Some Pesticides Occurrence in Air and Precipitation in Québec, Canada

Mar 22, 2005 - Higher concentrations levels were observed in air during hot ..... subject to large volatilization from the ocean during summer periods...
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Environ. Sci. Technol. 2005, 39, 2960-2967

Some Pesticides Occurrence in Air and Precipitation in Que´ bec, Canada FABIEN AULAGNIER AND LAURIER POISSANT* Section on Atmospheric Toxic Processes, Meteorological Service of Canada, Environment Canada, 105 McGill Street, Seventh Floor (Youville), Montre´al, Que´bec, Canada H2Y 2E7

The purpose of this paper is to study the presence of OC pesticides, previously used in the past or still currently, in the atmosphere and precipitations which may present a health risk for people and the environment. R-HCH, γ-HCH, HCB, γ-chlordane, DDT, DDE, and Mirex were compounds analyzed in these studies which may be present in the environment. Temporal trends and temperature dependence were examined in order to determine by which majority processes those compounds were found in the atmosphere.

Materials and Methods Air and precipitation samples were collected in three stations located in Que´ bec between January 1993 and March 1996 to determine spatial and seasonal variations of several organochlorine pesticides and metabolites (RHCH, γ-HCH, HCB, γ-chlordane, DDT, DDE, Mirex). R-HCH, γ-HCH, and HCB were more or less measured in large amounts at all sites, whereas γ-chlordane, DDT, and DDE concentrations were lower and Mirex was undetectable. Higher concentrations levels were observed in air during hot spring/summer periods except for HCB, indicating a probable temperature dependence. Ln concentrations vs reciprocal temperature plots and Henry’s law determinations helped to highlight the contribution of soil and/or water volatilization of those compounds. It was observed that R-HCH came mainly from Atlantic Ocean volatilization at Mingan, whereas sources of γ-chlordane and DDE were mostly due to volatilization from soils in southern Que´ bec. DDT may be present in the atmosphere by the way of transport from remote regions. Lindane sources were multiple: it may be found in the atmosphere by the processes of transport and volatilization coming from soil or water. Finally, a negative correlation between HCB and air temperature implies that processes other than volatilization are involved in transport of this compound.

Introduction In the past, extensive use of persistent organic pollutants (POPs) in Que´bec and other regions has led to the dispersal of these pollutants throughout the global environment (13) and bioaccumulation through food chains (4). This has focused international regulation on reducing emissions to air as UNECE protocol (5) and UNEP report (6). In Que´bec, a significant part of pesticide usage is due to the corn cultivation where production is increasing every year. The total corn surface area (grain, fodder, and sweetened) was about 350 000 hectares during the 1993-1996 period. It has increased by approximately 29% between 1996 and 2001 and covers currently ∼500 000 hectares (7). Soya cultivations, which also use large amount of organochlorine (OC) pesticides, made great strides in Que´bec 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 where OC are still used and re-emissions from agricultural soils in past usage region maintain current ambient levels. Therefore, high air concentration of an OC pesticide means it is currently used in a nearby area or had been transported from another region. * Corresponding author e-mail: [email protected]. 2960 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 9, 2005

