Using Passive Air Samplers To Assess Urban--Rural Trends for Persistent Organic Pollutants. I. Polychiorinated Biphenyls and Organochiorine Pesticides

Using Passive Air Samplers ToAssess Urban-Rural Trends forPersistent Organic Pollutants andPolycyclic Aromatic Hydrocarbons.2. Seasonal Trends for PAHs, PCBs,and Organochlorine PesticidesA N N E M O T E L A Y - M A S S E I , † , ‡ , |

T O M H A R N E R , * , † M A H I B A S H O E I B , †

M I R I A M D I A M O N D , ‡ G A R Y S T E R N , § A N DB R U N O R O S E N B E R G §

Meteorological Service of Canada, Environment Canada, 4905Dufferin Street, Toronto, Ontario, Canada M3H 5T4,Department of Geography, University of Toronto, Toronto,Ontario, Canada M5S 3G3, Departement de Geologie, UMRCNRS 6143, Faculte des Sciences et Techniques, Universite deRouen, France, and Freshwater Institute, Fisheries and OceansCanada, Winnipeg, Manitoba, Canada R3T 2N6

This is the second of two papers demonstrating thefeasibility of using passive air samplers to investigatepersistent organic pollutants along an urban-rural transectin Toronto. The first paper investigated spatial trends forpolychlorinated biphenyls (PCBs) and organochlorinepesticides (OCPs). This second paper investigates theseasonality of air concentrations for polycyclic aromatichydrocarbons (PAHs), PCBs, and OCPs along this transect.Air samplers, consisting of polyurethane foam (PUF)disks housed in stainless steel domed chambers, weredeployed for three 4-month integration periods from June2000 to July 2001. The seasonal variations of derived airconcentrations for PAHs, PCBs, and OCPs reflectedthe different source characteristics for these compounds.PAHs showed a strong urban-rural gradient withmaximum concentrations at urban sites during the summerperiod (July-October). These high summer values inToronto were attributed to increases in evaporative emissionsfrom petroleum products such as asphalt. PCBs alsoexhibited a strong urban-rural gradient with maximum airconcentrations (∼2-3 times higher) during the springperiod (April-June). This was attributed to increasedsurface-air exchange of PCBs that had accumulated inthe surface layer over the winter. R-HCH was fairly uniformlydistributed, spatially and temporally, as expected. Thispattern and the derived air concentration of ∼35 to ∼100pg m-3 agreed well with high volume air data from thisregion, adding confidence to the operation of the passivesamplers and showing that site-to-site differences insampling rates was not an issue. For other OCPs, highestconcentrations were observed during the spring period.

This was associated with either (i) their local and/orregional application (γ-HCH, endosulfan) and (ii) theirrevolatilization (chlordanes, DDT isomers, dieldrin, andtoxaphene). Principal component analysis resulted in clustersfor the different target chemicals according to theirchemical class/source type. The results of this studydemonstrate how such a simple sampling technique canprovide both spatial and seasonal information. These data,integrated over seasons, can be used to evaluatecontaminant trends and the potential role of large urbancenters as sources of some semivolatile compounds to theregional environment, including the Great Lakes ecosystem.

IntroductionPolycyclic aromatic hydrocarbons (PAHs), organochlorinepesticides (OCPs), and industrial organochlorines such aspolychlorinated biphenyls (PCBs) are compounds which,because of their physical-chemical properties, are persistentand mobile in the environment (1-4). These chemicals alsotend to bioaccumulate and be toxic, and therefore they poserisks to biota and humans (5).

Because the atmosphere plays a major role in the cyclingof these organic pollutants, international regulation hasfocused on reducing emissions to air. Thus, many programswere launched to measure levels in air and deposition ofthese pollutants: for instance, the Integrated AtmosphericDeposition Network (IADN) in North America (6) and theEuropean Monitoring and Evaluation Program (EMEP) inEurope (7). Moreover, international bodies such as the UnitedNations Economic Commission for Europe (UNECE) andthe United Nations Environment Program (UNEP) haveestablished priority lists for the elimination of the worstpersistent organic pollutants (POPs), including PCBs andsome OCPs. Although most of these contaminants are nolonger in use in industrialized regions, they continue to persistin the environment, including the atmosphere.

To respond to this increasing need for cost-effective andsimple tools for assessing concentrations in air simulta-neously at multiple sites, the use of passive sampling methodsto monitor airborne contaminants has greatly increased overthe past few years. Information obtained from such cam-paigns (8-13), on various scales, helps to address questionsregarding sources of PAHs and POPs, their seasonal pattern,and chemical signature and to improve our understandingof the role of the atmosphere in the transport of thesecontaminants. Only a few studies have employed passivesamplers in cities (8-10), which are known to be importantemission sources of many contaminant classes to theirsurrounding regions (11-13). This is especially relevant forcities such as Toronto that are situated on the shore and mayact as a source to the Great Lakes system. Furthermore, theassessment of risk associated with exposure and humanhealth concerns is especially relevant in these urban areaswhere the majority of population resides. In the city ofToronto, few data about atmospheric concentrations of POPsand PAHs have been published (16). However, measurementsin various compartments such as atmospherically derivedorganic film on impervious surfaces (17) and soils (18) showedhigh concentrations for several classes of compounds suchas OCPs, PCBs, PAHs, and PBDEs (polybrominated diphenyletherssa class of flame retardants that is ubiquitous in theenvironment) (19).

In this study, passive samplers comprised of polyurethanefoam (PUF) disks were deployed at seven sites along an

* Corresponding author phone: (416)739-4837; fax: (416)739-5708;e-mail: [email protected].

