26 (W)

Alert 20.5 (8.1) 27.4 (18.3) 23.6 (12.7) 32.7 (23.0) 28.3 (19.1) 28.4 (23.2) 28.0 (11.3)

5.7-30.5 1.8-94.7 1.7-55.6 8.4-94.7 7.1-148.0 15.0-148.0 7.1-56.2

3.8 (1.7) 5.8 (4.7) 4.2 (2.0) 8.1 (6.3) 6.1 (3.9) 5.7 (4.2) 6.7 (3.3)

0.7-6.0 0.2-25.9 0.2-8.4 1.1-25.9 1.2-26.4 3.0-26.4 1.2-16.7

1993 1993 1993 1994 1994 1994

Jan 7-Dec 30 Jan 7-Mar 25, Nov 4-Dec 30 (C) Apr 1-Oct 28 (W) Jan 6-Aug 18 Jan 6-Feb 24 (C) Mar 3-Aug 18 (W)

Tagish 17.0 (5.5) 19.7 (6.0) 15.9 (4.2) 18.4 (5.9) 19.3 (6.1) 18.1 (53.8)

9.4-32.2 11.1-32.2 9.4-25.6 4.1-29.7 8.6-29.7 4.1-27.8

3.7 (1.5) 4.2 (1.5) 3.2 (1.4) 3.7 (1.4) 3.8 (1.8) 3.6 (1.2)

0.9-8.3 2.2-8.3 0.9-6.5 0.4-6.8 0.9-6.8 0.4-6.4

1993 1993 1993

Mar 9-Dec 20 Mar 9-Apr 26, Nov 5-Dec 20 (C) May 3-Aug 30 (W)

Dunai 34.0 (16.7) 38.2 (20.9) 30.2 (10.5)

5.4-94.6 13.5-94.6 5.4-49.5

8.1 (4.4) 8.7 (5.5) 7.6 (3.1)

0.5-22.6 3.3-22.6 0.5-14.3

a Sum of CB4/10, 6, 7, 8/5, 16/32, 17, 18, 19, 22, 24/27, 25, 26, 28, 31, 33, 40, 41/71, 42, 44, 45, 46, 47, 48, 49, 52, 56/60, 64, 66, CB70/76, 74, 82, 83, 84/89, 85, 87, 91, 95, 97, 99, 101, 105, 110, 114, 118, 128, 130/176, 131, 132, 134, 136, 137, 138, 141, CB144/135, 146, 149, 151, 153, 156, 158, 170, 171, 172/197, 174, 175, 177, 178/129, 179, 180, 183, 185, 187, 189, 191, 193, CB194, 195, 196/203, 198, 199, 200, 201/157, 205, 206, 207, and 209. b Sum of CB28, 31, 52, 101, 105, 118, 138, 153, 156, and 180. C ) cold, W ) warm.

TABLE 2. Designated Cold (C) and Warm (W) Monitoring Periods for the Alert, Tagish, and Dunai Sampling Sites Alert (NWT)

monitoring period

year

temp (°C) (mean/range)

1992 Sept 14-Dec 28 (C) -23.3 (-10.2 f -34.6) 1993 Jan 5-Apr 26 (C) -27.2 (-12.0 f -36.7) Oct 4-Dec 27 May 3-Sept 27 (W) -4.0 (6.3 f -18.8) 1994 Jan 3-Apr 25 (C) -28.0 (-11.2 f -38.9) Oct 3-Dec 26 May 2-Sept 26 (W) -2.7 (6.7 f -16.5)

Tagish (Yukon)

monitoring period

Mar 3-Aug 18 (W)

Experimental Section To monitor spatial variation over a wide geographical area, three Arctic locations were selected (Figure 1). Two sites in Canada, Alert on Ellesmere Island (82.30° N, 62.20° W) and Tagish in the Western Yukon (60.20° N, 134.12° W) and one in Russia, on Dunai Island in Eastern Siberia (74.60° N, 124.30° E). A complete characterization of these sites is available in a report produced by BOVAR-CONCORD Environmental (19). Weekly sampling began at Alert in January 1992 and is still on going; however, data for the period of January through

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monitoring period


Jan 7-Mar 25 Mar 9-Apr 26 (C) -8.3 (-3.0 f -18.0) (C) -26.6 (-11.4 f -36.8) Nov 4-Dec 30 Nov 5-Dec 20 Apr 1-Oct 28 (W) 9.5 (15.7 f -1.2) May 03-Aug 30 (W) 0.2 (6.2 f -15.7) Jan 6-Feb 24 (C) -19.0 (-7.4 f -28.0)