Sampling Sites and Technique. The sampling stations were located at three sites along the St. Lawrence River, namely, St. Anicet, Villeroy, and Mingan. St. Anicet and Villeroy were rural areas (Figure 1) surrounded by farms and some wooded areas (9). St. Anicet was located at the entrance of the St. Lawrence River valley between Cornwall (Ontario) and Montre´al (Que´bec), 45°07′ N latitude and 74°17′ W longitude, while Villeroy was located about 10 km inland of the St. Lawrence River between Trois-Rivie`res and Que´bec City, 46°26′ N latitude and 71°56′ W longitude. Mingan was a remote site located on the north shore of the St. Lawrence River between Sept-Iles and Havre St. Pierre, 50°16′ N latitude and 64°14′ W longitude. Among the three sites, only St. Anicet was located within the Que´bec corn crop belt (see Figure 1). Samples were collected from January 1993 through December 1995 at Villeroy, from March 1994 through December 1995 at St. Anicet, and from June 1994 through June 1995 at Mingan. For air concentrations, samplers were installed on a platform, 1 m above the ground. Andersen PS-1 high-volume samplers were used to collect an air volume of approximately 280-400 m3. Sampler heads held a 10.2-cm diameter glass fiber filter (GFF, Gelman) for particle collection followed by a polyurethane foam plug (height ) 8 cm, inside diameter (i.d.) ) 6 cm, density ) 0.022 g‚cm-3, weight ) 4.98 g), which collected vapor phase. Atmospheric (24 h) samples (vapor and particulate phases) were collected at 6-day intervals. In concern of monthly precipitation concentrations, water was sampled by an automatic MIC (type B) precipitation collector. Before sampling, the precipitation collector was prerinsed by acetone and methanol. The volume of water collected varied between 0 and 37 L. Precipitation samples were passed though glass fiber filters and extracted by XAD-2 resin Teflon columns. PUFs and filters were precleaned to remove any adsorbed organic material through successive extraction with acetone followed by dichloromethane for 12 h in a Soxhlet apparatus. The PUFs and filters were dried in an oven for 12 h and then stored 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 glass cylinder which, once placed in metal casing, screws onto the bottom of the filter holder. After sampling, the PUFs and filters were stored at -12 °C until analysis (currently within a few weeks). XAD-2 resin was precleaned by successive extractions for 24 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 between two layers of glass wool in Teflon columns (1.5 cm i.d × 30 cm long) prerinsed by acetone, dichloromethane, and methanol 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 (3 cycles/h) in a Soxhlet apparatus with 150 mL of dichlo10.1021/es048361s CCC: $30.25

Published 2005 by the Am. Chem. Soc. Published on Web 03/22/2005

FIGURE 1. Location of the sampling sites and the extension of corn culture area in Que´ bec.

TABLE 1. Atmospheric Median Concentrations (pg‚m-3) of Several OC Pesticides Measured in Que´ bec from June 1, 1994 to June 8, 1995 at St. Anicet, Villeroy, and Mingana Villeroy St. Anicet Mingan a

r-HCH

HCB

Lindane

γ-chlordane

DDE

DDT

89 (74;115) 89 (72;111) 85 (66;120)

53 (35;74) 50 (38;74) 60 (44;81)

22 (9;50) 11 (2;67) 14 (8;18)

2 (2;7) 4 (2;10) 2 (2;2)

7 (3;9) 7 (5;17) 3 (2;4)

4 (2;4) 5 (2;7) 2 (2;3)

Mirex

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 Que´ bec from June 1, 1994 to June 8, 1995 at St. Anicet, Villeroy, and Mingana r-HCH Villeroy St. Anicet Mingan a

2000 (1130;3500) 1580 (300;2500) 2790 (1620;3790)

HCB

Lindane

60 (10;110)

1280 (1000;2000) 1430 (260;2820) 510 (10;2370)

γ-chlordane

DDE

DDT

110 (50;120)

30 (10;520) 510 (60;920) 360 (90;610)

890 (280;1570) 240 (80;440)

Mirex

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

romethane. PUFs, XAD-2, and filters were spiked prior to extraction with 1 mL of fortified solution containing internal isotopically labeled standards (i.e., d6-R-HCH; d8-p-p′-DDT) at a concentration of 100 pg‚µL-1. After volume reduction of the extract to 2 mL by evaporation and clean up, samples were fractionated by filtration through an Ag/Al/Silica chromatographic column using 30 mL of hexane. Chlorinated and non-chlorinated compounds were then further separated into fractions by a chromatographic column on XAD-4 resin, the resulting eluate was evaporated to 2 mL, and the external standard was added. These fractionations were necessary to eliminate the interference in chromatographic separations. Analyses were performed using a GC-MS (Fisons-MD800) in selected ion mode (SIM) equipped with a DB5 capillary column (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 limit of detection by GC-MS is 900 fg‚µL-1, which represents about 1 pg‚m-3 of air for the sampling volume used and about 0.4 ng per rain sample. Laboratory and field blanks were subject to the same analytical procedure as “samples”. Their concentrations were mostly undetectable or below the detection limits. The levels of pesticides were in almost all cases smaller than 5% of the pesticide concentrations in samples. For spiked PUFs, XAD-