† Environment Canada.‡ University of Toronto.§ Fisheries and Oceans Canada.| Universite de Rouen.

Environ. Sci. Technol. 2005, 39, 5763-5773

10.1021/es0504183 CCC: $30.25 2005 American Chemical Society VOL. 39, NO. 15, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 5763Published on Web 06/24/2005

urban-rural transect in Toronto. The operation of thesamplers and the method used to evaluate passive sampler-derived concentrations were described in detail in a previouscompanion paper (16). That paper reported on the spatialdistribution of PCBs and OCPs from July to October 2000.The objective of this second paper is to investigate seasonalityin ambient air concentration and spatial distribution of PCBs,OCPs, and PAHs during 1 whole year.

MethodologySample Collection. Atmospheric samples were collected atseven sites along an urban-rural transect extending ∼75 kmnorth of downtown Toronto (Figure 1). The three first sites(Junction Triangle, Gage Building, and South Riverdale )urban 1, 2, and 3, respectively) are located in south Torontoand are described as urban, high-density residential/industrial. Located 16 km north of downtown Toronto, theDownsview site (urban 4) is considered as urban, mediumdensity, and residential/industrial. Further north, two sub-urban sites (Richmond Hill and Aurora ) suburban 1 and 2)are characterized as low-density residential/industrial. Last,the rural site of Egbert (44°13′57′′ N/79°46′53′′ W) is situatedin an agricultural/farming region.

Air samplers were deployed for three 4-month integrationperiods from June 2000 to July 2001. Sample collection datesand number of days for the sampling periods are outlinedin Table 1. Mean temperatures at each site were assessedthrough the National Air and Water Monitoring ActivitiesArchive. Meteorological stations nearest the sampling siteswere selected for temperature data. However, because thetemperature differences for the three sampling periods werefairly small between sites, a common temperature of 16 °C,-3 °C, and 15 °C was used for all calculations for the samplingperiods 1, 2, and 3, respectively.

The passive air samplers consisted of PUF disks housedin stainless steel, domed chambers in order to reduce theinfluence of wind speed on uptake rate and also to protectthe PUF disks from precipitation, direct particle deposition,and UV sunlight. A detailed description of sampling, prepa-ration, workup, and theory of the PUF disk samplers is givenby Harner et al. (16). Briefly, the uptake of POPs by PUF disksamplers is air-side controlled with an outdoor samplingrate of approximately 3.5 m3 day-1. This sampling rate forPUF disks has been confirmed in more recent studies usingdepuration compounds added prior to deployment (9). ThePUF disk housings have also been shown to be effective indampening the wind-effect on sampling rate (20).

Prior to deployment, PUF disks comprised of virgin,untreated foam were precleaned by Soxhlet extraction using

acetone and then petroleum ether. After cleaning, the PUFdisks were desiccated under vacuum to remove excess solventand stored cool and in the dark in solvent-rinsed glass jarshaving Teflon-lined lids.

A separate sampling train consisting of a single glass fiberfilter and two PUF plugs was used at the Gage Building (urban2) and Egbert (rural 1) for total suspended particle deter-minations (TSP, µg of particles m-3 air). The filters werepreweighed after equilibration in a constant humiditychamber for 48 h at 20 °C over a saturated sodium chloridesolution. The same procedure was used after sampling toensure that any changes in filter mass were attributed onlyto particulate matter and not to differences in water content.The instrument provided measurements from a 24-h sam-pling period on 3- or 6-day sampling cycles.

Analysis. Samples were analyzed for 90 PCB congeners,43 OCPs, and 19 PAHs. Prior to extraction, PUF disks werefortified with PCB-30, which served as a surrogate forassessing method recoveries for each sample. PUF disksamples were Soxhlet extracted for 24 h with petroleum ether,concentrated to ∼1 mL under a gentle stream of clean, dry

FIGURE 1. Location of sampling sites across the Greater Toronto Area.

TABLE 1. Passive Sample Collection Informationa

sampling period

site start date end date

number ofsampling

days

Junction Triangle ) urban 1 1 2000/06/27 2000/10/31 1262 2000/10/31 2001/03/20 1413 2001/03/20 2001/07/23 125

Gage Building ) urban 2 1 2000/06/28 2000/11/01 1262 2000/11/01 2001/03/20 1403 2001/03/20 2001/07/23 125

South Riverdale ) urban 3 12 2000/10/31 2001/03/20 1403 2001/03/20 2001/07/23 125

Downsview ) urban 4 1 2000/06/22 2000/11/03 1342 2000/11/03 2001/04/03 1553 2001/04/03 2001/07/23 111

Richmond Hill ) suburban 1 1 2000/07/25 2000/10/31 982 2000/10/31 2001/04/03 1553 2001/04/03 2001/07/23 111

Aurora ) suburban 2 1 2000/06/27 2000/11/02 1282 2000/11/03 2001/04/02 1523 2001/04/02 2001/07/24 113

Egbert ) rural 1 1 2000/07/05 2000/10/31 1182 2000/10/31 2001/04/03 1543 2001/04/03 2001/07/23 111

a Period 1 ) July to Oct, 2000 (summer-fall). Period 2 ) Nov 2000to March 2001 (fall-winter). Period 3 ) April to June, 2001 (spring-summer).

