some pesticides occurrence in air and precipitation in québec, canada

Some Pesticides Occurrence in Airand Precipitation in Quebec, CanadaF A B I E N A U L A G N I E R A N DL A U R I E R P O I S S A N T *

Section on Atmospheric Toxic Processes, Meteorological Serviceof Canada, Environment Canada, 105 McGill Street, SeventhFloor (Youville), Montreal, Quebec, Canada H2Y 2E7

Air and precipitation samples were collected in threestations located in Quebec between January 1993 andMarch 1996 to determine spatial and seasonal variationsof several organochlorine pesticides and metabolites (R-HCH, γ-HCH, HCB, γ-chlordane, DDT, DDE, Mirex). R-HCH,γ-HCH, and HCB were more or less measured in largeamounts at all sites, whereas γ-chlordane, DDT, and DDEconcentrations were lower and Mirex was undetectable.Higher concentrations levels were observed in air during hotspring/summer periods except for HCB, indicating aprobable temperature dependence. Ln concentrations vsreciprocal temperature plots and Henry’s law determinationshelped to highlight the contribution of soil and/or watervolatilization of those compounds. It was observed that R-HCHcame mainly from Atlantic Ocean volatilization at Mingan,whereas sources of γ-chlordane and DDE were mostlydue to volatilization from soils in southern Quebec. DDT maybe present in the atmosphere by the way of transportfrom remote regions. Lindane sources were multiple: itmay be found in the atmosphere by the processes of transportand volatilization coming from soil or water. Finally, anegative correlation between HCB and air temperatureimplies that processes other than volatilization are involvedin transport of this compound.

IntroductionIn the past, extensive use of persistent organic pollutants(POPs) in Quebec and other regions has led to the dispersalof these pollutants throughout the global environment (1-3) and bioaccumulation through food chains (4). This hasfocused international regulation on reducing emissions toair as UNECE protocol (5) and UNEP report (6). In Quebec,a significant part of pesticide usage is due to the corncultivation where production is increasing every year. Thetotal corn surface area (grain, fodder, and sweetened) wasabout 350 000 hectares during the 1993-1996 period. It hasincreased by approximately 29% between 1996 and 2001 andcovers currently ∼500 000 hectares (7). Soya cultivations,which also use large amount of organochlorine (OC) pes-ticides, made great strides in Quebec during these last years.Although some OC pesticides were banned 10-20 years ago,they are still present in ambient air in the Great Lakes (8).Some mechanisms such as transport from countries whereOC are still used and re-emissions from agricultural soils inpast usage region maintain current ambient levels. Therefore,high air concentration of an OC pesticide means it is currentlyused in a nearby area or had been transported from anotherregion.

The purpose of this paper is to study the presence of OCpesticides, previously used in the past or still currently, inthe atmosphere and precipitations which may present ahealth risk for people and the environment. R-HCH, γ-HCH,HCB, γ-chlordane, DDT, DDE, and Mirex were compoundsanalyzed in these studies which may be present in theenvironment. Temporal trends and temperature dependencewere examined in order to determine by which majorityprocesses those compounds were found in the atmosphere.

Materials and MethodsSampling Sites and Technique. The sampling stations werelocated at three sites along the St. Lawrence River, namely,St. Anicet, Villeroy, and Mingan. St. Anicet and Villeroy wererural areas (Figure 1) surrounded by farms and some woodedareas (9). St. Anicet was located at the entrance of the St.Lawrence River valley between Cornwall (Ontario) andMontreal (Quebec), 45°07′ N latitude and 74°17′ W longitude,while Villeroy was located about 10 km inland of the St.Lawrence River between Trois-Rivieres and Quebec City,46°26′ N latitude and 71°56′ W longitude. Mingan was aremote site located on the north shore of the St. LawrenceRiver between Sept-Iles and Havre St. Pierre, 50°16′ N latitudeand 64°14′ W longitude. Among the three sites, only St. Anicetwas located within the Quebec corn crop belt (see Figure 1).

