Environ. Sci. Technol. 1993, 27, 910-914
Effects of Temperature and Wind Direction on the Atmospheric Concentrations of a-Endosulfan Thomas W. Burgoyne and Ronald A. Hltes’
School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405 ~
The atmospheric concentrations of endosulfan (a contact insecticide) were measured for 14 months in Bloomington, IN, at an average frequency of three times per month. Meteorological conditions were also measured during that period. Endosulfan was collected on polyurethane foam plugs with a high-volume air sampler and was analyzed by electron capture, negative ionization, gas chromatographic mass spectrometry. The average concentration of a-endosulfan over the 14-month period was 86 pg/m3 (3.8 X 10-l2Torr), and the highest concentration was 890 pg/m3. Multiple linear regression was used to relate the meteorological conditions with the atmospheric concentration. Variables used in the regression were inverse temperature and wind direction. This model showed a high effect of atmospheric temperature and a moderate effect of wind direction. The heat of vaporization calculated from these data was 95 f 13 kJ/mol.
multiple regression techniques to isolate the importance of temperature and wind direction. We selected endosulfan because of its toxicity and because of the availability of a rapid analytical method. Endosulfan (6,7,8,9,10,10-hexachloro1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide), also known as thiodan, is a wide range, contact and stomach insecticide, which is effective against numerous insects that vandalize cereals, coffee, cotton, fruit, oilseeds, potatoes, tea, and vegetables (11). Endosulfan exists as the exo and endo isomers. exo
endo
Introduction The atmospheric concentration of a pesticide at a given location and at a given time is controlled by factors relating to the source (such as the time, location, and amount of pesticide that is applied) and by factors relating to transport (such as atmospheric mixing height and wind direction and speed). Because neither farmers nor retailers are required to keep or release records of pesticide use or sales, direct information on sources is not available. However, source locations and strengths can often be determined by indirect measures. For example, because more pesticides are used during the warm growing season than in the winter, atmospheric temperature can be used as an indirect measure of source strength. Atmospheric temperature also affects the transport of pesticides by influencing their vapor pressures and their mixing heights. For all of these reasons, atmospheric temperature is the most important, measurable variable controlling the concentration of pesticides at a given location (1-7). In addition to temperature, wind direction may also play a role in affecting the atmospheric concentration of a pesticide at a given location. I t seems axiomatic that concentrations would be higher downwind from sources, and within short distances and short time scales, this is often true. However,when averaged over longer distances and over longer time scales, this relationship is frequently not obvious (8-10). In part, this is because winds tend to travel in different directions at different altitudes and because source strengths tend to be highly variable. Given these complexities, it is not surprising that no one has found a significant relationship between the atmospheric concentration of a pesticide and temperature and wind direction. This lack of data prompted us to address these relationships by repeated measurements of endosulfan at one location (Bloomington, IN) over a 14-month period. We determined the atmospheric concentrations and the appropriate meteorolgical parameters, and we used 910
Environ. Sci. Technol., Vol. 27, No. 5, 1993
a 1 p h a - e lidos u 1 f ai1
beta-endosulfan
The technical formulation is approximately 70 % exo (also called a-endosulfan or endosulfan I) and 30% endo (also called 8-endosulfan or endosulfan 11). However, because the a-isomer is by far the most abundant in the environment (see below), many authors refer to a-endosulfan simply as “endosulfan”. We will adopt the same convention. The oral LD50 for technical endosulfan in rats ranges from 18 to 355 mg/kg body weight (12,13),which makes it among the most toxic of the chlorinated insecticides. In 1988, the world’s production of technical endosulfan was about 10 000 t per year (14). Endosulfan is semivolatile (vapor pressure 9.8 X Torr; see ref 15) and photolytically stable in water (14, 16), and as a result, endosulfan is ubiquitous in the environment. It has been found in the atmosphere over the Arabian Sea, the Persian Gulf, and the Red Sea where concentrations ranged from 3 to 120 pg/m3. It is also present in the atmosphere over the Canadian High Arctic (18),the Arctic Ocean (19),the North Atlantic gyre (20), and Nova Scotia (21)at concentrations ranging from 2 to 140 pg/m3. Urban areas are also affected. Bidleman found that the average endosulfan concentration in the atmosphere of Columbia, SC, was 78 pg/m3 (22). Junk and Richard found that the average endosulfan concentration near pesticide disposal sites in Ames, IA, was 250 pg/m3 (23). Guichert and Schulting found an average annual endosulfan concentration of 170 pg/m3 with a maximum of 1130 pg/m3 in The Netherlands (24). Unfortunately, even though these authors took 55 samples, they did not explain the variations in the endosulfan concentrations. Hoff et al. (who took a highly timeresolved set of 73 samples) reported an average concentration for endosulfan of 350 pg/m3 with a maximum of 3700 pg/m3 in Egbert, Ontario, Canada (25, 26).
