Environ. Sci. Technol. 1997, 31, 1390-1398
Chlorpyrifos in the Air and Surface Water of Chesapeake Bay: Predictions of Atmospheric Deposition Fluxes L A U R A L . M C C O N N E L L , * ,† E R I C N E L S O N , ‡ CLIFFORD P. RICE,† JOEL E. BAKER,‡ W. EDWARD JOHNSON,† JENNIFER A. HARMAN,‡ AND KRYSTYNA BIALEK† U.S. Department of Agriculture, Agricultural Research Service, Environmental Chemistry Laboratory, Building 007, Room 225, Beltsville, Maryland 20705, and Chesapeake Biological Laboratory, Center for Environmental and Estuarine Studies, University of Maryland System, Solomons, Maryland 20688
A 1993 survey including eight stations down the center of the Chesapeake Bay mainstem, four times during the year, resulted in detection of chlorpyrifos in 100% of air and water samples. Water concentrations were higher in March and April, coinciding with the spring flush from the Susquehanna River (1.67-0.25 ng L-1). The lowest water concentrations were found in September (0.25-0.045 ng L-1). Air concentrations were lowest in March (2-3 pg m-3). Air concentrations were highest in June in the southern Bay region (95 pg m-3). Atmospheric loadings of chlorpyrifos to the Chesapeake Bay mainstem were estimated for the four sample collection periods using fugacity-based equations. Net volatile loss of chlorpyrifos across the surface area of the Bay was predicted in March and April at 147 and 145 g day-1, respectively, while net deposition was predicted for June and September at 85 and 56 g day-1, respectively. A comparison of atmospheric loadings to the Bay with total load within the surface water illustrates that, during the mid to late summer, atmospheric loadings become an important contributor to the Bay chlorpyrifos budget.
crops has recently been published (3). In addition to agricultural use, chlorpyrifos, whose formulated products include Dursban, Equity, and Tenure (Dow Elanco), is heavily used in urban areas as a termiticide. Chlorpyrifos is also used on turfgrass for pest control as well as in home pest control. Heavy agricultural activity as well as large human populations along the shorelines of waterways that feed the Chesapeake Bay and along the shore of the Bay itself may contribute to large amounts of chlorpyrifos being released into this productive, yet delicate, ecosystem. Bioconcentration factors (BCF) for various aquatic organisms have been measured under ambient conditions and range from 100 for bluegill (Leposmis macrochirus) at a chlorpyrifos concentration of 0.41 µg L-1 over 33 days in an artificial stream (4) to 1344 for largemouth bass (Micropterus salmoides) at a concentration of 0.3-2.9 µg L-1 over 3 days in a small pond (5). A comparison of various BCF studies show that bioconcentration of chlorpyrifos increases with increasing water concentration and decreases in the presence of suspended sediments in the water column (3). Also, chlorpyrifos is depurated quickly from the organisms if the treatment is stopped (3). Toxicity studies of chlorpyrifos for animals resulted in LC-50 (96 h) values ranging from 0.035 to 1.5 µg L-1 for aquatic invertebrates and teleosts and from 0.13 to 520 µg L-1 in fish (6). The fate of chlorpyrifos in surface waters and in the atmosphere has received little attention, especially within the Chesapeake Bay. Only one published study, limited to the northern Chesapeake Bay region, has included chlorpyrifos as a target analyte (7). Data included in this paper are part of a larger, on-going study of pesticide concentrations in the air and surface water of Chesapeake Bay. The occurrence of chlorpyrifos in virtually every sample collected at levels above limits of detection was unexpected and therefore led to this closer inspection. Air and surface water concentration data from four sample collection trips down the center of the Chesapeake Bay are presented. The physical-chemical properties of chlorpyrifos, the measured concentrations, and the environmental conditions found in Chesapeake Bay were incorporated in to a fugacity-based model developed by Mackay (8) that focuses on the transport processes which occur within the atmosphere and surface waters. The results will be used to determine the most important atmospheric processes that regulate the fate of chlorpyrifos within the Chesapeake Bay ecosystem.
