Seasonality in the "grasshopping" and atmospheric residence times of persistent organic pollutants over the oceans

Persistent Organic Pollutants (POPs) are toxic, bioaccumulable and semi-volatile compounds that have been detected in all environmental compartments, even in remote pristine regions where they have never been produced or used. Long range atmospheric transport (LRAT) and subsequent deposition is the major route of introduction of POPs to the oceans, including remote regions, and thus to the marine food-webs. It has been suggested that when POPs travel through the atmosphere, they tend to move in stages. This is known as the grasshopper effect, a repeated process of volatilization and deposition, even though the measure of grasshopping potential has been elusive. Here we show the spatial and seasonal variability of the grasshopper and LRAT potentials for polychlorinated biphenyls (PCB), a significant class of POPs. The number of hops that a chemical undergoes during LRAT over the oceans presents an important spatial and seasonal variability driven by biogeochemical processes occurring in the water column. These results have important implications for the understanding of the widespread distribution and fractionation processes of POPs at the global scale, showing that transport events to remote regions, such the Arctic, are maximized during seasons of low primary productivity.