Environ. Sci. Technol. 2009, 43, 2806–2811
Enantiomeric Signatures of Organochlorine Pesticides in Asian, Trans-Pacific, and Western U.S. Air Masses SUSAN A. GENUALDI,† S T A C I L . M A S S E Y S I M O N I C H , * ,†,‡ TOBY K. PRIMBS,† TERRY F. BIDLEMAN,§ LIISA M. JANTUNEN,§ KEON-SANG RYOO,| AND TONG ZHU⊥ Department of Chemistry, Oregon State University, Corvallis, Oregon, Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon, Science and Technology Branch, Environment Canada, Center for Atmospheric Research, Egbert, Ontario, Andong National University, Andong, South Korea, and College of Environmental Science, Peking University, Beijing, China
Received December 1, 2008. Revised manuscript received February 6, 2009. Accepted February 19, 2009.
The enantiomeric signatures of organochlorine pesticides were measured in air masses from Okinawa, Japan and three remote locations in the Pacific Northwestern United States: Cheeka Peak Observatory (CPO), a marine boundary layer site on the Olympic Peninsula of Washington at 500 m above sea level (m.a.s.l); Mary’s Peak Observatory (MPO), a site at 1250 m.a.s.l in Oregon’s Coast range; and Mt. Bachelor Observatory (MBO), a site at 2763 m.a.s.l in Oregon’s Cascade range. The enantiomeric signatures of composite soil samples, collected from China, South Korea, and the western U.S. were also measured. Thedatafromchiralanalysiswasexpressedastheenantiomeric fraction, defined as (+) enantiomer/(sum of the (+) and (-) enantiomers), where a racemic composition has EF ) 0.5. Racemic R-hexachlorocyclohexane (R-HCH) was measured in Asian air masses at Okinawa and in Chinese and South Korean soils. Nonracemic R-HCH (EF ) 0.528 ( 0.0048) was measured in regional air masses at CPO, and may reflect volatilization from the Pacific Ocean and regional soils. However, during trans-Pacific transport events at CPO, the R-HCH EFs were significantly more racemic (EF ) 0.513 ( 0.0003, p < 0.001). Racemic R-HCH was consistently measured at MPO and MBO in trans-Pacific air masses that had spent considerable time in the free troposphere. The R-HCH EFs in CPO, MPO, and MBO air masses were negatively correlated (p ) 0.0017) with the amount of time the air mass spent above the boundary layer, along the 10-day back air mass trajectory, prior to being sampled. This suggests that, on the West coast of the U.S., the R-HCH in the free troposphere is racemic. Racemic signatures of cis- and trans-chlordane were measured * Corresponding author e-mail:
[email protected]; phone: (541)737-9194; fax: (541)737-0497. † Department of Chemistry, Oregon State University. ‡ Department of Environmental and Molecular Toxicology, Oregon State University. § Environment Canada. | Andong National University. ⊥ Peking University. 2806
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in air masses at all four air sampling sites, suggesting that Asian and U.S. urban areas continue to be sources of chlordane that has not yet been biotransformed.
Introduction Organochlorine pesticides (OCPs) are semivolatile, undergo long-range atmospheric transport, and are persistent in the environment (1, 2). Although most OCPs have been banned in the U.S. for many years, they continue to be detected in ambient air (3, 4). In addition, several OCPs are classified as Persistent Organic Pollutants (POPs), and are being phased out by the United Nations Environmental Program (UNEP) (2). Revolatilization of OCPs from contaminated soils is considered to be a significant source of OCPs to the atmosphere (2, 3, 5). To understand the sources of OCPs to the atmosphere, the geographic origins of the emissions need to be identified (2). Some chiral OCPs are composed of two enantiomers that have the same physical and chemical properties. Therefore, abiotic (hydrolysis, photolysis, etc.) and transport processes (volatilization, deposition, etc.) affect the enantiomers equally (6). OCPs are manufactured and used in racemic form. However, microorganisms in soil and water can selectively degrade one enantiomer over the other, resulting in nonracemic signatures that are retained during transport processes, i.e. volatilized to the overlying air (2). The enantiomeric signatures of chiral OCPs in air masses can provide information about whether a pesticide has been transported from an area where it is currently being used or has not yet been biotransformed (a racemic signature) or has been transported from an area after historic use and biotransformation (a nonracemic signature). The trans-Pacific and regional atmospheric transport of OCPs has been reported at sites in Asia and in the Pacific Northwestern U.S. (1, 7-11). The objectives of this research were to use the enantiomeric signatures of OCPs to distinguish between air masses influenced by trans-Pacific and regional atmospheric transport and to determine if the sources of OCPs to the Pacific Northwestern U.S. were from current or historic use.
