Biogeochemical controls of the transport and cycling of persistent organic pollutants in the polar oceans

• Autores: Cristóbal José Galbán Malagón
• Directores de la Tesis: Agustín Sánchez-Arcilla Conejo (dir. tes.), Jordi Dachs Marginet (dir. tes.)
• Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2013
• Idioma: catalán
• Tribunal Calificador de la Tesis: Rafel Simó Martorell (presid.), Manuel Espino Infantes (secret.), Esteban Abad Holgado (voc.)
• Materias:
  • Química
    • Química analítica
      • Análisis microquímico
  • Ciencias de la tierra y del espacio
    • Ciencias del suelo
    • Ciencias del espacio
• Enlaces
  • Tesis en acceso abierto en: TDX
• Resumen

  • Humanity is currently using more than 200000 synthetic organic compounds in many industrial, agricultural and domestic applications. Many of these chemicals reach the environment and have a harmful effect on ecosystems and humans. Among them, the group of persistent organic pollutants (POPs) comprises several families of compounds that have physical and chemical properties that give them the ability to be distributed and impact globally (semivolatility, high persistence and bioaccumulation capacity due to their hydrophobicity). In the present thesis, the coupling of atmospheric transport and biogeochemical cycles in the Arctic and Southern Ocean has been studied for Hexachlorocyclohexanes (HCHs), Hexachlorobenzene (HCB) and Polychlorinated Biphenyls (PCBs). Three oceanographic cruises were conducted, one in the North Atlantic and the Arctic Ocean (2007) and two in the Southern Ocean surrounding the Antarctic Peninsula (2008 and 2009). During these campaigns, air (gas and particulate), water (dissolved and particulate) and biota (phytoplankton) were sampled simultaneously allowing to report a complete picture of POPs cycling in polar areas. In the case of the Southern Ocean, the largest data set available for PCBs, HCH and HCB has been generated. The atmospheric and seawater concentrations were low, among the lowest reported for the Polar Oceans, and in the case of the Southern Ocean there is a clear historical trend of decreasing concentrations, consistent with reduced emissions in source regions. Long range atmospheric transport was identified as the main POPs input to polar ecosystems agreeing with previous works. However, it has been found that secondary local sources from soil and snow influences strongly the atmospheric concentrations overland in the Antarctic region, and over the adjacent Southern ocean in the case of HCHs. Atmospheric residence times calculated from the measurements were in agreement with the prediction from environmental fate models. The atmospheric residence times were longer for the less hydrophobic PCBs and shorter for the more hydrophobic, consistent with the role of the biological pump sequestering atmospheric PCBs. Once POPs reach the Polar regions the main route of entry of these compounds to surface waters is by atmospheric deposition, mainly by diffusive exchange between the gas and dissolved phase with minor contributions from dry deposition of aerosol bound POPs. Estimated bioconcentration factors revealed that concentration of POPs in phytoplankton were correlated with the chemical hydrophobicity, but some discrepancies with model predictions were observed. The biological and degradative pumps are identified as the two main processes that control the fate and occurrence of POPs in the surface water column, and also are able to modulate the atmospheric transport of POPs to remote areas. POPs such HCHs are prone to be efficiently degraded by bacterial communities in surface waters, depleting the seawater concentrations and increasing the diffusive air-water exchange to the Arctic and Southern Ocean. Conversely, the biological pump decreases the dissolved phase concentrations of the more hydrophobic PCB congeners increasing the air to water fugacity gradients and enhancing the diffusive air-water exchange fluxes. This is the first time that the influence of the biological pump on POP cycling is demonstrated for Oceanic waters. Finally, HCB was close to air-water equilibrium showing that neither the biological and degradative pumps are efficient sequestration processes for the highly persistent and mid-hydrophobic compounds. Overall, the results show clearly that biogeochemical processes occurring in the water column affect the atmospheric deposition and long range transport of POPs to remote regions.The magnitude of these processes may show a clear seasonality and are suitable to be perturbed under the current scenario of climate change.