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N2, and then separated into two fractions. Half the extractunderwent cleanup and analysis for PAHs, while the otherhalf was for POPs. For POPs, analysis and quantificationdetails are presented elsewhere (19, 21, 22). Briefly, the extractwas cleaned up into three fractions using florisil (1.2%deactivated) column chromatography. These three fractionswere analyzed for several POPs classes including PCBs, OCPs,and PBDEs for which results are presented elsewhere (19).Each fraction was concentrated to ∼200 µL under nitrogen,after which aldrin was added to monitor analytical instrumentvariability.

Following cleanup on an alumina:silicic acid column (2:3), PAHs were analyzed on a Hewlett-Packard 5890 gaschromatograph equipped with a mass selective detector(Model HP5970) using a DB5-MS (30 m × 0.25 mm i.d.; 0.25µm film thickness) capillary column (J&W Scientific). Quan-tification was performed using the internal standard method,utilizing five deuterated PAHs (100 ng mL-1) spiked into thecleaned up extracts. PAH calibration standards of 25, 50,100, and 250 ng mL-1 containing all the target PAHs wereprepared from stock solution supplied by Supelco Chroma-tography Products (Oakville, Ontario).

Quality Control/Quality Assurance. All analyses weremonitored using strict quality assurance and control mea-sures. For PCBs and OCPs, quality assurance was identicalto those given in ref 16. For PAHs, laboratory and field blanksconsisted of pre-extracted PUF disks extracted and analyzedas samples. Practical detection limits were 0.24-8.82 pg m-3,depending on the compound. PAH recoveries were 84-114%.Consequently, reported values were not recovery correctedbut were blank corrected using the mean blank value. Blankvalues were less than 1.4% of sample amounts. Instrumentefficiencies were estimated using quality control standardsafter every five samples run on the GC-MS. Peaks were onlyintegrated when the signal-to-noise ratio was g 3.

Results and DiscussionAir concentrations for the target chemicals were derived fromthe amount accumulated in the PUF disk and the effectiveair volume. The eq 2 in ref 16 was used to estimate the effectiveair volumes (Vair, m3). Vair and resulting air concentrationsare given in Tables 2-4 for PAHs, PCBs, and OCPs,respectively. For most compounds, the effective air volumes(Vair, m3) were on the order of ∼380 m3 on average, based ona linear sampling rate 3.5 m3 d-1 and a deployment time of∼ 120 days. Lower molecular weight chemicals had lowervalues for Vair as they approach saturation (equilibrium) inthe PUF disk during the sampling period. This is due to theirlower octanol-air partitioning coefficient (KOA) values andhence lower PUF-air partition coefficient (KPUF-A) (16).

PAHs. PAHs are produced by incomplete combustion offossil fuels or organic matter and are considered as ubiquitouscontaminants in the environment. PAHs have a mainlyanthropogenic origin (automobile traffic, domestic heating,thermal power stations, and industrial emissions). They arerecognized as mutagenic compounds and known to becarcinogenic in animals and humans (23).

Table 2 provides a summary of the PAH concentrationsfor each period and for each analyzed compound. Σ 17 PAHconcentrations ranged from 11.5 to 61.4 ng m-3 for the period1 (July-Oct 2000), from 8.34 to 18.5 ng m-3 for the period2 (Nov 2000-March 2001), and from 3.53 to 18.8 ng m-3 forthe period 3 (April-June 2001) (Figure 2). These values weresimilar to those measured for urban sites worldwide. In Paris,Ollivon et al. (24) showed concentrations that ranged between3 and 15 ng m-3 (Σ 8 PAHs); in North America, Cotham andBidleman (25) reported values (Σ 13 PAHs) of 43, 57, 93, and195 ng m-3 in Columbia, Portland, Denver, and Chicago,respectively. In Toronto, polymer-coated glass samplers(POGs) deployed in the CN Tower (up to 360 m) showed a

strong vertical gradient of PAHs with higher concentrationsnear ground level (26). In all of these studies, phenanthrenewas the most predominant PAH, followed by fluorene andacenaphthene.

PAH concentrations showed a strong urban-rural gradi-ent, with total concentrations (Σ 17 PAHs) up to ∼5 timeshigher in urban sites than in the rural one (Figure 2). Thishas been showed previously in air (25, 27, 28), sediments(29), organic films on impervious surfaces (17, 30), soils (18),and atmospheric deposition (31). The gradient reflects PAHemission sources which are well-known to be proportionalto the population density (31). However, PAH profiles weredifferent for urban and rural sites with proportions of thehigher molecular weight PAHs (e.g. benzo[ghi]perylene)decreasing along the urban-rural transect (Figure 2). Thisurban-rural fractionation effect was reported in the previousstudy for PCBs and is caused by the greater volatility (transportpotential) of the low molecular weight PAHs. High molecularweight PAHs that are associated with particles to a greaterextent will be deposited closer to the source. The significanceof this fractionation is that it occurs over a relatively shortdistance of ∼75 km.

A seasonal fluctuation in concentrations was also evident(Figure 2). For all sites, the highest PAH concentrations (Σ17 PAHs) were found during period 1 (July-Oct), while thetwo other periods (Nov-March and April-June) showedsimilar concentrations.

Σ PAHs was dominated by phenanthrene which existsprimarily in the gaseous phase in ambient air. Since PUFdisks samplers have been shown to sample mainly the gasphase (32), the seasonal variation of Σ PAHs is thus linkedto phenanthrene concentrations. Higher summertime at-mospheric concentrations for phenanthrene were previouslyobserved in Toronto from 1987 to 1997 (33). The enrichmentin phenanthrene during the summer could be due toincreases in evaporative emissions from petroleum productssuch as asphalt, coal tar sealant, and roofing tar (33, 34). Thiscan also explain why this seasonal trend is more marked forthe urban areas (Figure 2), where this kind of surface is moreprevalent.

