Environ. Sci. Technol. 1997, 31, 1879-1882
Regional Patterns in Organochlorine Contamination of Saxifrage from Ellesmere Island in the High Arctic (77-81° N) R . L . F R A N C E , * ,† D . G . C . M U I R , ‡ A N D M. D. SEGSTRO‡ Harvard University, Graduate School of Design, 48 Quincy Street, Cambridge, Massachusetts 02138, and Department of Fisheries and Oceans, Freshwater Institute, 501 University Cresent, Winnipeg, Manitoba, Canada R3T 2N6
Previous atmospheric and precipitation sampling on Ellesmere Island in the Canadian High Arctic (76-83° N) has detected the presence of trace contaminants originating from both mid-latitudinal and trans-polar sources. Plant samples (Saxifraga oppositofolia) were collected along a latitudinal transect from seven remote sites on Ellesmere Island in order to determine the most likely influx pathway of organochlorine (OC) pollution to this region. Toxaphene, HCH, CBz, CHL, and DDT residues and selected PCB homolog groups decreased with northward distance indicating the predominance of North American sources. Further, all OC concentrations in saxifrage were found to be related to plant cesium-137 activities and therefore differences in the deposition of southerly-originating pollutants. The close association between these residues of micropollutants raises the possibility that the logistically much easier measurements of cesium-137 uptake could be used as a convenient environmental monitor of regional patterns in OC deposition in locations where pathways of atmospheric transport are similar.
Introduction Determination of the source vectors and bioaccumulation of anthropogenic chemicals in the North American Arctic has received considerable attention (e.g., refs 1-3). Ellesmere Island, the ninth largest island in the world and the northernmost land mass in North America (76-82° N), seems to be a receiving nexus for the deposition of trace contaminants that originate from different long-range transport pathways. Transects of cesium-137 activity in both soils and plants on Ellesmere Island indicate a south-to-north transport of pollution from mid-latitudinal sources (4,5). Analysis of lead concentrations and stable isotope ratios in plants and air from Ellesmere Island indicate, in contrast, a north-tosouth transport of trans-polar pollution from Eurasian sources (6; R. France and J. Blais, in preparation). Atmospheric and precipitation monitoring of organochlorine (OC) contaminants in the Canadian Arctic has suggested both North American (7) and Eurasian (8) sources. Because OCs have been detected in the air, snow, and biota from only localized sampling sites on Ellesmere Island (9-13), the present study was designed to undertake the first latitudinal * Author to whom correspondence should be addressed. † Harvard University. ‡ Freshwater Institute.
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transect of OC contamination in the High Arctic to determine the most likely influx pathway of OC pollution to this region.
Materials and Methods Saxifrage (Saxifraga oppositofolia) samples were collected from seven sites located along a transect from 81 to 77° N (5) during spring 1990 as part of the Arctic Light Trans-Ellesmere Island Ski Expedition (14). Additional saxifrage samples (unreplicated or duplicated) were collected from a site in Makinson Inlet on southern Ellesmere Island (77° N) and from another site on nearby Axel Heiberg Island (79°30′ N, 87°30′ W). Plants were obtained from windswept ridges thought to be free of snow for much of the year. Triplicate samples of nonflowering clumps (both live and dead material) were gathered from areas ranging between 10 and 50 m2 at each site and stored frozen in aluminum foil envelopes placed within sealed plastic bags. The sealed samples were shipped to the analytical laboratory where they were stored at -40 °C until analysis (5, 6, 13). In brief, for OC analysis, samples were partially thawed within their sealed bags, and 10-g (fresh weight) amounts were mixed with acetone and held at -10°C for 16 h to dry the sample and partially extract the OCs. Internal recovery surrogates of aldrin and octachloronaphthalene (OCN) were added at the extaction step. Moisture was determined on a separate subsample by drying to constant weight. The dried saxifrage residue was then blended with dichloromethane. Extracts were evaporated, exchanged into hexane, and fractioned on Florisil columns. OCs were measured by capillary gas chromatography using procedures described in Muir et al. (15, 16) and France et al. (13). Toxaphene and other OCs were confirmed by high-resolution electron ionization mass spectrometry (HREIMS) or electron capture negative chemcial ionization MS (13). Total PCBs (∑PCB) consisting of 85 peaks (including co-eluting congeners) were quantified using external standards (NRC, Halifax, NS; Ultra Scienitifc, Hope, RI) as described in Muir et al. (15, 16) and France et al. (13). Cesium-137 activity was measured on a GE counter as described in France et al. (5). Recovery efficiencies of the internal standards aldrin and OCN ranged from 85 to 95%. Blank analyses were free of major interfering GC-ECD peaks, which permitted low detection limits (13). Data presented here are for only the most abundant OC residues found in plants from Ellesmere Island: toxaphene, ∑HCH (sum of R-, β-, and γ-hexachlorocyclohexane isomers), ∑CBz (sum of 1,2,4,5-tetrachlorobenzene (T4CBz), 1,2,3,4-T4CBz, petacholobenzene, and heaxchlorobenzene (HCBz)), ∑CHL (sum of chlordane-related compounds cis- and trans-chlordane, cis and trans-nonoachlor, heptachlor, heptachlor epoxide, nonachlor III, and C5), ∑DDT (sum of o,p′-DDE, -DDD, and -DDT), and selected PCB homologs.