Samples were collected from January 1993 throughDecember 1995 at Villeroy, from March 1994 throughDecember 1995 at St. Anicet, and from June 1994 throughJune 1995 at Mingan.

For air concentrations, samplers were installed on aplatform, 1 m above the ground. Andersen PS-1 high-volumesamplers were used to collect an air volume of approximately280-400 m3. Sampler heads held a 10.2-cm diameter glassfiber filter (GFF, Gelman) for particle collection followed bya polyurethane foam plug (height ) 8 cm, inside diameter(i.d.) ) 6 cm, density ) 0.022 g‚cm-3, weight ) 4.98 g), whichcollected vapor phase. Atmospheric (24 h) samples (vaporand particulate phases) were collected at 6-day intervals.

In concern of monthly precipitation concentrations, waterwas sampled by an automatic MIC (type B) precipitationcollector. Before sampling, the precipitation collector wasprerinsed by acetone and methanol. The volume of watercollected varied between 0 and 37 L. Precipitation sampleswere passed though glass fiber filters and extracted by XAD-2resin Teflon columns.

PUFs and filters were precleaned to remove any adsorbedorganic material through successive extraction with acetonefollowed by dichloromethane for 12 h in a Soxhlet apparatus.The PUFs and filters were dried in an oven for 12 h and thenstored in aluminum foil and sealed in separate plastic bags.In the field, the filter was installed on a metal grill filter holder,and the PUF was installed in an acetone prerinsed glasscylinder which, once placed in metal casing, screws onto thebottom of the filter holder. After sampling, the PUFs andfilters were stored at -12 °C until analysis (currently withina few weeks).

XAD-2 resin was precleaned by successive extractions for24 h in a Soxhlet apparatus with various solvents (3-4 cycles/h) in the following sequence: acetone, dichloromethane,and methanol. XAD-2 resin (50 mL) was then placed betweentwo layers of glass wool in Teflon columns (1.5 cm i.d × 30cm long) prerinsed by acetone, dichloromethane, andmethanol and stored in plastic bags until their use (10).

Analytical Methodology and Quality Control. The PUFs,the XAD-2 resin, and the filters were extracted for 24 h (3cycles/h) in a Soxhlet apparatus with 150 mL of dichlo-* Corresponding author e-mail: [email protected].

Environ. Sci. Technol. 2005, 39, 2960-2967

2960 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 9, 2005 10.1021/es048361s CCC: $30.25 Published 2005 by the Am. Chem. Soc.Published on Web 03/22/2005

romethane. PUFs, XAD-2, and filters were spiked prior toextraction with 1 mL of fortified solution containing internalisotopically labeled standards (i.e., d6-R-HCH; d8-p-p′-DDT)at a concentration of 100 pg‚µL-1. After volume reduction ofthe extract to 2 mL by evaporation and clean up, sampleswere fractionated by filtration through an Ag/Al/Silicachromatographic column using 30 mL of hexane. Chlorinatedand non-chlorinated compounds were then further separatedinto fractions by a chromatographic column on XAD-4 resin,the resulting eluate was evaporated to 2 mL, and the externalstandard was added. These fractionations were necessary toeliminate the interference in chromatographic separations.

Analyses were performed using a GC-MS (Fisons-MD800)in selected ion mode (SIM) equipped with a DB5 capillarycolumn (30 m long, 0.25 mm i.d., and 0.25 µm film thickness)operated with helium carrier gas at 1.8 mL‚min-1. The limitof detection by GC-MS is 900 fg‚µL-1, which represents about1 pg‚m-3 of air for the sampling volume used and about 0.4ng per rain sample.

