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Atmospheric concentrations of current-use pesticides across south-central Ontario using monthly-resolved passive air samplers
Atmospheric Environment 42 (2008) 8096–8104
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Atmospheric concentrations of current-use pesticides across south-central Ontario using monthly-resolved passive air samplers T. Gouin a, *, M. Shoeib b, T. Harner b a b
University of Toronto at Scarborough, Department of Physical and Environmental Sciences, 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada Environment Canada, Science and Technology Branch, 4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 March 2008 Received in revised form 15 May 2008 Accepted 21 May 2008
In this study passive air samplers (PAS) were deployed on a monthly basis at a number of sites along a south-north transect, extending 700 km north from Toronto, Ontario, characterizing an urban-agricultural-forested gradient, to investigate the spatial and temporal trends of current-use pesticides (CUPs), between spring 2003 and spring 2004. The most frequently detected CUPs were chlorpyrifos, dacthal, trifluralin, and a-endosulfan. Highest air concentrations of chlorpyrifos were observed in May, whereas a-endosulfan and dacthal peaked in July and August, reflecting differences in usage patterns. At the agricultural site, representing the source region of CUPs, chlorpyrifos air concentrations (pg m3) varied from 2700 to 3.2 and a-endulsulfan from 1600 to 19. The most frequently detected legacy pesticides were the hexachlorocylcohexanes (a-HCH and g-HCH). For the forested sites, located on the Precambrian Shield, a region with limited agricultural activity, seasonal differences were less pronounced and air concentrations were observed to be much lower. For instance, air concentrations (pg m3) of chlorpyrifos and a-endosulfan ranged from 7.6 to 0.3 and 50 to 2.0, respectively. By combining PAS data with trajectory air shed maps it is demonstrated that potential source–receptor relationships can be assessed. Air shed maps produced in this study indicate a potential of increased deposition of CUPs to Lake Erie and Lake Ontario. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Current-use pesticides Passive air samplers Organic pollutants Back trajectories
1. Introduction The application of chemical pesticides in the Great Lakes Basin is cause for concern, since it represents an increased risk of exposure to both humans and sensitive ecosystems (Muir et al., 2004; Arya, 2005; Ritter et al., 2006). Several Canadian municipalities, for instance, have established pesticide by-laws in response to reports citing that the use of pesticides can result in an increased risk of harm to children and other population subsets (Arya, 2005; Ritter
* Corresponding author. Present address: University of Alaska Fairbanks, Department of Chemistry and Biochemistry, P.O. Box 756160, Fairbanks, AK 99775-6160, USA. Tel.: þ1 907 474 1966; fax: þ1 907 474 5640. E-mail address: [email protected] (T. Gouin). 1352-2310/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2008.05.070
et al., 2006). These include several municipalities along the north shore of Lake Ontario, including the City of Toronto, the Town of Newmarket, the Town of Oakville, the City of Peterborough, and the Township of Georgian Bay. While this action has focused on restricting the use of nonessential cosmetic pesticides in urban areas, the intensive use of pesticides in agricultural regions that surround these municipalities continues. It has been estimated that a total of approximately 44 million kg of pesticides was used in the seven states that border the Great Lakes (Illinois, Indiana, Michigan, Minnesota, Ohio, Pennsylvania, and Wisconsin) in 2003 (Kannan et al., 2006). In Ontario, the total usage of pesticides during 2003 was approximately 4 million kg (McGee et al., 2004). While there have been numerous studies reporting levels of organochlorine pesticides (OCPs) in the atmosphere of the Great Lakes (Monosmith and Hermanson,
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1996; Bidleman, 1999; Buehler and Hites, 2002; Blanchard et al., 2004; Buehler et al., 2004; Carlson et al., 2004), fewer studies have investigated levels of current-use pesticides (CUPs) in air (James and Hites, 1999; Peck and Hornbuckle, 2005; Yao et al., 2006). Generally, it is believed that because CUPs are relatively more water soluble, less persistent, and less bioaccumulative than the OCPs (Kannan et al., 2006), they are not likely to be present in the environment to the same extent. A recent study, however, suggests that under the prevailing conditions in the Great Lakes basin, many CUPs will be subject to regional-scale atmospheric transport that will enable them to be deposited to surface water (Muir et al., 2004) and possibly to municipalities in the region that have initiated a pesticide by-law. The design of CUPs to elicit a toxic biological effect, combined with their potential to move from source regions into remote locations, is cause for concern. To improve our understanding of the atmospheric pathway as a mode of transport, and the relative importance of atmospheric deposition of CUPs to the Great Lakes and urban areas where pesticide by-laws are in place, air concentration data along source–receptor transects for CUPs are needed. Monitoring levels of organic contaminants in the environment to establish source–receptor relationships is costly (Harner et al., 2006a). Passive air samplers (PAS), however, require no electricity, minimal maintenance, and
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are relatively inexpensive and simple to use when compared to active air sampling techniques, and are an attractive alternative for monitoring the spatial and temporal distribution of organic pollutants in air. Recent developments, aimed at improving the use of passive air samplers at the regional, continental, and global scales (Harner et al., 2004; Shen et al., 2004; Gouin et al., 2005; Shen et al., 2005; Harner et al., 2006b; Pozo et al., 2006), further demonstrate the feasibility of using PAS. In this study we present PAS data, collected monthly between May 2003 and May 2004, deployed along a 700 km transect across Ontario, Canada, to assess the feasibility of using PAS to monitor levels of CUPs in air. Source–receptor relationships for CUPs in Ontario are illustrated through the use of air shed trajectory maps. 2. Materials and methods 2.1. Air sampling Polyurethane foam (PUF) disk samplers were deployed monthly at eight sites along a south-north transect across Ontario, Canada, extending 700 km, which characterizes an urban-agricultural-forested gradient between Toronto and Fraserdale (n ¼ 56) (Fig. 1). PUF-disks were pre-cleaned by Soxhlet extraction for 24 h using acetone, and then for
Fig. 1. Location of passive air sampler sites.
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another 24 h using petroleum ether (Pozo et al., 2004). PUF-disks were then dried under vacuum, before being stored in solvent rinsed, 1 L amber jars, which were used to store the PUF-disks before and after shipping to each of the field sites. Field blanks, which involved inserting the PUFdisk into the sample chamber and then returning it to the glass jar, were deployed once at each site (n ¼ 8). Sample sites were located along an urban-agriculturalforested transect, to assess potential source–receptor relationships. This included deploying PUF-disk samplers in the source region of pesticides, i.e. in an agricultural region (Egbert), as well as at sites located along the periphery of intense pesticide use, including forested sites with low population densities (Fraserdale, Loxton Lake, Sprucedale, Trent Univesity, and Haliburton forest) and urban sites with high population densities (Toronto and Downsview). Fig. 1 illustrates the location of each of the sites in relation to the dominant vegetation type. Target pesticides included the insecticides endosulfan and chlorpyrifos, the fungicide chlorothalonil, and the herbicides pendimethalin and trifluralin. Fig. 2 illustrates the usage of insecticides, fungicides, and herbicides in the Great Lakes region, in relation to each of the sites, based on a survey of pesticide use in Ontario and each of the seven states that border the Great Lakes (Thelin and Gianessi, 2000; McGee et al., 2004). Details regarding the operation and theory of the PUFdisk samplers have been described elsewhere (Shoeib and Harner, 2002; Harner et al., 2004; Motelay-Massei et al., 2005). Briefly, uptake by the PUF-disk sampler is described by Fick’s Law of diffusion by linear uptake, integrated on a monthly basis. PUF-disk sampling rates, based on previous observations, are estimated as 3.5 m3 d1 (Shoeib and Harner, 2002; Gouin et al., 2005; Pozo et al., 2006). 2.2. Extraction and analysis Details regarding extraction and clean-up are presented elsewhere (Gouin et al., 2005). Briefly, PUF-disks were Soxhlet extracted for 18 h with 250 mL of petroleum ether. Extracts were reduced by rotary evaporation and nitrogen blow-down to 500 mL and solvent exchanged to isooctane. Mirex (100 ng) was added as an internal standard to all samples prior to analysis. Instrumental analysis was conducted on an Agilent 6890 gas chromatograph in splitless mode equipped with an auto-sampler (Agilent 7683) and a mass spectrometric detector (Agilent 5973) in negative chemical ionization mode. Helium and methane were used as the carrier and reagent gases. Pesticides were separated on a DB5-MS capillary column (60 m length 0.25 mm i.d., 0.25 mm film thickness, J&W Scientific). The temperature program started at 90 C for 1 min, 15 C min1 to 240 C, 6 C min1 to 270 C, then 25 C min1 to 290 C and held for 6 min. The inlet, transfer line, ion source, and quadrupole temperatures were 265, 250, 150, and 106 C, respectively. The detector was operated in negative chemical ionization (NCI) selective ion monitoring (SIM) mode to enhance sensitivity. SIM ions used to quantify pesticides were as follows: mirex (404), trifluralin (335, 336), dacthal (332, 330), HCHs (255, 257), dimethoate (157, 159), chlorothalonil (266, 264), metribuzin (198 199), malathion
Fig. 2. Annual county usage of herbicides, fungicides, and insecticides for 2003, in relation to each of the passive air sampling sites. Usage estimates for each of the seven states that border the Great Lakes is based on Thelin and Gianessi (2000), while pesticide use for Ontario is based on McGee et al. (2004).