Results and Discussion With the exception of ∑PCBs (not shown), the other OCs displayed decreases in saxifrage accumulation with northward distance on Ellesmere Island (Figure 1). In this respect, patterns in OC accumulation in saxifrage on Ellesmere Island are similar to that shown by cesium-137 (5) but not lead (R. France and J. Blais, in preparation). This evidence suggests that the primary source of OCs to this region of the High Arctic is through atmospheric deposition from mid-latitudinal North American sources and not as a result of trans-polar deposition from Eurasian sources. Other studies have recorded northward decreases in OC residues in northern hemisphere biota (e.g., refs 17-19) and sediments (16, 20) and have interpreted these latitudinal
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FIGURE 1. Variability in organochlorine contamination of saxifrage in relation to latitude on Ellesmere Island. Means ( SEs are based on two, three, and two independent sample sites for respective south-to-north latitudinal categories. Organochlorine contamination in plants at 80-81° N was significantly different (p < 0.05, Duncan’s multiple range test, ANOVA) from those at 79-80° N or 77-79° N, which in turn did not differ. gradients as being due to temperature-related processes of global fractionation and condensation (21, 22). In the present case, we believe that the limited 4° latitudinal range of our sampling transect is too narrow for differential fractionation processes to account for the observed pattern in OC accumulation shown in Figure 1. Instead, we suggest that differences in the saxifrage accumulation of OCs with latitude merely reflect consistent regional patterns in the deposition of southerly-originating pollutants. Expressing OC accumulation with respect to cesium-137 activity for saxifrage samples allows for inter-site comparisons to be made that accommodate differences in the localized deposition of trace contaminants due to variable precipitation. In the present case, this resulted in the reordering of two sampling sites that had been formerly based on latitude in Figure 1. Organochlorine concentrations in Ellesmere Island saxifrage were found to be related to plant cesium-137 activities, although steeper slopes existed for ∑DDT and toxaphene than for ∑HCH, ∑CBz, ∑CHL (Figure 2), and ∑PCB (Figure 3). Within the PCB group, octa- and heptachlorobiphenyls (not shown) were found to have steeper slopes in relation to cesium-137 activity than hexa-, penta-, tetra-, and trichlorobiphenyls (not shown). Other studies that have used actual precipitation data to estimate plant uptake of OCs have met with only limited success (15, 23). Independent samples from Makinson Inlet on Ellesmere Island (77° N) and across from Eureka at Buchanan Lake on Axel Heiberg Island (79° N) indicate that not only were all OC residues lower at the more northern site in support of the transect data in Figure 1 but also that the relative differences between the two sites were greater for toxaphene and ∑DDT than for any of the other OCs as would be expected from the trends shown in Figures 2 and 3 (Figure 4). Inter-site variability in OC accumulation in saxifrage was not related to differences in either the physical characteristics of the sampling sites (distance from the coast, elevation, substrate typology, site topography, immediate surface
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FIGURE 2. Relationships between organochlorine concentrations (mean normalized to facilitate comparison among different absolute concentrations) and cesium-137 activities in samples of Ellesmere Island saxifrage. Cesium-137 data are from France et al. (5). All slopes are significant at p ) 0.01. Presented OC data are sitespecific means, with average per site SDs (not shown for clarity) of (13% of these means. moisture conditions, windbreaks or obstructions within 100 m, surrounding area characteristics within 1000 m, and site orientation) or to differences in plant growth efficiencies due to water content as measured by stable carbon isotope analysis (R. France, unpublished data). We presently have no detailed explanation as to why cesium-137 acivity is more closely associated with toxaphene, ∑DDT, and the higher chlorinated PCB homologs than it is with ∑CBz, ∑CHL, and the lower chlorinated PCB homologs in saxifage, although it is possible that differing partitioning of these elements to the plant surfaces may be responsible. Saxifrage, a vascular plant, has a waxy outer surface on its branches making it ideal for scavenging airborne organics. The correspondence of high cesium with toxaphene and ∑DDT implies that these less volatile OCs, which have high proportions in the particle phase during winter temperatures, may reach the plants via a common (particle deposition) pathway. Although high volatility OCs (i.e., HCH and HCB) predominate in polar air (2, 24), they also readily volatilize from plant and soil surfaces because of their higher vapor pressures and lower plant-air partition coefficients. It is the less volatile, more chlorinated components that are retained on the plants in disproportionate amounts relative to their concentrations observed in air at Alert on northern Ellesmere
