Atmospheric Transport of Toxaphene from the Southern United States

Jul 10, 2002 - Toxaphene was used extensively as an insecticide on cotton in the southern United States until its use was restricted in 1982. Toxaphen...
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Research Atmospheric Transport of Toxaphene from the Southern United States to the Great Lakes Region RYAN R. JAMES AND RONALD A. HITES* Environmental Science Research Center, School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405

Toxaphene was used extensively as an insecticide on cotton in the southern United States until its use was restricted in 1982. Toxaphene has been found in the water and fishes from the Great Lakes, and several authors have qualitatively linked this observation to atmospheric transport from the southern United States, although no detailed field study has been done to confirm this suggestion. We implemented a sampling network to measure the gasphase concentrations of toxaphene near Lake Michigan at Sleeping Bear Dunes, MI; Bloomington, IN; Lubbock, TX; and Rohwer, AR. The toxaphene concentrations referenced to 288 K were 11 ( 1, 25 ( 1, 160 ( 3, and 950 ( 30 pg/ m3, respectively. We combined these concentration data with a nonparametric, backward trajectory, multiple regression model of the following form: ln(P) ) a0 + a1/T + a2θ where P is the partial pressure of toxaphene (in atm) in a given sample, T is the atmospheric temperature at the sampling site during sampling (in degrees Kelvin), and θ is 0 if the backward trajectory comes from the north and 1 if the trajectory comes from the south. The parameters of this model were generally significant, giving a temperature coefficient (a1) corresponding to 45 ( 8 kJ/mol and a positive directional coefficient (a2) of 0.6 ( 0.2 (except for Texas, which was not significant). The positive sign and magnitude of the directional coefficient indicates that the sources of toxaphene are located south of the sampling sites. We also compared the chemical behavior of toxaphene in the atmosphere and found that the congener ratios were similar at the different sampling sites but slightly different from various toxaphene standards.

Introduction Toxaphene was a broad-spectrum pesticide, consisting of a complex mixture of chlorinated bornanes and camphenes, which was used extensively for the control of insects on cotton throughout the southern United States. The Hercules Company first produced toxaphene in 1947 and patented the process in 1951 (1). First used as a piscicide during the 1950s in the upper Midwest and Canada (2, 3), over 108 kg of toxaphene was eventually used in the southern U.S. during the next 30 years. In fact, during the 1960s and 1970s, toxaphene’s use was encouraged as a replacement for DDT (4). Thus, following DDTs ban in 1972 by the U.S. Environmental Protection Agency (U.S. EPA), toxaphene’s use increased dramatically, and between 1966 and 1976 it was * Corresponding author e-mail: [email protected]. 3474

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the most heavily used pesticide in the U.S. (5). But soon, the U.S. EPA severely restricted toxaphene’s use, citing concerns over its toxicity and environmental persistence. Limited use of existing stocks was allowed until 1986, and all uses were banned in 1990 (6). Toxaphene is unique among the organochlorines (such as PCBs and DDT) in that it was used mainly for one purpose and mainly in one region of the United States: Over 85% of toxaphene’s use in the U.S. was in the cotton-growing states from Texas through Georgia (7), with only 1-4% of its use occurring in the upper Midwest, including the Great Lakes Basin (8). Stanley and Barney and Arthur et al. reported high atmospheric toxaphene concentrations (2000 and 900 ng/m3, respectively) over the Mississippi Delta in the early 1970s (9, 10). Soon thereafter, Bidleman and Olney suggested that the presence of toxaphene at Bermuda in the western North Atlantic Ocean was due to its atmospheric transport from the cotton growing regions of the U.S., which were over 1200 km away (11). Recently, high toxaphene concentrations have been found in Great Lakes water, fish, and sediment, prompting considerable research into the source of this contamination (12, 13). In 1981, Rice et al. placed air samplers at sites from Mississippi to Michigan and used backward trajectory analysis to qualitatively correlate high concentration samples in the Midwest with air masses arriving with southerly trajectories (14). Subsequently, several workers have used backward trajectories to explain unusually high or low concentration samples (15-17). For example, high concentrations have been explained by backward trajectories that originated out of areas of heavy toxaphene use, such as the southern United States, and low concentrations have been explained by back trajectories that originated in places, such as the western U.S. or Canada, where toxaphene was scarcely used. In addition, Voldner and Schroeder used a trajectory model to predict the environmental fate of toxaphene by incorporating use patterns, meteorological data, flux equations, and concentrations in different matrices (18). Their model predicted the northward movement of toxaphene from areas of heavy use in the southern United States. To fully investigate the atmospheric transport of toxaphene from the southern U.S. to the Great Lakes, we initiated an air-sampling network extending from near the Great Lakes to the southern U.S. to obtain toxaphene concentrations during the years 2000-2001. The objectives of this research were to compare the concentrations of toxaphene among the sampling sites, to combine the toxaphene atmospheric concentration data with the backward trajectory data for all the sampling dates in order to indicate source regions of toxaphene to the Great Lakes, and to study the differences (if any) among the toxaphene congener patterns in atmospheric samples and versus toxaphene standards.

