Polycyclic aromatic hydrocarbons and polychlorinated biphenyls in soils and atmosphere of Western Canadian mountains: The role of source proximity, precipitation, forest cover and mountain cold-trapping

Abstract

Soil was sampled and XAD-2 based passive air samplers were deployed for one year at several locations on four mountains and a mountain pass in British Columbia (BC), Canada. The mountains, ranging between ca. 1100–1500 m in altitude, varied in their proximity to likely sources of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). Considered mountain-by-mountain, proximity to sources determines the concentrations of PCBs: Grouse Mountain, immediately to the North of Vancouver, had the highest PCB concentrations in both atmospheric gas phase and soil, while three other mountains in southern BC had levels approximately a factor of three lower. PCB concentrations along the Chilkoot Trail in remote Northern BC were more than an order of magnitude lower. While Grouse Mountain also had the highest PAH concentrations, gas phase concentrations of PAHs elsewhere were only slightly lower and varied little between the different mountains. Soil concentrations of PAHs were highly elevated on urban Grouse Mountain and lowest on Blue Grouse Mountain, which stands out by having the driest climate. On a site-by-site basis, PCB concentrations in the atmospheric gas phase decreased with increasing elevation but show indication of upslope enrichment in the soils of three of the mountains. These include the most urban mountain and two rural mountains, which have more precipitation and forest coverage than the remaining two mountains. There was no difference between congeners in the extent of upslope enrichment, indicating that the temperature gradient along the mountains was not sufficiently large to cause fractionation. Atmospheric gas phase and soil concentrations of PAHs on a mountain decrease with distance from likely sources. Although sources of PAHs are too widespread to observe any trends of mountain cold-trapping, PCBs are clearly experiencing cold-trapping in Western Canadian mountains. Keywords: Persistent organic pollutants, Mountain, Passive air sampler, British Columbia, Cold trap, Soil contamination