To assess the importance of the atmosphere as a source of contaminants to the Arctic, a long term systematic air sampling program was established to provide detailed information on the temporal and spatial distribution of airborne concentrations and vapor-particle partitioning for a wide range of POPs (17). This paper is the first of a two part series in which the PCB data from three sites of this program, two of which are located in the Canadian Arctic and a third at a unique site located in the Russian Arctic (Figure 1), are presented. The Russian site has provided the first long-term database on POPs in the atmosphere of eastern Siberia. Part one, which is presented in this paper, deals with the spatial and temporal trends at these three sites (1992-1994), while part two takes a thermodynamic standpoint to examine the importance of long-range transport versus localized air/ surface exchange in controlling the air concentrations.

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Dunai (Russia)

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 31, NO. 12, 1997

9.7 (21.2 f -5.1)

August 1992 is not included in the results because of high PCB control concentrations. At the Tagish site, weekly sampling was carried out for just over two years, December 1992 through December 1994. Data from September to December 1994 has not yet been processed and therefore, could not be included in the results. Weekly sampling at the Dunai began in March 1993 and ended in December of the same year. No data, however, was available for the months of September and October due to equipment problems. Site maintenance, sample preparation, sampling, and data organization was carried out by Bovar Environmental (BE) in Toronto, Canada. Sample analysis was performed by the Freshwater Institute (FWI) in Winnipeg, Canada. Sample collection at each site was carried out using a highvolume air sampler consisting of a 10 µm diameter particle size-selective inlet and housing (Wedding and Associates, Fort Collins, CO). Air is drawn through a 20 cm diameter sample cartridge containing a glass-fiber filter for collection of airborne particles and two 4 cm thick 20 cm diameter polyurethane foam (PUF) plugs for collection of organic vapors. Once every four weeks, two filters were used instead of one to check for gaseous adsorption artifacts on the filter matrix. A field blank was obtained every four weeks by handling a PUF and filter in exactly the same way as a sample, but no air was introduced. In this way, possible contamination from the transport, handling, and storage procedures could be assessed. Volumetric flow control at 1.13 m3 min-1 was achieved using a critical flow device. This resulted in

FIGURE 2. Weekly concentrations of ∑PCBs (pg/m3) and corresponding air temperatures of the complete time series at the Alert, Tagish, and Dunai sampling sites. nominal air volumes of about 11 400 m3 over a collection period of 7 days. Large air volumes were required to achieve detectable concentrations, as many of the analytes are present in extremely low concentrations in the Arctic atmosphere. Throughout the course of a year, 52 weekly samples and 13 field blanks were collected from each site. Complete sampling details including sample preparation, have been reported previously by Fellin et al. (17). Throughout the entire analytical procedure, the two PUF plugs and glass fiber filters were processed separately so that information with regard to vapor-particle partitioning and the breakthrough amounts for each target analyte could be determined. PUF plugs and filters were Soxhlet extracted for 24 h with approximately 450 mL of a 1:1 mixture of hexane and dichloromethane. Extracts were dried over 8-10 g of anhydrous sodium sulfate and reduced in volume to 20 mL. After archiving half the extract, the remainder of the sample was split into two aliquots; one fraction for PAH analysis (17, 18) and the other for organochlorine (OC) analysis including PCBs. Following the addition of PCB-30 as a surrogate recovery standard, the OC aliquot was separated into three fractions of increasing polarity on Florisil (8 g; 1.2% v/w water deactivated). The first fraction was eluted with hexane and contained PCBs, DDE, trans-nonachlor, and mirex; the second fraction was eluted with hexane:DCM (85:15) and contained HCHs, most chlorinated bornanes (toxaphene), and chlordanes. Some chlorobornanes, most notably T2 (Parlar no. 26), were partially eluted with hexane. The third fraction, containing dieldrin and heptachlor epoxide, was eluted with a 1:1 mixture of hexane:DCM. Each fraction was analyzed for OCs by capillary gas chromatography (GC) with 63Ni electron capture detection (ECD) by means of an automated Varian 3400 GC (Varian Instruments, Palo Alto, CA). Samples were injected in splitless mode on a 60 m × 0.25 mm i.d. DB-5 column (film thickness

