Assessing the Potential of Persistent Organic Chemicals for Long-Range Transport and Accumulation in Polar Regions

Abstract

A zonally averaged global distribution model is used to identify chemical partitioning properties and emission scenarios that favor enrichment in Arctic ecosystems. An immediate and a long-term Arctic Contamination Potential (ACP) are defined as the fraction of the total amount in global surface media that is in the Arctic after 1 and 10 years of steady emissions with a generic zonal distribution. Simulations for a two-dimensional “space” of hypothetical chemical property combinations indicate that the ACP of a perfectly persistent organic chemical is determined by a complex set of processes but tends to be higher for two combinations of partitioning properties: relatively volatile (log K OA < 9) and water soluble (4 > log K AW > −0.5) substances and substances which are semivolatile (log K OA 6.5−10) and relatively hydrophobic (log K AW > −3). Very volatile chemicals with log K OA < 6.5 and log K AW > −0.5 remain in the atmosphere even under Arctic temperature conditions, whereas very involatile chemical with a log K OA > 10 are efficiently and irreversibly deposited with atmospheric particles before reaching the Arctic. The two sets of partitioning characteristics with elevated ACP overlap in the range 6.5 < log K OA < 10 and −0.5 > log K AW > −3, which also corresponds to a log K OW range of 5 to 8, i.e., comprises substances with a potential for bioaccumulation. Organic contaminants known to accumulate in the Arctic, such as hexachlorobenzene and the lighter PCBs, indeed have such partitioning properties. Marine currents contribute significantly to the long-range transport of chemicals with log K AW < −2. Emissions to surface media greatly reduce the ACP, except for chemicals with octanol/water partition coefficients log K OW < 5. The ACP of chemicals with different partitioning properties is sensitive to different sets of environmental parameters, reflecting the different pathways which determine their global transport behavior. The ACP of most chemicals is sensitive to the temperature dependence of the partition coefficients, temperature, atmospheric mixing coefficients, and sea ice cover.