Experimental Section Air Sampling. The air sampling sites included Hedo Station Observatory (HSO) on Okinawa, Japan (26.8° N, 128.2° E, 60 m.a.s.l) (9), Cheeka Peak Observatory (CPO) in Washington State (48.3° N, 124.6° W, 500 m.a.s.l) (10), Mary’s Peak Observatory (MPO) in Oregon’s Coast Range (44.5° N, 123.6° W, 1249 m.a.s.l) (10), and Mt. Bachelor Observatory (MBO) in Oregon’s Cascade Range (43.9° N, 121.7° W, 2763 m.a.s.l) (7, 8) (Figure SI.1). The distance from HSO to the East China Sea is 0.2 km, while the distances of CPO, MPO, and MBO to the Pacific Ocean are approximately 3, 26, and 120 km, respectively. HSO, CPO, MPO, and MBO have been previously used to study the atmospheric transport of semivolatile organic compounds (SOCs), including OCPs (1, 7-10). High-volume air samples were collected at HSO during spring 2004 (18 samples) (9), at CPO during 2003 (12 samples) (10), at MPO during 2003 (14 samples) (10), and at MBO during 2004, 2005, and spring 2006 (69 samples) (7, 8) (Table SI.2). Detailed information on the sample collection, OCP extraction procedures and analysis, including solvents and standards used, has been previously reported (7-10, 12) Soil Sampling. Soil samples were collected from four rice paddy fields in China (Nanjing, Tianjin, Guangzhou, and Tangdian) in summer 2006 (Figure SI.1). The sampling sites 10.1021/es803402q CCC: $40.75
2009 American Chemical Society
Published on Web 03/18/2009
were chosen based on their proximity to intense agricultural regions, including the Yangtze and Pearl River Deltas. Rice paddies were chosen because of the large amount of technical HCH historically used in these areas. In 1980, approximately 50% of the HCH applied to agricultural fields in China was applied to rice paddies (13). Technical HCH was banned in China in 1983 and in South Korea in 1985. A previous study estimated the historical usage of technical HCH in China to be extremely high (usage density >40 t/kha) and in South Korea to be very high (usage density 10-40 t/kha) (14). Soil samples were collected from 7 agricultural fields containing beans and hot peppers in provinces in South Korea (Kyeongbuk, Gangwon, Chungnam, Jeonbuk, Jeonnam, Kyeongnam, Ulsan City) in spring 2007. The latitude, longitude, and elevation of each of the soil sampling locations can be found in Table SI.1. Twenty composite soil samples were collected in China, while twenty-one samples were collected from South Korea. Each composite soil sample was collected from 100 m2 × 100 m2 agricultural plots and consisted of 5 random surface (0-20 cm) samples combined and mixed thoroughly. The samples collected were representative of 200,000 m2 (China) and 210,000 m2 (South Korea) of land. Composite soil samples were also collected from CPO, MPO, and agricultural fields in the Willamette Valley, Oregon. A composite soil sample was not collected from MBO due to snow cover and volcanic rock present at the site location. Additional information on the soil extraction and OCP analysis is given in the Supporting Information. Chiral Analysis. Chiral analysis was performed using an Agilent 6890 GC and 5973N MSD (GC/MS) in electron capture negative ionization mode (ECNI). A DB-5MS (28 m, 0.25 mm id., 0.25 µm film thickness, J&W Scientific, USA) column connected to a BGB 172 chiral column (10 m, 0.25 mm id, 0.25 µm film thickness, BGB Analytik, Germany) was used for the enantiomer separation of R-HCH, heptachlor exoepoxide (HEPX), oxychlordane (OXY), cis-chlordane (CC), trans-chlordane (TC), and o,p′-DDT. The DB-5 column minimized interferences during the chiral separation on the BGB 172 column. Extracts were injected (2 µL) using splitless injection with an initial oven temperature of 90 °C. After a 1 min hold, the following temperature program was used: 15 °C/min to 140 °C, 55 min hold, 2 °C/min to 180 °C, 40 min hold, 15 °C/min to 240 °C, 10 min hold, resulting in a total run time of 133 min. The temperatures of the ion source and quadrupole were both 150 °C and the methane gas was 60% of 5 mL/min. The following ions were monitored in