(In,
0013-936X/93/0927-0910$04.00/0
0 1993 American Chemical Society
Experimental Section loot
Air was sampled with a Hi-vol sampler (Sierra Misco, Berkeley, CA) equipped with a filter to collect the particles and with an adsorbent trap to collect the vapor-phase compounds. The filters were type AIE, 20-cm by 25-cm glass fiber filters (Gelman Sciences, Ann Arbor, MI), and the adsorbent traps were 10 cm long and 9 cm diameter polyurethane foam plugs (PUF) (Olympic Products, Greensboro, NC). The PUF plugs were precleaned by Soxhlet extraction with acetone for 24 h, with dichloromethane for 24 h, and with petroleum ether for 24 h. All solvents were from E. M. Sciences (Gibbstown, NJ) and were spectral grade. After the extraction process was completed, the PUF was held at about 40 "C under vacuum for 24 h to remove solvent and then was stored in metal containers in a freezer until needed. Glass fiber filters were precleaned by heating them in a muffle furnace at 450 "C for 6 h, and then they were stored in a freezer. Air samples were taken approximately three times per month; the sampler was located on the patio of the School of Public and Environmental Affairs building on the campus of Indiana University in Bloomington, IN. The air flow rate was regulated at 0.79 m3/min, and the total sampling time averaged 24 h. Therefore, the total volume of an air sample averaged 1140 m3. During the sampling event, the air temperature was recorded on an Omega chart recorder. After collection, the PUF plug was spiked with a-endosulfan-d4 (MSD Isotopes, St. Louis, MO) and Soxhlet extracted with 1.5 L of hexane for 24 h. The extract was concentrated by rotary evaporation and then blown down by a gentle stream of nitrogen to a volume of approximately 0.5 mL. The glass fiber filter was discarded. Initially, glass fiber filters were analyzed with the PUF plugs; however, after experiments were conducted to determine vaporlparticulate partitioning, it was found that the concentration of endosulfan on the glass fiber filter was below the detection limit (about 0.3 pg). This observation indicated that virtually all atmospheric endosulfan was in the vapor phase at even the lowest temperatures. Nevertheless, glass fiber filters were checked every five samples to ensure that there was no loss of analyte. All extracts were analyzed on a Hewlett-Packard 5985 gas chromatographic mass spectrometer operating in the electron capture, negative ionization (ECNI) mode. A 30-m by 0.25-mm i.d., DB-5, gas chromatographic column (J&W Scientific, Folsom, CA) was used. The ion source temperature was 100 "C; the reagent gas was methane at a pressure of 0.45 Torr. Full-scan and selected-ion monitoring were both used to analyze endosulfan. The ECNI mass spectrum of endosulfan gave two characteristic ions at mlz 404 [M-I and 370 [(M - C1+ H)-l with six and five chlorine isotopic patterns, respectively (see Figure 1). The internal standard had four deuterium atoms; thus, it gave two characteristic ions at mlz 408 and 374. These sets of masses are unique to endosulfan in its GC retention time window; hence, no cleanup of the sample was required. The endosulfan concentration was calculated by integration of the mass chromatogram peaks due to both endosulfans and endosulfan-d4. Since a known amount of the latter was added to the sample, the unknown amounts of a- and @-endosulfancould be calculated by ratio after correction for the instrumental responses for the natural and deuterated compounds. Isotopic overlaps
300
325
350
mass
375
/ charge
400
425
Flgure 1. Electron capture, negative ionization mass spectrum of a-endosulfan.