2, and filters, the recovery results were above 85% for γ-chlordane, DDE, DDT, and Mirex. For the most volatile compounds HCB, R-HCH, and γ-HCH, the recovery results were comprised between 65 and 90%. Therefore, data has been corrected with recovery results. All sampling and analytical procedures were submitted to internal and external quality controls in order to ascertain the quality of measurements. Participation in the Integrated Atmospheric Deposition Network program in 1994 (11) provided quality control. All regression analyses and statistical calculations were performed with the Excel program and F tests (12).

Results and Discussion Spatial Time Series. The atmospheric median concentrations of several OC pesticides during a 1-year sampling period at the three sampling sites in air and precipitation are presented in Tables 1 and 2, respectively. As particulate concentrations represented less than 5% of gaseous concentrations for all samples or under limit of detection, only the sum of particulate and gaseous concentrations will be discussed here. r-HCH. R-HCH was the most important OC found in Que´bec air and precipitation in the 1990s providing evidence VOL. 39, NO. 9, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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of previous large use of technical HCH in this region for its insecticide properties and that transport was still active. Median R-HCH concentrations in air were recorded between 80 and 90 pg‚m-3 at the three sites in Que´bec highlighting a long-range distance transport or volatilization from soil and water (13). The concentrations were in similar range to those reported in other North American studies (14-16). A higher variability was observed on the other hand in precipitation than in air concentrations. In concern of precipitation samples, concentrations were higher for Mingan than Villeroy and St. Anicet. It might be explained by the fact that Mingan was much closer to the ocean (17) where important amounts might be volatilized from the ocean or by a lower average annual temperature at this place. This is in agreement with other studies that showed that this compound was in more important concentrations at higher latitudes levels because of lower temperatures allowing the condensation of this species (18). Lindane. Lindane was one of the major OC pesticides dominating air and precipitation concentrations. Lindane is the γ-HCH isomer and is still in use in Canada (registration revocation in December 2004) since technical HCH compounds have been banned from Canada in the 1970s. Despite that, air concentrations were 4-8 times lower than the R-HCH isomer. This is due to a seasonal use of Lindane during spring/ summer application and a reduced amount of the γ-HCH isomer needed to obtain the same insecticide efficiency as the technical HCH. More Lindane was found in precipitation samples compared to R-HCH due to a higher solubility of the γ-HCH isomer (9). In air samples, Lindane was present in slightly higher concentrations at the Villeroy station during this period. Villeroy was mostly influenced by Lindane uses from a large corn culture area (Figure 1) just located at 50 km southwest of the site. In precipitation samples, Lindane concentrations were much lower in Mingan due to a contribution of precipitating water coming from the Atlantic Ocean where lindane concentrations should be lower than inland water contaminated by pesticide applications on soils (19). More detailed results of both R-HCH and γ-HCH isomers have already been presented in Garmouma and Poissant (17). HCB. HCB had also been observed in notable air concentrations in Que´bec, whereas it was at very low concentrations or undetected in precipitation samples due to its high volatility (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 1972 and 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 the manufacturing of paintings, coal, steel, and pulp paper. HCB is also believed to be extremely persistent in the environment, and due to reaction with the hydroxyl radical, it has an atmospheric lifetime of about 80 days (20), allowing a longrange transport. HCB was relatively uniformly distributed and 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 used in Canada and the U.S. for its insecticide properties. Because of its extremely toxic nature, chlordane usage was restricted to termiticide applications and banned in the late 1980s in most countries even if it was still in use in Mexico (24). The chlordane found in ambient air today may emanate from residues in agricultural soils and from volatilization of termiticides applied to buildings. The median concentration of γ-chlordane was always below 4 pg‚m-3 for all sites which is in agreement with the restricted use of this pesticide for several years. 2962