selective ion monitoring (SIM) mode: R-HCH (m/z 253, 255, 257), HEPX (m/z 316, 318), OXY (m/z 350, 352), CC and TC (m/z 408, 410, 412), and o,p′-DDT (m/z 246, 248). The enantiomer elution order was determined for R-HCH, CC, and TC using enantiomer (+) pure standards (Dr. Ehrenstorfer, D-86199 Augsburg, Germany). The elution order on the DB-5 column in tandem with the BGB column was (-)R-HCH, (+)R-HCH, (+)TC, (-)TC, (+)CC, (-)CC, (+)HEPX, (-)HEPX, (+)OXY, (-)OXY, (-)o,p′-DDT, (+)o,p′-DDT (15). The concentrations of OCPs in field and laboratory blanks were below the detection limit for chiral analysis (S/N < 3:1). Enantiomer fractions (EFs) are calculated using the following: EF ) area of the (+) enantiomer area of the (+) enantiomer + area of the (-) enantiomer A macro was used to smooth the chromatograms in MSD ChemStation (G1701DA) before manual integration was performed. Seven replicate injections of racemic standards (25 pg/µL) were used to determine the racemic ranges (95% confidence intervals) for R-HCH (0.499 ( 0.0095), TC (0.499 ( 0.0052), and CC (0.497 ( 0.0059). Because the EF precision
of the standards was four decimal places, all EFs are reported to 3 decimal places. To ensure there were no interferences, ion ratios were monitored and required to fall within 20% of the standards. The detection limit for chiral analysis was defined as a S:N ratio >3:1. Although all samples were analyzed for oxychlordane, heptachlor epoxide, and o,p′-DDT, their concentrations were below the detection limit for chiral analysis. Air Mass Back Trajectories and Source Region Impact Factors (SRIFs). Four-day (HSO) and ten-day (CPO, MPO, MBO) air mass back trajectories were calculated for each of the sampling dates using NOAA’s Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) (7-10, 16). Source region impact factors (SRIFs) were calculated to assess the impact of Asia, Siberia, and agriculturally intense areas in Eastern Washington, the Willamette Valley in Oregon, and the Central Valley in California on sampled air masses. SRIFs were calculated by determining the percentage of time an air mass spent in a given source region (Asia, Siberia, California, W. Oregon, E. Washington) during the total 10day (or 4-day in the case of HSO) trajectory time. Details of the calculation of SRIFs have been previously reported and the SRIFs for all air masses are given in Table SI.2 (7-10). The air mass back trajectories were also used to assess the influence of boundary layer (1000 m) air on air masses sampled at MBO and have been previously reported for the air masses sampled at MPO and CPO (Table SI.2) (10).
Results Enantiomeric Signatures of r- HCH. Asia. Six of the eighteen HSO air masses sampled during the spring of 2004 had R-HCH concentrations above the chiral analysis detection limit (S/N > 3:1). In addition, all of these samples had racemic R-HCH signatures, which is defined as EFs falling within the 95% CI of the racemic standard, EF ) 0.499 (Table SI.2). Source region impact factors (SRIFs) were previously calculated for each HSO air mass to identify their source regions, including China, Korea, Japan, Russia, and ocean/local (9). The concentrations of R-HCH ranged from 5.94 to 36.2 pg/m3, and elevated concentrations were measured in air masses associated with China (9). Of the six HSO air masses with R-HCH concentrations above the detection limit for chiral analysis, three were primarily from China (Apr 1-2, Apr 2-3, Apr 3-4, 2004) and the other three were primarily from ocean/local (Mar 30-31, Apr 26-27, Apr 27-28) (Table SI.2). All of these HSO air masses had racemic R-HCH signatures, suggesting that the R-HCH outflow from China and Japan is racemic. Racemic R-HCH signatures were also measured in all of the Chinese and South Korean soil samples that had concentrations above the detection limit for chiral analysis, including 10 of 20 composite soil samples collected from rice paddies in China and in 4 of 21 composite soil samples from agricultural fields in South Korea (Table SI.1). The R-HCH concentrations ranged from