Experimental Methods Atmospheric Sample Collection. Air samples were collected at four sampling sites: (a) the United States Department of Agriculture, Agricultural Research Service Cropping Systems Research Laboratory in Lubbock, TX (33°34′33′′ N, 101°52′31′′ W); (b) the University of Arkansas Southeast Research and Extension Center near Rohwer, AR (33°45′39′′ N, 91°16′32′′ W); (c) Indiana University in Bloomington, IN (39°10′00′′ N, 86°31′17′′ W); and (d) the Integrated Atmospheric Deposition Network site located near Sleeping Bear Dunes National Lakeshore, which lies on the northeastern shore of Lake 10.1021/es011392s CCC: $22.00

 2002 American Chemical Society Published on Web 07/10/2002

FIGURE 1. Map of the central United States indicating the location of the sampling sites at Sleeping Bear Dunes, MI (MI); Bloomington, IN (IN); Rohwer, AR (AR); and Lubbock, TX (TX). Michigan (44°48′47′′ N, 86°03′32′′ W). These sampling site locations are shown in Figure 1. In Texas, the sampler was located on the roof of the one story Cropping Systems Research Laboratory building built in 1999, which is located near the northern edge of the city of Lubbock (population: 250 000) on the campus of Texas Tech University. The Arkansas sampler was located in the backyard of the Southeast Research and Extension Center’s office, which is a converted ranch-style house built in 1960, which is located on a fully functioning agricultural experimental farm about 2 km north of the town of Rohwer (population: 150). The Indiana sampler was located on a porch adjacent to the School of Public and Environmental Affairs building, which was built in 1982 and is located on the northeast side of the city of Bloomington (population: 60 000) on the Indiana University campus. The Michigan air sampler was about 1 km from the shore of Lake Michigan and about 15 km south of the town of Empire (population: 500). The southern sampling sites (Arkansas and Texas) were chosen based on their proximity to cotton growing areas and their position in areas where the backward trajectories from Michigan often originate. (An analysis of about 100 trajectories over a 2-year period revealed that backward trajectories from Michigan originated over the area bordered on the east by the Mississippi River and on the west by the western edge of Texas about 20-40% of the time.) The Indiana site was chosen in order to have a convenient mid-latitude site between the Texas and Arkansas sites and the Michigan site. The Arkansas and Texas samples were collected using Andersen high-volume samplers (Andersen Instrument Inc., Smyrna, GA; Model PS-1). An older, Sierra-Misco version of the same sampler was used at the Indiana and Michigan sites. All of these samplers draw air through a filter to collect the particle-bound compounds and then through an adsorbent to collect the gas-phase compounds. Atmospheric