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(157, 172), chlorpyrifos (313, 315), pendimethalin (281, 282), a- and b-endosulfan (406, 404), and a-endosulfan sulfate (386, 388). Limits of quantification (LOQ) in air samples were defined as the average field blanks (n ¼ 8) plus ten times the standard deviation. Blanks were generally below the instrument detection limit, with the exception of trifluarlin, chlorothalonil, chlorpyrifos, dacthal, and a-endosulfan, which had LOQ values of 1.1, 13.6, 2.0, 0.4, and 7.0 pg m3, respectively. The instrument quantification limit (IQL) is 2.5 pg mL1 or 0.1 pg m3. 2.3. Air shed map trajectories Air shed map trajectories are based on three-day backward or forward air trajectory analysis, calculated for each day PUF-disk samplers were deployed at each site, at 6 h intervals, using the Canadian Meteorological Centre Trajectory Model. Data from the back trajectories are plotted on a 1 1 degree grid, and a probability density is calculated for each grid (i.e. probability density ¼ number of trajectories per grid/total number of trajectories). Note that in this analysis data pertaining to the sample site itself are omitted, with the assumption that there is a high probability that local air masses will have the largest influence on air concentrations. Backward air shed maps thus illustrate where the air masses most frequently pass before arriving at a particular site, whereas forward air shed maps illustrate where air masses most frequently pass after leaving a particular site. 3. Results Concentrations in air were dominated by the current-use fungicide chlorothalonil and the current-use insecticide a-endosulfan, with air concentrations ranging from below the instrument detection limit to 3300 and 2260 pg m3, respectively. Lindane (g-HCH) also showed elevated levels
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during spring 2003, with a maximum air concentration of 260 pg m3 observed at the Egbert field site. Usage of Lindane as a seed treatment in Canada was discontinued in 2003, primarily in the Canadian prairies, with limited use occurring throughout southern Ontario during this time (Aulagnier and Poissant, 2005). Table 1 summarizes the air concentrations for the various pesticides analyzed in this study. Air concentrations for all CUPs were greatest during the growing season, i.e. April–September, and were typically below the IQL during the non-growing season, i.e. November–March. Consequently we have limited our interpretation of the data to the growing season. Concentrations were generally elevated in the source region, with strong agricultural-forest gradients being observed. Concentration gradients along agricultural-urban gradients, however, were less pronounced. 4. Discussion 4.1. PAS sample rates Sequestering a sufficient amount of analyte to get above detection limits, when deploying PUF-disk passive air samplers for the relatively short deployment period of one month, is important if meaningful interpretation of the data is to occur. In this study, levels of CUPs in air during the growing season were typically well above the LOQ, making it possible to interpret monthly deployed passive air samplers for the CUPs. The short deployment period can also be problematic in terms of estimating an effective sample volume, since the use of depuration compounds spiked onto the PUF-disk sampling medium prior to deployment may not result in a significant loss to calculate sampler-specific sampling rates (Gouin et al., 2005; Pozo et al., 2006). In this study, the uniform distribution of a-HCH in the atmosphere, using a sample rate of 3.5 m3 d1, shown in Fig. 3, provides an
Table 1 Mean air concentrations (pg m3) for current-use pesticides observed at eight sites along a south-north transect in Ontario, Canada, during the 2003 growing season (between May 2003 and October 2003) Compound
Mean air concentration (pg m3) Urban
Rural
Forested
TOR
DOW
EGB
TNT
Fungicide Chlorothalonil
480 (nd)
460 (nd)
1740 (nd)
Herbicide Dacthal Metribuzin Pendimethalin Trifluralin
100 50 50 30
(15) (10) (4) (4)
30 5 80 30
(7) (12) (5) (4)
20 15 140 50
(7) (10) (5) (7)
4 4 8 3
(1) (nd) (nd) (nd)
3 nd 2 1
(1) (nd) (nd) (nd)
3 0.5 2 1
(2) (nd) (nd) (nd)
2 1 1 nd
(nd) (nd) (nd) (nd)
5 nd 5 nd
(nd) (nd) (nd) (nd)
Insecticide a-Endosulfan a-Endosulfan sulphate b-Endosulfan Chlorpyrifos Lindane (g-HCH)
550 5 120 330 100
(20) (3) (4) (40) (30)
390 10 80 60 40
(20) (3) (4) (12) (20)
820 8 125 65 70
(30) (3) (7) (12) (35)
55 2 6 4 12
(7) (nd) (2) (nd) (10)
32 2 4 2 10
(5) (4) (1) (nd) (5)
30 1 2 3 10
(7) (1) (nd) (nd) (5)
20 2 2 3 10
(3) (3) (nd) (nd) (3)
40 3 6 nd 10
(nd) (nd) (nd) (nd) (nd)
2 (nd)
HAL 7 (nd)
SPR 10 (nd)
LOX 1 (nd)
FRA 15 (nd)
Data in parentheses represent mean air concentrations during the non-growing season (November 2003–April 2004); nd denotes data below the IQL, defined as 2.5 pg mL1 or 0.1 pg m3.
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period (July 22–August 19, 2003) at Egbert (Yao et al., 2006) (discussed below). These observations thus lend confidence for the assumed sample rate of 3.5 m3 d1 used to estimate air concentrations of the CUP at each of the sites. Future studies, however, are needed to more accurately assess sample rates for the CUPs by PAS. 4.2. Spatial and temporal distributions
Fig. 3. Estimated monthly air concentration for a-HCH and g-HCH during the growing season of 2003 at each of the passive air sampling sites in Ontario, based on an air sampling rate of 3.5 m3 d1.