Laboratory and field blanks were subject to the sameanalytical procedure as “samples”. Their concentrations weremostly undetectable or below the detection limits. The levelsof pesticides were in almost all cases smaller than 5% of thepesticide concentrations in samples. For spiked PUFs, XAD-

2, and filters, the recovery results were above 85% forγ-chlordane, DDE, DDT, and Mirex. For the most volatilecompounds HCB, R-HCH, and γ-HCH, the recovery resultswere comprised between 65 and 90%. Therefore, data hasbeen corrected with recovery results.

All sampling and analytical procedures were submittedto internal and external quality controls in order to ascertainthe quality of measurements. Participation in the IntegratedAtmospheric Deposition Network program in 1994 (11)provided quality control. All regression analyses and statisticalcalculations were performed with the Excel program and Ftests (12).

Results and DiscussionSpatial Time Series. The atmospheric median concentrationsof several OC pesticides during a 1-year sampling period atthe three sampling sites in air and precipitation are presentedin Tables 1 and 2, respectively. As particulate concentrationsrepresented less than 5% of gaseous concentrations for allsamples or under limit of detection, only the sum ofparticulate and gaseous concentrations will be discussed here.

r-HCH. R-HCH was the most important OC found inQuebec air and precipitation in the 1990s providing evidence

FIGURE 1. Location of the sampling sites and the extension of corn culture area in Quebec.

TABLE 1. Atmospheric Median Concentrations (pg‚m-3) of Several OC Pesticides Measured in Quebec from June 1, 1994 to June8, 1995 at St. Anicet, Villeroy, and Mingana

r-HCH HCB Lindane γ-chlordane DDE DDT Mirex

Villeroy 89 (74;115) 53 (35;74) 22 (9;50) 2 (2;7) 7 (3;9) 4 (2;4)St. Anicet 89 (72;111) 50 (38;74) 11 (2;67) 4 (2;10) 7 (5;17) 5 (2;7)Mingan 85 (66;120) 60 (44;81) 14 (8;18) 2 (2;2) 3 (2;4) 2 (2;3)

a The values in parentheses represent the 25th and 75th percentiles, respectively.

TABLE 2. Precipitation Median Concentrations (pg‚L-1) of Several OC Pesticides Measured in Quebec from June 1, 1994 to June8, 1995 at St. Anicet, Villeroy, and Mingana


Villeroy 2000 (1130;3500) 1280 (1000;2000) 30 (10;520)St. Anicet 1580 (300;2500) 1430 (260;2820) 510 (60;920) 890 (280;1570)Mingan 2790 (1620;3790) 60 (10;110) 510 (10;2370) 110 (50;120) 360 (90;610) 240 (80;440)

a The values in parentheses represent the 25th and 75th percentiles, respectively.

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of previous large use of technical HCH in this region for itsinsecticide properties and that transport was still active.Median R-HCH concentrations in air were recorded between80 and 90 pg‚m-3 at the three sites in Quebec highlightinga long-range distance transport or volatilization from soiland water (13). The concentrations were in similar range tothose reported in other North American studies (14-16). Ahigher variability was observed on the other hand inprecipitation than in air concentrations.

In concern of precipitation samples, concentrations werehigher for Mingan than Villeroy and St. Anicet. It might beexplained by the fact that Mingan was much closer to theocean (17) where important amounts might be volatilizedfrom the ocean or by a lower average annual temperatureat this place. This is in agreement with other studies thatshowed that this compound was in more important con-centrations at higher latitudes levels because of lowertemperatures allowing the condensation of this species (18).

Lindane. Lindane was one of the major OC pesticidesdominating air and precipitation concentrations. Lindane isthe γ-HCH isomer and is still in use in Canada (registrationrevocation in December 2004) since technical HCH com-pounds have been banned from Canada in the 1970s. Despitethat, air concentrations were 4-8 times lower than the R-HCHisomer. This is due to a seasonal use of Lindane during spring/summer application and a reduced amount of the γ-HCHisomer needed to obtain the same insecticide efficiency asthe technical HCH. More Lindane was found in precipitationsamples compared to R-HCH due to a higher solubility ofthe γ-HCH isomer (9).