) 0.25 µm). H2 was used as the carrier gas (1 mL/min) and N2 as the make-up gas (40 mL/min). Individual PCB congeners were quantified by use of external standard mixtures (Ultra Scientific, North Kingstown, RI). Recoveries of several target compounds were assessed by spiking of the blank media at concentrations representative of field samples. The extraction recoveries tested in this manner were found to be greater than 90% for triplicate filters and PUFs fortified with standard solutions containing a PCB 1242 mixture. In addition, recoveries of the surrogate, PCB-30, was also uniformly greater than 90%. Quality Controls and Assurance. For each sample, documentation was maintained using field data reporting forms which also noted unusual events or conditions which might have occurred during a specific sampling period. All analytical data were manually reviewed to verify that resolution, peak shapes, and automatic baseline selection were appropriate. Manual processing of peaks was performed to rectify inaccurate quantification. Field blanks were used to calculate the method detection limits (MDLs). MDLs for each sampling year were defined as the average blank value of the filters and PUFs (or a combination of the two, weighted according to the proportion of the PCB congener found on each) plus 3 times the standard deviation of the filter and PUF media blank values combined in the same proportion as was used for the blank media (Supporting Information, Tables S1 and S2). Other quality assurance measures included the reanalysis of one in every ten samples as a test for analytical precision, inclusion of clean-up recovery and internal standards in each sample extract, analysis of standard reference materials from the EPA repository, as well as routine participation in interlaboratory round-robins. As part of the overall quality assurance, the total data set including laboratory data, field comments, and final air volume corrected concentrations were incorporated into a statistical database called RDMQ. A flagging system


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FIGURE 3. Monthly PCB-homolog group profiles (%∑PCBs) for each sampling year at the Alert, Tagish. and Dunai sampling sites. was developed and utilized to avoid simply deleting data on the grounds that a compound was below its MDL (19). The RDMQ system could be programmed to select data for one specific flag type (i.e., those sample weeks when filter and/or PUF concentrations were above or below the MDL for a particular compound). These flags helped to (i) screen for breakthrough and (ii) qualify best estimates for total vapor

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phase concentrations. Generally, in all three sites, the most reliable results were obtained for the di- to pentachlorinated biphenyls. Incidents of significant breakthrough (PUF2/PUF1 > 0.333) averaged less than 3% for all PCB congeners over the annual monitoring periods at all three sites. Not surprisingly, due to their lower vapor pressures and the colder Arctic temperatures, the hepta- to decachlorinated biphenyls were

TABLE 3. Total (PUF + filter) Mean Monthly PCB Concentrations (pg/m3) site

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sept

Oct

Nov

Dec

Alert 93 Alert94 Tagish93 Tagish94 Dunai93

14.0 57.3 26.3 20.1 NA

40.4 24.9 17.8 18.5 NA

21.9 28.8 21.5 21.2 55.4

29.5 29.1 16.2 25.2 51.7

32.6 29.5 18.7 20.6 31.9

9.9 23.6 14.8 17.5 30.7

64.1 36.7 12.7 12.3 32.2

27.8 32.1 15.9 11.3 26.9

19.0 16.9 14.7 NAa NA

20.5 18.6 13.3 NA NA

22.8 20.9 14.4 NA 23.8

16.2 22.8 18.9 NA 21.4

a

NA, Data not available due to equipment breakdown or incomplete processing.

characterized by problems associated with low vapor phase concentrations.