opportunity to qualitatively assess the assumption that the passive air samplers were sampling at an assumed rate of 3.5 pg m3. The uniform distribution and estimated air concentrations for a-HCH are consistent with previous observations (Shen et al., 2004; Gouin et al., 2005; IADN, 2005). For instance Gouin et al. (2005), using sample rates of approximately 3.5 m3 d1, report an annual average air concentration for a-HCH at their Toronto and Egbert sites of 23 and 15 pg m3, respectively, which is consistent with an annual average of 25 and 21 pg m3 observed in this study at the respective sites. Furthermore, concentrations of chlorothalonil, trifluralin, and a-endosulfan, based on the assumed sample rate of 3.5 m3 d1, are shown to be consistent with active air samples collected for a similar
The spatial and temporal distributions of various CUPs are shown in Fig. 4. As mentioned earlier, elevated levels are observed at Egbert, Downsview, and Toronto, during the growing season. All three sites are in close proximity to agricultural regions, where intensive use of CUPs occurs (Fig. 2). The elevated levels of CUPs in the atmosphere are thus to be expected. Chlorothalonil is a broad-spectrum foliar fungicide, used in Ontario to control mould contamination, such as anthracnose fruit rot in the cultivation of tomatoes (Poysa et al., 1993). Levels of chlorothalonil are about an order of magnitude higher at the Egbert field site during the months of July and September than at other Ontario sites, implying significant use of chlorothalonil during these periods than at other times of the year. The observed concentration of about 3000 pg m3 during the month of July, 2003 using the PAS in this study, is consistent with data reported using an active high volume air sampler for a similar period (July 22–August 19, 2003) at Egbert of 5200 pg m3 (Yao et al., 2006). Concentrations of chlorothalonil observed at the forested sites in northern Ontario, which range from below the LOQ to 30 pg m3 during the growing season, are also consistent with previous observations in non-agricultural regions of the Great Lakes (30–100 pg m3) (James and Hites, 1999). Chlorothalonil has a measured log octanol–air partition coefficient (KOA) of 8.11 at 20 C, suggesting that it has semi-volatile properties that are characteristic with compounds classified as persistent organic pollutants (Yao et al., 2007). The half-life in air is estimated to be about 1 week (Mackay et al., 2006), and previous studies have reported its presence in remote surface waters (Muir et al., 2004), implying that it has the potential for long-range atmospheric transport. The herbicides, trifluralin and pendimethalin, were among the top 10 pesticide active ingredients used in the U.S. in 1999 (Kannan et al., 2006). Elevated levels of each were observed at Egbert during the early spring (May and June, 2003), with the highest levels of pendimethalin in air (400 pg m3 in May) being about four times greater than the highest levels of trifluralin (85 pg m3 in May). Concentrations in air of trifluralin observed at Egbert for the month of July (55 pg m3) are consistent with active high volume air sampling data for the same period (91.1 pg m3) (Yao et al., 2006). Like chlorothalonil, trifluralin also has semi-volatile properties, with a measured log KOA of 7.93 at 20 C (Yao et al., 2007), and has an estimated air half-life of 1 week (Mackay et al., 2006), suggesting the potential for regional-scale long-range atmospheric transport. Data for pendimethalin were not available, but similar spatial concentration profiles suggest the possibility for similar behavior.
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Fig. 4. Estimated monthly air concentrations for current-use pesticides during the growing season of 2003 in Ontario.
Air concentrations of a-endosulfan, an insecticide used as a form of chemical control in a wide range of crops, including fruits, vegetables, and grains, were highest during the month of August, 2003, at Egbert (2260 pg m3). Concentrations during the month of July 2003 (1200 pg m3) are consistent with high volume air samples collected during the same period at Egbert (717 pg m3) (Yao et al., 2006). Concentrations of dacthal, a pre-emergent herbicide used for weed-control on turf grass, were observed to be elevated during April 2003 at Toronto (265 pg m3), implying significant urban use during this period. Average concentrations of dacthal in air at Egbert between May and August, 2003 (25 pg m3) are similar to observations during the growing season of 2004 based on PAS data (10 pg m3) (Yao et al., 2007). Average air concentrations at Downsview during the growing season of 2003 (70 pg m3) are also similar to those observed during 2004 at Downsview based on the collection of PAS (49.1 pg m3) (Yao et al., 2007). Both dacthal and a-endosulfan are estimated to have high potential for long-range atmospheric transport (Muir et al., 2004; Yao et al., 2007). Monitoring their spatial distribution in the atmosphere is thus necessary to better understand their mobility and environmental fate.
Similar to dacthal, elevated concentrations in air for chlorpyrifos, an organophosphate insecticide used in the control of insect pests in fruits and vegetables, were highest at Toronto in May 2003 (670 pg m3), implying widespread residential use, most likely associated with home gardens. The log KOA of chlorpyrifos is 8.88 (Yao et al., 2007), however, unlike the other CUPs discussed above, its half-life in air is estimated to be relatively short, <1 day, implying that it may have limited potential for long-range atmospheric transport (Muir et al., 2004). 4.3. Potential source–receptor relationships and air shed maps It is notable that nearly all CUPs show strong concentration gradients along a south-north transect. One possible explanation could be that sites located near agricultural activity are largely influenced by local sources, whereas sites far from sources are not subjected to this influence. This suggests that atmospheric transport of CUPs to remote forested regions is limited, and that various loss processes, such as atmospheric degradation, wet and dry deposition, or the possible influence of a forest filter effect, may inhibit their transport potential. This suggestion,
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however, contradicts observations from previous studies, which suggest that a number of CUPs have the potential for long-range atmospheric transport (Muir et al., 2004; Tuduri et al., 2006; Yao et al., 2006; Yao et al., 2007). Thus, a second explanation for the data shown in Fig. 4 is that the mobility of the CUPs is likely to be strongly influenced by the direction of air flow in the region. Therefore, to better understand the relationship between the various sites along the transect investigated in this study, a series of air shed maps have been produced for each site as a method for assessing the air flow patterns in the region. Fig. 5 illustrates a series of forward trajectory air shed maps for CUPs during the periods elevated concentrations in air were observed. The forward trajectory air shed maps in Fig. 5 indicate that air masses moving away from the source regions of CUPs generally move to the south-west of the source region. For instance, levels of trifluralin are highest during May 2003 at Egbert, and the air mass moving away from Egbert in May 2003 (Fig. 5a) indicates the potential for a strong source–receptor relationship between agricultural regions in south-western Ontario and southern regions of Lake Ontario, whereas poor source–receptor relationships are apparent between the source regions and northern Ontario. The concentration gradient along these transects appear to be consistent with the forward trajectory air shed maps, i.e. low levels in June. Similar trends are apparent in Fig. 5b, which illustrates the forward trajectory air shed map for Egbert during June 2003 in relation to elevated levels of pendimethalin and during July 2003 in relation to
elevated levels of a-endosulfan (Fig. 5c). During April 2003, elevated levels of dacthal were observed at Toronto, and the forward trajectory air shed map for this period (Fig. 5d) is also seen to be consistent with observations shown in Fig. 5a, i.e. strong source–receptor relationships are likely to exist between Toronto and southern regions of Lake Ontario and north-eastern New York State. Since it has been suggested that each of these CUPs have the potential for long-range atmospheric transport, particularly for dacthal and a-endosulfan, areas to the east and south of southern Ontario may experience enhanced deposition of these pesticides during periods of intensive use in the source regions. The city of Toronto, for instance, initiated a pesticide bylaw beginning in 2004; thus it would be useful for the city to monitor the CUPs used in the agricultural belt that surround the city of Toronto as a method for assessing the effectiveness of the by-law. It would also be prudent to monitor the deposition of CUPs to Lake Ontario as a method for assessing exposure to organisms in the lake. Back trajectory air shed maps for the northern sites in this study indicate limited movement of air masses from source regions in southern Ontario. Fig. 6, for instance, illustrates the back trajectory air shed maps of the northern sites during August 2003, when elevated levels of a-endosulfan were observed at Egbert. The field site at Trent University (Fig. 6c) has the strongest relationship with the source region, which may explain elevated levels of a-endosulfan at Trent University during this period. This relationship, however, appears to be diluted by the
Fig. 5. Forward air trajectory air shed maps for select CUPs shown as a probability density: (a) Egbert, showing elevated levels of trifluralin and forward air shed map observed during May, 2003; (b) Egbert, showing elevated levels of pendimethalin and forward air shed map observed during June, 2003; (c) Egbert, showing elevated levels of a-endosulfan and forward air shed map observed during July, 2003; (d) Toronto, showing elevated levels of dacthal and forward air shed map observed during April, 2003.