In air samples, Lindane was present in slightly higherconcentrations at the Villeroy station during this period.Villeroy was mostly influenced by Lindane uses from a largecorn culture area (Figure 1) just located at 50 km southwestof the site. In precipitation samples, Lindane concentrationswere much lower in Mingan due to a contribution ofprecipitating water coming from the Atlantic Ocean wherelindane concentrations should be lower than inland watercontaminated by pesticide applications on soils (19). Moredetailed results of both R-HCH and γ-HCH isomers havealready been presented in Garmouma and Poissant (17).

HCB. HCB had also been observed in notable air concen-trations in Quebec, whereas it was at very low concentrationsor undetected in precipitation samples due to its highvolatility (elevated Henry’s Law constant: 134 Pa‚m3‚mol-1

at 25C). Median concentrations varied from 50 to 59 pg‚m-3

from June 1, 1994 to June 8, 1995. HCB has multiple sources;it was employed as fungicide on seeds and cereals until 1972and is still used for industrials applications as solvents,dielectric fluids, and the synthesis of organic compounds.Moreover, it is also emitted by waste incineration and themanufacturing of paintings, coal, steel, and pulp paper. HCBis also believed to be extremely persistent in the environment,and due to reaction with the hydroxyl radical, it has anatmospheric lifetime of about 80 days (20), allowing a long-range transport. HCB was relatively uniformly distributedand in the range of what was measured in the Arctic (21),reflecting its persistence and high degree of mixing in air.

γ-Chlordane. γ-Chlordane is one of the 140 compounds(22, 23) contained in the technical chlordane previously usedin Canada and the U.S. for its insecticide properties. Becauseof its extremely toxic nature, chlordane usage was restrictedto termiticide applications and banned in the late 1980s inmost countries even if it was still in use in Mexico (24). Thechlordane found in ambient air today may emanate fromresidues in agricultural soils and from volatilization oftermiticides applied to buildings. The median concentrationof γ-chlordane was always below 4 pg‚m-3 for all sites whichis in agreement with the restricted use of this pesticide forseveral years.

DDT and DDE. DDT is one of the most famous pesticidesfor its known harmful effects on peoples’ health and itsimplication on the decreasing number of various species,notably the bald eagle (25). DDT affects the liver, nervousand reproductive systems, and probably causes cancer inhumans. However it was not officially banned until 1989 inCanada and might have been in use in South Americancountries (26). In soil, DDT is microbially transformed to thestable and toxic metabolites DDE and DDD (27 and referencestherein). As for γ-chlordane, DDT median concentration wasbelow 4 pg‚m-3 for all the sites and is thus less disturbingconcerning its toxicity. In general, a ratio DDT/DDE > 1 isindicative of fresh application confirming that DDT presencein Quebec (DDT/DDE < 0.8) was due to past uses or transportfrom South America where it may be still in use. Despiteeverything, some events which presented a higher ratiosuggest that more recent applications of DDT have occurredin foreign countries.

Mirex. Mirex was used as insecticide in many countriesexcept in Canada. On the other hand, it was also employedto make plastics resistant to fire, for the preparation of certainpaintings, and in the products against intestinal worms. Since1978, Canada does not allow the importation, the treatment,or the production of Mirex if those activities can result in anemission in the environment. Mirex was not measured abovedetection limit concentrations providing evidence that thispesticide was not used in Quebec and close areas.

Annual Time Series. Annual times series for several OCand temperature variations at the three sites are shown inFigures 2 and 3. No time-series data are presented for Mirexdue to low concentrations that were below the detectionlimit as discussed above. Particulate atmospheric OC con-centrations were also neglected for the same reason.

Most of the OC compounds had seasonal cycles in air,whereas it was less obvious for precipitation. In the air, thecompounds such as R-HCH, lindane, γ-chlordane, DDT, andDDE showed maximum concentrations in spring/summer,contrary to HCB, which presents higher concentrations inwinters.