Although combustion-derived PAH emissions may beelevated during the colder months, PAH gas-phase concen-trations will be reduced by partitioning to particles and snowwhich is enhanced at cold temperature. This effect will begreatest in urban areas where particle concentrations arehighest. For instance, total suspended particulate (TSP) inthe ambient air along the urban-rural transect was 75.2 and18.2 µg m-3 in March 2000 for urban 2 and rural 1, respectively.

PCBs. The emission of PCBs in the atmosphere peakedin late 1960s (35). Nowadays, the use of these chemicals isprohibited or restricted in many countries. Emissions toambient air are likely due to revolatilization of previouslyemitted compounds (36, 37) and to continued release frompoint sources such as old industrial/urban areas where theywere previously heavily used and still exist (35). Theconcentrations for 13 of the more dominant congeners arelisted in Table 3. Σ 13 PCB concentrations ranged from 72to 550 pg m-3 for period 1 (July-Oct 2000), from 65.6 to 506pg m-3 for period 2 (Nov 2000-March 2001), and from 129to 1350 pg m-3 for period 3 (April-June 2001). For all seasons,PCB concentrations showed a strong decrease with distancefrom the urban area (Figure 3), confirming the continuingrole of urban/industrial areas in Toronto as emission sourcesof PCBs (16), possibly due to the outgassing of PCBs frombuildings (38).

Seasonal variability is also apparent. PCB air concentra-tions were ∼2-3 times higher during the spring-summer(period 3; mean temperature ) 15 °C) than during the periods1 and 2 (16 and -3 °C, respectively) which showed similarvalues. This is consistent with a spring pulse effect (39)

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TABLE 2. Passive Sampler-Derived Air Concentrations (ng m-3) for PAHs along the Urban-Rural Transect in Toronto in 2000-2001a

ACY ACE FLU PHE ANT FTH PYR BaA CHR BbF BkF BeP BaP Per IcdP DahA BghiP Σ 17 PAHs

July-Oct 2000urban 1 7.09 11.8 13.8 24.3 0.63 1.97 1.28 0.08 0.12 0.10 0.03 0.09 0.06 0.01 0.04 0.01 0.04 61.4urban 2 5.11 8.51 12.1 23.6 0.77 2.28 1.70 0.21 0.25 0.27 0.11 0.24 0.18 0.04 0.11 0.02 0.11 55.6urban 3urban 4 4.30 5.05 7.84 11.1 0.30 0.72 0.50 0.02 0.04 0.03 0.01 0.03 0.01 <0.005 0.01 <0.005 0.02 30.0suburban 1 1.80 3.07 6.01 8.30 0.15 0.56 0.34 0.01 0.03 0.02 <0.005 0.02 0.01 <0.005 0.01 <0.005 0.01 20.3suburban 2 1.86 2.60 5.00 6.28 0.10 0.38 0.20 0.01 0.02 0.01 <0.005 0.01 <0.005 <0.005 <0.005 <0.005 <0.005 16.5rural 1 0.91 1.37 3.89 4.63 0.09 0.35 0.19 0.01 0.02 0.01 <0.005 0.01 <0.005 nd <0.005 <0.005 <0.005 11.5Vair, m3 25 29 78 183 183 380 380 431 431 438 438 438 438 438 439 439 439

Nov-March 2001urban 1 0.63 2.78 4.44 6.33 0.12 1.95 1.62 0.05 0.17 0.08 0.03 0.05 0.07 0.02 0.08 0.02 0.09 18.5urban 2 0.52 1.80 3.67 5.63 0.08 1.69 1.40 0.06 0.17 0.09 0.04 0.06 0.06 0.02 0.07 0.01 0.08 15.5urban 3 0.64 2.31 4.33 5.96 0.15 1.85 1.58 0.05 0.16 0.07 0.03 0.05 0.05 0.01 0.07 0.01 0.08 17.4urban 4 0.51 1.68 4.11 5.61 0.08 1.35 1.10 0.03 0.10 0.04 0.02 0.03 0.02 <0.005 0.04 <0.005 0.05 14.8suburban 1 0.20 0.95 2.72 4.11 0.02 1.11 0.75 0.01 0.07 0.02 0.01 0.01 0.01 <0.005 0.02 <0.005 0.03 10.1suburban 2rural 1 0.22 0.94 2.46 3.37 0.05 0.71 0.45 0.01 0.05 0.02 0.01 0.01 0.01 <0.005 0.01 <0.005 0.02 8.34Vair, m3 135 155 294 400 400 477 477 490 490 491 491 491 491 491 491 491 491

April-June 2001urban 1 0.49 2.68 2.56 8.28 0.20 2.15 1.32 0.14 0.25 0.22 0.08 0.12 0.10 0.03 0.11 0.02 0.09 18.8urban 2 0.30 2.18 1.63 7.24 0.21 1.81 1.26 0.21 0.32 0.28 0.10 0.25 0.12 0.03 0.08 0.01 0.10 16.1urban 3 0.57 3.58 2.88 6.53 0.13 1.33 0.82 0.09 0.16 0.13 0.06 0.08 0.06 0.02 0.06 0.01 0.06 16.6urban 4 0.21 0.96 1.21 3.68 nd 0.74 0.43 0.01 0.06 0.04 0.02 0.03 0.01 <0.005 0.02 <0.005 0.03 7.45suburban 1 0.02 0.05 0.31 1.66 nd 0.86 0.41 0.01 0.09 0.04 0.02 0.02 0.01 <0.005 0.02 <0.005 0.02 3.53suburban 2 0.09 0.39 0.71 2.32 nd 0.44 0.20 <0.005 0.03 0.02 0.01 0.01 0.01 <0.005 0.01 nd 0.01 4.26rural 1 0.02 0.05 0.31 1.66 nd 0.86 0.41 0.01 0.09 0.04 0.02 0.02 0.01 <0.005 0.02 <0.005 0.02 3.53Vair, m3 64 75 180 307 307 430 430 453 453 456 456 456 456 456 456 456 456