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DDT and DDE. DDT is one of the most famous pesticides for its known harmful effects on peoples’ health and its implication on the decreasing number of various species, notably the bald eagle (25). DDT affects the liver, nervous and reproductive systems, and probably causes cancer in humans. However it was not officially banned until 1989 in Canada and might have been in use in South American countries (26). In soil, DDT is microbially transformed to the stable and toxic metabolites DDE and DDD (27 and references therein). As for γ-chlordane, DDT median concentration was below 4 pg‚m-3 for all the sites and is thus less disturbing concerning its toxicity. In general, a ratio DDT/DDE > 1 is indicative of fresh application confirming that DDT presence in Que´bec (DDT/DDE < 0.8) was due to past uses or transport from South America where it may be still in use. Despite everything, some events which presented a higher ratio suggest that more recent applications of DDT have occurred in foreign countries. Mirex. Mirex was used as insecticide in many countries except in Canada. On the other hand, it was also employed to make plastics resistant to fire, for the preparation of certain paintings, and in the products against intestinal worms. Since 1978, Canada does not allow the importation, the treatment, or the production of Mirex if those activities can result in an emission in the environment. Mirex was not measured above detection limit concentrations providing evidence that this pesticide was not used in Que´bec and close areas. Annual Time Series. Annual times series for several OC and temperature variations at the three sites are shown in Figures 2 and 3. No time-series data are presented for Mirex due to low concentrations that were below the detection limit as discussed above. Particulate atmospheric OC concentrations 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, the compounds such as R-HCH, lindane, γ-chlordane, DDT, and DDE showed maximum concentrations in spring/summer, contrary to HCB, which presents higher concentrations in winters. For old unused pesticides and their metabolites (R-HCH, γ-chlordane, DDT, and DDE), the higher summer concentrations were the result of volatilization from soil and water during the warm season. R-HCH appears to be more variable at the Mingan site (ranging from 34 to 153 pg‚m-3 during June 1994 to June 1995) than the St. Anicet site (ranging from 60 to 127 pg‚m-3 during March 1994 to March 1996). It might be related to the proximity of Mingan from the Atlantic coast subject to large volatilization from the ocean during summer periods. On the contrary, it should be noted that for DDE and γ-chlordane the variability of the concentrations was much more important at the Villeroy and St. Anicet sites than at the Mingan site assuming a greater storage of these species in soil than in seawater. In concern of Lindane, which was still in use, sharp increases in air and precipitation concentrations (from 0 to 175 pg‚m-3 and from 0 to 15 ng‚L-1) occurred during the late spring/early summer period. It corresponded to the applications of this pesticide in the fields as reported in past studies by Poissant and Koprivnjak (28). This trend was better observed at the Villeroy and St. Anicet sites where Lindane sources were much closer than at the Mingan site. The higher abundance of HCB in winter might result in greater urban air emission sources of HCB such as combustions and incineration (29). It was also possible that HCB can undergo “cold condensation” onto solid phases from the atmospheric gas phases as it was observed in other studies in Europe where higher HCB concentrations were found in colder, northerly latitudes (30, 31). Temperature Dependence and Air-Water Equilibrium. If the amount of OC that is present in the atmosphere is

