Sources and environmental fate of pyrogenic polycyclic aromatic hydrocarbons (PAHs) in the Arctic

Polycyclic aromatic hydrocarbons (PAHs) are large class of hydrophobic, semi-volatile organic contaminants that may enter the environment from both natural sources and anthropogenic activities. Pyrogenic PAHs arise from the incomplete combustion of fossil fuels and organic matter and following dispersal via long-range transport and may subsequently deposit in surface waters, soils and sediments of remote regions, including the Arctic. The current review summarizes and discusses Arctic data that is available for combustion-derived PAHs between 2004 and early 2018, focusing largely on data collected from remote, unexploited Arctic regions and from studies that provide some evidence of a pyrogenic origin. The increasing use of attribution ratios, which aid in discriminating PAHs from petrogenic or pyrogenic sources, suggest PAHs found in Arctic marine waters and sediment predominantly originate from natural underwater seeps, while those measured in air, freshwater, and terrestrial environments are likely to have originated from atmospheric and combustion-derived sources. Modeling efforts indicate that atmospheric PAHs in the Canadian and Norwegian Arctic are likely to have originated in the northern hemisphere – predominantly from Western Russia, northern Europe, and North America. East Asia appears to be a minor source of PAHs to the Arctic, despite contributing more than 50% of global PAH emissions. In comparison to the growing data for atmospheric PAHs, environmental data for these compounds in terrestrial and freshwater environments remain scarce. PAHs have been detected in Arctic biota from terrestrial, freshwater and marine environments, indicating exposure, however, levels are generally low, as most organisms efficiently metabolize parent PAHs. Globally, PAH emissions are expected to decline in the future, however models suggest the Arctic may not experience the same magnitude of decline projected for other world regions. Furthermore, future changes in climate may contribute to a re-volatilization of environmental PAHs, providing a source of secondary emissions to the Arctic atmosphere, emphasizing the importance of future monitoring for understanding the sources, fate and impacts of PAHs in the Arctic.