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Fig. 6. Backward air trajectory air shed maps for non-agricultural-forested sites during the month of August, 2003: (a) Fraserdale; (b) Sprucedale; (c) Trent University; (d) Haliburton.
influence of non-source regions, such as Georgian Bay in Lake Huron and regions to the north of the site. For the field sites at Haliburton, Sprucedale and Fraserdale, it can be seen that the relationship between each of these sites and the source regions in south-western Ontario diminishes for sites that are further north. The low concentrations observed at each of the sites seem to support the weak source–receptor relationships shown in Fig. 6. By combining data from the monthly integrated PAS and the various air shed maps it is thus possible to better understand the transport of CUPs within a region. In this instance it appears that the tendency for air masses to move in a south-easterly direction may result in increased deposition of CUPs to the southern Great Lakes, whereas sites to the north are likely subject to limited deposition associated with episodic transport events. 5. Conclusions These data suggest that pesticide usage in the agricultural regions of southern Ontario likely result in atmospheric transport to south-eastern locations, such as Toronto, for which there is a pesticide by-law, and Lake Ontario, leading to enhanced deposition to these environments. Research is warranted to assess the validity of a pesticide by-law to
reduce exposure to pesticides, particularly if there is significant agricultural activity occurring in the surrounding areas, and to measure the deposition of CUPs to the southern Great Lakes, particularly to Lake Ontario. In this study passive air samplers deployed on a monthly basis are shown to be an effective tool for assessing source– receptor relationships of CUPs, particularly when combined with forward and backward air shed maps. This is because levels in the atmosphere tend to be elevated during the growing season, implying that shorter deployment durations are sufficient for detecting target analytes.
Acknowledgements The authors wish to acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support and Jacinthe Racine of Environment Canada for backward and forward air trajectory data.
References Arya, N., 2005. Pesticides and human health: why public health officials should support a ban on non-essential residential use. Canadian Journal of Public Health 96, 89–92.
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Aulagnier, F., Poissant, L., 2005. Some pesticides occurrence in air and precipitation in Quebec, Canada. Environmental Science and Technology 39, 2960–2967. Bidleman, T.F., 1999. Atmospheric transport and air-surface exchange of pesticides. Water Air and Soil Pollution 115, 115–166. Blanchard, P., Audette, C.V., Hulting, M.L., Basu, I., Brice, K.A., Chan, C.H., Dryfhout-Clark, H., Froude, F., Hites, R.A., Neilson, M., 2004. Atmospheric deposition of toxic substances to the Great Lakes: IADN results through 2000, in: publication, E.C.a.U.E.P.A. (Ed.), PWGSC#En45–156/2000-1E, USEPA Report #905-R-04-900. Buehler, S.S., Basu, I., Hites, R.A., 2004. Causes of variability in pesticide and PCB concentrations in air near the Great Lakes. Environmental Science and Technology 38, 414–422. Buehler, S.S., Hites, R.A., 2002. The Great Lakes’ integrated atmospheric deposition network. Environmental Science and Technology 36, 354A–359A. Carlson, D.L., Basu, I., Hites, R.A., 2004. Annual variations of pesticide concentrations in great lakes precipitation. Environmental Science and Technology 38, 5290–5296. Gouin, T., Harner, T., Blanchard, P., Mackay, D., 2005. Passive and active air samplers as complementary methods for investigating persistent organic pollutants in the Great Lakes Basin. Environmental Science and Technology 39, 9115–9122. Harner, T., Bartkow, M., Holoubek, I., Klanova, J., Wania, F., Gioia, R., Moeckel, C., Sweetman, A.J., Jones, K.C., 2006a. Passive air sampling for persistent organic pollutants: Introductory remarks to the special issue. Environmental Pollution 144, 361–364. Harner, T., Shoeib, M., Diamond, M., Stern, G., Rosenberg, B., 2004. Using passive air samplers to assess urban–rural trends for persistent organic pollutants. 1. Polychlorinated biphenyls and organochlorine pesticides. Environmental Science and Technology 38, 4474–4483. Harner, T., Shoeib, M., Gouin, T., Blanchard, P., 2006b. Polychlorinated naphthalenes in Great Lakes air: assessing spatial trends and combustion inputs using PUF disk passive air samplers. Environmental Science and Technology 40, 5333–5339. IADN, 2005. Data request via http://www.msc-smc.ec.gc.ca/iadn/index_e. html. James, R.R., Hites, R.A., 1999. Chlorothalonil and Dacthal in Great Lakes air and precipitation samples. Journal of Great Lakes Research 25, 406–411. Kannan, K., Ridal, J. and Struger, J. (2006). Pesticides. In: Hites, R.A. (Ed.), Handbook of Environmental Chemistry, vol. 5, Persistent Organic Pollutants in the Great Lakes. Springer-Verlag Publishers, pp. 151–200. Mackay, D., Shiu, W., Ma, K.-C., Lee, S.C., 2006. Physical–chemical Properties and Environmental Fate for Organic Chemicals, third ed. CRC Press, Boca Raton, FL. McGee, B., Berges, H., Callow, K., 2004. Survey of Pesticide Use in Ontario, 2003: Estimates of Pesticides Used in Field Crops, Fruit and Vegetable Crops, and Other Agricultural Crops. Ontario Ministry of Agriculture and Food, Guelph, Ontario, p. 18. Monosmith, C.L., Hermanson, M.H., 1996. Spatial and temporal trends of atmospheric organochlorine vapors in the central and upper Great Lakes. Environmental Science and Technology 30, 3464–3472.
Motelay-Massei, A., Harner, T., Shoeib, M., Diamond, M., Stern, G., Rosenberg, B., 2005. Using passive air samplers to assess urban–rural trends for persistent organic pollutants and polycyclic aromatic hydrocarbons. 2. Seasonal trends for PAHs, PCBs, and organochlorine pesticides. Environmental Science and Technology 39, 5763–5773. Muir, D.C.G., Teixeira, C., Wania, F., 2004. Empirical and modeling evidence of regional atmospheric transport of current-use pesticides. Environmental Toxicology and Chemistry 23, 2421–2432. Peck, A.M., Hornbuckle, K.C., 2005. Gas-phase concentrations of currentuse pesticides in Iowa. Environmental Science and Technology 39, 2952–2959. Poysa, V., Brammall, R.A., Pitblado, R.E., 1993. Effects of foliar fungicide sprays on disease and yield of processing tomatoes in Ontario. Canadian Journal of Plant Science 73, 1209–1215. Pozo, K., Harner, T., Shoeib, M., Urrutia, R., Barra, R., Parra, O., Focardi, S., 2004. Passive-sampler derived air concentrations of persistent organic pollutants on a north-south transect in Chile. Environmental Science and Technology 38, 6529–6537. Pozo, K., Harner, T., Wania, F., Muir, D.C.G., Jones, K.C., Barrie, L.A., 2006. Toward a global network for persistent organic pollutants in air: Results from the GAPS study. Environmental Science and Technology 40, 4867–4873. Ritter, L., Goushleff, N.C.I., Arbuckle, T., Cole, D., Raizenne, M., 2006. Addressing the linkage between exposure to pesticides and human health effects – Research trends and priorities for research. Journal of Toxicology and Environmental Health, Part B: Critical Reviews 9, 441–456. Shen, L., Wania, F., Lei, Y.D., Teixeira, C., Muir, D.C.G., Bidleman, T.F., 2004. Hexachlorocyclohexanes in the North American atmosphere. Environmental Science and Technology 38, 965–975. Shen, L., Wania, F., Lei, Y.D., Teixeira, C., Muir, D.C.G., Bidleman, T.F., 2005. Atmospheric distribution and long-range transport behavior of organochlorine pesticides in north America. Environmental Science and Technology 39, 409–420. Shoeib, M., Harner, T., 2002. Characterization and comparison of three passive air samplers for persistent organic pollutants. Environmental Science and Technology 36, 4142–4151. Thelin, G.P., Gianessi, L.P., 2000. Method for Estimating Pesticide Use for County Areas of the Conterminous United States. U.S. Geological Survey, Sacramento, CA, p. 67. Tuduri, L., Harner, T., Blanchard, P., Li, Y.F., Poissant, L., Waite, D.T., Murphy, C., Belzer, W., 2006. A review of currently used pesticides (CUPS) in Canadian air and precipitation. Part 2: Regional information and perspectives. Atmospheric Environment 40, 1579–1589. Yao, Y., Harner, T., Ma, J.M., Tuduri, L., Blanchard, P., 2007. Sources and occurrence of dacthal in the Canadian atmosphere. Environmental Science and Technology 41, 688–694. Yao, Y., Tuduri, L., Harner, T., Blanchard, P., Waite, D., Poissant, L., Murphy, C., Belzer, W., Aulagnier, F., Li, Y.-F., Sverko, E., 2006. Spatial and temporal distribution of pesticide air concentrations in Canadian agricultural regions. Atmospheric Environment 40, 4339– 4351.