particles were collected on glass-fiber filters (Whatman, Clifton, NJ); atmospheric gas-phase organic compounds were collected on polyurethane foam (PUF) adsorbent (Tisch Environmental, Inc., Village of Cleves, OH and Netherlands Rubber Co., Cincinnati, OH). The sampler flow rates were calibrated once every 5 months, and the flow rates were recorded at the start and finish of each sampling period. Sampling took place every 12 days starting in late March 2000 and running continuously through June 2001. Sampling in Michigan lagged 2 days behind that in Texas and Arkansas, and that in Michigan lagged 1 day behind that in Indiana. Sampling ran from 9:00 AM to 9:00 AM at the Michigan site and from midnight to midnight at the other sites. This scheduling was selected to maintain the potential for sampling the same air mass more than once. Because toxaphene concentrations near the Great Lakes approached detection limits in other studies and because concentrations in the South have been shown to be relatively high, different sample volumes were collected over the same time period at the different sites. A typical sample from Arkansas and Texas was about 400 m3 of air, and one from Indiana and Michigan was about 1400 m3. Site operators at each site performed the sampling and shipped the samples to Indiana University for analysis. Since more than 90% of toxaphene exists in the gas-phase under ambient conditions (15, 17), only the gas-phase samples (the PUF adsorbents) were analyzed. Sample Preparation. The analytical method for the atmospheric samples is based on that of Swackhamer et al. (19) and Glassmeyer et al. (20). Air samples were Soxhlet extracted for 24 h with 50% acetone in hexane, and then the solvent was exchanged to hexane and reduced in volume to about 1 mL. The primary samples and blanks were spiked with a known mass of the internal standard, isotopically labeled γ-13C10-chlordane (Cambridge Isotope Laboratories, Andover, MA), before extraction. Silica column chromatography was used to remove interferences from the air extracts. Disposable 13-cm Pasteur pipets plugged with glass wool were used as columns. Approximately 1 g of 1% water deactivated silica (Davidson Chemical, Baltimore, MD) was loaded onto the columns and topped with 0.1 g of anhydrous Na2SO4. Three solvents in 8 mL volumes (hexane, 40% dichloromethane in hexane, and dichloromethane) were used to fractionate the samples. The second fraction was solvent exchanged to hexane, reduced in volume to about 50 µL, and spiked with a known mass of the recovery standard, 2,2′,3,4,4′,5,6,6′-octachlorobiphenyl (PCB 204) (AccuStandard Inc., New Haven, CT), prior to analysis. Analysis by Gas Chromatographic Mass Spectrometry. An Agilent 5973 mass spectrometer, operating in the electroncapture negative-ionization mode, was used to analyze the atmospheric extracts for toxaphene. The extracts were injected into an Agilent gas chromatograph fitted with a 60-m DB-5MS column (250-µm i.d.; 0.25-µm film thickness; J&W Scientific, Folsom, CA) in 2 µL volumes using the splitless mode. Helium was used as the carrier gas. The injection port temperature was maintained at 285 °C to ensure complete volatilization of the sample. The temperature program for the column began with a 1-min hold at 80 °C; it was then ramped at 10 °C/min to 210 °C, ramped at 0.8 °C/min to 250 °C, and ramped at 10 °C/min to 310 °C, where it was held for 10 min. The total run-time was 80.5 min. The GC to MS transfer line was heated to 280 °C, and the ion source of the mass spectrometer was held at 150 °C. Methane was used as the reagent gas at a manifold pressure of 2 × 10-4 Torr. The electron-capture negative-ionization GC-MS analysis procedure was developed by Swackhamer et al. and modified slightly for subsequent use (19, 20). The M- or (M-Cl)- ions of the hexa- to decachlorinated bornanes and camphenes were monitored in the selected ion-monitoring (SIM) mode. VOL. 36, NO. 16, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. Gas-Phase Atmospheric Toxaphene Concentrations (Ca,g) in pg/m3, Average Air Temperature (T) in K, and Partial Pressure of Toxaphene (P) in Femtoatmospheres start date

site

Ca,g

T

P

start date

site

25-Mar-00 5-Apr-00 15-Apr-00 28-Apr-00 10-May-00 22-May-00 3-Jun-00 15-Jun-00 27-Jun-00 9-Jul-00 21-Jul-00 2-Aug-00 14-Aug-00