Introduction
Experimental Section
The most heavily used insecticide within the Chesapeake Bay watershed (Figure 1) is chlorpyrifos [O,O-diethyl O-(3,4,5trichloro-2-pyridyl)phosphorothioate]. Annual usage of chlorpyrifos in the United States for agricultural and nonagricultural applications was estimated at 4.5-9 million kg yr-1 in 1990/1991 (1). Within the estuarine drainage area (areas directly surrounding estuaries) of the Mid-Atlantic region, 66 000 kg yr-1 of chlorpyrifos was used in 1987 on agricultural crops such as corn and alfalfa, with the largest portion (45 000 kg yr-1) used within the Chesapeake Bay drainage area (2). In the vicinity of the Chesapeake Bay, agricultural use of this broad spectrum insecticide is mainly during the months of April, May, and June (2). The standard application rate is 0.56-2.24 kg a.i. ha-1 for corn, and an extensive review of application rates and methods for various
Four separate collection trips were conducted in 1993 aboard the University of Maryland R/V Aquarius. The dates were as follows: 3/8-3/11, 4/12-4/14, 6/1-6/4, and 9/20-9/23. Eight stations were selected to collect water samples (Figure 1). Cruises were initiated from the Chesapeake Biological Laboratory in Solomons, MD. The cruise track began by traveling to station 1 at the northern end of the Chesapeake Bay. Typically stations 1 and 2 were sampled the first day, stations 3 and 4 were sampled the second day, and stations 5-8 were sampled on the third day. Water was pumped onboard using a length of clean tygon tubing lowered to approximately 2 m below the water surface attached to a peristaltic pump. Fifty liters of water was pumped through a 293 mm diameter glass fiber filter (Schleicher & Schuell No. 25, 0.7 µm nominal pore size) into a clean 50-L stainless steel tank. The water was then pulled through a 2.54 cm i.d. glass column containing a 10-cm bed of XAD-2 resin at approximately 200 mL min-1 using a small peristaltic pump. Methods used for precleaning of the XAD-2 resin and for extraction of columns are described in detail
* Corresonding author telephone: (301) 504-6298; fax: (301) 5045048; e-mail:
[email protected]. † U.S. Department of Agriculture. ‡ Chesapeake Biological Laboratory.
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S0013-936X(96)00614-1 CCC: $14.00
1997 American Chemical Society
FIGURE 1. Map of the Chesapeake Bay and the Chesapeake Bay watershed illustrating water sample collection stations and the segmentation scheme of model calculations including surface area (SA) and volume of water (Vol) within each segment. elsewhere (9). Glass fiber filter samples were not extracted in this study. The sample material was extracted using a Soxhlet apparatus with a 1:1 acetone:hexane solvent mixture. The extract was concentrated using a nitrogen gas blowdown. In order to determine the collection efficiency of the XAD-2 column, two breakthrough experiments were conducted onboard ship. A second XAD-2 column was placed in line behind the first to collect pesticide residues that were not collected by the first column. The ratio of chlorpyrifos found on the second column to that on the first was 0.018 for the first experiment and 0.066 for the second, confirming excellent collection efficiency by the XAD-2 column method. Three laboratory single-column spike recovery experiments of 50 L of distilled water confirmed adequate collection efficiency of the column with 60-85% chlorpyrifos recovered. The stainless steel tanks were rinsed with hexane and acetone
after each sample, and this solvent was collected and combined with the resin extracts for that sample. Duplicate 50-L samples were collected and extracted side by side on three occasions over the four cruises, and the results of these duplicate samples differed by 1.5%, 10%, and 24% (Figure 2). The largest differences between the duplicate samples were found for those with the lowest concentrations. Three laboratory and two field blank XAD-2 columns were extracted and analyzed. Chlorpyrifos was detected in only one out of five blanks at a level equal to 0.26 ng or to a 0.005 ng L-1 water sample concentration. This blank value is equal to 10% of the lowest sample concentration observed in this project. Therefore, no attempt was made to correct for blank values. The limit of detection for chlorpyrifos was defined as 10% below the lowest point of the four-point calibation curve or 0.0045 ng µL-1 or 2.25 ng at an extract volume of 500 µL.
