Pesticides in Western Canadian Mountain Air and Soil

Abstract

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 a-hexachlorocyclohexane 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 intemperate mountain soils that are rich in organic matter and receive large amounts of cold precipitation.