Research Weathering and Dispersal of Polychlorinated Biphenyls from a Known Source in the Canadian Arctic STEPHEN DOUGLAS WILLIAM KENNETH
L. A. T. J.
G R U N D Y , * ,† BRIGHT,† DUSHENKO,† AND R E I M E R * ,‡
Applied Research Division, Royal Roads University, 2005 Sooke Road, Victoria, British Columbia, Canada V9B 5Y2, and Environmental Sciences Group, Royal Military College of Canada, Kingston, Ontario, Canada K7K 5L0
The results of a PCB weathering experiment (i.e., losses from soil and changes in PCB composition from soil over time) at Cambridge Bay, Northwest Territories, in the Canadian Arctic are presented. Nine plots representing three different general substrate types (dry barren, dry moss, and wet grass) were treated with three different PCB Aroclor formulations (1254, 1260, and a 1:1 mixture). Soil and plant samples were collected annually over a 5-year period and analyzed for individual PCB congeners. The results showed a high degree of variability between treatments that was ascribed to the presence of vegetation as well as non-homogenous PCB application and/ or soil heterogeneity (e.g., biomass, organic carbon, and moisture content) within individual plots. Where readily interpretable data were available, the first-order rate constant for the loss of PCBs from the substrate was calculated to be approximately 0.5 yr-1 (t1/2 ) 1.1 yr) (range ) 0.3-1.0 yr-1 for individual congeners). For the dry barren area, the rate of loss from soil of individual congeners was negatively correlated with the planar total surface area of the congener (or positively correlated with vapor pressure). For a wet grass area or a dry moss area, the rate of loss was not correlated with any of the standard physical constants, suggesting that live and detrital vegetation may play a key role in the release and retention of PCBs. The estimated loss rates for the three plots * Corresponding authors (S.L.G.) telephone 604-391-2579; fax: 604391-2522; e-mail address:
[email protected]; (K.J.R.) telephone: 613-541-6000, ext 6161, fax 613-541-6596; e-mail address:
[email protected]. † Royal Roads University. ‡ Royal Military College of Canada.
S0013-936X(95)00493-7 CCC: $12.00
1996 American Chemical Society
may or may not be applicable to PCB-contaminated soils in general, where PCB volatility may be reduced by the presence of hydrocarbon-based carriers or influenced by other factors not considered in this study.
Introduction The concentrations of polychlorinated biphenyls (PCBs) in various environmental compartments have been extensively documented (1-5). PCBs enter the environment largely through accidental spills and emissions from disposal sites and then may cycle through atmospheric, aqueous, or biotic pathways. Few detailed studies have assessed the dispersal mechanisms from PCB spills, although recent studies indicate that redistribution may be controlled by vapor pressure (6), the organic content of the substrate, and perhaps the stereochemistry of the PCBs (7). Even less is known about the lifetime and redistribution of PCBs in cold climate environment soils. There has been a considerable amount of research on the long-range transport of anthropogenic materials, both organic and inorganic, to the Canadian Arctic (8). The presence of PCBs in higher marine mammals have been largely ascribed to transboundary contamination via atmospheric transport (9). The hypothesis of global fractionation whereby the more volatile components in multicomponent mixtures, such as organochlorines, accumulate in colder climates) has been proposed to account for the presence of semivolatile compounds in polar regions where they have not been used (10). We have recently shown that short-range atmospheric redistribution of PCBs from local sources in the Canadian Arctic has resulted in elevated levels in soils, plants, and marine systems some distance (10 km) from the original source (11, 12). In order to gain insight into the mechanism of PCB redistribution from a local spill, a series of test plots were set up in Cambridge Bay, Northwest Territories. The experiment was designed so that three different substrate types commonly encountered in the Arctic could be dosed with different PCB Aroclor formulations and monitored annually in order to see how concentrations and congener distributions varied over time. This paper presents the results of the first 5 years of monitoring.
Experimental Section General. Cambridge Bay is situated in the central Arctic (69°07′ N, 105°08′ W). The experimental area was located next to the North Warning System long-range radar facility, CAM-M, a former Distant Early Warning (DEW) site. Three areas were chosen in 1990 to represent different substrate types: type 1 was a dry barren area (where polygons resulting from the frost-heaving of soils precluded vegetation); type 2 was a dry moss and lichen-covered area; type 3 was a low-lying wet sedge (Carex sp.) area. Soils in the three areas were not characterized in terms of their moisture
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or organic carbon content; however, soils at CAM-M and other DEW Line sites collected from similar areas to the dry moss (type 2) and wet sedge (type 3) plots tended to exhibit a range of approximately 10-60% organic matter content at or near the soil surface as estimated from loss on ignition (16). These soil types, with high concentrations of humic material comprising a shallow (10 cm) over mineral soil, also exhibit an extreme seasonal variation in moisture content (from completely saturated to moderately dry) as well as considerable microscale vertical and spatial heterogeneity. The dry barren area in contrast was typical of areas where frost-heaves have exposed sandy-silt to clay mineral soils. Very little organic matter is present in such areas [