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FIGURE 2. Dissolved-phase concentrations of chlorpyrifos from different stations in the Chesapeake Bay during four sample collection cruises (ng L-1). Note duplicate results in March, station 7; June, station 2; and September, station 8. Sample concentrations were not corrected for spike recovery values. Air samples were collected from onboard the R/V Aquarius during each cruise. A General Metal Works modified highvolume sampler (Model GPNY1123) was equipped with two 20.3 × 25.4 cm rectangular glass fiber filters (Gelman A/E) followed by two 7.6 × 7.6 cm polyurethane foam plugs held within a glass sleeve. The flow rate through the sampler ranged from 0.47 to 0.84 m3 min-1, and the total air volume collected was 273-660 m3. Three air samples were collected during each cruise. The first sample of each cruise was collected in the northern half of the Bay during the trip from Solomons, MD, to the first collection station, to the second station, and then to Sandy Point State Park near Annapolis, MD. The second air sample of each cruise was collected during the trip from Sandy Point to stations 3 and 4 and to Solomons. The third sample was collected during the trip from Solomons to stations 5-7 (and sometimes 8) and to the docking area near Norfolk, VA. Polyurethane foam plugs were cut with a drill from foam sheets (Olympic Products Corp., Greensboro, NC, Type 3014) using an untreated wood template and a key-hole saw attachment. Foam plugs were precleaned using deionized, distilled water, followed by Soxhlet extraction techniques with pesticide-grade acetone followed by petroleum ether (Burdick and Jackson, high purity solvent), and dried within a vacuum desiccator and kept in solvent-rinsed glass jars with Teflon-lined lids until use. Filters were wrapped individually in aluminum foil pockets and baked at 400 °C before use. After collection, the filter was folded face inward and placed back into the clean foil pocket, and PUF plugs were returned to the original jars and kept frozen until extraction. The sampler was mounted on the upper deck of the R/V Aquarius, and collections were made
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during the day while the vessel was under way and while at the stations. Exhaust from the vessel was located under the water at the stern of the ship, minimizing the possibility of contamination. Foam plugs were extracted separately using a Soxhlet extraction apparatus with petroleum ether for 12 h. Extracts were reduced to 5-10 mL using a rotary evaporator and further reduced to 250 µL using a gentle stream of chromatographic grade (99.9%) N2 gas. Air filters were also extracted using a Soxhlet extraction apparatus using chromatographic grade methylene chloride (Burdick and Jackson, high purity solvent) for 12 h. Two unused foam plugs were transported with sample plugs and were extracted along with samples for each cruise to observe any matrix interferences or any contamination from the field or from laboratory procedures. While traces of chlorpyrifos were observed in four out of eight blanks, all were below the limit of detection (LOD ) 2.25 ng). Therefore, sample results were not corrected for blank levels. One foam plug per cruise was spiked with a mixture of target analytes including chlorpyrifos. Recovery of chlorpyrifos ranged from 81 to 95%. Sample concentrations were not corrected for spike recovery results. Chlorpyrifos was detected in 100% of the front polyurethane foam extracts from this study. Breakthrough to the second foam plug was generally 1000) is determined for a specific phase, equilibrium concentrations within that phase are expected to be higher. In the case of chlorpyrifos, the particle phases in air and water have the highest values of Z. For example for sample 1-1, Za ) 4.26 × 10-4 (air), Zw ) 5.5 (water), ZR ) 4.5 (rain), Zq ) 4.9 × 105 (air particles), and Zp ) 1.7 × 104 (water particles). Therefore, you would expect the highest concentration of chlorpyrifos to be found in the particle phases of the air and water. As stated earlier, levels of chlorpyrifos in filter extracts were below the limit of detection. This is due to the small amount of particulate material actually sampled. The volume fraction (v) of particulate material within the bulk air or bulk water is small ( Dq (rain-particle) > Dv (air-water gas) > Dd (dry particle). Next, the fugacity (or partial pressure) of chlorpyrifos within the bulk air and bulk water (fa and fw) are calculated utilizing a linear relationship (8):
C ) Zf
(8)
The bulk air and bulk water concentrations are combined with Zba and Zbw to obtain fugacity for the air and water (fa and fw). Then, the flux, N, of chlorpyrifos across the airwater interface from the various processes is calculated from the general equation:
N ) fD
(9)
Model predictions were generated for each water sample, and results were combined to calculate flux values for each of the five segments of the Bay for each cruise (Figure 1). In the case where two stations fell within one segment or if duplicate measurements were made at one station, the results were averaged. Figure 5 is a representation of the predicted total flux (in mg km-2 day-1) from air to water for each segment of the Bay for each cruise. Each bar is divided to show the contribution of different types of flux: wet dissolved, wet particle, dry particle, and net air-water gas exchange. Some bars have positive values and represent a flux from water to air or net volatilization. In the case where there are positive and negative bars for one segment, the net overall flux is the difference between the positive and negative values. During the March and April cruises, the net exchange across the air-water interface was dominated by volatile loss from the surface water by gas exchange. The gas exchange