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Atmospheric concentrations of current-use pesticides across south-central Ontario using monthly-resolved passive air samplers T. Gouin a, *, M. Shoeib b, T. Harner b a b
University of Toronto at Scarborough, Department of Physical and Environmental Sciences, 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada Environment Canada, Science and Technology Branch, 4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 March 2008 Received in revised form 15 May 2008 Accepted 21 May 2008
In this study passive air samplers (PAS) were deployed on a monthly basis at a number of sites along a south-north transect, extending 700 km north from Toronto, Ontario, characterizing an urban-agricultural-forested gradient, to investigate the spatial and temporal trends of current-use pesticides (CUPs), between spring 2003 and spring 2004. The most frequently detected CUPs were chlorpyrifos, dacthal, trifluralin, and a-endosulfan. Highest air concentrations of chlorpyrifos were observed in May, whereas a-endosulfan and dacthal peaked in July and August, reflecting differences in usage patterns. At the agricultural site, representing the source region of CUPs, chlorpyrifos air concentrations (pg m3) varied from 2700 to 3.2 and a-endulsulfan from 1600 to 19. The most frequently detected legacy pesticides were the hexachlorocylcohexanes (a-HCH and g-HCH). For the forested sites, located on the Precambrian Shield, a region with limited agricultural activity, seasonal differences were less pronounced and air concentrations were observed to be much lower. For instance, air concentrations (pg m3) of chlorpyrifos and a-endosulfan ranged from 7.6 to 0.3 and 50 to 2.0, respectively. By combining PAS data with trajectory air shed maps it is demonstrated that potential source–receptor relationships can be assessed. Air shed maps produced in this study indicate a potential of increased deposition of CUPs to Lake Erie and Lake Ontario. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Current-use pesticides Passive air samplers Organic pollutants Back trajectories
1. Introduction The application of chemical pesticides in the Great Lakes Basin is cause for concern, since it represents an increased risk of exposure to both humans and sensitive ecosystems (Muir et al., 2004; Arya, 2005; Ritter et al., 2006). Several Canadian municipalities, for instance, have established pesticide by-laws in response to reports citing that the use of pesticides can result in an increased risk of harm to children and other population subsets (Arya, 2005; Ritter
* Corresponding author. Present address: University of Alaska Fairbanks, Department of Chemistry and Biochemistry, P.O. Box 756160, Fairbanks, AK 99775-6160, USA. Tel.: þ1 907 474 1966; fax: þ1 907 474 5640. E-mail address: [email protected] (T. Gouin). 1352-2310/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2008.05.070
et al., 2006). These include several municipalities along the north shore of Lake Ontario, including the City of Toronto, the Town of Newmarket, the Town of Oakville, the City of Peterborough, and the Township of Georgian Bay. While this action has focused on restricting the use of nonessential cosmetic pesticides in urban areas, the intensive use of pesticides in agricultural regions that surround these municipalities continues. It has been estimated that a total of approximately 44 million kg of pesticides was used in the seven states that border the Great Lakes (Illinois, Indiana, Michigan, Minnesota, Ohio, Pennsylvania, and Wisconsin) in 2003 (Kannan et al., 2006). In Ontario, the total usage of pesticides during 2003 was approximately 4 million kg (McGee et al., 2004). While there have been numerous studies reporting levels of organochlorine pesticides (OCPs) in the atmosphere of the Great Lakes (Monosmith and Hermanson,
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1996; Bidleman, 1999; Buehler and Hites, 2002; Blanchard et al., 2004; Buehler et al., 2004; Carlson et al., 2004), fewer studies have investigated levels of current-use pesticides (CUPs) in air (James and Hites, 1999; Peck and Hornbuckle, 2005; Yao et al., 2006). Generally, it is believed that because CUPs are relatively more water soluble, less persistent, and less bioaccumulative than the OCPs (Kannan et al., 2006), they are not likely to be present in the environment to the same extent. A recent study, however, suggests that under the prevailing conditions in the Great Lakes basin, many CUPs will be subject to regional-scale atmospheric transport that will enable them to be deposited to surface water (Muir et al., 2004) and possibly to municipalities in the region that have initiated a pesticide by-law. The design of CUPs to elicit a toxic biological effect, combined with their potential to move from source regions into remote locations, is cause for concern. To improve our understanding of the atmospheric pathway as a mode of transport, and the relative importance of atmospheric deposition of CUPs to the Great Lakes and urban areas where pesticide by-laws are in place, air concentration data along source–receptor transects for CUPs are needed. Monitoring levels of organic contaminants in the environment to establish source–receptor relationships is costly (Harner et al., 2006a). Passive air samplers (PAS), however, require no electricity, minimal maintenance, and
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are relatively inexpensive and simple to use when compared to active air sampling techniques, and are an attractive alternative for monitoring the spatial and temporal distribution of organic pollutants in air. Recent developments, aimed at improving the use of passive air samplers at the regional, continental, and global scales (Harner et al., 2004; Shen et al., 2004; Gouin et al., 2005; Shen et al., 2005; Harner et al., 2006b; Pozo et al., 2006), further demonstrate the feasibility of using PAS. In this study we present PAS data, collected monthly between May 2003 and May 2004, deployed along a 700 km transect across Ontario, Canada, to assess the feasibility of using PAS to monitor levels of CUPs in air. Source–receptor relationships for CUPs in Ontario are illustrated through the use of air shed trajectory maps. 2. Materials and methods 2.1. Air sampling Polyurethane foam (PUF) disk samplers were deployed monthly at eight sites along a south-north transect across Ontario, Canada, extending 700 km, which characterizes an urban-agricultural-forested gradient between Toronto and Fraserdale (n ¼ 56) (Fig. 1). PUF-disks were pre-cleaned by Soxhlet extraction for 24 h using acetone, and then for
Fig. 1. Location of passive air sampler sites.
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another 24 h using petroleum ether (Pozo et al., 2004). PUF-disks were then dried under vacuum, before being stored in solvent rinsed, 1 L amber jars, which were used to store the PUF-disks before and after shipping to each of the field sites. Field blanks, which involved inserting the PUFdisk into the sample chamber and then returning it to the glass jar, were deployed once at each site (n ¼ 8). Sample sites were located along an urban-agriculturalforested transect, to assess potential source–receptor relationships. This included deploying PUF-disk samplers in the source region of pesticides, i.e. in an agricultural region (Egbert), as well as at sites located along the periphery of intense pesticide use, including forested sites with low population densities (Fraserdale, Loxton Lake, Sprucedale, Trent Univesity, and Haliburton forest) and urban sites with high population densities (Toronto and Downsview). Fig. 1 illustrates the location of each of the sites in relation to the dominant vegetation type. Target pesticides included the insecticides endosulfan and chlorpyrifos, the fungicide chlorothalonil, and the herbicides pendimethalin and trifluralin. Fig. 2 illustrates the usage of insecticides, fungicides, and herbicides in the Great Lakes region, in relation to each of the sites, based on a survey of pesticide use in Ontario and each of the seven states that border the Great Lakes (Thelin and Gianessi, 2000; McGee et al., 2004). Details regarding the operation and theory of the PUFdisk samplers have been described elsewhere (Shoeib and Harner, 2002; Harner et al., 2004; Motelay-Massei et al., 2005). Briefly, uptake by the PUF-disk sampler is described by Fick’s Law of diffusion by linear uptake, integrated on a monthly basis. PUF-disk sampling rates, based on previous observations, are estimated as 3.5 m3 d1 (Shoeib and Harner, 2002; Gouin et al., 2005; Pozo et al., 2006). 2.2. Extraction and analysis Details regarding extraction and clean-up are presented elsewhere (Gouin et al., 2005). Briefly, PUF-disks were Soxhlet extracted for 18 h with 250 mL of petroleum ether. Extracts were reduced by rotary evaporation and nitrogen blow-down to 500 mL and solvent exchanged to isooctane. Mirex (100 ng) was added as an internal standard to all samples prior to analysis. Instrumental analysis was conducted on an Agilent 6890 gas chromatograph in splitless mode equipped with an auto-sampler (Agilent 7683) and a mass spectrometric detector (Agilent 5973) in negative chemical ionization mode. Helium and methane were used as the carrier and reagent gases. Pesticides were separated on a DB5-MS capillary column (60 m length 0.25 mm i.d., 0.25 mm film thickness, J&W Scientific). The temperature program started at 90 C for 1 min, 15 C min1 to 240 C, 6 C min1 to 270 C, then 25 C min1 to 290 C and held for 6 min. The inlet, transfer line, ion source, and quadrupole temperatures were 265, 250, 150, and 106 C, respectively. The detector was operated in negative chemical ionization (NCI) selective ion monitoring (SIM) mode to enhance sensitivity. SIM ions used to quantify pesticides were as follows: mirex (404), trifluralin (335, 336), dacthal (332, 330), HCHs (255, 257), dimethoate (157, 159), chlorothalonil (266, 264), metribuzin (198 199), malathion
Fig. 2. Annual county usage of herbicides, fungicides, and insecticides for 2003, in relation to each of the passive air sampling sites. Usage estimates for each of the seven states that border the Great Lakes is based on Thelin and Gianessi (2000), while pesticide use for Ontario is based on McGee et al. (2004).