a Vair, m3 was estimated using eq 2 in ref 16; Log KOA were calculated according to ref 60. ACY ) acenaphthylene, ACE ) acenaphthene, FLU ) fluorene, PHE ) phenanthrene, ANT ) anthracene, FTH ) fluoranthene,PYR ) pyrene, BaA ) benzo[a]anthracene, CHR ) chrysene, BbF ) benzo[b]fluoranthene, BkF ) benzo[k]fluoranthene, BeP ) benzo[e]perylene, BaP ) benzo[a]pyrene, Per ) perylene, IcdP ) indeno[1,2,3-cd]pyrene,DahA ) dibenz[ah]anthracene, BghiP ) benzo[ghi]perylene.

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whereby chemicals that are accumulated in the surface layerduring the winter are released to the atmosphere as theground warms in the springtime. One could speculate thatthis phenomenon may be enhanced in urban areas that havehigher particle concentrations and PCB deposition duringthe wintertime. PCB accumulation in organic films onimpervious urban surfaces during the cold months may alsocontribute to enhance surface-air exchange during the springperiod when these surfaces are warmed and partitioning tothe atmosphere is favored (17).

OCPs. The spatial distribution of OCPs was previouslyreported for the July-October 2000 period by Harner et al.(16) including a comparison with other measurements inthe region. Here, the discussion will focus on variations inOCPs for the three sampling seasons. Results are presentedin Table 4 and Figure 4.

R- and γ-HCH. Hexachlorocyclohexane (HCH) is apesticide used worldwide. Whereas the technical formulation

(R: 60-70%, â: 4-12%, γ: 10-12%, δ: 9-10%) is no longerused, lindane (99% γ-HCH) is still in use in some countries.Air concentrations of R-HCH showed little spatial andseasonal variability (Figure 4a): from 39.8 to 61.5 pg m-3 forsummer-fall (period 1), from 36.9 to 98.5 pg m-3 for fall-winter (period 2), and from 47.0 to 74.7 pg m-3 for spring-summer (period 3). These concentrations are consistent withlevels reported by IADN (40) and reflect homogeneousbackground levels, which due to R-HCH volatility is fairlyuniformly distributed throughout the global atmosphere (41,42). These results, both in terms of absolute concentrationsand uniformity across the gradient, help to confirm thepassive sampler-derived air concentrations. To explainfurther, if the method used to derive air concentrations wasflawed and/or subject to large variability in sampling rates(between sites and/or between seasons) this would bereflected through more variable R-HCH concentrations,which is not the case. Recent studies using PUF disks samplers

FIGURE 2. PUF disk-derived air concentrations (ng m-3) across an urban-rural transect for Σ 17 PAHs during July-Oct 2000, Nov-March2001, and April-June 2001.

TABLE 3. Passive Sampler-Derived Air Concentrations (pg m-3) for PCBs along the Urban-Rural Transect in Toronto in2000-2001

congeners

31 28 52 49 44 95 101 110 149 118 153 138 180 Σ 13 PCB

July-Oct 2000urban 1 34.0 40.3 68.5 26.3 30.8 88.6 63.6 45.4 43.3 23.3 39.5 31.4 7.82 550urban 2 24.6 28.1 54.9 18.5 18.2 54.7 39.6 29.7 18.3 17.1 18.1 15.8 2.58 345urban 3urban 4 15.5 18.0 24.0 9.09 12.7 23.3 16.8 13.3 7.93 7.87 8.65 6.71 1.04 168suburban 1 9.44 11.4 13.5 4.86 6.86 15.3 9.30 9.16 5.68 4.29 7.86 4.99 1.06 109suburban 2 8.13 10.8 7.76 3.72 4.73 5.62 7.28 5.67 3.55 2.55 5.81 3.62 0.73 71.9rural 1 11.3 12.8 13.3 6.17 9.42 23.0 9.10 8.01 4.53 4.09 8.08 4.82 0.67 120Vair, m3 256 271 335 341 362 401 414 426 431 432 435 438 441

Nov-March 2001urban 1 64.4 46.5 70.7 26.5 34.7 55.0 53.6 27.7 36.7 20.4 31.3 25.1 6.51 506urban 2 37.3 23.6 68.7 21.9 27.3 37.0 40.2 20.4 17.7 15.4 13.2 13.89 2.30 342urban 3 38.7 27.2 39.6 19.0 19.1 26.9 26.0 14.9 12.7 9.80 12.1 9.83 0.09 258urban 4 16.3 9.73 18.6 7.12 7.88 11.3 9.68 6.35 4.27 3.92 3.19 2.88 0.22 102suburban 1 11.2 6.54 11.9 4.68 5.73 7.85 5.86 3.57 2.65 2.29 2.11 1.92 0.22 66.6suburban 2 11.9 7.64 7.55 4.37 8.27 7.32 3.92 2.29 2.85 1.74 2.69 2.44 0.61 65.6rural 1Vair, m3 439 440 464 466 473 483 486 489 490 490 490 491 491