For old unused pesticides and their metabolites (R-HCH,γ-chlordane, DDT, and DDE), the higher summer concen-trations were the result of volatilization from soil and waterduring the warm season. R-HCH appears to be more variableat the Mingan site (ranging from 34 to 153 pg‚m-3 duringJune 1994 to June 1995) than the St. Anicet site (ranging from60 to 127 pg‚m-3 during March 1994 to March 1996). It mightbe related to the proximity of Mingan from the Atlantic coastsubject to large volatilization from the ocean during summerperiods. On the contrary, it should be noted that for DDEand γ-chlordane the variability of the concentrations wasmuch more important at the Villeroy and St. Anicet sitesthan at the Mingan site assuming a greater storage of thesespecies in soil than in seawater.

In concern of Lindane, which was still in use, sharpincreases in air and precipitation concentrations (from 0 to175 pg‚m-3 and from 0 to 15 ng‚L-1) occurred during the latespring/early summer period. It corresponded to the ap-plications of this pesticide in the fields as reported in paststudies by Poissant and Koprivnjak (28). This trend was betterobserved at the Villeroy and St. Anicet sites where Lindanesources were much closer than at the Mingan site.

The higher abundance of HCB in winter might result ingreater urban air emission sources of HCB such as combus-tions and incineration (29). It was also possible that HCB canundergo “cold condensation” onto solid phases from theatmospheric gas phases as it was observed in other studiesin Europe where higher HCB concentrations were found incolder, northerly latitudes (30, 31).

Temperature Dependence and Air-Water Equilibrium.If the amount of OC that is present in the atmosphere is

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partly controlled by temperature-dependent revolatilizationfrom soils, vegetation, and water bodies, the measuredconcentrations should be related to ambient temperature(28). It was previously shown that some OC presented aseasonal pattern, following temperature variations. This pointis discussed in this section.

The volatilization of SVOCs (semivolatile organic com-pounds) from surface to air depends on several physical andchemical properties among which the vapor pressure andthe enthalpy of vaporization of the chemicals (32, 33) are themost important. The vapor pressure temperature dependencyof the compound is well defined by the Clausius-Clapeyronequation when the system is at equilibrium. The logarithmof the gas-phase concentration or the partial pressure (of thegas) can be plotted against reciprocal temperature (eq 1)

where P is the partial pressure of the compound (in atm), ∆His the enthalpy of vaporization of the compound (kJ‚mol-1),R is the gas constant, and T is the average temperature duringthe day of sampling (in Kelvin). Because the partial pressureis proportional to the concentrations interpretations will bebased on the ln of concentrations. Regression coefficientsobtained for ln(concn) ) f(1/T) and ∆Hexp calculated fromthe slope of the correlation curve for R-HCH, HCB, lindane,γ-chlordane, DDE, DDT, and Mirex are summarized in Tables3 and 4, respectively. An example plot of ln(concn) ) f(1/T)is presented in Figure 4. The more the values presented inTable 3 are close to 1, the better is the correlation betweenthe observed concentrations and the temperature. The valuesobtained when the atmospheric temperature was below 273K were not used for the calculations due to the nonlinearity

of the Clausius-Clapeyron plot for SVOCs below thistemperature (34). Data for compounds present in concen-trations below the detection limit were not included in thecalculations.

The equilibrium distribution of a chemical in air and wateris defined by the Henry’s Law constant. When the chemicalis in equilibrium, the experimental Henry’s Law constant(Hexp) is estimated by the following equation

where Ca,eq and Cw,eq are the concentrations of gaseous anddissolved OC assumed to be in equilibrium in air and water(both in ng‚m-3), RC is the gas constant and is equal to 8.314J‚mol-1‚K-1, and T is the temperature in units of Kelvins.