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(157, 172), chlorpyrifos (313, 315), pendimethalin (281, 282), a- and b-endosulfan (406, 404), and a-endosulfan sulfate (386, 388). Limits of quantification (LOQ) in air samples were defined as the average field blanks (n ¼ 8) plus ten times the standard deviation. Blanks were generally below the instrument detection limit, with the exception of trifluarlin, chlorothalonil, chlorpyrifos, dacthal, and a-endosulfan, which had LOQ values of 1.1, 13.6, 2.0, 0.4, and 7.0 pg m3, respectively. The instrument quantification limit (IQL) is 2.5 pg mL1 or 0.1 pg m3. 2.3. Air shed map trajectories Air shed map trajectories are based on three-day backward or forward air trajectory analysis, calculated for each day PUF-disk samplers were deployed at each site, at 6 h intervals, using the Canadian Meteorological Centre Trajectory Model. Data from the back trajectories are plotted on a 1 1 degree grid, and a probability density is calculated for each grid (i.e. probability density ¼ number of trajectories per grid/total number of trajectories). Note that in this analysis data pertaining to the sample site itself are omitted, with the assumption that there is a high probability that local air masses will have the largest influence on air concentrations. Backward air shed maps thus illustrate where the air masses most frequently pass before arriving at a particular site, whereas forward air shed maps illustrate where air masses most frequently pass after leaving a particular site. 3. Results Concentrations in air were dominated by the current-use fungicide chlorothalonil and the current-use insecticide a-endosulfan, with air concentrations ranging from below the instrument detection limit to 3300 and 2260 pg m3, respectively. Lindane (g-HCH) also showed elevated levels
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during spring 2003, with a maximum air concentration of 260 pg m3 observed at the Egbert field site. Usage of Lindane as a seed treatment in Canada was discontinued in 2003, primarily in the Canadian prairies, with limited use occurring throughout southern Ontario during this time (Aulagnier and Poissant, 2005). Table 1 summarizes the air concentrations for the various pesticides analyzed in this study. Air concentrations for all CUPs were greatest during the growing season, i.e. April–September, and were typically below the IQL during the non-growing season, i.e. November–March. Consequently we have limited our interpretation of the data to the growing season. Concentrations were generally elevated in the source region, with strong agricultural-forest gradients being observed. Concentration gradients along agricultural-urban gradients, however, were less pronounced. 4. Discussion 4.1. PAS sample rates Sequestering a sufficient amount of analyte to get above detection limits, when deploying PUF-disk passive air samplers for the relatively short deployment period of one month, is important if meaningful interpretation of the data is to occur. In this study, levels of CUPs in air during the growing season were typically well above the LOQ, making it possible to interpret monthly deployed passive air samplers for the CUPs. The short deployment period can also be problematic in terms of estimating an effective sample volume, since the use of depuration compounds spiked onto the PUF-disk sampling medium prior to deployment may not result in a significant loss to calculate sampler-specific sampling rates (Gouin et al., 2005; Pozo et al., 2006). In this study, the uniform distribution of a-HCH in the atmosphere, using a sample rate of 3.5 m3 d1, shown in Fig. 3, provides an
Table 1 Mean air concentrations (pg m3) for current-use pesticides observed at eight sites along a south-north transect in Ontario, Canada, during the 2003 growing season (between May 2003 and October 2003) Compound
Mean air concentration (pg m3) Urban
Rural
Forested
TOR
DOW
EGB
TNT
Fungicide Chlorothalonil
480 (nd)
460 (nd)
1740 (nd)
Herbicide Dacthal Metribuzin Pendimethalin Trifluralin
100 50 50 30
(15) (10) (4) (4)
30 5 80 30
(7) (12) (5) (4)
20 15 140 50
(7) (10) (5) (7)
4 4 8 3
(1) (nd) (nd) (nd)
3 nd 2 1
(1) (nd) (nd) (nd)
3 0.5 2 1
(2) (nd) (nd) (nd)
2 1 1 nd
(nd) (nd) (nd) (nd)
5 nd 5 nd
(nd) (nd) (nd) (nd)
Insecticide a-Endosulfan a-Endosulfan sulphate b-Endosulfan Chlorpyrifos Lindane (g-HCH)
550 5 120 330 100
(20) (3) (4) (40) (30)
390 10 80 60 40
(20) (3) (4) (12) (20)
820 8 125 65 70
(30) (3) (7) (12) (35)
55 2 6 4 12
(7) (nd) (2) (nd) (10)
32 2 4 2 10
(5) (4) (1) (nd) (5)
30 1 2 3 10
(7) (1) (nd) (nd) (5)
20 2 2 3 10
(3) (3) (nd) (nd) (3)
40 3 6 nd 10
(nd) (nd) (nd) (nd) (nd)
2 (nd)
HAL 7 (nd)
SPR 10 (nd)
LOX 1 (nd)
FRA 15 (nd)
Data in parentheses represent mean air concentrations during the non-growing season (November 2003–April 2004); nd denotes data below the IQL, defined as 2.5 pg mL1 or 0.1 pg m3.
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period (July 22–August 19, 2003) at Egbert (Yao et al., 2006) (discussed below). These observations thus lend confidence for the assumed sample rate of 3.5 m3 d1 used to estimate air concentrations of the CUP at each of the sites. Future studies, however, are needed to more accurately assess sample rates for the CUPs by PAS. 4.2. Spatial and temporal distributions
Fig. 3. Estimated monthly air concentration for a-HCH and g-HCH during the growing season of 2003 at each of the passive air sampling sites in Ontario, based on an air sampling rate of 3.5 m3 d1.