April-June 2001urban 1 98.9 101 165 81.2 82.4 164 169 86.6 117 60.7 95.5 85.1 20.9 1346urban 2 69.4 63.7 124 56.4 59.0 103 104 56.9 55.2 50.7 45.3 47.2 7.60 853urban 3urban 4 30.3 22.7 48.4 21.3 28.9 37.5 37.1 26.0 19.6 20.0 20.7 17.2 3.07 336suburban 1suburban 2 13.4 16.3 10.8 4.82 10.0 22.7 14.1 6.81 8.00 5.25 7.30 7.51 1.23 129rural 1 29.9 22.9 35.6 17.7 28.4 30.7 23.7 14.9 16.2 10.4 19.1 12.2 2.17 269Vair, m3 237 239 277 280 292 313 319 326 328 328 330 331 333

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have employed depuration compounds (added to the PUFdisk prior to deployment) as a confirmation of the samplingrate for each site (9).

Values of γ-HCH showed greater variability (Table 4,Figure 4b). Mean concentrations were quite constant for thetwo first periods (32.2 and 26.6 pg m-3, respectively) butpeaked during the third period (spring-summer) with valuesranging between 159 and 1020 pg m-3, the rural site showingthe highest value. The higher concentrations during thespring-summer period may be explained by local and/orregional use of lindane. Technical HCH has an R-HCH toγ-HCH ratio of about 3 to 7 (43). The low ratios found in airsamples in this study (1.6, 3.1 and 0.27 for summer-fall,fall-winter, and spring-summer, respectively) support thisconclusion of fresh inputs of γ-HCH. High levels of γ-HCHin spring are likely associated with transport from the Prairieregion of Canada (44, 45) which accounts for 98% of thelindane used in Canada. Ma et al. (44, 45) showed that usageof lindane in Ontario and Quebec has a negligible impact onair concentrations in the Great Lakes region compared tothe influence of the prairie sources. Air trajectory analysiswas performed for the spring period using the CanadianMeteorological Centre Trajectory Model (46). Calculationswere performed daily at 100 m above ground. The results(not shown) confirm that during the period following theapplication of lindane in the Prairies, some of the air massesarriving in the Toronto region had stemmed from the Prairies.

Chlordanes. Chlordane was first synthesized in 1944 andintroduced as a pesticide in the United States. Since 1988,the use of chlordane was discontinued. Technical chlordaneis a mixture of components including trans-chlordane (TC),cis-chlordane (CC), trans-nonachlor (TN), and cis-nonachlor(CN) in the proportion of 1.00/0.77/0.62/0.15, respectively(47). Concentrations of Σ-chlordanes (presented here as TC+ CC + TN + CN) ranged from 26.2 to 90.9 pg m-3 in July-Oct 2000, from 13.2 to 96.5 pg m-3 in Nov-March 2001, andfrom 68.4 to 186 pg m-3 in April-June 2001 (Table 4, Figure4c,d). The principal metabolite of chlordanes, oxychlordane(OXY), was found at significantly lower concentrations, withmean values of 3.3, 3.5, and 14 pg m-3, respectively. MeanTC/CC/TN/CN ratios were 1/1.04/0.85/0.06, 1/0.68/0.61/0.04, and 1/0.95/0.93/0.09 for periods 1, 2, and 3, respectively,indicating that atmospheric chlordane is similar to thetechnical grade. There were no clear differences between

rural and urban sites. Among the urban sites however, theolder downtown sites did have higher concentrations. Aseasonal trend was also evident with higher concentrationsin spring, as was seen for PCBs. Given that chlordane wasrestricted in the 1970s, the observed trend is likely due torevolatilization from secondary sources rather than to freshapplication. Previous studies have postulated that urban/residential areas may be important emission sources ofchlordanes which were historically applied to lawns andhouse foundations (16, 48). This is consistent with theobserved higher concentrations at the older urban sites. Theseasonal trend may also be influenced by other factors suchas chemical stability. The TC/CC ratio was lower during thetwo warm periods. This may be attributed to increasedphotodegradation of the trans-chlordane at this time of theyear (49).

Dieldrin. This insecticide was deregistered in NorthAmerica in the late 1980s. Dieldrin air concentrations in thisstudy ranged from 14 to 76 pg m-3 for summer-fall, from6 to 30 pg m-3 for fall-winter, and from 64 to 407 pg m-3 forspring-summer. There is no urban-rural gradient, but therural site showed the highest concentrations, consistent withthe view that revolatilization from previous agricultural useis the main source of dieldrin to atmosphere (Table 4). As forPCBs and chlordanes, this revolatilization was higher duringthe spring-summer period, with values between 4 and 14times higher than during the two other periods.

Toxaphene. Technical toxaphene is a highly complexmixture of chlorinated camphene derivatives. Prior to its banin 1982 by the U.S. Environmental Protection Agency,toxaphene was the most heavily used insecticide in the UnitedStates. Li et al. (50) estimate that 29 kt of toxaphene remainsin agricultural soil in the U.S. and that 360t was emitted tothe air in 2000. MacLeod et al. (51) conducted a dynamicmass budget of toxaphene for North America and suggestedthat although most of the toxaphene in air of the Great Lakesbasin arrives from outside the region; the region itselfcontributed on average∼30% to air burdens through surface-air exchange of residual toxaphene. Results for toxaphene(Table 4, Figure 4e) showed concentrations of 1.3-23.1 pgm-3 during the winter, 9.8-29.7 pg m-3 during the summer-fall period, and highest concentrations during the springperiod -7.1-62.7 pg m-3. Historical data from the rural siteis available for the late 1980s with an average value of 36 (

FIGURE 3. PUF disk-derived air concentrations (pg m-3) across an urban-rural transect for Σ 13 PCBs during July-Oct 2000, Nov-March2001, and April-June 2001.

