Organic contaminant release from melting snow. 1. Influence of chemical partitioning

A melting snowpack can deliver organic contaminants to terrestrial and aquatic ecosystems in the form of short and concentrated pulses. The mechanisms and kinetics of the underlying processes need to be understood to successfully integrate them into contaminant and water quality models. Controlled laboratory-based snowmelt experiments using artificially produced snow spiked with organic target contaminants reveal how chemical behavior during melting is dependent on the partitioning between the different phases within the bulk snow. Behaving similar to inorganic ions, water soluble organic chemicals, such as atrazine, are preferentially released at an early stage of melting, because such chemicals, accumulated at the snow grain surface, dissolve in the downward percolating meltwaterfront. Hydrophobic substances attached to particles, such as the larger polycyclic aromatic hydrocarbons, are often released at the very end of the melt period, because particle coagulation and snow densification render the melting snowpack an efficient filter trapping the particles. A notable fraction of volatile chemicals, such as naphthalene, will transfer from the melting snowpack to the lower atmosphere due to evaporation. Organic pollutants with intermediate partition properties, such as lindane, can easily switch between the bulk snow phases and their elution behavior is therefore more sensitive to varying snow and melt characteristics.