opportunity to qualitatively assess the assumption that the passive air samplers were sampling at an assumed rate of 3.5 pg m3. The uniform distribution and estimated air concentrations for a-HCH are consistent with previous observations (Shen et al., 2004; Gouin et al., 2005; IADN, 2005). For instance Gouin et al. (2005), using sample rates of approximately 3.5 m3 d1, report an annual average air concentration for a-HCH at their Toronto and Egbert sites of 23 and 15 pg m3, respectively, which is consistent with an annual average of 25 and 21 pg m3 observed in this study at the respective sites. Furthermore, concentrations of chlorothalonil, trifluralin, and a-endosulfan, based on the assumed sample rate of 3.5 m3 d1, are shown to be consistent with active air samples collected for a similar
The spatial and temporal distributions of various CUPs are shown in Fig. 4. As mentioned earlier, elevated levels are observed at Egbert, Downsview, and Toronto, during the growing season. All three sites are in close proximity to agricultural regions, where intensive use of CUPs occurs (Fig. 2). The elevated levels of CUPs in the atmosphere are thus to be expected. Chlorothalonil is a broad-spectrum foliar fungicide, used in Ontario to control mould contamination, such as anthracnose fruit rot in the cultivation of tomatoes (Poysa et al., 1993). Levels of chlorothalonil are about an order of magnitude higher at the Egbert field site during the months of July and September than at other Ontario sites, implying significant use of chlorothalonil during these periods than at other times of the year. The observed concentration of about 3000 pg m3 during the month of July, 2003 using the PAS in this study, is consistent with data reported using an active high volume air sampler for a similar period (July 22–August 19, 2003) at Egbert of 5200 pg m3 (Yao et al., 2006). Concentrations of chlorothalonil observed at the forested sites in northern Ontario, which range from below the LOQ to 30 pg m3 during the growing season, are also consistent with previous observations in non-agricultural regions of the Great Lakes (30–100 pg m3) (James and Hites, 1999). Chlorothalonil has a measured log octanol–air partition coefficient (KOA) of 8.11 at 20 C, suggesting that it has semi-volatile properties that are characteristic with compounds classified as persistent organic pollutants (Yao et al., 2007). The half-life in air is estimated to be about 1 week (Mackay et al., 2006), and previous studies have reported its presence in remote surface waters (Muir et al., 2004), implying that it has the potential for long-range atmospheric transport. The herbicides, trifluralin and pendimethalin, were among the top 10 pesticide active ingredients used in the U.S. in 1999 (Kannan et al., 2006). Elevated levels of each were observed at Egbert during the early spring (May and June, 2003), with the highest levels of pendimethalin in air (400 pg m3 in May) being about four times greater than the highest levels of trifluralin (85 pg m3 in May). Concentrations in air of trifluralin observed at Egbert for the month of July (55 pg m3) are consistent with active high volume air sampling data for the same period (91.1 pg m3) (Yao et al., 2006). Like chlorothalonil, trifluralin also has semi-volatile properties, with a measured log KOA of 7.93 at 20 C (Yao et al., 2007), and has an estimated air half-life of 1 week (Mackay et al., 2006), suggesting the potential for regional-scale long-range atmospheric transport. Data for pendimethalin were not available, but similar spatial concentration profiles suggest the possibility for similar behavior.
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Fig. 4. Estimated monthly air concentrations for current-use pesticides during the growing season of 2003 in Ontario.
Air concentrations of a-endosulfan, an insecticide used as a form of chemical control in a wide range of crops, including fruits, vegetables, and grains, were highest during the month of August, 2003, at Egbert (2260 pg m3). Concentrations during the month of July 2003 (1200 pg m3) are consistent with high volume air samples collected during the same period at Egbert (717 pg m3) (Yao et al., 2006). Concentrations of dacthal, a pre-emergent herbicide used for weed-control on turf grass, were observed to be elevated during April 2003 at Toronto (265 pg m3), implying significant urban use during this period. Average concentrations of dacthal in air at Egbert between May and August, 2003 (25 pg m3) are similar to observations during the growing season of 2004 based on PAS data (10 pg m3) (Yao et al., 2007). Average air concentrations at Downsview during the growing season of 2003 (70 pg m3) are also similar to those observed during 2004 at Downsview based on the collection of PAS (49.1 pg m3) (Yao et al., 2007). Both dacthal and a-endosulfan are estimated to have high potential for long-range atmospheric transport (Muir et al., 2004; Yao et al., 2007). Monitoring their spatial distribution in the atmosphere is thus necessary to better understand their mobility and environmental fate.
Similar to dacthal, elevated concentrations in air for chlorpyrifos, an organophosphate insecticide used in the control of insect pests in fruits and vegetables, were highest at Toronto in May 2003 (670 pg m3), implying widespread residential use, most likely associated with home gardens. The log KOA of chlorpyrifos is 8.88 (Yao et al., 2007), however, unlike the other CUPs discussed above, its half-life in air is estimated to be relatively short, <1 day, implying that it may have limited potential for long-range atmospheric transport (Muir et al., 2004). 4.3. Potential source–receptor relationships and air shed maps It is notable that nearly all CUPs show strong concentration gradients along a south-north transect. One possible explanation could be that sites located near agricultural activity are largely influenced by local sources, whereas sites far from sources are not subjected to this influence. This suggests that atmospheric transport of CUPs to remote forested regions is limited, and that various loss processes, such as atmospheric degradation, wet and dry deposition, or the possible influence of a forest filter effect, may inhibit their transport potential. This suggestion,
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however, contradicts observations from previous studies, which suggest that a number of CUPs have the potential for long-range atmospheric transport (Muir et al., 2004; Tuduri et al., 2006; Yao et al., 2006; Yao et al., 2007). Thus, a second explanation for the data shown in Fig. 4 is that the mobility of the CUPs is likely to be strongly influenced by the direction of air flow in the region. Therefore, to better understand the relationship between the various sites along the transect investigated in this study, a series of air shed maps have been produced for each site as a method for assessing the air flow patterns in the region. Fig. 5 illustrates a series of forward trajectory air shed maps for CUPs during the periods elevated concentrations in air were observed. The forward trajectory air shed maps in Fig. 5 indicate that air masses moving away from the source regions of CUPs generally move to the south-west of the source region. For instance, levels of trifluralin are highest during May 2003 at Egbert, and the air mass moving away from Egbert in May 2003 (Fig. 5a) indicates the potential for a strong source–receptor relationship between agricultural regions in south-western Ontario and southern regions of Lake Ontario, whereas poor source–receptor relationships are apparent between the source regions and northern Ontario. The concentration gradient along these transects appear to be consistent with the forward trajectory air shed maps, i.e. low levels in June. Similar trends are apparent in Fig. 5b, which illustrates the forward trajectory air shed map for Egbert during June 2003 in relation to elevated levels of pendimethalin and during July 2003 in relation to
elevated levels of a-endosulfan (Fig. 5c). During April 2003, elevated levels of dacthal were observed at Toronto, and the forward trajectory air shed map for this period (Fig. 5d) is also seen to be consistent with observations shown in Fig. 5a, i.e. strong source–receptor relationships are likely to exist between Toronto and southern regions of Lake Ontario and north-eastern New York State. Since it has been suggested that each of these CUPs have the potential for long-range atmospheric transport, particularly for dacthal and a-endosulfan, areas to the east and south of southern Ontario may experience enhanced deposition of these pesticides during periods of intensive use in the source regions. The city of Toronto, for instance, initiated a pesticide bylaw beginning in 2004; thus it would be useful for the city to monitor the CUPs used in the agricultural belt that surround the city of Toronto as a method for assessing the effectiveness of the by-law. It would also be prudent to monitor the deposition of CUPs to Lake Ontario as a method for assessing exposure to organisms in the lake. Back trajectory air shed maps for the northern sites in this study indicate limited movement of air masses from source regions in southern Ontario. Fig. 6, for instance, illustrates the back trajectory air shed maps of the northern sites during August 2003, when elevated levels of a-endosulfan were observed at Egbert. The field site at Trent University (Fig. 6c) has the strongest relationship with the source region, which may explain elevated levels of a-endosulfan at Trent University during this period. This relationship, however, appears to be diluted by the
Fig. 5. Forward air trajectory air shed maps for select CUPs shown as a probability density: (a) Egbert, showing elevated levels of trifluralin and forward air shed map observed during May, 2003; (b) Egbert, showing elevated levels of pendimethalin and forward air shed map observed during June, 2003; (c) Egbert, showing elevated levels of a-endosulfan and forward air shed map observed during July, 2003; (d) Toronto, showing elevated levels of dacthal and forward air shed map observed during April, 2003.
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Fig. 6. Backward air trajectory air shed maps for non-agricultural-forested sites during the month of August, 2003: (a) Fraserdale; (b) Sprucedale; (c) Trent University; (d) Haliburton.
influence of non-source regions, such as Georgian Bay in Lake Huron and regions to the north of the site. For the field sites at Haliburton, Sprucedale and Fraserdale, it can be seen that the relationship between each of these sites and the source regions in south-western Ontario diminishes for sites that are further north. The low concentrations observed at each of the sites seem to support the weak source–receptor relationships shown in Fig. 6. By combining data from the monthly integrated PAS and the various air shed maps it is thus possible to better understand the transport of CUPs within a region. In this instance it appears that the tendency for air masses to move in a south-easterly direction may result in increased deposition of CUPs to the southern Great Lakes, whereas sites to the north are likely subject to limited deposition associated with episodic transport events. 5. Conclusions These data suggest that pesticide usage in the agricultural regions of southern Ontario likely result in atmospheric transport to south-eastern locations, such as Toronto, for which there is a pesticide by-law, and Lake Ontario, leading to enhanced deposition to these environments. Research is warranted to assess the validity of a pesticide by-law to
reduce exposure to pesticides, particularly if there is significant agricultural activity occurring in the surrounding areas, and to measure the deposition of CUPs to the southern Great Lakes, particularly to Lake Ontario. In this study passive air samplers deployed on a monthly basis are shown to be an effective tool for assessing source– receptor relationships of CUPs, particularly when combined with forward and backward air shed maps. This is because levels in the atmosphere tend to be elevated during the growing season, implying that shorter deployment durations are sufficient for detecting target analytes.
