Incorporation and Distribution of Polycyclic Aromatic Hydrocarbons in Experimental Sea-Ice

Rapid melting of sea-ice makes the Arctic more accessible for marine shipping and other industrial activities, increasing the risk of oil spills in the Arctic Ocean. Polycyclic aromatic hydrocarbons (PAHs) are among the most toxic substances in petroleum oil, yet their behavior in sea-ice-covered waters remains poorly studied. Here, we report an outdoor microcosm study to examine the partitioning behavior of four PAHs (naphthalene, phenanthrene, pyrene, and benzo(a)pyrene) across the seawater-sea-ice-atmosphere interface in the presence of particulate humic acid as a surrogate for particulate organic carbon (POC). We show that the higher the molecular weight of the PAH, the higher its concentration in sea-ice and the POC fraction. The POC-aqueous phase (seawater or bulk sea-ice) partition coefficients, K_d, are reasonably well explained by temperature and salinity for all four PAHs in seawater and for phenanthrene and pyrene in sea-ice. Relationships of K_d with temperature and salinity in sea-ice and freezing seawater are complex and nonunidirectional, most likely due to the dynamic nature of sea-ice and seawater under such temperatures. This suggests that conventional equilibrium-based approaches developed for open-water conditions need to be revisited when describing the behavior of PAHs in ice-covered waters.