TX TX TX TX TX TX TX TX TX TX TX TX TX

766 250 99 130 276 251 1550 1130 586 198 217 275 319

290 285 288 292 299 301 296 297 298 301 301 301 302

45.6 14.6 5.8 7.7 16.9 15.5 94.0 68.8 35.8 12.2 13.3 17.0 19.8

26-Aug-00 7-Sep-00 19-Sep-00 1-Oct-00 13-Oct-00 25-Oct-00 6-Nov-00 18-Nov-00 30-Nov-00 20-Dec-00 5-Jan-01 17-Jan-01 29-Jan-01

TX TX TX TX TX TX TX TX TX TX TX TX TX

25-Mar-00 5-Apr-00 15-Apr-00 27-Apr-00 9-May-00 21-May-00 2-Jun-00 14-Jun-00 26-Jun-00 9-Jul-00 21-Jul-00 2-Aug-00 14-Aug-00

AR AR AR AR AR AR AR AR AR AR AR AR AR

1620 1210 2450 921 3150 2720 1960 2250 4140 2110 911 771 763

291 289 293 290 292 297 299 300 301 302 298 301 299

96.9 71.4 147 54.8 189 166 120 139 255 131 55.7 47.5 46.8

24-Mar-00 17-Apr-00 29-Apr-00 11-May-00 23-May-00 4-Jun-00 16-Jun-00 25-Jun-00 28-Jun-00 10-Jul-00 3-Aug-00 15-Aug-00 27-Aug-00

IN IN IN IN IN IN IN IN IN IN IN IN IN

139 35 11 109 11 8 65 21 18 37 63 35 56

291 282 286 294 292 290 296 296 294 299 294 298 295

7-Apr-00 18-Apr-00 30-Apr-00 12-May-00 24-May-00 5-Jun-00 17-Jun-00 11-Jul-00 23-Jul-00 4-Aug-00 17-Aug-00

MI MI MI MI MI MI MI MI MI MI MI

1 6 7 30 10 6 20 5 8 10 14

273 279 284 286 285 285 286 294 288 289 289

T

P

start date

site

Ca,g

T

P

Texas 276 131 185 149 587 469 111 44 92 64 114 52 35

302 302 293 298 294 289 280 273 281 279 279 271 275

17.1 8.1 11.1 9.1 35.4 27.8 6.4 2.5 5.3 3.6 6.5 2.9 2.0

10-Feb-01 22-Feb-01 6-Mar-01 18-Mar-01 30-Mar-01 11-Apr-01 23-Apr-01 5-May-01 17-May-01 29-May-01 10-Jun-01 22-Jun-01

TX TX TX TX TX TX TX TX TX TX TX TX

32 135 125 132 197 37 27 171 543 628 246 114

270 277 285 275 285 287 286 289 298 297 302 298

1.8 7.7 7.3 7.4 11.5 2.2 1.6 10.1 33.2 38.3 15.3 7.0

26-Aug-00 7-Sep-00 19-Sep-00 1-Oct-00 13-Oct-00 25-Oct-00 6-Nov-00 18-Nov-00 20-Dec-00 5-Jan-01 17-Jan-01 29-Jan-01

Arkansas AR 5570 AR 398 AR 866 AR 1230 AR 385 AR 476 AR 2500 AR 315 AR 246 AR 577 AR 549 AR 1580

304 293 295 294 291 294 291 275 271 277 277 284

347 23.9 52.4 74.0 23.0 28.8 149 17.8 13.7 32.8 31.2 92.2

10-Feb-01 22-Feb-01 6-Mar-01 18-Mar-01 30-Mar-01 11-Apr-01 23-Apr-01 5-May-01 17-May-01 29-May-01 10-Jun-01 22-Jun-01

AR AR AR AR AR AR AR AR AR AR AR AR

169 1020 207 510 1550 5020 1620 1510 2830 3090 1570 1520

275 277 280 280 284 297 296 297 299 297 298 296

9.5 58.0 11.9 29.3 90.4 306 98.1 91.6 173 188 96.2 92.0

8.3 2.1 0.6 6.5 0.7 0.4 3.9 1.3 1.1 2.3 3.8 2.1 3.4

8-Sep-00 20-Sep-00 2-Oct-00 14-Oct-00 26-Oct-00 7-Nov-00 19-Nov-00 1-Dec-00 21-Dec-00 6-Jan-01 18-Jan-01 30-Jan-01

