Chlordane Enantiomers and Temporal Trends of...
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Research Chlordane Enantiomers and Temporal Trends of Chlordane Isomers in Arctic Air T E R R Y F . B I D L E M A N , * ,† LIISA M. M. JANTUNEN,† PAUL A. HELM,‡ EVA BRORSTRO ¨ M - L U N D EÄ N , § A N D SIRKKA JUNTTO# Meteorological Service of Canada, 4905 Dufferin Street, Downsview, Ontario, M3H 5T4, Canada, Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario, M5S 1A4, Canada, Swedish Environmental Research Institute, Box 47086, Gothenburg, SE-402 58, Sweden, and Finnish Meteorological Institute, Sahaajankayu 20E, FIN-00810, Helsinki, Finland
A 14-year data set (1984-1998) for chlordane compounds in arctic air was examined to discern temporal trends. transChlordane (TC), cis-chlordane (CC), and trans-nonachlor (TN) declined significantly (p < 0.001-0.02), with apparent times for 50% reduction of 4.9-9.7 y. The isomer fraction of TC ) (TC/(TC + CC) also declined significantly (p < 0.0010.014) over the same time period. The enantiomeric composition of TC and CC was determined in air samples collected at arctic stations in Canada (1993-1996), Russia (1994), and Finland (1998), and a temperate station on the Swedish west coast (1998). Enantiomer fractions, EF ) (+)/[(+) + (-)], were significantly different from measured EFs of racemic standards (0.498-0.501) at all stations for TC (p < 0.001) and two stations for CC (p < 0.001 to 90%. Samples from Pallas and Ro¨rvik were Soxhlet extracted with acetone. The acetone was diluted with water, and the analytes were partitioned into pentane-ethyl ether. Surrogates of o,p′-DDD and -hexachlorocyclohexane (-HCH) were added, and cleanup was achieved by shaking with concentrated sulfuric acid. The extract was then fractionated on aluminum oxide. Determination was made by capillary GC with electron capture detection using a 50-m × 0.25 mm i.d. CP-Sil 8CB column (Chrompack, Holland). Samples were corrected for the surrogate recoveries, which ranged from 50 to 70%. Enantiomers were separated by chiral-phase capillary gas chromatography with detection by negative ion mass spectrometry using a Hewlett-Packard 5890GC - 5989B MSEngine or 6890 GC - 5973 Mass Selective Detector and two columns: (a) 20% permethylated β-cyclodextrin in SPB-25 (Betadex-120, Supelco, U.S.A., 30 m × 0.25 mm i.d., 0.25 µm film) and (b) 20% tert-butyldimethylsilyl-β-cyclodextrin in OV-1701 (BGB-172, BGB Analytik, Switzerland, 30 m × 0.25 mm i.d., 0.25 µm film). These two columns are referred to
TABLE 2. Temporal Trends of Chlordane Concentrations (pg/m3) and FTC in Arctic Air slope (m)
p
Ln TC ) m*year + b -0.1409 0.1). EFs of HEPX were determined in 3-7 samples from each station and were highly nonracemic (p < 0.001) in all cases with enrichment of the (+) enantiomer (Table 3). Chlordanes and HEPX are often nonracemic in agricultural soils (18, 19, 33, 34) and overlying air (35) and in ambient air of the Great Lakes region (19, 20, 21, 35) and show the same order of enantiomer depletion/enrichment as the air samples in this study (Table 4). Soils from the U.K. also contained nonracemic TC and CC (Table 4) (36). Chlordanes in ambient air in or near southern U.S.A. municipalities are racemic (1). The source of chlordane in this situation may be its former usage as a termiticide. Indoor air sampled in eight southern U.S. (1, 20) and 30 midwestern U.S. (37) homes contained
racemic chlordanes and at concentrations orders of magnitude higher than ambient air levels. The nonracemic chlordanes and HEPX in arctic air provide strong evidence that soil-derived pesticides are revolatilizing in warmer regions of the Northern Hemisphere and undergoing longrange atmospheric transport. Have chlordanes in arctic air always been nonracemic? This is difficult to answer because no air samples from the 1980s and earlier are available for examination. However, chlordanes in Arctic Ocean surface water were racemic (EFs ) 0.499 for TC and 0.501 for CC) for samples collected in 1994. Most of these samples were collected between 72 and 90° latitude and under ice cover (9), and the surface water would thus have been removed from the influence of atmospheric exchange. The racemic EFs in water may represent chlordane loadings to the Arctic Ocean sometime in the past. HEPX in ocean water was nonracemic with an average EF ) 0.639 (9). Racemic chlordane and nonracemic HEPX EFs in arctic cod (Boreogadus saida), which feed on zooplankton, reflect those in water (38). Sources of HEPX include metabolism of heptachlor in soils and photochemical oxidation of heptachlor. The former process is thought to yield HEPX enriched in the (+) enantiomer, as occurs when heptachlor is metabolized by rat liver microsomes, while the second yields racemic HEPX (39). The nonracemic HEPX in air samples from temperate regions suggests that emission from soils is the primary source (35). Current EFs of HEPX in arctic air (0.662-0.703) are somewhat higher than those in Arctic Ocean surface water (0.639) suggesting that in the past atmospheric transport of heptachlor and photochemical production of HEPX was greater than today. Photolysis of heptachlor, either in arctic air or at lower latitudes and advected into the Arctic, is indicated by the occurrence of photoheptachlor in ringed seal blubber from the Canadian Arctic (13). It appears that sources of chlordane have shifted over time, from atmospheric transport of the freshly applied VOL. 36, NO. 4, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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pesticide to a greater proportion of chlordane “recycled” from soils. The nonracemic HEPX in arctic air and seawater exemplifies the volatilization of soil residues on a large scale and the influence on atmospheric levels in remote regions. Fresh releases of organochlorine pesticides are expected to cease under the recently signed global POPs protocol, and chemical markers will become increasingly useful for distinguishing “old” and “new” sources.
Acknowledgments Support for this work was provided by Indian and Northern Affairs Canada, Northern Contaminants Program. We thank Phil Fellin and Henrik Li, AirZOne, for supplying archived air sample extracts from Alert and Dunai. Thanks also to Pierrette Blanchard and Hayley Hung (MSC) for sharing their data on chlordane levels in air prior to publication.
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Received for review July 17, 2001. Revised manuscript received October 1, 2001. Accepted October 17, 2001. ES011142B