5768 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 15, 2005

TABLE 4. Passive Sampler-Derived Air Concentrations (pg m-3) for OCPs along the Urban-Rural Transect in Toronto in 2000-2001a

r-HCH γ-HCH ratio r/γ TC CC TN CN OXY TC/CC ΣChlord Dieldp,p′-DDT

p,p′-DDE

o,p′-DDT Σ DDT Endo 1 TOX

July-Oct 2000urban 1 40.8 29.1 1.41 18.9 17.1 13.1 1.09 2.36 1.10 50.2 26.2 14.4 33.5 13.0 61.0 384 29.7urban 2 55.2 52.2 1.06 35.9 33.1 20.4 1.56 3.05 1.08 90.9 35.6 27.0 59.6 21.7 108.3 370 25.6urban 3urban 4 41.4 25.6 1.62 8.69 8.87 8.07 0.61 2.33 0.98 26.2 19.4 10.5 30.1 8.01 48.6 408 16.1suburban 1 51.7 22.3 2.32 12.6 14.3 12.2 0.93 3.06 0.89 40.0 26.4 17.5 38.8 13.7 70.0 405 13.2suburban 2 39.8 23.9 1.67 9.17 10.1 9.08 0.58 2.76 0.91 28.9 13.6 11.7 27.0 9.67 48.4 465 9.81rural 1 61.5 40.2 1.53 16.4 19.2 15.1 1.26 6.18 0.85 51.9 75.8 52.9 305 40.3 398 254 17.4Vair, m3 164 227 401 411 427 399 261 401 436 434 429 817 411

Nov-March 2001urban 1 69.7 25.5 2.73 18.9 13.8 10.1 1.00 3.71 1.37 43.8 21.2 13.1 21.8 7.80 42.7 25.1 23.1urban 2 98.5 60.4 1.62 43.4 31.2 20.7 1.17 4.42 1.39 96.5 29.9 16.1 36.3 14.2 66.5 45.2 12.9urban 3 77.1 27.6 2.80 37.1 26.9 17.9 0.38 4.16 1.38 82.3 27.3 10.1 24.1 7.27 41.5 19.5 4.30urban 4 36.9 10.2 3.63 5.67 3.43 3.72 0.38 1.88 1.65 13.2 6.04 2.65 6.87 2.55 12.1 12.6 2.60suburban 1 81.9 20.5 4.00 8.96 6.57 6.73 0.51 4.11 1.36 22.8 17.0 6.34 14.6 4.26 25.2 26.8 3.03suburban 2 57.3 14.9 3.85 6.46 3.77 5.04 0.35 2.73 1.72 15.6 10.7 4.94 10.7 3.16 18.8 19.1 1.32rural 1Vair, m3 360 410 487 487 490 490 471 481 490 490 489 480 488

April-June 2001urban 1 54.7 159 0.34 45.6 36.9 35.5 3.19 9.98 1.24 121 79.8 49.2 99.0 33.6 182 888 62.5urban 2 61.5 225 0.27 73.1 65.0 43.9 3.90 12.7 1.12 186 136 90.7 168 53.5 312 970 44.7urban 3urban 4 60.6 170 0.36 22.4 22.6 23.2 2.79 10.7 0.99 71.0 83.1 28.0 123 22.2 173 940 29.2suburban 1suburban 2 47.0 167 0.28 22.9 21.4 22.4 1.71 9.84 1.07 68.4 63.5 48.8 87.6 31.9 168 861 7.05rural 1 74.8 1020 0.07 50.7 56.1 63.9 6.59 24.8 0.90 177 407 156 899 99.2 1154 1283 61.3Vair, m3 159 205 316 317 326 329 284 311 330 329 327 302 322

a Vair, m3 was estimated using eq 2 in ref 16; Log Koa were calculated according to ref 60. HCH ) hexachlorocyclohexane, TC ) trans-chlordane, CC ) cis-chlordane, TN ) trans-nonachlor, CN ) cis-nonachlor,OXY ) oxychlordane, Chlord ) TC + CC + TN + CN, Dield ) dieldrin, DDT ) p,p′-DDT + o,p′-DDT + p,p′-DDE, Endo ) endosulfan, TOX ) toxaphene.

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32 pg m-3 (52). More recently, Jantunen et al. (53) reportedtoxaphene concentrations in air over Lake Superior in therange 5-39 pg m-3 during cruises in 1996 (August) and 1997(May). This range of values agrees well with the passive

sampler-derived values presented here. These concentrationsare about an order of magnitude lower than the concentra-tions reported in source regions in the southern U.S. wheretoxaphene was heavily used (54). At the sites that showed

FIGURE 4. PUF disk-derived air concentrations (pg m-3) across an urban-rural transect for Σ 6 OCPs during July-Oct 2000, Nov-March2001, and April-June 2001.

5770 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 15, 2005

elevated toxaphene air concentrations, highest values oc-curred during the spring. This may be associated withenhanced soil-air exchange in the region and/or advectionfrom southern sources. Toxaphene is fairly stable in air andhence capable of efficient long-range transport (55).

