Environ. Sci. Technol. 2007, 41, 2172-2177
Vertical and Temporal Distribution of Persistent Organic Pollutants in Toronto. 1. Organochlorine Pesticides ELODIE MOREAU-GUIGON,† ANNE MOTELAY-MASSEI,‡ T O M H A R N E R , * ,§ K A R L A P O Z O , § MIRIAM DIAMOND,| MARC CHEVREUIL,⊥ AND HE ´ LE ` NE BLANCHOUD⊥ Science and Technology Branch, Environment Canada, Toronto, Ontario, M3H 5T4, Canada, UPMC, UMR Sisyphe, 4 place Jussieu 75252 Paris Cedex 05, France, UMR 6143 CNRS Morphodynamique Continentale et Coˆtie`re, Universite´ de Rouen, France, Geography Department, University of Toronto, Toronto, Canada, and Laboratoire Hydrologie et Environnement, EPHE/UMR Sisyphe, 4 place Jussieu 75252 Paris Cedex 05, France
From May to September 2005, five passive air samples were deployed over five, 1-month periods at five elevations on the CN Tower in Toronto, Canada, to investigate the vertical distribution, seasonality, and sources of organochlorine pesticides. A strong seasonality was observed between spring and the end of summer. Vertical profiles differed for different pesticide classes. For instance, R- and γ-hexachlorocyclohexane exhibited higher concentrations (60-80 pg m-3, respectively) near the ground during the spring and early summer, suggesting that surface-air exchange within the city or nearby Lake Ontario may be important sources. The vertical profile for chlordane isomers was variable, suggesting that both advective and local inputs are important. For dieldrin, no obvious trend with elevation was observed, suggesting that concentrations could reflect a regional air mass contamination. Strongest seasonality was observed for the endosulfans, a widely used pesticide in North America, that reached peak concentrations of 750-850 pg m-3 during June/July. Advective inputs of endosulfan from regional or more distant agricultural regions can explain the relatively uniform concentrations with elevation throughout the study period. The approach used in this study demonstrates that monthly average vertical concentration profiles differ between pesticide groups and reflect their use as well as the relative magnitude of input from local versus regional sources.
Introduction Organochlorine pesticides (OCPs) were widely used, mainly in agriculture and also in cities, for the control of unwanted pests. Although many OCPs have been banned, their residues in soil continue to be a source of atmospheric contamination (1, 2). OCPs are persistent organic pollutants (POPs), which * To whom correspondence should be addressed e-mail:
[email protected]. † UPMC, UMR Sisyphe. ‡ Universite ´ de Rouen. § Environment Canada. | University of Toronto. ⊥ EPHE/UMR Sisyphe. 2172
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means that they persist in the environment, become widely distributed geographically, bioaccumulate through the food web, and are toxic to humans and wildlife (3). Current-use and banned OCPs are released to the atmosphere, either directly, during application or by volatilization from soil and vegetation following their use (4-6). They are susceptible to long-range atmospheric transport, to varying degrees, as demonstrated by the contamination of remote sites (7-15). The occurrence of pesticides in cities is an important issue with implications related to human exposure and potential health effects (cancer, reproductive disorders, and other abnormalities) (16-19). In some cases, cities may be sources of pesticidessMotelay-Massei et al. showed that Toronto was a regional source of chlordane, related to its historic use on house foundations and lawns (10). In most cases, cities are receptors of pesticides that are used in nearby or even distant agricultural regions (20). For instance Ma et al. showed how the Great Lakes region can be impacted by long-range transport of pesticides from far off agricultural source regionssthe Canadian Prairies in the case of lindane transport (21, 22) and the southern United States in the case of toxaphene transport (23, 24). In many cases, the advection inputs exhibit a strong seasonal pattern, maximizing during the spring and summer. For current-use pesticides, this is due to their use patterns that typically peak in this period. For legacy OCPs that volatilize from contaminated soil, this is associated with higher soil-air fluxes during the warmer months and in some cases a “spring-pulse” effect (25). Seasonal variations in meteorology and air pattern movements are also contributing factors (23, 24). Farrar et al. (26) measured the vertical distribution of POPs in the urban boundary layer in Toronto by collecting weekly passive samples at several heights up to 270 m. Samples were collected on the CN Tower, the world’s tallest freestanding building, situated in downtown Toronto, Canada. The study showed that compound distributions in the atmospheric boundary layer (ABL) were a complex function of emissions, advection, and vertical mixing rates (26) and can be classified into three different concentration profiles: (i) An even distribution with height means that ABL is well mixed, fresh emissions are minimal, and advection dominates; (ii) higher concentrations at ground level may occur where primary sources at ground level are substantial enough to overcome vertical mixing; (iii) higher concentrations with height, which may be tied to nearby emissions toward the upper ABL (e.g., from stacks) or stratified air masses near ground level and with height. However, because the samples were collected over a relatively short period (1-week periods), it was not possible to investigate the longer temporal variability that is expected for pesticides. In this study, we used longer term passive samplers (PUF disk samplers) (10, 11, 27-29), deployed at the same heights (up to 270 m on the CN Tower) over several consecutive 1-month periods, to investigate how vertical profiles of legacy and current-use pesticides change with time and in relation to meteorological factors.
Materials and Methods Sample Collection. PUF disk passive air samplers were installed on the exterior of the northwest leg of the CN Tower at different altitudes (30, 90, 150, 210, 270 m). The samplers were mounted to stainless steel hatches that were accessible from the interior of the Tower. The sampler consists of a PUF disk housed in stainless steel, domed chambers in order to reduce the influence of wind speed on uptake rate and also to protect the PUF disk from rainfall, direct particle 10.1021/es062705s CCC: $37.00
2007 American Chemical Society Published on Web 03/03/2007
FIGURE 1. Schematic of the PUF disk passive air sampler and location of sampling points on the CN Tower.
TABLE 1. Details of PUF-Disk Samples Collected on the CN Tower period
start date
end date
1 2 3 4 5
2005/05/13 2005/06/16 2005/07/22 2005/08/25 2005/09/30
2005/06/16 2005/07/22 2005/08/25 2005/09/30 2005/11/04
duration sampling ratea mean (m3 day-1) temp (°C)b (days) 1.70 ( 0.39 3.00 ( 0.76 6.70 ( 0.74 4.70 ( 0.53 4.80 ( 0.38
16.1 21.8 22.1 19.4 11.2
34 36 34 36 35
a Mean value ( SD for 5 sites, derived from depuration compound recoveries using eq 2 in ref 11 and reported KOA values (46-50). b From nearest meteorological station.
deposition, and UV sunlight (Figure 1). The PUF disks (10.8 cm diameter; 1.3 cm thick; 227 cm2 surface area; 119 cm3 volume; 2.53 g; 0.0213 g cm-3 density; Pacwill Environmental, Stoney Creek, ON) were deployed over five, 1-month periods from May 2005 to November 2005 (Table 1). One field blank was collected during each period. The field blank was installed in the sampler and then removed and stored as a sample. Prior to exposure, PUF disks were rinsed with water and then cleaned by Soxhlet extraction using acetone (24 h) followed by petroleum ether (PE, 24 h) and then dried in a desiccator. One day prior to their deployment, PUF disks were fortified with four depuration compounds (γHCH-d6, PCB 30, PCB 107, and PCB 198). These compounds do not exist naturally in air. The loss or “depuration” of these chemicals from the PUF disk is used to assess the sampling rate for each sampler and hence the effective air sample volume that is required to estimate an air concentration (28, 29). Small differences in sampling rates between samplers may be caused by the different wind speeds at the different elevated sites (30, 31). PUF disk passive samplers are now widely used for measuring air concentrations of POPs (10, 11, 27-29, 32-34). Analyses. Samples were screened for 20 OCPs. All sample PUF disks were extracted by Soxhlet apparatus for 24 h with
