Rapid changes in PCB and OC pesticide concentrations in Arctic snow

The short-term fate of polychlorinated biphenyl (PCB) and organochlorine (OC) pesticides in the surface snowpack was investigated by taking consecutive air and snow samples over a 12 day period at Tromso in the Norwegian Arctic. A wide range in PCB and OC pesticide concentrations was observed in snow and was attributed to the systematic decrease in concentrations that occurred over the study period. For example, Sigma PCB concentrations ranged from 2500 to 300 pg L-1 (meltwater) with a rapid decrease observed during the first 96 h. Rates of decline (ks) conformed to first-order kinetics, with similar rates observed for all compounds measured in this study (ks = 0.01 +/- 0.001 h(-1)). Because the particle bound fraction accounted for < 10% of the individual PCB and OC burden in the snow, then the fraction lost may be accounted for by desorption, following notable increases in snow density (and presumably, decreases in snow surface area). The fraction of chemical present in the fresh snow (phi s) was found to be exponentially related to changes in snow density (Delta p). Relatively small increases in p following snowfall result in a large loss of sorbed chemical, presumably due to decreases in snow surface area. Later sampling of the same snow layer, but buried under fresh snowfall, revealed a notable increase in both PCB and OC concentrations. This would indicate a possible downward migration of these chemicals from the fresh snow into deeper snow layers, suggesting that re-emission of desorbed chemical from the interstitial pore spaces to the overlying atmosphere may be complicated by this process.