flux was driven by high water concentrations in combination with low air concentrations. Wet and dry deposition processes made only minor contributions to the net flux as a limited amount of chlorpyrifos was present in the atmosphere. Despite the cold water temperatures and low effective KH values favoring absorption, net volatile loss through gas exchange was observed in each segment of the bay. In June and September, gas exchange was also the most important contributor to the overall flux; however, the direction of the net flux was from air to water. Higher air concentrations were the controlling factor during this time period with the highest fluxes for gas exchange, dry deposition, and wet deposition predicted in the two southern sections where the highest air concentrations were observed. These two sections also represent large surface areas as compared to the northernmost sections. Thus, despite higher surface water temperatures that would favor volatile loss from the surface water by increasing the effective KH for chlorpyrifos, water concentrations were too low to force the flux from water to air. The total load (in g day-1) for each section of the bay for each of the four months was calculated from the flux rate (Figure 5) and the surface area of the sections (Figure 1) to obtain a total load for the Bay. During March, the predicted overall loss rate from the entire Bay surface area was 147 g day-1, and in April the predicted net loss was 145 g day-1. If a constant loss rate over the entire month of March and April is assumed, this loss would account for approximately 13% and 11%, respectively, of the total chlorpyrifos in the surface layer of water in the Bay. In June and September, the net transfer into the Bay surface water from the atmosphere was 85 and 56 g day-1, respectively, or 0.88% and 0.83% of the total surface water load, respectively. At a constant loading
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rate over the month of June, the surface water budget could be increased by 26%, and in September the increase could equal 25%. These results suggest that, in the spring, inputs from river flow are the most important source of chlorpyrifos to the Bay with approximately 10% loss to the atmosphere per month. However, between June and September riverine inputs decrease and atmospheric inputs become more important as a source to the Bay due to increased air concentrations. While this study was limited to only eight stations, the differences in results from site to site and season to season illustrate the need for more detailed studies of atmospheric deposition fluxes within the Chesapeake Bay. Air and surface water and rain concentration measurements from several sites over at least 1 year are needed to gain a truly accurate picture of the atmospheric deposition loadings cycles for chlorpyrifos. Measurements of degradation product concentrations are also needed to estimate environmental half-lives of chlorpyrifos in Bay surface water and air. Disclaimer. Mention of a specific product or supplier is for identification only and does not imply endorsement by the U.S. Department of Agriculture to the exclusion of other suitable products or suppliers.
Supporting Information Available A sample spreadsheet containing all equations and showing all calculations for a single sample station (3 pp) will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the Supporting Information from this paper or microfiche (105 × 148 mm, 24× reduction, negatives) may be obtained from Microforms Office, American Chemical Society, 1155, 16th St. NW, Washington, DC 20036. Full bibliographic citation (journal, title of article, names of authors, inclusive pagination, volume number, and issue number) and prepayment, check or money order for $12.00 for photocopy ($14.00 foreign) or $12.00 for microfiche ($13.00 foreign), are required. Canadian residents should add 7% GST. Supporting Information is also available via the World Wide Web at URL http://www.chemcenter.org. Users should select Electronic Publications and then Environmental Science and Technology under Electronic Editions. Detailed instructions for using this service, along with a description of the file formats, are available at this site. To download the Supporting Information, enter the journal subscription number from your mailing label. For additional information on electronic access, send electronic mail to
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Literature Cited (1) Johnson, W. E.; Plimmer, J. R.; Kroll, R. B.; Pait, A. S. In Perspectives on Chesapeake Bay, 1994: Advances in Estuarine Sciences; Nelson, S., Elliott, P., Eds.; Chesapeake Research Consortium: Edgewater, MD, 1994; pp 105-145. (2) Pait, A. S.; DeSouza, A. E.; Farrow, D. R. G. Agricultural Pesticide Use in Coastal Areas: A National Summary; National Oceanic and Atmospheric Administration: Rockville, MD, 1993; 112 pp.