PE. The extract was reduced to ∼5 mL by a rotary evaporator under vacuum, transferred to a vial, and reduced under a gentle stream of nitrogen to 0.5-1 mL. When required (samples from periods 3-5), samples were further cleaned on a 5-g column consisting of an [alumina (deactivated with 6% water)]/[silicic acid (deactivated with 3% water)] column (2: 3). The column was prewashed with 20 mL of dichloromethane (DCM) followed by 20 mL of PE. After application of the sample, the column was eluted with 30 mL of PE and then with 20 mL of DCM. The OCPs were captured in this second DCM fraction. Each aliquot was solvent exchanged into 1 mL of isooctane, transferred to a 2-mL GC vial, and further reduced to a final volume of ∼0.5 mL. Mirex (100 ng) was added as an internal standard to correct for volume difference. Samples were analyzed on a Hewlett-Packard 6890 gas chromatography equipped with a mass-selective detector (model HP 5973) and a splitless injector. OCPs were analyzed in negative chemical ionizationselective ion mode with methane as the reagent gas, using a DB5 (60 m × 0.25 mm i.d., 0.25-µm film thickness) capillary column (J&W Scientific) with helium as the carrier gas. The standard mixture was obtained from Ultra Scientific (North Kingstown, RI). Additional details have been previously published (10, 28).
Results and Discussion Quality Assurance/Quality Control. Method recoveries were assessed previously for all of the target compounds (10, 11). They were generally >85% for OCPs, so reported values were not recovery corrected. Analytes in field blanks were always less than 2% of the sample amount, and reported values are blank corrected. Peaks were only integrated when the signalto-noise ratio was g3. Although the samples were screened for 20 OCPs, results are only reported for 9 compounds that were consistently detected in all samples. These included the following: R-hexachlorocyclohexane (HCH), γ-HCH, dieldrin, trans-chlordane, cis-chlordane, trans-nanochlor, VOL. 41, NO. 7, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Air concentrations of γ- HCH and r-HCH. endosulfan 1, endosulfan 2, and endosulfan SO4. Depuration Compounds. Recoveries of depuration compounds were used to calculate sampling rates based on the methods described in previous publications (28, 29, 32). These are summarized in Table 1. The variation in sampling rates at each elevation was low within a particular period, as indicated by the low SD values that ranged from ∼10 to 25%, and the average value was used for calculating the sampling rate and chemical specific sample volumes, as outlined in Table 1. However, larger differences were observed between periodssranging from a low of 1.7 m3 day-1 in period 1 to a high of 6.7 m3 day-1 for period 3. This large, period to period, variation for a particular site was not observed in previous studies (28, 29, 32). However, in previous studies, PUF disk samplers were mounted to posts or similar objects and exposed to the wind from all directions. For the CN Tower study, the samplers were situated on the northwest leg of the tower and positioned up against its concrete surface. The Tower would have acted as a barrier, sheltering the samplers from the wind, with the exception of winds from the northwest sectorsroughly between 225° and 45°. This may partly explain the higher sampling rate during period 3 (Table 1). During July-August 2005, there was a greater proportion of NW winds observed at the nearest meteorological station (http://www.wunderground.com/ history.html), whereas during May-June 2005, the proportion of NW winds were reduced and the sampler was sheltered from the wind and subject to relatively still air. Similarly, the higher sampling rate during period 5 can be explained by elevated wind speeds. The effect of wind speed on PUF disk sampling rate is a topic of continued and further research (30, 31). The average sampling rate for all sites for the five periods was 4.2 m3 day-1. This compares favorably to the value of 3.9 m3 day-1 recently derived for these samplers deployed for 3 months across 40 global sites (29) Air Mass Back Trajectory Analysis. To examine the influence of air mass movement from source regions, 5-day air parcel back trajectories were performed for each sampling location using the Canadian Meteorological Centre (CMC) Trajectory Model. Trajectories were calculated at 30 and 270 m above the ground every 6 h for each day of the deployment period. The resulting trajectories are displayed as “spaghetti” plots in the Supporting Information. The resulting plots show good agreement between the 30- and 270-m sitesswith a slightly larger area covered by the trajectories arriving at 270 m. Information form the spaghetti plots was converted to airshed maps to better visualize regions of air mass origin. Spaghetti plots and airshed maps are presented in the Supporting Information. Vertical and Temporal Profiles for OCPs. (1) CurrentUse or Recent-Use OCPs (i.e., Endosulfans and γ-HCH). γ-HCH. Lindane (comprising mainly γ-HCH) was widely used in Canada, especially in the Canadian prairie region and also 2174