Results and Discussion Range and mean concentrations of ∑PCB (PUF + filter) and a subset of ten congeners in Alert, Tagish, and Dunai air for the annual, cold, and warm monitoring periods are listed in Table 1. For Alert and Dunai, cold and warm monitoring periods are defined by months in which mean weekly temperatures remain below and above -15 °C, respectively, for at least 2 of 4 or 3 of 5 weeks in any one month. At the Tagish site, they are defined by months in which mean weekly temperatures remain below and above 0 °C, respectively (Table 2). Mean ∑PCB concentrations for 1993, the year when all three sites were running simultaneously, were 27.4, 17.0, and 34.0 pg/m3 at Alert, Tagish, and Dunai, respectively. Tagish had the lowest mean ∑PCB concentrations during both the warm and cold monitoring periods. Oehme et al. (12) reported a mean annual (1993) ∑PCB concentration of 13.1 pg/m3 at Ny-A° lesund, Spitzbergen. This result, however, is based on concentrations of the 10 PCBs which were routinely monitored in other matrices such as biota and sediment, under the AMAP program. The equivalent annual mean concentrations for Alert, Tagish and Dunai were, 5.8, 3.7, and 8.1 pg/m3, respectively. Range and mean concentrations of the 100 individual PCB congeners at all three sites for the cold and warm monitoring periods as well as the number of samples having concentrations greater than their calculated MDLs are presented in the Supporting Information (Tables S3-S8). With the exception of Tagish (1993), at least 90 of the congeners measured for each sample, in both the warm and cold monitoring periods, had concentration above their calculated MDLs over 80 percent of the time. This dropped to 65 and 78 congeners for each sample in the cold and warm monitoring periods, respectively, over 70 percent of the time in the Tagish 1993 data. To retain the maximum possible information for characterization of trends, means, analysis of variance, and other statistical calculations, samples with concentrations less than their calculated MDLs, were left unchanged. Temporal concentration profiles of ∑PCBs with corresponding air temperatures over the complete time series at each site are shown in Figure 2. With the exception of elevated concentrations from July 5th to the 19th, 1993, at Alert (weeks 27 and 28, respectively), no obvious seasonal trends were observed. The episode of elevated PCB concentrations in week two of January, 1994, at the Alert site occurs when the air received originates predominantly from western Russia and will be discussed further in part two of this series of papers. The observed lack of seasonal variation in ∑PCB concentrations is in agreement with observations made at Ny-A° lesund (79° N) (12) but are in contrast with those observed for Egbert Ontario (44° N) (7). The latter site was much closer to source regions and had much higher annual mean temperatures than Ny-A° lesund and the three sites studied in this report. Increased concentrations of PCBs as well as HCH and ΣDDT during the spring and summer at Egbert was attributed to volatilization of previously deposited material. Oehme et al. (12) suggested that temperatures above 10 °C are needed over a substantial time period for the

TABLE 4. Regression Parameters (P < 0.05) for PCB Homolog Groups [%∑PCB ) b + m (temp (°C))] homolog

N

R2

P

m ( (sd)

b ( (sd)

di tria penta hexa hepta

12 11 12 12 12

0.64 0.42 0.59 0.69 0.60

Alert93 0.0017 -0.28 (0.07) 0.0317 -0.20 (0.08) 0.0036 0.20 (0.05) 0.0008 0.18 (0.04) 0.0030 0.14 (0.04)

di hexa hepta

12 12 12

0.70 0.59 0.67

Alert94 0.0006 -0.24 (0.05) 0.0035 0.15 (0.04) 0.0012 0.21 (0.05)

4.58 (1.09) 10.19 (0.88) 9.08 (1.03)

di tri tetra penta hexa hepta octa

12 12 12 12 12 12 12

0.54 0.50 0.43 0.51 0.74 0.72 0.48

Tagish93 0.0065 -0.20 (0.06) 0.0098 -0.68 (0.21) 0.0210 0.21 (0.08) 0.0089 0.21 (0.07) 0.0003 0.21 (0.04) 0.0005 0.16 (0.03) 0.0126 0.06 (0.02)

7.98 (0.58) 39.06 (2.15) 19.33 (0.78) 14.76 (0.66) 9.00 (0.39) 5.86 (0.31) 2.90 (0.21)

tri tetra penta

8 8 8

0.84 0.71 0.72

Dunai93 0.0015 -0.53 (0.10) 0.0089 0.48 (0.13) 0.0075 0.02 (0.06)

27.42 (1.92) 28.86 (2.50) 13.30 (1.10)

a

4.02 (1.45) 41.74 (1.67) 15.38 (1.16) 10.95 (0.87) 8.09 (0.80)

Month of February excluded.