FIGURE 2. Evolution of air OC concentrations at (A) Villeroy, (B) St. Anicet, and (C) Mingan. partly controlled by temperature-dependent revolatilization from soils, vegetation, and water bodies, the measured concentrations should be related to ambient temperature (28). It was previously shown that some OC presented a seasonal pattern, following temperature variations. This point is discussed in this section. The volatilization of SVOCs (semivolatile organic compounds) from surface to air depends on several physical and chemical properties among which the vapor pressure and the enthalpy of vaporization of the chemicals (32, 33) are the most important. The vapor pressure temperature dependency of the compound is well defined by the Clausius-Clapeyron equation when the system is at equilibrium. The logarithm of the gas-phase concentration or the partial pressure (of the gas) can be plotted against reciprocal temperature (eq 1)

ln P ) -

∆H 1 + constant R T

()

(1)

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

of the Clausius-Clapeyron plot for SVOCs below this temperature (34). Data for compounds present in concentrations below the detection limit were not included in the calculations. The equilibrium distribution of a chemical in air and water is defined by the Henry’s Law constant. When the chemical is in equilibrium, the experimental Henry’s Law constant (Hexp) is estimated by the following equation

Hexp )

Ca,eq R T Cw,eq C

(2)

where Ca,eq and Cw,eq are the concentrations of gaseous and dissolved OC assumed to be in equilibrium in air and water (both in ng‚m-3), RC is the gas constant and is equal to 8.314 J‚mol-1‚K-1, and T is the temperature in units of Kelvins. The theoretical value of H at a given temperature can be calculated from the Henry’s Law constant at a reference temperature and the enthalpy of vaporization by the relationship (35)

Hth ) HR exp

[

(

-∆HV,T 1 1 RC TT TR

)]

(3)

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

∆HV,T ) ∆HV,B

[

1 - TT/TC 1 - TB/TC

]

n

(4)

where ∆HV,B is the enthalpy of vaporization at the normal VOL. 39, NO. 9, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. Evolution of precipitation OC concentrations at (A) Villeroy, (B) St. Anicet, and (C) Mingan. boiling point (J‚mol-1), TB is the normal boiling point in K, and TC is the critical temperature in K. The exponent n is selected from the TB/Tc ratio as presented in Table 5. The equilibrium state of a compound between air and water can be studied from comparison of the Henry’s law constant (Hexp) calculated from air and precipitation measurements by eq 2, with the one calculated from the theoretical value (Hth) at a reference temperature by eq 3. The Hexp/Hth ratio is presented in Table 6. A ratio greater or less than 1 indicated that the compound is close to the airwater equilibrium, whereas a ratio distant to 1 indicates that other processes than air-water exchange are dominant. The temperature dependence does not appear to be similar for the different OCs at the three different sites. Moreover, regression coefficients shown in Table 3 are always lower than 0.5, indicating that only a part of the variability can be explained by temperature fluctuations. In general, a difference between Villeroy and St. Anicet (continental sites) on one hand and Mingan (coastal site) on the other hand was observed. For continental sites, temperature dependence of R-HCH levels appears to be weaker than for the coastal site, whereas the contrary is observed for HCB. We suggest that the lack of temperature relationship for the R-HCH species may be due to the fact that continental sites are relatively distant from areas of recent HCH use. Therefore re-evaporation of this species close to the sampling sites should be limited. It was rather likely that the most of the measured R-HCH had been advected into the sampling area as it was also observed in some previous studies in Ontario (37), Minnesota (38), and in southern Norway (39). The better correlation observed for the coastal site must be due to the proximity of the Atlantic Ocean. The enthalpy of vaporization calculated from the slope of the correlation curve (Table 4) was closer to the theoretical value for this location 2964