Indiana IN 15 IN 42 IN 31 IN 25 IN 37 IN 111 IN 12 IN 16 IN 6 IN 6 IN 9 IN 31

293 293 295 291 292 287 275 275 263 272 274 277

0.9 2.5 1.9 1.5 2.2 6.6 0.7 0.9 0.3 0.3 0.5 1.8

11-Feb-01 23-Feb-01 7-Mar-01 19-Mar-01 31-Mar-01 12-Apr-01 24-Apr-01 6-May-01 18-May-01 30-May-01 11-Jun-01 23-Jun-01

IN IN IN IN IN IN IN IN IN IN IN IN

3 9 8 5 9 53 11 26 104 26 41 32

270 275 274 276 284 291 282 293 294 291 297 292

0.2 0.5 0.5 0.3 0.5 3.2 0.6 1.5 6.3 1.5 2.5 1.9

0.06 0.3 0.4 1.8 0.6 0.3 1.2 0.3 0.5 0.6 0.8

28-Aug-00 9-Sep-00 21-Sep-00 3-Oct-00 15-Oct-00 27-Oct-00 8-Nov-00 20-Nov-00 2-Dec-00 21-Dec-00 19-Jan-01

Michigan MI 23 MI 20 MI 4 MI 10 MI 5 MI 5 MI 5 MI 2 MI 9 MI 2 MI 1

294 297 282 287 282 281 278 272 271 271 264

1.4 1.2 0.2 0.6 0.3 0.3 0.3 0.1 0.5 0.1 0.1

31-Jan-01 24-Feb-01 8-Mar-01 20-Mar-01 1-Apr-01 13-Apr-01 25-Apr-01 7-May-01 19-May-01 1-Jun-01 13-Jun-01

MI MI MI MI MI MI MI MI MI MI MI

6 12 3 4 5 2 6 27 6 9 36

273 273 271 274 275 278 285 287 282 290 288

0.3 0.7 0.2 0.2 0.3 0.1 0.3 1.6 0.3 0.5 2.1

Interference ions, such as those produced by chlordane and the 13C-contributions from toxaphene fragment ions, were also monitored. The background subtracted, selected ion chromatograms were integrated using an Agilent data analysis program with a macro that generated an output file of peak areas and retention times of potential toxaphene peaks. This file was imported into a Qbasic program that selected valid toxaphene peaks based on chlorine isotope ratios and corrected for interfering compounds. Complete details are given elsewhere (20). Due to the complex nature of the toxaphene mixture, the relative response factor (RRF) was not linear over all concentration ranges. Less abundant toxaphene congeners drop below the limit of detection as the concentration of 3476

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Ca,g

toxaphene decreases. This phenomenon causes the RRF to vary according to a power function with respect to the total toxaphene peak area in the standard. The calculated RRFs from each standard were plotted against the total peak area for that standard. A power function was fit to the data, from which an individual RRF was calculated for each sample based on its total toxaphene peak area. In general, we estimate that the total toxaphene concentrations have a constant relative precision of about (35%. Congener Identification. Three standards, comprising 27 congeners of technical toxaphene, were analyzed in order to determine retention indices so that individual congeners could be identified in the atmospheric samples. The first was the commercially available Parlar 22 standard (Dr.