volatilization process to become a factor. At the Tagish site, however, temperatures were above this minimum threshold for 17 and 12 consecutive weeks in 1993 (May 13-Sep 02) and 1994 (Jun 02-Aug 18), respectively, with a maximum temperature of 21.2 °C occurring in the week of August 04, 1994. No increase of the PCB levels in ambient air during these warm periods was observed. If anything, a decrease in concentration prevailed from April to August of 1994. Figure 3 shows the percentage of the mean monthly ∑PCB concentrations (Table 3) each homolog group represents in the various sampling years at all three sites. In 1993, monthly concentrations at Alert peaked in July (64.1 pg/m3) and February (40.4 pg/m3), the warmest (mean temperature, xj ) 5.6 °C) and one of the coldest (xj ) -29.9 °C) months of the year, respectively. The lighter di- and trichlorinated PCBs were most predominant in February, accounting for 80% of ∑PCB, while the tetra- through decachlorinated congeners dominating in July accounted for 55% of ∑PCB. Although no correlation between mean monthly temperatures and ∑PCB concentrations was observed, temperature was found to be strongly negatively correlated with the percent contribution of the dichlorinated PCBs to ∑PCB and if the month of February is excluded, weakly negative correlated to the trichlorinated congeners (Table 4). Strong positive correlations with the percent contribution of the penta- through heptachlorinated PCBs were also observed. In 1994, peak ∑PCB concentrations were, once again, observed in one of the coldest (xj ) -33.4 °C) and warmest (xj ) 3.6 °C) months of the year, January (57.3 pg/m3) and July (36.7 pg/m3), respectively. The tetra- through decachlorinated PCBs were most predominant in July, accounting for 64% of ∑PCB. Temperature was strongly negatively correlated with the


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FIGURE 4. Score and loading plots showing the pattern similarities and differences between mean monthly concentrations of individual PCB congeners with mean monthly temperatures over the warm and cold monitoring periods (Table 1) at the Alert, Tagish, and Dunai sampling sites. Objects are defined by the sampling site [A, Alert; Y, Yukon (Tagish); D, Dunai], sampling month and year (Score a) and as the sampling site and mean monthly temperature (Score b). Variables (PCB congeners) are defined as the homolog group they belong to (Loading c) and as their congener number (Loading d). and April, and at a minimum in November and December, percent contributions of the dichlorinated PCBs and positively averaging 53.6 and 22.6 pg/m3, respectively. Levels remained correlated with that of the hexa- and heptachlorinated congeners (Table 4). fairly constant from May through August averaging 30.4 pg/ At the Tagish site in 1993, the highest and lowest monthly m3. The di- and trichlorinated PCBs on average accounted temperatures occurred in July (xj ) 14.5 °C) and January (xj for 54% of ∑PCB in November, December, and March, and ) -12.8 °C), respectively. ∑PCB levels were at a maximum only 34% from May through August. In June, the tetrain January (26.3 pg/m3) and, contrary to the Alert site, were through decachlorinated PCBs accounted for over 70% of ∑PCBs, half of which correspond to pentachlorinated conat a minimum in July (12.7 pg/m3). In fact, ∑PCB concentrageners, in particular, CB95, 101, 110, and 118 (67% of 5Cl). tions were found to be negatively correlated, albeit weakly, Temperature was found to be strongly negatively correlated with the mean monthly temperatures (∑PCB (pg/m3) ) 17.64 with the percent contribution of the trichlorinated PCBs and - 0.23 (°C), r2 ) 0.38, p ) 0.0329). As was observed at Alert, strongly positively correlated with the contributions of the the di- and trichlorinated PCBs peaked in the colder months, tetra- and pentachlorinated congeners (Table 4). accounting for 67% of ∑PCB in January, while contributions Principal Component Analysis. PCA (20) was conducted of the tetra- through decachlorinated PCBs maximized in to examine pattern similarities and differences between mean July, accounting for almost 70% of ∑PCB. Strong negative monthly concentrations of individual PCB congeners with correlations between temperature and the contributions from mean monthly temperatures for the cold and warm monitorboth the di- and trichlorinated PCBs (Table 4) were observed. ing periods at the Alert, Tagish, and Dunai sampling sites Conversely, moderate positive correlations were observed for (Table 1). Mean monthly concentrations were block norcontributions from the penta- through heptachlorinated malized (expressed as a fraction of the combined sum of the PCBs. In 1994, mean monthly ∑PCB concentrations peaked concentrations of all PCBs) to avoid the influence of absolute in April (25.2 pg/m3) and were at a minimum in July (12.3 concentrations. Autoscaling to unit variance was used to pg/m3) and August (11.3 pg/m3). From January to June, the minimize any statistical bias associated with the order-ofsum contributions from the di- and trichlorinated PCBs were magnitude differences in chemical concentrations. Using almost equal to that of the tetra- through to decachlorinated cross validation (21), it was determined that the first and congeners. In July and August, however, the latter composecond principal components accounted for 36.6 and 12.2%, nents, accounted for almost 65% of ∑PCB. No significant respectively, of the total variability in the data set. Three correlations between temperature and the percent contribudistinct clusters are observed in the resulting score plot (Figure tion of the different PCB homolog groups were observed. 4a,b). The first is aligned with the positive axis of the second At the Dunai site, based on an incomplete set of annual principal component and is comprised of the warmer months results, ∑PCB concentrations were at a maximum in March