Acknowledgements The authors wish to acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support and Jacinthe Racine of Environment Canada for backward and forward air trajectory data.
References Arya, N., 2005. Pesticides and human health: why public health officials should support a ban on non-essential residential use. Canadian Journal of Public Health 96, 89–92.
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Aulagnier, F., Poissant, L., 2005. Some pesticides occurrence in air and precipitation in Quebec, Canada. Environmental Science and Technology 39, 2960–2967. Bidleman, T.F., 1999. Atmospheric transport and air-surface exchange of pesticides. Water Air and Soil Pollution 115, 115–166. Blanchard, P., Audette, C.V., Hulting, M.L., Basu, I., Brice, K.A., Chan, C.H., Dryfhout-Clark, H., Froude, F., Hites, R.A., Neilson, M., 2004. Atmospheric deposition of toxic substances to the Great Lakes: IADN results through 2000, in: publication, E.C.a.U.E.P.A. (Ed.), PWGSC#En45–156/2000-1E, USEPA Report #905-R-04-900. Buehler, S.S., Basu, I., Hites, R.A., 2004. Causes of variability in pesticide and PCB concentrations in air near the Great Lakes. Environmental Science and Technology 38, 414–422. Buehler, S.S., Hites, R.A., 2002. The Great Lakes’ integrated atmospheric deposition network. Environmental Science and Technology 36, 354A–359A. Carlson, D.L., Basu, I., Hites, R.A., 2004. Annual variations of pesticide concentrations in great lakes precipitation. Environmental Science and Technology 38, 5290–5296. Gouin, T., Harner, T., Blanchard, P., Mackay, D., 2005. Passive and active air samplers as complementary methods for investigating persistent organic pollutants in the Great Lakes Basin. Environmental Science and Technology 39, 9115–9122. Harner, T., Bartkow, M., Holoubek, I., Klanova, J., Wania, F., Gioia, R., Moeckel, C., Sweetman, A.J., Jones, K.C., 2006a. Passive air sampling for persistent organic pollutants: Introductory remarks to the special issue. Environmental Pollution 144, 361–364. Harner, T., Shoeib, M., Diamond, M., Stern, G., Rosenberg, B., 2004. Using passive air samplers to assess urban–rural trends for persistent organic pollutants. 1. Polychlorinated biphenyls and organochlorine pesticides. Environmental Science and Technology 38, 4474–4483. Harner, T., Shoeib, M., Gouin, T., Blanchard, P., 2006b. Polychlorinated naphthalenes in Great Lakes air: assessing spatial trends and combustion inputs using PUF disk passive air samplers. Environmental Science and Technology 40, 5333–5339. IADN, 2005. Data request via http://www.msc-smc.ec.gc.ca/iadn/index_e. html. James, R.R., Hites, R.A., 1999. Chlorothalonil and Dacthal in Great Lakes air and precipitation samples. Journal of Great Lakes Research 25, 406–411. Kannan, K., Ridal, J. and Struger, J. (2006). Pesticides. In: Hites, R.A. (Ed.), Handbook of Environmental Chemistry, vol. 5, Persistent Organic Pollutants in the Great Lakes. Springer-Verlag Publishers, pp. 151–200. Mackay, D., Shiu, W., Ma, K.-C., Lee, S.C., 2006. Physical–chemical Properties and Environmental Fate for Organic Chemicals, third ed. CRC Press, Boca Raton, FL. McGee, B., Berges, H., Callow, K., 2004. Survey of Pesticide Use in Ontario, 2003: Estimates of Pesticides Used in Field Crops, Fruit and Vegetable Crops, and Other Agricultural Crops. Ontario Ministry of Agriculture and Food, Guelph, Ontario, p. 18. Monosmith, C.L., Hermanson, M.H., 1996. Spatial and temporal trends of atmospheric organochlorine vapors in the central and upper Great Lakes. Environmental Science and Technology 30, 3464–3472.
Motelay-Massei, A., Harner, T., Shoeib, M., Diamond, M., Stern, G., Rosenberg, B., 2005. Using passive air samplers to assess urban–rural trends for persistent organic pollutants and polycyclic aromatic hydrocarbons. 2. Seasonal trends for PAHs, PCBs, and organochlorine pesticides. Environmental Science and Technology 39, 5763–5773. Muir, D.C.G., Teixeira, C., Wania, F., 2004. Empirical and modeling evidence of regional atmospheric transport of current-use pesticides. Environmental Toxicology and Chemistry 23, 2421–2432. Peck, A.M., Hornbuckle, K.C., 2005. Gas-phase concentrations of currentuse pesticides in Iowa. Environmental Science and Technology 39, 2952–2959. Poysa, V., Brammall, R.A., Pitblado, R.E., 1993. Effects of foliar fungicide sprays on disease and yield of processing tomatoes in Ontario. Canadian Journal of Plant Science 73, 1209–1215. Pozo, K., Harner, T., Shoeib, M., Urrutia, R., Barra, R., Parra, O., Focardi, S., 2004. Passive-sampler derived air concentrations of persistent organic pollutants on a north-south transect in Chile. Environmental Science and Technology 38, 6529–6537. Pozo, K., Harner, T., Wania, F., Muir, D.C.G., Jones, K.C., Barrie, L.A., 2006. Toward a global network for persistent organic pollutants in air: Results from the GAPS study. Environmental Science and Technology 40, 4867–4873. Ritter, L., Goushleff, N.C.I., Arbuckle, T., Cole, D., Raizenne, M., 2006. Addressing the linkage between exposure to pesticides and human health effects – Research trends and priorities for research. Journal of Toxicology and Environmental Health, Part B: Critical Reviews 9, 441–456. Shen, L., Wania, F., Lei, Y.D., Teixeira, C., Muir, D.C.G., Bidleman, T.F., 2004. Hexachlorocyclohexanes in the North American atmosphere. Environmental Science and Technology 38, 965–975. Shen, L., Wania, F., Lei, Y.D., Teixeira, C., Muir, D.C.G., Bidleman, T.F., 2005. Atmospheric distribution and long-range transport behavior of organochlorine pesticides in north America. Environmental Science and Technology 39, 409–420. Shoeib, M., Harner, T., 2002. Characterization and comparison of three passive air samplers for persistent organic pollutants. Environmental Science and Technology 36, 4142–4151. Thelin, G.P., Gianessi, L.P., 2000. Method for Estimating Pesticide Use for County Areas of the Conterminous United States. U.S. Geological Survey, Sacramento, CA, p. 67. Tuduri, L., Harner, T., Blanchard, P., Li, Y.F., Poissant, L., Waite, D.T., Murphy, C., Belzer, W., 2006. A review of currently used pesticides (CUPS) in Canadian air and precipitation. Part 2: Regional information and perspectives. Atmospheric Environment 40, 1579–1589. Yao, Y., Harner, T., Ma, J.M., Tuduri, L., Blanchard, P., 2007. Sources and occurrence of dacthal in the Canadian atmosphere. Environmental Science and Technology 41, 688–694. Yao, Y., Tuduri, L., Harner, T., Blanchard, P., Waite, D., Poissant, L., Murphy, C., Belzer, W., Aulagnier, F., Li, Y.-F., Sverko, E., 2006. Spatial and temporal distribution of pesticide air concentrations in Canadian agricultural regions. Atmospheric Environment 40, 4339– 4351.