Ehrenstorfer GmbH, Augsburg Germany), consisting of 23 toxaphene congeners. The second mixture contained two congeners, B7-1412 and B8-1453. [Vetter et al. identified and isolated congeners B7-1412 and B8-1453 from a toxaphene standard (21, 22). In this notational scheme, “B7” and “B8” refer to hepta- and octa-chlorinated bornanes (23).] The third mixture contained two compounds, B6-923 and B7-1001, commonly referred to as Hx-Sed and Hp-Sed, respectively. [Stern et al. characterized Hx-Sed and Hp-Sed as persistent environmental degradation products of toxaphene (24).] The second and third standards are not commercially available at this time. These standards were analyzed using the same GC-MS method and conditions that were used for the sample extracts. Quality Assurance. All solvents were spectroscopic grade. Silica was pre-extracted using dichloromethane, and the Na2SO4, glass wool, and disposable pipets were heated at 450 °C overnight prior to use. A procedural blank, containing only glass wool, and a spike recovery sample, containing toxaphene (Hercules Co.), were extracted with every batch of 16-21 samples. No toxaphene peaks were ever present in the procedural blanks. The recovery of toxaphene in the spike recovery samples was 107 ( 19% (N ) 11), and the average recovery of the internal standard was 64 ( 22% (N ) 145). The sample concentrations were corrected for the loss of the internal standard. The instrument detection limit, defined as the concentration at which we can no longer reliably measure the hexa- and deca-chlorinated homologues of toxaphene, was 0.1 ng/extract, but the method detection limits for each site were determined by multiplying the amount of toxaphene in the field blanks by three. These limits were 1 pg/m3 at Michigan and Indiana and 15 pg/m3 at Arkansas and Texas. Trajectory Generation. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to generate 96-h backward trajectories (25). This model is available on the National Oceanic and Atmospheric Administration (NOAA) Air Resource Laboratory worldwide web site (26). The 145 trajectories used in this work were generated from the Eta Data Assimilation System (EDAS) database of archived meteorological data. The physics and mathematics of this model are described by Draxler in several publications (25-28). The latitude and longitude coordinates of the sampling site, sampling date and time (we used the mid time of the sampling period), and starting altitude (we selected starting altitudes of 500, 1000, and 1500 m) were submitted to the NOAA server, and within seconds, a map of North America with the trajectory was output and printed. Actually, the output of this model is latitude and longitude coordinates (called “endpoints”), which represent the hourly location of the trajectory. For example, a 96-h trajectory would be made up of 96 latitude and longitude endpoints. We used 96 h trajectories because longer trajectories would extend outside of the Unites States boundaries and because shorter trajectories would not include enough endpoints.

Results and Discussion Atmospheric Toxaphene Concentrations. Table 1 lists the gas-phase concentrations of toxaphene in all of the atmospheric samples collected at Texas, Arkansas, Indiana, and Michigan. It has been shown that the gas-phase atmospheric concentration of toxaphene in the Great Lakes region is strongly temperature dependent (15-17, 29), and the Clausius-Clapeyron equation can be used to describe this relationship (30). The integrated form of the ClausiusClapeyron equation is

lnP )

-∆H 1 + const R T

()

(1)

FIGURE 2. Gas-phase temperature dependence of toxaphene partial pressure (in atm) at all four sampling sites (see Table 1). Each sampling site is represented by a different symbol and line pattern. where P is the partial pressure of the compound (in atmospheres), ∆H is a phase-transition energy, R is the gas constant, and T is temperature (in Kelvin). In this application, ∆H is not the energy needed for a mole of a chemical to overcome its own attractive forces in the liquid phase and to enter the gas phase. Rather it is a composite value, representing the energy needed to move a mole of, in this case, toxaphene from soil, vegetation, and/or water into the gas phase. The partial pressures (see Table 1) are calculated from the concentrations using the ideal gas law, assuming an average molecular weight for toxaphene of 400 g/mol (15). The natural logarithms of the partial pressures of toxaphene versus reciprocal atmospheric temperature are plotted for each of the sampling sites in Figure 2. The correlation between the logarithms of the partial pressure and the reciprocal temperature is significant at the 99% confidence level for each of the four sites. Table 2 (top) summarizes the concentration and Clausius-Clapeyron data from each of the sites and gives the equations for the linear regressions. In our study, the consistency of the temperature-dependent behavior of toxaphene, as evidenced by the slopes of the four linear regressions in Figure 2 that represent four separate sampling sites and two models of samplers, lends substantial credibility to our data. The overall average ∆H value for our data was 49 ( 9 kJ/mol. Historically reported slopes of toxaphene ClausiusClapeyron plots have been quite variable. James et al. over Lakes Michigan and Superior in 1997-1998 (76 ( 10 kJ/mol), Glassmeyer et al. at Eagle Harbor in 1997 (47 ( 22 kJ/mol), and Hoff et al. at Egbert, ON in 1988-1989 (91 kJ/mol) and at Point Petre, ON in 1992 (35 kJ/mol) and 1995-1997 (44 kJ/mol) have all measured different values (15-17, 29). In addition, Jantunen and Bidleman recently measured the energy for the water-air transport of toxaphene to be 61 kJ/mol (31). Given the geographical and methodological variety of these ∆H values, we suggest that they be treated as replicate measurements, which have an average of 59 ( 9 kJ/mol. Our result of 49 ( 9 kJ/mol is similar, within experimental error. Figure 2 also demonstrates the concentration difference among the sampling sites by the vertical shift of the regression lines. As expected, the two sites in cotton growing regions of the southern U.S., Arkansas, and Texas, have much higher partial pressures of toxaphene than the Indiana and Michigan sites. The concentration range at Michigan (1-36 pg/m3) was lower than at Indiana (3-140 pg/m3), but the average temperature during sampling in Indiana was 5 °C warmer than in Michigan. The concentration at 288 K (the average VOL. 36, NO. 16, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 2. Summary of the Concentration Data (in pg/m3) and Regression Results for Each Sampling Site site