The theoretical value of H at a given temperature can becalculated from the Henry’s Law constant at a referencetemperature and the enthalpy of vaporization by therelationship (35)

where Hth is the dimensional (Pa‚m3‚mol-1) Henry’s Lawcoefficient at the Kelvin temperature TT, ∆HV,T is the enthalpyof vaporization at TT in units of J‚mol-1, and TR is the referencetemperature for Henry’s Law (HR) in K. The enthalpy ofvaporization, ∆HV,T, is estimated from (36)

where ∆HV,B is the enthalpy of vaporization at the normal

FIGURE 2. Evolution of air OC concentrations at (A) Villeroy, (B) St. Anicet, and (C) Mingan.

ln P ) - ∆HR (1

T) + constant (1)

Hexp )Ca,eq

Cw,eqRCT (2)

Hth ) HR exp[-∆HV,T

RC( 1TT

- 1TR

)] (3)

∆HV,T ) ∆HV,B[1 - TT/TC

1 - TB/TC]n

(4)


boiling point (J‚mol-1), TB is the normal boiling point in K,and TC is the critical temperature in K. The exponent n isselected from the TB/Tc ratio as presented in Table 5.

The equilibrium state of a compound between air andwater can be studied from comparison of the Henry’s lawconstant (Hexp) calculated from air and precipitation mea-surements by eq 2, with the one calculated from thetheoretical value (Hth) at a reference temperature by eq 3.The Hexp/Hth ratio is presented in Table 6. A ratio greater orless than 1 indicated that the compound is close to the air-water equilibrium, whereas a ratio distant to 1 indicates thatother processes than air-water exchange are dominant.

The temperature dependence does not appear to besimilar for the different OCs at the three different sites.Moreover, regression coefficients shown in Table 3 are alwayslower than 0.5, indicating that only a part of the variabilitycan be explained by temperature fluctuations. In general, adifference between Villeroy and St. Anicet (continental sites)on one hand and Mingan (coastal site) on the other handwas observed. For continental sites, temperature dependenceof R-HCH levels appears to be weaker than for the coastalsite, whereas the contrary is observed for HCB.

We suggest that the lack of temperature relationship forthe R-HCH species may be due to the fact that continentalsites are relatively distant from areas of recent HCH use.Therefore re-evaporation of this species close to the samplingsites should be limited. It was rather likely that the most ofthe measured R-HCH had been advected into the samplingarea as it was also observed in some previous studies inOntario (37), Minnesota (38), and in southern Norway (39).The better correlation observed for the coastal site must bedue to the proximity of the Atlantic Ocean. The enthalpy ofvaporization calculated from the slope of the correlation curve(Table 4) was closer to the theoretical value for this location

than the two continental sites, indicating the relatively greaterimportance of volatilization. This may also indicate that themajor source of R-HCH was the Atlantic Ocean from whereit was volatilized and transported inland as described byGarmouma and Poissant (17). Moreover, a gradient of thecalculated enthalpy of volatilization with latitude wasobserved. The calculated value was much more importantas the latitude increase (R ) 0.99998 with p < 0.01) due toa preferential partitioning into water at colder temperatures(21). These observations seem to show that R-HCH wasmainly stored in water as confirmed by the Hexp/Hth ratioclose to 1, indicating a relatively good air/water balance.

In concern of HCB, even if regression coefficients aresignificant, the calculated enthalpy of vaporization is ab-solutely different than the theoretical value. Values below 0indicate an anticorrelation with temperature, which meansthat HCB concentrations in air were higher with coldertemperatures due to greater urban air emission sources or“cold condensation” onto solid phases as explained previ-ously. Mingan did not observe any correlation with tem-perature in consequence of its distance to anthropogenicactivities. HCB that was present at this site was exclusivelytransported from other regions; no local source had beenexpected to occur in this location. The Hexp/Hth ratio wasvery different than 1 since HCB has a low solubility indicatingweak exchange between air and water.