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than the two continental sites, indicating the relatively greater importance of volatilization. This may also indicate that the major source of R-HCH was the Atlantic Ocean from where it was volatilized and transported inland as described by Garmouma and Poissant (17). Moreover, a gradient of the calculated enthalpy of volatilization with latitude was observed. The calculated value was much more important as the latitude increase (R ) 0.99998 with p < 0.01) due to a preferential partitioning into water at colder temperatures (21). These observations seem to show that R-HCH was mainly stored in water as confirmed by the Hexp/Hth ratio close to 1, indicating a relatively good air/water balance. In concern of HCB, even if regression coefficients are significant, the calculated enthalpy of vaporization is absolutely different than the theoretical value. Values below 0 indicate an anticorrelation with temperature, which means that HCB concentrations in air were higher with colder temperatures due to greater urban air emission sources or “cold condensation” onto solid phases as explained previously. Mingan did not observe any correlation with temperature in consequence of its distance to anthropogenic activities. HCB that was present at this site was exclusively transported from other regions; no local source had been expected to occur in this location. The Hexp/Hth ratio was very different than 1 since HCB has a low solubility indicating weak exchange between air and water. As DDE is one of the DDT metabolites, these two compounds will be discussed together. DDE levels show a significant dependence on temperature at continental sites, whereas no dependence of this compound was observed at the coastal site. Moreover, no temperature dependence was noted for DDT at any place. The enthalpies of vaporization calculated for DDT at these three sites were very different from the theoretical value, which implies that no DDT

TABLE 3. Regression Coefficients between ln Concentration and the Reciprocal Temperature of Several OC Pesticides Measured in Que´ bec during the Sampling Periods at St. Anicet, Villeroy, and Mingan r-HCH

HCB

Villeroy 0.10 0.41 St. Anicet 0.0041 0.31 Mingan 0.24 0.0041

Lindane γ-chlordane DDE 0.21 0.24 0.17

0.18 0.30 0.34

DDT Mirex

0.25 0.005 0.18 0.029 0.036 0.061

TABLE 4. Experimental Enthalpy of Vaporization ∆Hexp (kJ‚mol-1) Calculated from the Slope of the Linear Correlation between ln Concentration and the Reciprocal Temperature of Several OC Pesticides Used in Que´ bec during the Sampling Periods at St. Anicet, Villeroy, and Mingan r-HCH HCB Lindane γ-chlordane DDE DDT Mirex Villeroy St. Anicet Mingan ∆Hth

8 2 26 63

-57 -30 5 60

43 55 45 63

49 46 36 57

36 31 24 63

-5 14 23 92

FIGURE 4. Ln of the Lindane concentrations plotted against the reciprocal of the temperature at Villeroy during the 1993-1996 period. The solid line is the regression of the data. volatilization should occur from soil. Long-range transport from other areas, for example, Southern U.S. (15) or Asia, is a more probable source. In concern of DDE, the calculated enthalpies of vaporization were closer to the theoretical value at continental sites than the coastal one. It is probable that DDT was used in Que´bec and that the soils were still containing a detectable amount of its metabolite DDE. This compound, resulting from the decomposition of the DDT, was gradually re-emitted in the atmosphere by volatilization when the temperatures were high in summer. A fraction of the DDE might also come from atmospheric long-range

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

n

0.71

0.30 0.74(TB/TC) - 0.116 0.41

TABLE 6. Experimental Henry’s Law Coefficient to Theoretical Henry’s Law Coefficient Ratio of Several OC Pesticides Measured in Que´ bec during the Sampling Periods at St. Anicet, Villeroy, and Mingan r-HCH HCB Lindane γ-chlordane DDE Villeroy St. Anicet Mingan Hth (Pa‚m3/ mol-1) (25 °C)