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in southern Ontario and Quebec, until it was phased out during the period 2002-2004 (35). At the time of the CN Tower sampling in 2005, it is believed that no lindane was used in Canada, but in the United States and Mexico, this product is still used, although uses in Mexico were being phased out. The occurrence of lindane in the atmosphere can thus be associated with a variety of sources: (i) continued use of lindaneseither unauthorized/unintended use in Canada; (ii) advection of lindane from use regions in the United States, Mexico, or more distant source regions; (iii) revolatilization of previously applied lindane from contaminated soil. This last possibility also includes lindane associated with technical HCH that was once a heavily used pesticide worldwide (1, 22). Results for γ-HCH show highest levels during the spring period and then a sharp decline to baseline levels for periods 3-5 (Figure 2). A spring maximum (with γ-HCH concentrations of ∼50-80 pg m-3) has been observed previously in the Great Lakes region. Such elevated concentrations usually correspond to the application of lindane as a seed dressing at the start of the growing season in southern Ontario (35) and also in the Canadian prairie region, where the largest Canadian use of lindane occurred (21). Ma et al. have shown the important contribution of prairie-derived lindane to the air burdens and deposition of this chemical in the Great Lakes region (21). However, lindane use was discontinued in Canada in 2004 and so elevated concentrations in the spring should only be due to emission of residual lindane contained in Canadian soils or transport from the United States where lindane was used until 2006 (35). Yao et al. (35) observed an interesting and unexplained 1-day spike of lindane measured on June 27, 2005 (i.e., after the lindane ban) at two different sites in Toronto: ∼3000 pg m-3 in downtown Toronto and ∼600 pg m-3 in north Toronto (Downsview). The contribution of this 1-day event could explain more than half of the lindane captured by the passive samplers in period 2. It is possible that a similar, unexplained spring time event(s) may have contributed to the elevated levels during period 1. The vertical profile of lindane shows higher concentrations near the surfacessuggesting a local, ground-level source, implicating Toronto (or possibly the nearby Lake Ontario). It is also noteworthy that, during the early periods when γ-HCH was elevated, there were few instances of air masses arriving from the prairiesssuggesting the possible continued contribution of residual lindane from this past source region does not explain the elevated concentrations (see Supporting Information, SI, for back trajectory and airshed maps). Later in the study period (periods 3-5), air concentrations return to “background” levels of ∼10 pg m-3. Endosulfans. Endosulfan is a widely and currently used pesticide in North America (36). It is produced as a mixture of mainly two isomers, endosulfan 1 and 2, in a proportion
FIGURE 3. Air concentrations of endosulfan1, endosulfan2, and endosulfan SO4. of 7:3. In the environment, endosulfan isomers degrade to endosulfan SO4. The air concentrations of each isomer and its degradation compound show a strong temporal trend (Figure 3) with highest concentrations occurring during the spring (periods 1 and 2) and close to ∼700 pg m-3 for endosulfan1, 200 pg m-3 for endosulfan2, and 35 pg m-3 for endosulfan sulfate. This reflects current use of the pesticide during this time of year. Concentrations drop-off steeply during the late summer and fall periods. It is interesting that the concentration of endosulfan SO4 (which is continually being produced from the endosulfan precursors) is more uniform throughout the study. Endosulfans exhibit a uniform distribution with height, suggesting that advective inputs are the main sources to the atmosphere of Toronto. This is consistent with the widespread use of endosulfan in North America and also within southern Ontario. The back trajectories for the various sampling periods extend across large portions of Canada and the United Statess including agricultural regions where endosulfan would certainly be used (see SI).