FIGURE 4. Scatter plot between slopes of organochlorine concentrations to cesium-137 activities from Figures 2 and 3, and ratios between organochlorine concentrations in saxifrage from a site in Makinson Inlet on Ellesmere Island (77° N) compared to a site on Axel Heiberg Island (79° N). Organochlorines having steeper slopes with respect to latitude (toxaphene and DDT) display greater differences between these two additional sampling sites than do the other OCs with shallower slopes. Ratios for individual PCB homolog groups (not shown) ranged from 0.8 to 1.3. surface soils or lake sediments (16, 20), circumvents food web difficulties and may offer promise toward increasing our understanding of geographic trends in OC deposition. As data already exist on latitudinal patterns in the atmospheric concentration (30, 31), terrestrial deposition (4), plant uptake (4, 5), and biogeochemical processing (32) of radionuclides, development of empirical relationships between these measurements with similar ones for OCs would be a profitable direction worth pursuing further. FIGURE 3. Relationships between slopes of PCB and selected PCB homologs (mean normlized to facilitate comparison among different absolute concentrations) and cesium-137 activities in samples of Ellesmere Island saxifrage. Cesium-137 data are from France et al. (5). Slopes for octa- and pentachlorobiphenyls are significant at p ) 0.05. Presented data are site-specific means, with average per site SDs (not shown for clarity) of (16% of these means. Island (2, 24). Lead et al. (25) found that over time (19771990) the proportions of higher chlorinated PCBs increased in moss samples from northern Norway relative to sites in the south. The capability of environmental scientists for measuring cesium-137 accumulation is much easier and more widespread than that for accurately quantifying OC contamination. The close association between residues of these two micropollutants in saxifrage from Ellesmere Island, despite probable differences in their precise atmospheric transport processes and vegetation partioning mechanisms, raises the possibility that cesium-137 uptake could be used as a surrogate environmental monitor for studies on regional patterns in OC deposition in those locations where the overall source pathways are similar. Although there is a general agreement between both cesium and OC abundance within components of aquatic ecosystems (26), difficulties in developing empirical conversions between the two is dependent on understanding the influences of water chemistry and metabolic functions (27) and how these are affected by food web interactions (3, 28). Sampling terrestrial plants (21, 29) and, even better,
Acknowledgments The Arctic Light Trans-Ellesmere Island Ski Expedition was sponsored by the World Wildlife Fund Canada and the Royal Canadian Geographical Society and was organized by J. Dunn, M. Sharp, and G. Magor. Logistic support was provided by (among others) Asnes, Chorophylle, J. Ingle Insurance, Calgary Herald, Bolle, Paris Gloves, Coll-tex, Harvest Foodworks, MSR, North Face, Leki, and the Canadian Himalayan Foundation. Samples from Ellesmere Island were shipped south by the Canadian Atmospheric Environment Service and Polar Continental Shelf Project through D. Whelpdale. B. Billeck collected samples from Buchanan Lake on Axel Heiberg Island. Confirmation of toxaphene and other OC pesticides by high-resolution mass spectrometry was carried out by G. Stern. Funding to R.L.F. during manuscript preparation was provided by an NSERC Strategic Grant. Conversations with J. Rasmussen were beneficial to manuscript preparation.
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Received for review June 17, 1996. Revised manuscript received February 12, 1997. Accepted February 21, 1997.X ES960524S X
Abstract published in Advance ACS Abstracts, April, 15, 1997.
