Pesticides in Western Canadian Mountain Air and Soil GILLIAN L. DALY, † YING D. LEI, † CAMILLA TEIXEIRA, ‡ DEREK C. G. MUIR, ‡ AND FRANK WANIA* ,† Department of Chemistry and Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, Canada M1C 1A4, and Aquatic Ecosystem Protection Research Division, Environment Canada, 867 Lakeshore Road, Burlington, Ontario, Canada L7R 4A6 The distribution of organochlorine pesticides (OCP; in past and current use) in the mountains of western Canada was determined by sampling air, soil, and lichen along three elevational transects in 2003-2004. Two transects west of the Continental Divide were located in Mount Revelstoke and Yoho National Park, while the Observation Peak transect in Banff National Park is east of the divide. XAD- based passive air samplers, yielding annually averaged air concentrations, were deployed, and soils were collected at all 22 sampling sites, whereas lichen were only sampled in Revelstoke. Back trajectory analysis showed limited air mass transport from the Prairies to the east, but a high frequency of air arriving from the southwest, which includes agricultural regions in British Columbia and Washington State. Endosulfan, dieldrin, and R-hexachlo- rocyclohexane were the most prevalent OCPs in air and soil; hexachlorobenzene was only abundant in air; chlorothalonil, dacthal, and pentachloronitrobenzene were also consistently present. OCP air concentrations were similar across the three transects, suggesting efficient atmospheric mixing on a local and regional scale. Soil concentrations and soil/air concentration ratios of many OCPs were significantly higher west of the Continental Divide. The soil and lichen concentrations of most OCPs increased with altitude in Revelstoke, and displayed maxima at intermediate elevations at Yoho and Observation Peak. These distribution patterns can be understood as being determined by the balance between atmospheric deposition to, and retention within, the soils. Higher deposition, due to more precipitation falling at lower temperatures, likely occurs west of the divide and at higher elevations. Higher retention, due to higher soil organic matter content, is believed to occur in soils below the tree line. Highest pesticide concentrations are thus found in temperate mountain soils that are rich in organic matter and receive large amounts of cold precipitation. Introduction Semivolatile organic compounds have the potential to undergo long-range atmospheric transport, often as a result of repeated cycles of deposition and evaporation. Some such compounds tend to preferentially deposit and accumulate in remote cold environments, both at high latitudes (1, 2) and elevations (3, 4). Temperate mountains, in particular, experience effective upslope air transport and enhanced deposition at high elevations due to low temperatures and efficient snow-scavenging (5). The presence of these com- pounds in alpine areas is cause for concern because of their tendency to bioaccumulate and biomagnify along aquatic and terrestrial food chains, which has been documented in the lichen-caribou-wolf food chain of Canada’s Arctic (6), in aquatic food chains in an alpine lake in the Canadian Rocky Mountains (7), and in mountain streams of south- western British Columbia (BC), Canada (8), as well as along the ocean-salmon-bear pathway in coastal BC (9). Deliberately released into the environment and by definition toxic, semivolatile pesticides merit particular concern. Organochlorine pesticide (OCP) residues are present in air (10), snow (3, 11), vegetation (10, 12), runoff (10), aquatic amphipods (13), and lake trout (9, 14) from western Canadian mountains. This includes OCPs banned in North America for several decades (e.g., R-HCH, chlordanes, DDTs, and dieldrin) and those still in use (endosulfan) or banned recently (lindane). Although a review of levels of other current use pesticides in Canadian air and precipitation (15, 16) lists few data for the mountains of Western Canada, their atmospheric transport from intensive agricultural use areas to higher elevations has been documented for tropical and subtropical mountains (17, 18). The detection of dacthal, chlorothalonil, and chlorpyrifos in U.S. mountain (19) and Arctic snow (20) and remote Canadian lake water (21) is further indication of their potential for long-range transport. In this study, air, soil, and lichen were sampled along three transects in the mountains of western Canada and analyzed for OCPs of past and current use. The objective was to evaluate pesticide transport into the mountains of western Canada, both historically and presently. Most previous studies in the region consisted of one transect and thus lacked the ability to assess the extent of variation across the region, based on different source proximity and meteorological conditions. The current study therefore attempts to compare pesticide accumulation patterns along different mountain slopes and to relate those patterns to chemical properties, emissions, and meteorology. Experimental Section Sampling Locations. The three transects, located in moun- tainous National Parks of western Canada and labeled Revelstoke (R1 to R8), Yoho (Y1 to Y6), and Observation Peak (O1 to O8), are described in detail in the Supporting Information. Figures 1 and 2 show the locations of the 22 sampling sites and Table S1 lists their elevations and coordinates. Sampling Methods. Air was sampled passively using an XAD-based method (22) that had previously been used to monitor OCPs across North America (23). Samplers were deployed in duplicate from late August 2003 to late August 2004, yielding annual average air concentrations. Along the mountain slopes, they were deployed on metal and plastic poles at heights above the maximum expected snowpack level, which in some cases is several meters (photographs in the Supporting Information). Major siting criteria were elevation, accessibility, and representativeness. Evaluation and calibration of this sampler has been described previously (22). A Riverside style auger (7 cm i.d.) was used to collect soil at each air sampling site. Shallow and rocky soils limited * Corresponding author phone: (416) 287-7225; e-mail: frank.wania@utoronto.ca. † University of Toronto Scarborough. ‡ Environment Canada. Environ. Sci. Technol. 2007, 41, 6020-6025 6020 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 41, NO. 17, 2007 10.1021/es070848o CCC: $37.00  2007 American Chemical Society Published on Web 08/01/2007