Organic Contaminant Release from Melting Snow

Snow efficiently scavenges organic contaminants from the atmosphere. Those chemicals can be released in short, concentrated pulses during spring snowmelt, potentially affecting both aquatic and terrestrial environments. In order to investigate the behavior of organic contaminants in melting snow laboratory experiments were conducted using artificial snow spiked with the organic target substances naphthalene, phenanthrene, pyrene, benzo(ghi)perylene, lindane, and atrazine. The behavior of those substances during melting is dependent on their partitioning between the different phases present within the bulk snow. Very water soluble organic chemicals, such as atrazine, are preferentially released at an early stage of melting similar to inorganic ions. This first chemical flush becomes more pronounced when a deep, aged, and relatively homogeneous snow pack is exposed to intense melting. Hydrophobic substances attached to particles, such as high molecular weight polycyclic aromatic hydrocarbons, are often released at the very end of the melt period. Dirt cones at the surface of a deep snow pack amplify this late chemical enrichment. Whereas chemicals that are clearly hydrophilic or hydrophobic are likely to be released in pulse loads, the snowmelt behavior of chemicals with intermediate partitioning properties, such as lindane, is more dependent on the varying snow pack and melt characteristics. A notable fraction of volatile chemicals may transfer from the melting snow pack to the lower atmosphere due to evaporation. Shallow snow covers in temperate regions with depths below 10cm that are exposed to recurrent melt phases during the winter are less likely to lead to pulse releases. When the melt water runs off as overland flow over frozen ground, pollutants are directly transferred into catchment streams, and their water quality is affected most. Melt water flow along the soil subsurface dilutes and buffers organic contaminant loads. The findings of this laboratory study may assist in the development of contaminant fate models that includes snowmelt processes. The results may further help to explain observations of organic contaminants in natural snow environments.Ph