(2) Banned OCPs (i.e., r-HCH, Dieldrin, and Chlordanes). R-HCH. Sources of R-HCH include technical HCH (a once widely used pesticide mixture that contains several isomers: R, 60-70%; β, 4-12%; γ, 10-12%; δ, 9-10%). R-HCH is also produced as a waste, byproduct in the manufacture of lindane (37), and some studies have shown that γ-HCH may be transformed to R-HCH in the environment (38-40). The results for R-HCH demonstrate a seasonal variability with highest concentrations during the spring (periods 1 and 2) ranging from 25 to 60 pg m-3 with highest concentrations near the ground as for γ-HCH (Figure 2). During later periods, concentrations at all elevations decrease to background levels of ∼10 pg m-3. This range of values is consistent with recent (2003) measurements of R-HCH across agricultural regions in Canada where concentrations ranged from nondetectable to ∼50 pg m-3 (36). As for γ-HCH, the profiles of R-HCH during spring periods suggest an input from sources in Toronto or possibly nearby Lake Ontario. However, the possibility of Lake Ontario as a source is contrary to the findings of Ridal et al. that showed net deposition to the lake during the spring and net volatilization during the summer period (41). It is also possible that some component of the R-HCH in the atmosphere is associated with isomerization of previously deposited γ-HCH to R-HCH (42-44). However, no field measurements confirming this pathway have been reported in the literature. Dieldrin. Dieldrin was deregistered in North America in 1970 for agricultural uses and in 1987 for termite control. Air concentrations of dieldrin were highest during period 1 (∼150-250 pg m-3) and then decreased sharply over the course of the study to background levels of ∼25-50 pg m-3 (Table 2). These background levels are consistent with the range of values reported in agricultural regions across Canada (36) and also with previous ground-level passive sampling measurements in Toronto (10). There were no obvious trends with elevation, suggesting that these concentrations reflected a regional air mass. Meijer et al. showed that agricultural regions in southern Ontario are still contaminated with dieldrin and acting as sources of dieldrin to the regional atmosphere (6). A similar conclusion was postulated by Bidleman and Leone, who investigated dieldrin residues in agricultural soils from the southern United States (1). It is likely that mechanical mixing of agricultural soils during the early spring across North America, coupled with rising surface temperatures, may result in a spring pulse of dieldrin to the ambient air. Chlordanes. Technical chlordane is a mixture of components comprising mainly trans-chlordane (TC), cis-chlordane (CC), and trans-nanochlor (TN) in the proportion 1.00/ 0.77/0.62 (i.e., TC/CC ) 1.3), respectively (45). It was used in agriculture (corn) and on lawns and gardens until 1973 and for termite control until 1988. The air concentration profiles for chlordanes (Table 2) did not show strong differences between elevations, indicating that the ABL is relatively well mixed and that the contribution of local sources is likely not dominating the air burden. Air concentrations