were eliminated by integration of mlz 404 [M-J for the natural compounds and mlz 414 [(M + 61-1 for the deuterated compound. Areas were then adjusted by the known isotopic ratios between these ions [M:(M + 6) = 1.451. Incidentally, a-endosulfan-d4 elutes just before the natural endosulfan, which is a useful aid in the identification of the latter. Reagent blanks were measured approximately every five samples. Field blanks were also analyzed. No endosulfan was detected in any blank sample. Breakthrough experiments were conducted by analyzing a PUF plug that was cut in half and by determining the concentrations in the front and back plugs. No endosulfan was detected in the back half of the plug; hence, there was no loss of endosulfan due to breakthrough. The meterological station was located approximately 1.2 km northeast of the sampling site. This station was equipped with a temperature and relative humidity probe (LiCor, Lincoln, NE), wind speed and direction indicator, pyranometer, and aneroid barometer (all from Climatronics, Bohemia, NY). All instruments were wired into a Campbell scientific CRlO data logger, which sampled each instrument every 60 s. The meteorological data were collected in half-hour intervals and averaged over the sampling period. The data were acquired at a local elevation of 2.2 m. The temperatures recorded at this meteorological station were compared to those acquiried with the Omega chart recorder located near the air sampler, and the data were in good agreement. Meteorologicaldata and endosulfan concentrations were analyzed with the Statistical Analysis System (Cary, NC) using multiple linear regression procedures. Results and Discussion Table I gives the dates on which the samples were taken, the measured a-and @-endosulfanconcentrations (in pg/ m3),and the atmospheric temperature and wind direction as averaged over the sampling period. Note that @-endosulfan was detected in only two samples at very low levels relative to the a-isomer. This observation confirms the results of other workers who also found that a-endosulfan is the major isomer present in the environment (21,23). The @-isomerwill be ignored in the following analysis. The average concentration of endosulfan was 86 pglm3 (3.82 X 10-l2Torr); the highest and lowest concentrations Environ. Sci. Technol., Vol. 27, No. 5, I993 911
Table I. Endosulfan Concentrations in Bloomington, IN, on Dates Indicated and Average Atmospheric Temperature and Wind Direction During Sampling Period
Table 11. Statistical Parameters Calculated from Multiple Regression Model (see eq 2)
variable
endosulfan concn (pgim3)
temp
date
day0
0I
P
("0
wind direction (de&
Jan 10,1991 Jan 17,1991 Jan 22,1991 Feb 5,1991 Feb 12,1991 Feb 26,1991 Mar 11,1991 Mar 18,1991 Apr 16,1991 Apr 22,1991 Apr 30,1991 May 8,1991 May 30,1991 Jun 12,1991 Jun 18,1991 Jul18,1991 Jul25,1991 Aug 7,1991 Aug 21,1991 Sep 19,1991 Sep 26,1991 Oct 4,1991 Oct 24,1991 Nov 21,1991 Dec 12,1992 Jan 16,1992 Jan 23,1992 Jan 30,1992 Feb 6,1992 Feb 27,1992
10 17 22 36 43 57 70 77 106 112 120 128 150 163 169 199 206 219 233 262 269 276 297 325 346 381 388 395 402 423
12.6 3.0 0.6 20.8 4.8 4.5 6.0 5.6 9.5 2.8 33.3 40.2 81.9 126 159 689 268 887 68.6 6.5 5.4 45.4 51.4 15.0 22.9 1.3 2.3 3.2 2.9 9.4
ndb nd nd nd nd nd nd nd nd nd nd nd nd nd nd 20 nd 67.4 nd nd nd nd nd nd nd nd nd nd nd nd
2.4 0.1 -3.3 16.0 7.9 2.0 10.8 6.6 21.7 15.5 21.8 20.5 27.9 27.0 27.0 25.9 23.8 22.9 21.7 12.6 15.6 22.9 16.8 7.0 10.5 -7.0 1.4 8.3 8.1 12.4
74.6 269.3 219.5 70.4 187.6 256.5 117.7 275.1 241.5 246.2 239.9 127.9 228.0 109.6 112.0 103.1 309.0 117.3 232.9 318.8 270.4 228.0 197.4 190.9 231.1 225.6 287.3 321.4 278.9 270.6
ln[ENDOl = a,
I a
-
400
-
200
-
//
aa
jLIII -
U(,a
0
0
100
a 200
300
400
d a y number Flgure 2. Endosulfan concentration versus day number. Day 1 is January 1, 1991.