As DDE is one of the DDT metabolites, these twocompounds will be discussed together. DDE levels show asignificant dependence on temperature at continental sites,whereas no dependence of this compound was observed atthe coastal site. Moreover, no temperature dependence wasnoted for DDT at any place. The enthalpies of vaporizationcalculated for DDT at these three sites were very differentfrom the theoretical value, which implies that no DDT

FIGURE 3. Evolution of precipitation OC concentrations at (A) Villeroy, (B) St. Anicet, and (C) Mingan.


volatilization should occur from soil. Long-range transportfrom other areas, for example, Southern U.S. (15) or Asia, isa more probable source. In concern of DDE, the calculatedenthalpies of vaporization were closer to the theoretical valueat continental sites than the coastal one. It is probable thatDDT was used in Quebec and that the soils were stillcontaining a detectable amount of its metabolite DDE. Thiscompound, resulting from the decomposition of the DDT,was gradually re-emitted in the atmosphere by volatilizationwhen the temperatures were high in summer. A fraction ofthe DDE might also come from atmospheric long-range

transport. The Hexp/Hth ratio was far from the theoreticalvalue, confirming that atmospheric DDE is rather volatilizedfrom soil than from water. The same trends were observedfor DDT giving evidence that these two species may not bestored in the Atlantic Ocean due to their low solubility (40).

Then, Lindane presented a moderate correlation withreciprocal temperature without any clear distinction betweencontinental and coastal sites. For this species, the calculatedenthalpies of vaporization were very close to the theoreticalvalue providing evidence of re-evaporation from surface.Because Lindane has had a long history of use in Quebecand elsewhere, continuous exchange between environmentalcompartments can be expected. Lindane concentrationsdepend on the temperature but also on emissions. Inconnection with temperature relationship, volatilizationseems to occur as well in soils as in seawater. As the Hexp/Hth

ratio is much weaker than 1, it was assumed that exchangebetween air and water was lower than exchange between airand soil or that steady state was not applicable due to freshuse of Lindane.

Last, γ-chlordane also presented a moderate correlationwith reciprocal temperature and calculated enthalpies ofvaporization close to the theoretical value for the three sites.Because the Hexp/Hth ratio is very different from 1, the air-water balance does not seem to be reached for this species,reflecting a preferential vaporization from soil where chlo-rdane was in use.

Influence of Snow/Ice on Pesticide Concentrations.Snow and ice are present in the polar region, at high altitude,

TABLE 3. Regression Coefficients between ln Concentrationand the Reciprocal Temperature of Several OC PesticidesMeasured in Quebec during the Sampling Periods at St.Anicet, Villeroy, and Mingan


Villeroy 0.10 0.41 0.21 0.18 0.25 0.005St. Anicet 0.0041 0.31 0.24 0.30 0.18 0.029Mingan 0.24 0.0041 0.17 0.34 0.036 0.061

TABLE 4. Experimental Enthalpy of Vaporization ∆Hexp(kJ‚mol-1) Calculated from the Slope of the LinearCorrelation between ln Concentration and the ReciprocalTemperature of Several OC Pesticides Used in Quebec duringthe Sampling Periods at St. Anicet, Villeroy, and Mingan


Villeroy 8 -57 43 49 36 -5St. Anicet 2 -30 55 46 31 14Mingan 26 5 45 36 24 23∆Hth 63 60 63 57 63 92

FIGURE 4. Ln of the Lindane concentrations plotted against thereciprocal of the temperature at Villeroy during the 1993-1996 period.The solid line is the regression of the data.

FIGURE 5. Weekly median concentration of r-HCH (full black line) during the 1993-1995 period and temperature (dotted black line) atVilleroy compared to the modelized concentrations (full and dotted gray lines) obtained by Daly and Wania (44). Model calculation wasmade for specific snow surface area of 0.1 m2‚g-1.

