Orographic Cold-Trapping of Persistent Organic Pollutants by Vegetation in Mountains of Western Canada

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Abstract
Conifer needles from mountain areas of Alberta and British Columbia, Canada, were collected from sites that ranged in altitude from 770 to 2200 masl and were analyzed for polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCs) to determine if they are progressively concentrated in colder, more elevated mountain areas, where temperatures decrease as elevation increases. Concentrations of OCs in needles ranged from 43 to 2430 pg g-1, 55−17500 pg g-1, and 11−2930 pg g-1 (dry weight), for total hexachlorocyclohexanes (HCHs), PCBs, and endosulfans, respectively. The more volatile OCs, with subcooled liquid vapor pressures (PL) > 0.1 Pa at 25 °C, increased at higher altitudes, whereas the less volatile OCs were either unrelated or inversely correlated with altitude. These spatial patterns were similar for species of spruce (Picea engelmannii and glauca) and pine (Pinus contorta and albicaulis). Back trajectories revealed that air masses arriving at these sites traveled over Asia and the Pacific Ocean before reaching the Rocky Mountains. Results from this study demonstrate that alpine ecosystems accumulate these chemicals to the same degree that is observed in polar environments that are known to receive contaminants by long-range transport.