were 887 and 0.6 pg/m3, respectively. The highest concentrations were in late July and early August; note days 199 (689 pg/m3) and 219 (887 pg/m3) in Figure 2. Both of these values were measured when the wind was coming from the east (103" and 117"). In between these two samples, another sample was taken (on day 206) during which time the wind was coming from the west (309"), and the concentration was much lower (268pg/m3). More on this later. All else being equal, the atmospheric concentration of a given compound can be related to its vapor pressure at a given temperature. The relationship between vapor 912
Envlron. Sci. Technol., Vol. 27, No. 5, 1993
0.0362 0.0001 0.0118 0.8269 0.760
d(ln P)/d(l/T) = -H,,,/R (1) where P i s the vapor pressure in Torr, Tis the temperature in Kelvin, R is the gas constant (8.314 J/Kmol), and Hvap is the heat of vaporization in J/mol. Given that this equation relates the natural logarithm of the vapor pressure to the inverse of the temperature, we first transformed our concentration data frompg/m3into Torr (this involved a slight temperature correction) and then took the natural logarithm of the result. The temperatures were transformed into their reciprocals. The sines and cosines of the wind directions were used in the statistical analysis. This conversion was required because wind direction is a circular function (0" and 360°, although different numbers, represent the same direction). After these transformations, the regression equation was
800 -
600
probability
pressure and temperature was worked out some time ago by Clausius and Clapeyron; it is
" January 1,1991, is day 1. nd, not detected at a detection limit of about 0.3 pg. 1000,
coefficient
intercept 12.05 f 5.46" UT -11410 f 1566 sin(WD) 0.651 f 0.240 cos(WD) -0.079 f 0.357 overall r2 Standard error of the estimate.
+ a,/T + a2 sin(WD) + a3 cos(WD)
(2)
where the ai's are the fitted parameters, END0 is the endosulfan concentration in Torr, and WD is the wind direction in degrees. The parameters were fit using multiple linear regression. Table I1 shows the variables, coefficient estimates and their standard errors, probabilities of significance, and overall correlation coefficient for eq 2. Several points are clear from these results. Temperature. Temperature is the major significant predictor of atmospheric endosulfan concentrations; its coefficient is highly significant ( P < 0.0001). The magnitude of the a l / T term averages about 40, which is 200 times higher than the next most significant term. The coefficient of the reciprocal temperature term is -H,,,/R (see eq 1) from which we can calculate the heat of vaporization for endosulfan to be 95 f 13 kJ/mol. Wind Direction. Wind direction plays an important, but secondary, role in predicting endosulfan concentrations, The average value of a2 sin(WD) is 0.2, which is 200 times smaller than the temperature term. The average value of a3 cos(WD) is 0.02, which is 2000 times smaller than the temperature term. Nevertheless, the sine of the wind direction is highly significant (P < 0.012); the cosine is not (P< 0.83). Because the coefficient of the sine term is positive and because sines of angles between 0" and 180" are also positive, we conclude that winds coming to Bloomington from the east (wind directions between 0" and 180") carry higher endosulfan concentrations than winds coming from the west. This agrees with the qualitative observation presented above. In addition, since the cosine term was not significant, we conclude that winds coming from the north or south have no effect on the atmospheric endosulfan concentrations in Bloomington.