Cav ( SE

C @ 288 Ka

range

N

regression eq

R

∆H (kJ/mol)b

Michigan Indiana Texas Arkansas

10 ( 2 34 ( 6 280 ( 50 1600 ( 250

11 ( 1 25 ( 1 160 ( 3 950 ( 30

1-36 3-140 27-1600 170-5600

33 37 38 37

-6255/T - 13.26 -5854/T - 13.83 -5492/T - 13.22 -5984/T - 9.73

0.700 0.707 0.662 0.708

52 ( 10 49 ( 8 46 ( 9 50 ( 8

site

Nc

regression eq

r

SE on directional coeff

∆H (kJ/mol)b

Michigan Indiana Texas Arkansas

32 34 36 35

-6546/T + 0.62θ - 12.37 -4789/T + 0.70θ - 17.87 -4966/T + 0.22θ - 15.21 -5432/T + 0.58θ - 12.03

0.760 0.771 0.679 0.758

0.25 (p < 0.02) 0.24 (p < 0.006) 0.25 (p < 0.4) 0.23 (p < 0.02)

54 ( 9 40 ( 8 41 ( 8 45 ( 8

a Calculated using the Clausius-Clapeyron equation. b Transition energy (see text). c Number of data is less than above because a few trajectories could not be calculated.

TABLE 3. Comparison of Our Measurements with Literature Atmospheric Toxaphene Concentration Ranges and Average Gas-Phase Toxaphene Concentrations (Ca,g) source and locale

a

year sample taken

range

Ca,g

units

20-280 0.1-160a 1.5-10 0.9-10 0.1-63 3-70 1-36

80 26 4.9 3.8 6 16 10

pg/m3 pg/m3 pg/m3 pg/m3 pg/m3 pg/m3 pg/m3

360 258 82 160 7.3 0.18 1.6

ng/m3 ng/m3 ng/m3 ng/m3 ng/m3 ng/m3 ng/m3

Rice et al., Lake Michigan (14) Hoff et al., Egbert, Ontario (16) Shoeib et al., Lake Ontario (29) Shoeib et al., Lake Ontario (29) Glassmeyer et al., Lake Superior (15) James et al., Lakes Mich. and Sup. (17) this study, Michigan

Great Lakes Region 1981 1988-1989 1992 1995-1997 1997 1997-1998 2000-2001

Stanley and Barney, Mississippi (9) Arthur et al., Mississippi (10) Arthur et al., Mississippi (10) Arthur et al., Mississippi (10) Rice et al., Mississippi (14) Jantunen and Bidleman, Alabama (31) this study, Arkansas

Southern United States 1967-68 62-1300 1972