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FIGURE 5. Air mass trajectory distribution (%) for the May-August sampling period (1993) at the Alert, Tagish, and Dunai sampling sites. at the Alert and Dunai sites (the month of April at the Dunai site seems to be the exception). The second cluster lies along the positive axis of the first principal component and consists of the warmer months at the Yukon (Tagish) site with the exception of the month of June in the 1993 sampling year at Alert (Jun 93). The final cluster lies in the quadrant associated with the negative axes of both principal components and is comprised of the coldest months at the Alert and Dunai sites. The importance of individual PCB congeners in determining the positions of the clusters of monthly mean temperatures at the three sampling sites along the principal component axes is partially explained by the principal component loading plots (Figure 4c,d). The loading plots show that the warmer months at the Alert and Dunai sites are characterized by higher proportions of tetra-, penta-, and hexachlorinated PCBs, while the colder months are associated with higher proportions lower chlorinated di- and trichorinated PCBs. The greatest loadings of the higher chlorinated congeners (hexa-deca) are associated with the warmer months at the Tagish site. These results are consistent with the variation of the homolog profiles with temperature discussed in the previous section. Influence of Long-Range Transport on Concentrations. To examine the influence of air mass movement from source regions, two periods, May-August and November-December, were selected to represent the warm and cold monitoring periods designated in Table 2. For each of these periods, air mass back trajectories were calculated to examine the influence of air mass movement from anthropogenic source regions on each of the sample sites. Six geographical source regions defined by Worthy et al. (22), based on economic

activity, were utilized. However, due to the geographical diversity of the three sites in this study, several of the sectors were classed together; these included eastern and western Russia (sectors 3 + 4) and Europe and the North Atlantic (sectors 5 + 6). The sectors are displayed for each site in Figure 5. During the periods of interest, air mass back trajectories (lagrangian) were calculated four times a day with each trajectory extending back over 120 h (or 5 days). The trajectories were sorted according to the appropriate sector, with a trajectory being assigned if >70% of the trajectory points fell within a sector’s boundaries. The frequency distribution of trajectories to each sector over the May-August period are presented for the three sites in Figure 5. Alert was affected largely by air arriving from Northern Canada and the Pacific region, whereas Dunai mainly receives air from continental North America and Russia; approximately 60% of the trajectories were from these two sectors. Tagish, on the other hand, is dominated by air from the Pacific, with over 70% of the trajectories originating from this sector. Sample weeks were matched to periods when air was derived from a particular sector. For many of the sectors, the air trajectories occurred sporadically rather than consistently over a 7 day period (the time taken to collect one sample). However, consecutive six or seven day periods of continuous air flow were apparent for those sectors with the largest proportion of the trajectories, allowing the selection of several sample weeks in which air flow was predominantly from one sector. For the three sites, the PCB homolog profiles for sample weeks belonging to three of the sectors (1, 2, and


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FIGURE 6. PCB homolog group profiles for selected May-August (1993) sample weeks with trajectories originating from to the Russian (3 + 4), North American (1), and the Pacific (2) sectors for the Alert, Tagish, and Dunai sampling sites. 3 + 4) are displayed in Figure 6. For those weeks when air flow was from sector 3 + 4 (Russia) there was a clear difference in profile compared to the other sectors. With air flow from Russia, each site showed a reduction in the trichlorinated homolog compared to those sample weeks when air was from sectors 1 and 2. An enhancement of the heavier penta- and hexachlorinated homologs was also apparent, particularly for Dunai, the site closest to Russian source regions. Sample weeks representing air from sector 1 (North America) and sector 2 (Pacific region) are marked by the trichlorinated homolog making the largest contribution, notably at Alert and Tagish (∼40% of the total PCB). For sector 2, the Pacific region, the profile is not as uniform at the three sites relative to the other sectors. Unlike Tagish, Alert and Dunai are further away from this region, with the air having to cross the Arctic Ocean and either Canada or eastern Russia to reach these sites; this is likely to further influence the PCB composition. This effect of increasing contributions by the heavier homologs when air originates from the Russian side of the Arctic may be due to the composition of the PCB mixtures used in Russia. In commercial formulations of PCBs manufactured in United States and western Europe (Aroclors 1016,