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(3) Racke, K. D. Rev. Environ. Contam. Toxicol. 1993, 131, 1-54. (4) Eaton, J.; Arthur, J.; Hermanutz, R.; Kiefer, R.; Mueller, L.; Anderson, R.; Erickson, R.; Nordling, B.; Rogers, J.; Pritchard, H. In 8th Symposium on Aquatic Toxicology and Hazard Assessment; Bahner, R. C., Hansen, D. J., Eds.; ASTM: Philadelphia, PA, 1985; pp 85-118. (5) Macek, K. J.; Walsh, D. F.; Hogan, J. W.; Holz, D. D. Trans. Am. Fish. Soc. 1972, 3, 420-427. (6) Odenkirchen, E. W.; Eisler, R. Chlorpyrifos hazards to fish, wildlife, and invertebrates: a synoptic review. U.S. Fish Wildl. Serv. Biol. Rep. 1988, 85, 1.13, 34 pp. (7) Kroll, R. B.; Murphy, D. L. Pilot Monitoring Project for 14 Pesticidesin Maryand Surface Water; Maryland Department of the Environment: Baltimore, MD, 1993. (8) Mackay, D. Multimedia environmental models, the fugacity approach; Lewis: Chelsea, MI, 1991; 257 pp. (9) Baker, J. E.; Eisenreich, S. J. J. Great Lakes Res. 1989, 15, 84-103. (10) Schubel, J. R.; Pritchard, D. W. In Contaminant problems and management of living Chesapeake Bay resources; Majumdar, S. K., Hall, L. W., Ausin, H. M., Eds.; Pennsylvania Academy of Science: Easton, PA, 1987; pp 1-32. (11) Meikle, R. W.; Youngson, C. R. Arch. Environ. Contam. Toxicol. 1978, 7, 13-22. (12) Gianessi, L. P.; Puffer, C. A. The use of selected herbicides and insecticides in the coastal counties of the United States; Quality of the Environment Division, Resources for the Future: Washington, DC, 1990; Contract NA89AA-D-0M012; 110 pp. (13) Wauchope, R. D.; Young, J. R.; Chalfant, R. B.; Marti, L. R.; Summer, H. R. Pestic. Sci. 1991, 32, 235-243. (14) Whang, J. M.; Schomburg, C. J.; Glotfelty, D. E.; Taylor, A. W. J. Environ. Qual. 1993, 22, 173-180. (15) Rice, C. P.; Chernyak, S. M.; McConnell, L. L. J. Agric. Food Chem. In press. (16) Majewski, M. S.; Glotfelty, D. E.; Seiber, J. N. Atmos. Environ. 1989, 23, 929-938. (17) U.S. Department of Agriculture Pesticide Properties Database. Systems Research Laboratory, Beltsville, MD, 1990. (18) Glotfelty, D. E.; Seiber, J. N.; Liljedahl, L. A. Nature 1987, 325, 602-605. (19) Leister, D. L.; Baker, J. E. Atmos. Environ. 1994, 28, 1499-1520. (20) Thomann, R. V.; Collier, J. R.; Butt, A.; Casman, E.; Linker, L. C. Response of the Chesapeake Bay water quality model to loading scenarios; U.S. EPA, Chesapeake Bay Program: Annapolis, MD, 150 pp. (21) Mackay, D.; Yuen, A. T. K. Environ. Sci. Technol. 1983, 17, 211217. (22) Junge, C. E. In Fate of Pollutants in the Air and Water Environments; Suffet, I. H., Ed.; Wiley: New York, 1977; Part I, pp 7-26. (23) Bidleman, T. F. Environ. Sci. Technol. 1988, 22, 361-367. (24) Cotham, W. E.; Bidleman, T. F. Environ. Sci. Technol. 1992, 26, 469-478. (25) Whitby, K. T. Atmos. Environ. 1978, 12, 135-159. (26) Spencer, W. F.; Cliath, M. M. Residue Rev. 1983, 85, 57-69.
Received for review July 15, 1996. Revised manuscript received January 3, 1997. Accepted January 14, 1997.X ES960614X X
Abstract published in Advance ACS Abstracts, March 15, 1997.
