Occurence of legacy and emerging persistent organic pollutants at the Ross Sea and circumpolar deep water convergence (Antarctica)

Persistent organic pollutants (POPs) have attracted the attention of scientists and policy makers in recent decades due to their extreme persistence, semi-volatility, capacity to bio-accumulate in the food chain, and toxic properties. Despite its geographical isolation, extreme meteorological conditions and an almost total absence of local point sources, the Antarctic continent is vulnerable to contamination by POPs, due to the ability of these chemicals to undergo long range atmospheric transport (LRAT) and deposition in the open sea. In a few cases and for limited areas, POPs may be also introduced into the Antarctic ecosystem by human activities (scientific stations, fishing, tourism, accidental oil pills, waste incineration and sewage). Even if various studiesi.e.1,2,3,4,5 have revealed the presence of POPs in air, seawater, sediments and biota in Antarctica, more investigations are needed to implement the number of observations, integrate the data series and meet the indications of the Stockholm Convention and the UNECE protocol in terms of improving knowledge of the temporal and spatial trends of POPs in biotic and abiotic environmental compartments. In this study we present POP concentrations in water samples collected along vertical water columns from seven oceanographic stations located in the Ross Sea and close to the Circumpolar Convergence (see Figure 1). Moreover, the occurrence of emerging and legacy POPs, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated naphthalenes (PCNs), organochlorine pesticides (OCPs) and polybrominated diphenylethers (PBDEs) were investigated in order to evaluate their possible sources and relationship with physical and biological processes taking place in the water column. The Ross sea is the formation site of two shelf waters which constitute an important part of the Antarctic Bottom Water (AABWs): the High Salinity Shelf Water (HSSW), which is relatively cold and generated inside the Ross Sea basin and the Ice Shelf Water (ISW). The Ross sea is influenced by only one water mass of external origin, the Circumpolar Deep Water (CDW), which is the largest circulation feature of the Southern Ocean, manly responsible for possible exchange processes between the Antarctic seas and the outer oceans, and thus a possible source of persistent organic pollutants (POPs)2 . The CDW is a relatively warm, salty and nutrient rich water mass carried around Antarctica by the Antarctic Circumpolar Current (ACC)6. Associated with the ACC is the Antarctic Convergence where the cold Antarctic waters meet the warmer waters of the subantarctic creating a zone of upwelling nutrients. Moreover, the Drygalski Glacie Tongue plays an important role in the Polynya development in the Terra Nova Bay, in the Ross sea. An important environmental concern is the accelerated glacier and snow melting that represent a massive release of both naturally occurring chemical substances and organic/inorganic pollutants of anthropogenic origin, which are stored in the deeper layers of the ice and may be delivered to surrounding ecosystems.