-26
-
-28
-
-30
-
d V
2 0 .V k
a
I
*/
-32 I -32
I
-28
-30
-24
-26
-22
measured conc. Flgure 3. Natural logarithms of the predicted (see eq 2) versus the measured endosulfan concentrations (in Torr). The line has a slope of 1.0. 500
I
I
a i PI
v
much longer and a slightly later application season. In fact, in the central Indiana area, endosulfan can be used over a 7-month period, which may lead to the higher FWHM value (27). The Canadian average and maximum concentrations were higher than the values we measured (346 versus 86 pg/m3 and 3700 versus 890 pg/m3, respectively). This may indicate higher endosulfan use in Ontario as compared to Indiana. Our value for endosulfan’s heat of vaporization was 95 f 13 kJ/mol. There are two values to which we can compare this: (a) Hinkley et al. estimated the heat of vaporization to be 82 kJ/mol based on gas chromatographic retention data (28). (b) Hoff et al. did not report the heat of vaporization directly; however, a plot of the common logarithm of endosulfan concentrations versus inverse temperatures was given (26). From this graph, we estimated the heat of vaporization to be 170 kJ/mol. Our value is about the same as Hinkley’s value, but both of these values are significantly lower (by about a factor of 2) than Hoff s value. This may indicate that Hoff et al. had sampled endosulfan that had entered the air from recent or local applications of the pesticide and that had not yet reached an equilibrium based on its vapor pressure.
Conclusion
400
300 0
t
I
1
t
2
2oo
Le
l o no r
-0
\
I
/ I 0 e, .
1
2
3
4
5
6
I
I
7
8
* , 0 ( 0 9
,
0*\
.j
10 1 1 12 13 1 4 15
month Flgure 4. Endosulfan concentrationsaveraged by month versus month number. Month 1 is January 1991.
Other Parameters. Other variables, such as wind speed, barometric pressure, radiant power, and relative humidity were not included in the model because preliminary statistical analysis indicated that they had an insignificant impact on endosulfan concentrations or because they covaried with some other parameter. For example, inverse temperature and radiant power were correlated. We plotted the predicted versus the measured concentrations (see Figure 3) and looked for patterns which might indicate that information had been left out of our model. No patterns were seen, although the model significantly underpredicts the three highest concentrations. The model was recalculated after the cosine term, and the three highest concentrations were dropped; no significant differences were noted. Comparisonto Other Studies. In comparing our data to those of Hoff et al. (25,26), several similarities are noted. First, we also observed the bell-shaped curve that results from averaging the endosulfan concentration by month and plotting them versus month number (see Figure 4). A cubic spline curve was plotted through the points, and the full width at half maximum (FWHM) and month at maximum concentration were determined. The FWHM and maximum were 2.1 and 7.8 months, respectively. Compared to the Canadian data (FWHM of 0.8 month and maximum at 6.7 months), Indiana seems to have a
Although temperature is the major factor in determining the atmospheric concentrations of endosulfan, wind direction also plays a significant role. In Bloomington, atmospheric concentrations of endosulfan are highest when the air is warmest and when the wind is out of the east. This may indicate that this pesticide is used primarily east of the city. Other meteorological conditions such as wind speed, relative humidity, barometric pressure, and radiant power proved to be insignificant contributors in our model. The seasonal distribution of endosulfan is similar to that found by Hoff et al. (25,26). This similarity is remarkable given that our frequency of data collection was considerably less (3 versus 15 samples per month).