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1242, 1254, and 1260; Clophens A30, A40, A50, and A60) (23), the weight percent contribution of the pentachlorinated congeners range from about 1% in Aroclor 1016 to approximately 51 and 55% in Chlophen A50 and Arochlor 1254, respectively. Sovol and Trichlorodiphenyl, Soviet technical PCB mixtures, were found to have a similar composition to that of Aroclor 1242 and 1254, respectively (24). Approximately 100 000 tonnes of Solvol was produced between the 1940s and the 1990s, as compared to 25 000 tonnes of the lighter Trichlorodiphenyl (24, 25). Indeed, air samples taken in the Lake Baikal region (25, 26) show patterns characteristic of a “mixture” of these two formulations, with enhanced concentrations of several pentachlorinated congeners. This predominant use of Sovol and its subsequent dispersion in the environment may account for the contribution of the penta- and hexachlorinated homologs during these warmer months, most notably at Dunai, and marked in particular when air flow is from Russia. For the May-August period, differences between 1993 and 1994 were also evident most notably at Tagish. For instance, in Figure 3, the May-August period of 1993 shows the characteristic decline in the contribution by the trichlorinated

FIGURE 7. PCB homolog group profiles for selected November-December (1993) sample weeks with trajectories originating from to the Russian (3 + 4), North American (1), and the Pacific (2) sectors for the Alert, Tagish, and Dunai sampling sites. homolog, in particular during the month of July. In the corresponding period of 1994 this pattern is not repeated. Examining the frequency distribution of trajectories for both periods, the air movement from sector 3 + 4 (Russia) was reduced in the 1994 period. For instance, during 1993, 16% of the air flow was from sector 3 + 4 compared to 4% in 1994. In addition, all the trajectories from this sector in the 1993 period occurred in July, the month showing the greatest contribution by the heavier homologs. It is therefore reasonable to suggest that air from the Russian source region will have a marked effect on the PCB profile in the Yukon atmosphere during these warmer months, with air flow from this sector accounting for the July 1993 profile. Trajectories were calculated throughout the colder period of November-December 1993 and assigned to the various sectors in the same procedure as Figure 5. Changes in air flow relative to the warmer months was observed. For instance, over 60% of the trajectories to Dunai were from the Russian interior compared to 30% in the May-August period, while >95% of the trajectories to Tagish originate from over the Pacific, compared to 70% in the warmer months. Changes in air flow to Alert were not as marked; however, there was less of an influence from the Pacific region and an increase

in air flow from North America. Interestingly, the homolog profiles shown in Figure 7, for selected sample weeks tend to show a uniformity regardless of sector influence, with a general trend of decreasing contributions with increasing chlorination. At Dunai, however, the sector 3 + 4 sample does show an enhancement of the heavier homologs (tetra and above) over the sector 1 sample, but the general pattern is the same. Indeed, the monthly summary of homolog contributions (Figure 3) clearly shows the predominance of the lighter trichlorinated homologs during the colder months at all three sites.

Acknowledgments Financial assistance for this work was provided by the Arctic Environmental Strategy Northern Contaminants Program, Department of Indian Affairs, and Northern Development (DIAND).

Supporting Information Available Eight tables (8 pages) will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the Supporting Information from this paper or microfiche


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(105 × 148 mm, 24× reduction, negatives) may be obtained from Microforms Office, American Chemical Society, 1155 16th St. NW, Washington, DC 20036. Full bibliographic citation (journal, title of article, names of authors, inclusive pagination, volume number, and issue number) and prepayment, check or money order for $19.50 for photocopy ($21.50 foreign) or $12.00 for microfiche ($13.00 foreign), are required. Canadian residents should add 7% GST. Supporting Information is also available via the World Wide Web at URL http: //www.chemcenter.org. Users should select Electronic Publications and then Environmental Science and Technology under Electronic Editions. Detailed instructions for using this service, along with a description of the file formats, are available at this site. To download the Supporting Information, enter the journal subscription number from your mailing label. For additional information on electronic access, send electronic mail to [email protected] or phone (202)872-6333.

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Received for review April 29, 1997. Revised manuscript received July 22, 1997. Accepted August 5, 1997.X ES970375T X

Abstract published in Advance ACS Abstracts, September 15, 1997.

Polychlorinated Biphenyls in Arctic Air. 1. Temporal ... - ACS Publications

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