DDT Isomers. Technical grade DDT is p,p′-DDT (80-85%)and o,p′-DDT (15-20%). The concentration of total DDT(p,p′-DDT + o,p′-DDT + p,p′-DDE) varied from 12.1 (urban4, Nov-March 2001) to 1154 pg m-3 (rural site, April-June2001). DDT and DDE concentrations were homogeneousalong the urban-rural transect. A seasonal trend is evidentwith higher concentrations during the spring-summerperiod. DDT was heavily used in the tobacco belt region ofSouthern Ontario (56), and higher springtime concentrationsmay reflect enhanced volatilization due to soil ploughingand/or warming. The DDT contamination source can betraced by the relative residues of p,p′-DDT to its metabolite(p,p′-DDE). The p,p′-DDE concentrations were higher thanthose of the parent compounds. The ratio of p,p′-DDT/p,p′-DDE ranged from 0.17 to 0.60 and was slightly higher duringthe cold period (0.46 versus 0.38 and 0.40 for the two otherperiods), showing that the degradation is less importantduring this period.

Endosulfan 1. Endosulfan was used as an insecticide sincethe 1950s. The contemporary use of the active ingredient inthe eight states surrounding the Great lakes is on the orderof 100 tons per year (57), whereas for the province of Ontario∼3700 kg (∼4 t) was used in 2003 (58). Few measurementsof endosulfan concentrations in air were carried out in theGreat Lakes region. In this study, endosulfan concentrationsranged from 254 to 817 pg m-3 in July-Oct 2000, from 12.6to 45.2 pg m-3 in Nov-March 2001, and from 861 to 1283 pgm-3 in April-June 2001 (Table 4, Figure 4f). No cleardifferences were found between rural and urban sites, buta seasonal trend was evident with higher concentrationsduring the spring, particularly for the rural site. These highspring and summertime concentrations agree with recent

high volume air samples collected in southern Ontario underthe Canadian Atmospheric Network for Current-Use Pesti-cides (CANCUP) for 2003 (59) and are consistent with theexpected local/regional use that would occur during this timeof the year.

Principal Component Analysis. To further evaluate spatialand temporal differences and differences between compoundclasses, principal component analysis (PCA) was used. ThePCA was performed (XLstat 6.0 software) on 43 subjectsconsisting of standardized organic pollutant concentrations.The seasons and the nature of the sampling sites were theactive variables. The first axis represents 31% of the explainedvariance level, and the second one represents 24%. Relation-ships between subjects (samples) and between variables(pollutant concentrations) are therefore well represented ina 2D plot (explained variance: 55% of the total variance).The PCA (Figure 5) showed four distinct clusters: PAHs, PCBs,OCPs, and R-HCH. The clusters reflect the variety of differentsources for these compounds. PAHs are emitted from a varietyof combustion and noncombustion sources, mainly in urbanareas; PCBs are also released mainly in urban areas but moreassociated with ‘old’ sources (e.g. older buildings andequipment) with some contribution from surface-air ex-change; OCPs may be released from several sources includingcurrent-use and re-emission of residual chemical fromagricultural soils and or historical urban uses. The separationof R-HCH is also of significance. Because it is fairly persistentand volatile, R-HCH is a ubiquitous POP. Air burdens of thiscompound are more a reflection of continental levels ratherthan source-related on a local or regional scale.

The first principal component reflects chemicals thatexhibit an urban-suburban transect. PCBs and the highmolecular weight PAHs showed a high correlation coefficientwith this axis. This highlights the continuing role of olderurban/industrial areas in Toronto as ongoing emissionsources of PCBs. OCPs are strongly and positively correlatedto the second factor, which can be associated with the

FIGURE 5. PCA projections of scores and loadings for the first two principal components for the analysis of all samples. Score plot indicatessampling sites and periods, loading plot the variables ([).

VOL. 39, NO. 15, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 5771

observed levels at the rural site. There was also a clearseparation of the sampling periods. The spring-summerperiod (top right of plot) was clearly distinguished from theother two periods. This is due to the elevated air concentra-tions for PCBs and several OCPs during this period. However,care should be taken not to overinterpret the PCA, since itis based on relatively few samples.

ImplicationsPassive samplers were used to show large diversity in spatialand temporal trends for several POPs classes over a relativelyshort transect. This extended from downtown Toronto nearthe lake shore to an rural region approximately 75 km northof the city. PCBs and PAHs showed strong urban-ruralgradients, while OCPs varied depending on their physical-chemical properties and urban use-history. Elevated con-centrations of PCBs and several OCPs occurred during thespring period. These were explained by enhanced air-surfaceexchange and or current-use during the period.

The results of this study are significant for two reasons.First, they demonstrate how such a simple sampling tech-nique can yield insightful data which until now were notavailable. Second, it highlights the potential role of large urbancenters as sources of some POPs to the regional environment.As was observed here for some classes of chemicals, thissource may also exhibit seasonality. For cities situated onthe shores of the Great Lakes, this is of great relevance, asthese sources may lead to substantial loadings to the lakewaterssboth through atmospheric deposition and runoff.

AcknowledgmentsThis work was supported by the Toxic Substances ResearchInitiative (Project 227), a research program managed jointlyby Health Canada and Environment Canada, and the NationalScience and Engineering Research Council (NSERC) (ProjectSTP-258056). We are also grateful to Craig Butt, Fiona Wong,and Bagher Bahavar for their help with sample deployment.

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(59) Harner, T.; Tuduri, L.; Blanchard, P.; Waite, D.; Belzer, W.; Froude,F.; Murphy, C.; Poissant, L.; Sproull, J. CANCUP: CanadianAtmospheric Network for Current-Use Pesticides. The 4thAnnual SETAC (Society for Environmental Toxicology andChemistry) World Congress, November 2004, Portland, U.S.A.

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Received for review February 28, 2005. AcceptedMay 19, 2005.

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