0.483 0.435 0.499 1.07

0.099 0.019 0.026 134

0.098 0.225 0.132 1.42

0.107 0.071 0.078 4.91

0.044 0.101 0.147 2.13

DDT Mirex 0.200 0.144 0.178 0.821

transport. The Hexp/Hth ratio was far from the theoretical value, confirming that atmospheric DDE is rather volatilized from soil than from water. The same trends were observed for DDT giving evidence that these two species may not be stored in the Atlantic Ocean due to their low solubility (40). Then, Lindane presented a moderate correlation with reciprocal temperature without any clear distinction between continental and coastal sites. For this species, the calculated enthalpies of vaporization were very close to the theoretical value providing evidence of re-evaporation from surface. Because Lindane has had a long history of use in Que´bec and elsewhere, continuous exchange between environmental compartments can be expected. Lindane concentrations depend on the temperature but also on emissions. In connection with temperature relationship, volatilization seems to occur as well in soils as in seawater. As the Hexp/Hth ratio is much weaker than 1, it was assumed that exchange between air and water was lower than exchange between air and soil or that steady state was not applicable due to fresh use of Lindane. Last, γ-chlordane also presented a moderate correlation with reciprocal temperature and calculated enthalpies of vaporization close to the theoretical value for the three sites. Because the Hexp/Hth ratio is very different from 1, the airwater balance does not seem to be reached for this species, reflecting a preferential vaporization from soil where chlordane was in use. Influence of Snow/Ice on Pesticide Concentrations. Snow and ice are present in the polar region, at high altitude,

FIGURE 5. Weekly median concentration of r-HCH (full black line) during the 1993-1995 period and temperature (dotted black line) at Villeroy compared to the modelized concentrations (full and dotted gray lines) obtained by Daly and Wania (44). Model calculation was made for specific snow surface area of 0.1 m2‚g-1. VOL. 39, NO. 9, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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and in winter at high latitude areas affecting the fate and chemical reaction of pollutants (21, 41). Organic chemicals in the atmosphere can be scavenged during snowfall events (42), released, or taken up by the snowpack (43), usually decreasing atmospheric concentrations in the lower layers. Moreover, the presence of a snowpack can prevent exchange of gaseous pollutants between the atmosphere, lakes, rivers, or seawater and soil. On the contrary, during the melting period, chemicals formerly adsorbed into the snowpack are quickly volatilized in the atmosphere leading to an increase of the atmospheric concentrations. Que´bec experiences winter weather for 3-5 months each year, and the effect of snowpack and low temperatures in reducing volatilization is reflected by reduced concentrations of some pesticides during winter months (Figures 2). It was the 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 were becoming lower than 0 °C and almost undetectable during the colder period. Then, concentrations increased suddenly when temperatures rose above 0 °C after the winter period. It is supposed that these organic chemicals were volatilized from soil during spring, summer, and autumn seasons, but during winter, no volatilization could occur because of the snowpack that prevents exchange between air and soil. R-HCH presents a slightly different pattern. The monthly median atmospheric concentration at Villeroy is presented in Figure 5. This result is close to the modelized air concentrations simulated by Daly and Wania (44) for R-HCH. During December, January, and February, concentrations were lower than the remaining year due to successive snowfall events that scavenge chemicals. In March during the snowmelting season; concentrations increased drastically due to quick volatilization from the snowpack until the beginning of May. Concentrations were even higher than in summer. After May, concentrations decreased to a value generally included between 70 and 100 pg‚m-3 until the end of November. On the other hand, a concentration of 120 pg‚m-3 was observed in November which was much higher than it should be for this season. It might be explained by a snowfall period 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-HCH scavenged a few weeks before. The effect of the snow was also observed at the St. Anicet and Mingan sites (not shown). This effect shows that the temperature dependence for organic compounds could be disturbed by the influence of snowfall events and snowpack presence. This phenomenon could explain the relatively weak correlation coefficients found for some pesticides in this study.

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Acknowledgments The authors would like to thank Jean-Franc¸ ois Koprivnjak (formerly from Environment Canada) for his field work and Michel Bertrand (University of Montreal) for his laboratory work and support. This project is a result of the St. Lawrence Action Plan (Phases II and III). F.A. would like to thank the Meteorological Service of Canada and SLAP IV for supporting his NSERC Canadian Laboratory postdoctoral fellowship. Also, thanks to Antoinette Taddeo and Sofia Khodorkovskaya for their help in rereading this paper.

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Received for review October 20, 2004. Revised manuscript received January 25, 2005. Accepted February 9, 2005. ES048361S

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