peaked in period 1 (TC, CC, and TN in the range of 22-56 , 27-58, and 26-45 pg m-3, respectively) and then decreased gradually over the course of the study to fallstime concentrations that were a factor of ∼2-5 lowerstypically 5-10 pg m-3. This is consistent with concentrations reported by Motelay-Massei et al. (10) for Toronto and by Yao et al. in agricultural sites across Canada (36). The TC/CC ratio was constant over the entire study period and between 0.9 and 1.1 in more than 90% of samples (Table 2). This is similar to the technical mixture value of 1.3 and is indicative of relatively fresh chlordane, in contrast to the aged signatures, where TC/CC is much less than 1 due to the faster degradation of TC. For instance, the TC/CC that is typically observed in the Canadian arctic, a receptor site, is VOL. 41, NO. 7, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Air Concentrations (pg‚m-3) of Organochlorine Pesticides in CN Tower Samples r-HCH
period
Vair, m3
1
30 m 90 m 150 m 210 m 270 m
Vair, m3
2
30 m 90 m 150 m 210 m 270 m
Vair, m3
3
30 m 90 m 150 m 210 m 270 m
Vair, m3
4
30 m 90 m 150 m 210 m 270 m
Vair, m3
5
30 m 90 m 150 m 210 m 270 m
γ-HCH
transchlordane
cischlordane
trans nonachlor
50
52
57
57
57
57.33 61.34 28.46 28.46 29.87
68.58 81.42 69.35 52.68 55.17
32.42 55.67 42.99 22.02 44.04
37.65 57.71 50.14 27.80 49.44
29.51 45.22 39.11 25.84 38.06
75
83
35.92 44.04 24.48 23.95 25.28
61.64 80.35 58.64 46.05 21.59
111 8.64 9.45 9.99 9.63 6.93 104 11.43 11.52 10.37 10.66 8.74 123 10.34 14.32 9.20 9.77 11.64
135 8.32 7.72 7.72 7.42 8.76 120 8.44 9.03 9.19 6.94 6.69 135 5.68 6.42 4.65 3.62 7.60
102 18.49 28.28 20.74 25.93 32.09 202 9.24 13.54 17.69 13.68 35.18 158 11.41 17.06 30.43 15.22 32.65 162 8.62 9.98 13.85 8.62 24.01
103
204
15.73 22.40 15.92 21.64 26.50 214
10.10 13.72 18.33 14.51 33.48 159
163
165
56 580.14 689.23 747.95 553.27 479.95
endosulfan 1 56
100
100
100 236.68 241.20 162.57 207.20 219.23
192
192
24.54 36.72 34.42 31.11 31.11
43.53 22.01 23.13 20.64 20.77
125.12 65.42 68.02 7.12 12.90 152 13.97 11.87 1.71 8.40 2.10 159 5.60 13.47 0.25 0.00 6.92
27.93 45.71 50.03 32.92 39.37 152 19.09 32.34 16.99 25.32 11.35 159 6.36 6.80 3.34 3.15 5.04
r-/γHCH
TC/ CC
0.84 0.75 0.41 0.54 0.54
0.86 0.96 0.86 0.79 0.89
0.58 0.55 0.42 0.52 1.17
0.97 0.96 0.93 0.93 0.89
1.04 1.22 1.29 1.30 0.79
0.91 0.99 0.96 0.94 1.05
1.35 1.28 1.13 1.54 1.31
0.99 0.97 1.01 0.92 0.99
1.82 2.23 1.98 2.70 1.53
1.06 1.03 0.99 0.91 1.09
56 31.50 103.04 30.79 30.79 23.31
742.44 826.28 560.21 737.02 664.21
27.38 41.88 39.31 50.25 32.18
endosulfan SO4
131.87 175.29 185.25 129.20 123.68
88.38 111.50 65.74 115.81 126.49
166
6.53 7.02 9.56 6.78 12.10
endosulfan 1
106
166
8.52 12.93 20.35 14.83 19.55
8.17 9.70 13.94 9.46 22.04
151.59 262.55 231.98 206.01 179.51
221
8.42 10.61 13.00 11.83 26.93
11.54 17.60 30.09 16.59 33.12 163
57
105
19.01 29.44 22.42 27.98 36.26
dieldrin
28.38 27.78 19.16 24.27 31.39 192 18.88 26.37 13.16 21.79 9.67 152 9.18 17.65 10.82 14.56 9.05 159 4.78 3.90 2.90 2.14 2.64
in the range 0.4-0.6 (7). Motelay-Massei et al. also reported a TC/CC ratio of ∼1 during the spring and summer periods in Toronto (10).
previously deposited γ-HCH to R-HCH.
