Polychlorobiphenyls and polycyclic aromatic hydrocarbons in the sea-surface micro-layer and the water column at Gerlache Inlet, Antarctica

Abstract

The enrichment of PCBs (polychlorobiphenyls) and PAHs (polycyclic aromatic hydrocarbons) in the sea-surface micro-layer and depth profile of these pollutants in the water column were investigated at Gerlache Inlet, Terra Nova Bay, Antarctica. Depth profile samplings were repeated three times during the Antarctic summer (from November to February). PCBs and PAHs showed a concentration range in the water column of 30–120 pg l⁻¹ and 150–400 pg l⁻¹, respectively, and these values were very much dependent on the suspended matter content. A nearly two-fold decrease in the pollutant concentration was also observed in the depth profile obtained in February, i.e. late summer, which might be correlated both with the high content of suspended matter and the reduction of the pollutant input. Moreover, isomer ratios of PAHs, such as LMW/HMW and PHE/ANT, highlight that the main PAH source might be petrogenic in nature, whereas the pyrolytic source seems to be less important. Sea surface micro-layer (SML) and sub-surface sea water (SSW) samples were simultaneously collected in the same site by a remote controlled rotating drum-based sampling system, a prototype named MUMS (Multi-User Micro-layer Sampler). Sea surface micro-layer samples showed a total content of PCBs and PAHs in the range 400–450 pg l⁻¹ and 2000–3000 pg l⁻¹, respectively, whereas the mean content of the sub-surface sea water samples was 48 pg l⁻¹ and 325 pg l⁻¹, respectively. The mean enrichment factors of PCBs and PAHs in sea-surface micro-layer were about 10 and 7, respectively. The surface excess concentrations of PCBs and PAHs were about 35 000 and 200 000, respectively. A fairly good correlation was observed between the concentration of pollutants and water solubility. Based on the assumption that POPs are confined in a very thin top layer of the SML about 0.01–0.001 μm thick, namely the sea-surface nano-layer, and also on an estimated thickness of the sampled sea-surface layer of about 100 μm, an enrichment factor of 10⁵–10⁶ for the sea-surface nano-layer was calculated. Such a very high concentration increase was related to the two-fold increase of PAH concentration observed in the underlying 20 cm of the water column in late summer.