TABLE 5. Value of Exponent n According to the TB/TC Ratio

TB/TC ratio n

<0.57 0.300.57-0.71 0.74(TB/TC) - 0.116

>0.71 0.41

TABLE 6. Experimental Henry’s Law Coefficient to TheoreticalHenry’s Law Coefficient Ratio of Several OC PesticidesMeasured in Quebec during the Sampling Periods at St.Anicet, Villeroy, and Mingan


Villeroy 0.483 0.099 0.098 0.107 0.044 0.200St. Anicet 0.435 0.019 0.225 0.071 0.101 0.144Mingan 0.499 0.026 0.132 0.078 0.147 0.178Hth (Pa‚m3/

mol-1)(25 °C)

1.07 134 1.42 4.91 2.13 0.821


and in winter at high latitude areas affecting the fate andchemical reaction of pollutants (21, 41). Organic chemicalsin the atmosphere can be scavenged during snowfall events(42), released, or taken up by the snowpack (43), usuallydecreasing atmospheric concentrations in the lower layers.Moreover, the presence of a snowpack can prevent exchangeof gaseous pollutants between the atmosphere, lakes, rivers,or seawater and soil. On the contrary, during the meltingperiod, chemicals formerly adsorbed into the snowpack arequickly volatilized in the atmosphere leading to an increaseof the atmospheric concentrations.

Quebec experiences winter weather for 3-5 months eachyear, and the effect of snowpack and low temperatures inreducing volatilization is reflected by reduced concentrationsof some pesticides during winter months (Figures 2). It wasthe case for γ-chlordane and DDE at St. Anicet and Villeroy,which were mainly contained in soil in these two sites. Indeed,concentrations decreased sharply when temperatures werebecoming lower than 0 °C and almost undetectable duringthe colder period. Then, concentrations increased suddenlywhen temperatures rose above 0 °C after the winter period.It is supposed that these organic chemicals were volatilizedfrom soil during spring, summer, and autumn seasons, butduring winter, no volatilization could occur because of thesnowpack that prevents exchange between air and soil.

R-HCH presents a slightly different pattern. The monthlymedian atmospheric concentration at Villeroy is presentedin Figure 5. This result is close to the modelized airconcentrations simulated by Daly and Wania (44) for R-HCH.During December, January, and February, concentrationswere lower than the remaining year due to successive snowfallevents that scavenge chemicals. In March during the snow-melting season; concentrations increased drastically due toquick volatilization from the snowpack until the beginningof May. Concentrations were even higher than in summer.After May, concentrations decreased to a value generallyincluded between 70 and 100 pg‚m-3 until the end ofNovember. On the other hand, a concentration of 120 pg‚m-3

was observed in November which was much higher than itshould be for this season. It might be explained by a snowfallperiod at the beginning of November (temperature below 0°C) followed by a short thaw period at the end of the month(temperature above 0 °C) with quick volatilization of R-HCHscavenged a few weeks before. The effect of the snow wasalso observed at the St. Anicet and Mingan sites (not shown).

This effect shows that the temperature dependence fororganic compounds could be disturbed by the influence ofsnowfall events and snowpack presence. This phenomenoncould explain the relatively weak correlation coefficientsfound for some pesticides in this study.

AcknowledgmentsThe authors would like to thank Jean-Francois Koprivnjak(formerly from Environment Canada) for his field work andMichel Bertrand (University of Montreal) for his laboratorywork and support. This project is a result of the St. LawrenceAction Plan (Phases II and III). F.A. would like to thank theMeteorological Service of Canada and SLAP IV for supportinghis NSERC Canadian Laboratory postdoctoral fellowship.Also, thanks to Antoinette Taddeo and Sofia Khodorkovskayafor their help in rereading this paper.

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Received for review October 20, 2004. Revised manuscriptreceived January 25, 2005. Accepted February 9, 2005.

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some pesticides occurrence in air and precipitation in québec, canada

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