With the exception of chlordanes, all of the OCPs showed elevated concentrations during periods 1 and 2 and then a decline with time. This effect was most pronounced for the current-use and recent-use pesticidessendosulfan and γ-HCHsand this is likely associated with freshly applied chemical. For dieldrin and R-HCH, the effect was less pronounced and likely associated with re-emission of historically applied/deposited chemical, which is maximized during the spring period as surface temperatures rise. The results for R-HCH during periods 1 and 2 showed a pattern that was consistent with a local, ground-level source.
We are grateful to CN Tower management and staff for their assistance: Robert Farrell, Allan Campbell, and Carl Martin. We also thank Jacinthe Racine (Environment Canada) for providing back trajectory maps.
This study builds on the previous work by Farrar et al. (26) that first demonstrated the dynamic nature of POPs in the ABL. In this study, we have uncovered longer scale variability that is associated with various source inputs and meteorological factors. For the current-use OCPs, i.e., endosulfans, the vertical profile is homogeneous, suggesting a more regional origin, reflecting the widespread use of endosulfan in North America. For γ-HCH, a recent-use OCP, banned in Canada during the time of the study, concentrations decrease with the elevation during the spring periods, indicating the presence of an important local source. In the class of banned OCPs, two patterns were observed. For dieldrin and chlordanes, the vertical profile did not show a clear, consistent trend. This likely reflects the contribution from numerous regional, legacy sourcessagricultural and possibly residential (in the case of chlordanes)swith neither source dominating greatly. R-HCH showed the same distribution as γ-HCH, with concentrations increasing close to the groundsindicating again the potential of Toronto as a local source. This may reflect re-emission from old sources of R-HCH within Toronto or possibly the transformation of
(1) Bidleman, T. F.; Leone, A. D. Soil-air exchange of organochlorine pesticides in the Southern United States. Environ. Pollut. 2004, 128, 49-57. (2) Kurt-Karakus, P. B.; Bidleman, T. F.; Staebler, R. M.; Jones, K. C. Measurement of DDT Fluxes from a Historically Treated Agricultural Soil in Canada. Environ. Sci. Technol. 2006, 40, 4578-4585. (3) Stockholm Convention On Persistent Organic Pollutants (POPs), 2001; http://www.pops.int/. (4) Voldner, E. C.; Li, Y.-F. Global usage of selected persistent organochlorines. Sci. Total Environ. 1995, 160-161, 201-210. (5) Bidleman, T. F.; Falconer, R. L.; Walla, M. D. Toxaphene and other organochlorine compounds in air and water at Resolute Bay, N.W.T., Canada. Sci. Total Environ. 1995, 160-161, 55-63. (6) Meijer, S. N.; Shoeib, M.; Jantunen, L. M. M.; Jones, K. C.; Harner, T. Air-Soil Exchange of Organochlorine Pesticides in Agricultural Soils. 1. Field Measurements Using a Novel in Situ Sampling Device. Environ. Sci. Technol. 2003, 37, 1292-1299. (7) Halsall, C. J.; Bailey, R.; Stern, G. A.; Barrie, L. A.; Fellin, P.; Muir, D. C. G.; Rosenberg, B.; Rovinsky, F. Y.; Kononov, E. Y.; Pastukhov, B. Multi-year observations of organohalogen pesticides in the Arctic atmosphere. Environ. Pollut. 1998, 102, 51-62. (8) Kallenborn, R.; Oehme, M.; Wynn-Williams, D. D.; Schlabach, M.; Harris, J. Ambient air levels and atmospheric long-range
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Acknowledgments
Supporting Information Available Additional information as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org.
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Received for review November 13, 2006. Revised manuscript received January 22, 2007. Accepted January 23, 2007. ES062705S VOL. 41, NO. 7, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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