Acknowledgments We thank Bernard Flury for helpful discussions on the statistical aspects of this study and Susan Grimmond for the meteorological data.
Literature Cited Bidleman, T. F.; Wideqvist, V.; Jansson, B.; Soderlund, R. Atmos. Environ. 1987, 21, 641-654. Manchester-Neesvig, J. B.; Andren, A. W. Enuiron. Sci. Technol. 1989, 23, 1138-1148. Yamasaki, H.; Kuwata, K.; Miyamoto, H. Environ. Sci. Technol. 1982,16, 189-194. Keller, C. D.; Bidleman, T. F. Atmos. Environ. 1984, 18, 837-845. Kishida, F.; Takahashi, N.; Matsuo, M.; Yamada, H. Chemosphere 1990,21, 647-657. Nash, R. G.; Gish, T. J. Chemosphere 1989,18,2353-2362. Hermanson, M. H.; Hites, R. A. Enuiron. Sci. Technol. 1989, 23, 1253-1258. Sweet, C. W.; Vermette, S. J. Enuiron. Sci. Technol. 1992, 26, 165-173. Smith, R. M.; O’Keefe, P. W.; Aldous, K.; Connor, S. Chemosphere 1990, 20, 1447-1453. Oliver,K. D.Proceedings ofthe81stAPCAAnnualMeeting; APCA: Pittsburgh, PA, 1988; paper 88i150.6. Worthing, C. A. The Pesticide Manual, 8th ed.; The British Crop Protection Council: Thornton Heath, U.K., 1987; p 335. Environ. Sci. Technol., Vol. 27, No. 5, 1993
a13
(12) Gaines, T. B. Toxicol. Appl. Pharmacol. 1969,14,515-534. (13) Boyd, E. M.; Dobos, I. Protein Deficiency and Pesticide Toxicity;Charles C. Thomas: Springfield, IL, 1972; pp 195205. (14) World Health Organization, Environmental Health Criteria 40-Endosulfan, 1984. (15) Barlow, F. Fourth International Congress of Pesticide Chemistry, Zurich, July 24-28, 1978. (16) Singh, N. C.; Dasgupta, T. P.; Roberts, E. V.; Mansingh, A. J. Agric. Food Chem. 1991, 39, 575-579. (17) Bidleman, T. F.; Leonard, R. Atmos. Environ. 1982, 16, 1099-1107. (18) Patton, G. W.; Hinkley, D. A.; Walla, M. D.; Bidleman, T. F. Tellus 1989,41B, 243-255. (19) Hargrave, B. T.; Vass, W. P.; Erickson, P. E.; Fowler, B. R. Tellus 1988, 40B, 480-493. (20) Bidleman,T. F.; Christensen, E. J.;Billings, W. N.;Leonard, R. J. Mar. Res. 1981, 39, 443-464.
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(21) Bidleman, T. F.; Cotham, W. E.; Addison, R. F.; Zinck, M. E. Chemosphere 1992,24, 1389-1412. (22) Bidleman, T. F. Atmos. Environ. 1981, 15, 619-624. (23) Junk, G. A.; Richard, J. J. ACS Symp. Ser. 1984, No. 259, 69-95. (24) Guicherit, R.; Schulting, F. L. Sci. Total Enuiron. 1985,43, 193-219. (25) Hoff, R. M.; Muir, D. C. G.; Grift, N. P. Enuiron. Sci. Technol. 1992, 26, 266-275. (26) Hoff, R. M.; Muir, D. C. G.; Grift, N. P. Enuiron. Sci. Technol. 1992,26, 276-283. (27) Phillips, J., Cory Orchard Supply Co., personal communication, Apr 1991. (28) Hinckley, D. A.; Bidleman, T. A.; Foreman, W. T.;Tuschall, J. R. J. Chem. Eng. Data 1990,35, 232-237.
Received for review June 15, 1992. Revised manuscript received December 23, 1992. Accepted January 12, 1993.
