Potential of degradable organic chemicals for absolute and relative enrichment in the Arctic

Model simulations of the fate of numerous hypothetical substances in the global environment can provide considerable insight into how an organic chemical's degradability and partitioning properties influence its absolute and relative Arctic enrichment behavior, as quantified by the Arctic Contamination Potential. For substances that degrade faster in water than in soil, but are quite persistent in the atmosphere, highest Arctic contamination is expected to occur if the substances have intermediate volatility and high hydrophobicity. Organic substances that are degradable in the atmosphere can still accumulate in the Arctic if they are soluble and highly persistent in water. These latter substances, which reach the Arctic in the ocean, also show the highest potential for relative enrichment in the Arctic, i.e., high amounts in northern high latitudes relative to the amounts in the total global environment. Beyond a threshold persistence in surface media of the order of several months to a year, chemical degradability leads to further relative enrichment. This is because only chemicals that are sufficiently long-lived get transferred to polar regions and once there can persist longer than at lower latitudes. The model simulations can inform the search for new potential Arctic contaminants, and can highlight combinations of properties which should be avoided in high production volume chemicals with the potential for environmental release. Three categories of organic substances are singled out for troublesome combinations of persistence, distribution, and potential bioaccumulation characteristics, only one of which contains "classical" Arctic POPs. Examples of potential Arctic contaminants within each of these categories are named.