Transport of contaminants to the Arctic: partitioning, processes and models

This paper presents a review of the processes by which organic contaminants are transported to the Arctic and become subject to deposition and absorption into terrestrial, aquatic and marine ecosystems, with subsequent transport and transformation within the abiotic and biotic media that comprise these ecosystems. The rates of these processes are controlled by the physico-chemical properties of the contaminants, notably vapor pressure, solubility in water and various partition coefficients such as those to organic carbon, lipids, plant matter and snow and ice surfaces. These properties are, in turn, profoundly affected by temperature, especially those involving air to condensed phase partitioning. Calculations of contaminant behavior in generic environments suggest that the unexpectedly high concentrations of certain organochlorine chemicals in polar regions can be explained, at least in part, by the temperature dependence of these partitioning phenomena. At low temperatures, partition coefficients from the atmosphere to condensed phases such as water, soil and biota increase significantly, thus causing higher ecosystem concentrations. Further, the rates of transport from the atmosphere may increase because of partitioning to acrosols and reduced water side mass transfer resistances. The authors propose a simple model to explain the migration and condensation of a contaminant from warm to cold regions, which we hope will represent a hypothesis that can be tested experimentally. We conclude that (1) there is a need to measure and correlate these fundamental properties and partition coefficients over the relevant range of temperatures, (2) the full implications of the effects of low temperatures on chemical fate can become clear only through construction of models describing the multimedia partitioning, transport and transformation in representative ecosystems and validating these models with experimental data, and (3) there is a need to identify the characteristics of the class of chemicals susceptible to what has been termed ‘cold condensation’ in polar regions.