Occurrence, Transport and Fate of Persistent Organic Pollutants in the Global Ocean = Presencia, Transporte y Destino de Contaminantes Orgánicos Persistentes en el Océano Global

Abstract

[eng] The Open Ocean has been recognized as playing a key role on global dynamics of pollutants due to its large coverage of the planet surface, its high degradation potential and its sink and accumulation capacities towards anthropogenic chemicals. Nevertheless, there is a dearth of measurements of contaminants in the Open Ocean lower atmosphere, water column and trophic chain as a result of its remoteness and wide spatial reach. Persistent organic pollutants (POPs) are an important class of chemical contaminants due to their particular characteristics such as persistency, bioaccumulation potential, high toxicity and long range environmental transport capacity. Even though previous studies report their occurrence in the marine environment, the processes and magnitude of their fate, transport and sinks in the Open Ocean remain uncharacterized. In this Thesis two groups of organic contaminants have been selected in order to study POPs dynamics and fate in the oceanic environment. Polycyclic Aromatic Hydrocarbons (PAHs) are organic pollutants generated during incomplete combustion of fossil fuels and organic matter, but as well coming from petrogenic and biogenic natural sources. PAHs are semivolatile and highly mobile between the atmosphere and aqueous systems. Perfluoroalkylated substances (PFASs) are anthropogenic halogenated pollutants, recently developed for industrial and consumer goods usage. They are extremely persistent and exhibit higher solubility and lower hydrophobicity than most POPs, which makes them prone to be found in aqueous matrixes. During the Malaspina 2010 circumnavigation cruise across the Atlantic, Pacific and Indian oceans (35°N- 40°S), 64 PAHs were measured in the gas, aerosol, rainwater, dissolved, particulate and plankton matrixes, and 11 PFASs were quantified in dissolved phase at surface and deep chlorophyll maximum depth seawater. Degradation and atmospheric deposition of PAHs was assessed for dry deposition, wet deposition and diffusive air-water exchange, suggesting approaches for their global estimation, and proposing a global budget for PFAS, PAHs, and other semivolatile aromatic-like compounds, and their effect in the carbon global cycle. Dry deposition was obtained by direct measurements on board and parametrized for the whole tropical and subtropical Ocean; wet deposition was quantified from the precipitation rainwater gathered during the cruise; and diffusive exchange was calculated from the measured PAHs concentrations in the gas and dissolved phases, concurrently with the environmental parameters affecting volatilization and absorption (temperature, wind speed, salinity, dissolved organic carbon among others). Moreover, vertical distribution processes and influencing parameters in the surface mixed layer of the water column were assessed for PAHs and PFASs. Processes evaluated for PAHs include the vertical fluxes associated to the organic matter sinking (biological pump), biomass dilution, planktonic degradation, and air-water-particle exchange. For PFASs, the biological pump and eddy diffusive fluxes (based on turbulence eddy diffusion coefficients measured concurrently to the PFASs sampling) were assessed empirically for the first time in literature. The analysis of the complex feedback established between atmospheric depositional fluxes and the diffusive, degradative and biological pumps fluxes in the marine water column at a global scale is also covered. Furthermore, a wide array of understudied environmental parameters are reviewed as plausible factors affecting POPs fate in the Open Ocean, and a proposal of the research directions to follow and missing gaps to be filled is done. Amongst the innovative outcomes of this study, it can be highlighted the comprehensive sampling covering the tropical and subtropical global oceans, and the large amount of experimentally determined processes and influencing factors in order to better understand the global fate of chemical organic pollutants in the Open Ocean.

[spa] El Océano Abierto está reconocido como un ambiente clave en la dinámica global de la contaminación debido a que representa un gran porcentaje de la superficie terrestre, su alto potencial de degradación y su capacidad como sumidero de sustancias químicas antropogénicas. En esta Tesis dos grupos de contaminantes orgánicos han sido seleccionados para ilustrar la dinámica de los COP y su destino en el medio ambiente oceánico: los hidrocarburos aromáticos policíclicos (PAHs) y las sustancias perfluoroalquiladas (PFASs). Durante la campaña de circunnavegación Malaspina 2010 a través de los océanos Atlántico, Pacífico e Índico (35°N- 40°S), se midieron 64 PAHs en las matrices gas, aerosol, agua de lluvia, disuelto, particulado y en el plancton; y 11 PFAS se cuantificaron en la fase disuelta de agua marina superficial y de la profundidad del máximo de clorofila. La degradación y la deposición atmosférica de los PAHs se evaluaron mediante las medidas de deposición seca, deposición húmeda e intercambio difusivo aire-agua, sugiriéndose métodos para su cuantificación global y proponiéndose un cómputo global para estos contaminantes y otros compuestos semivolátiles aromáticos, así como su efecto en el ciclo del carbono. Asimismo, se midieron los procesos de distribución vertical y los parámetros que afectan a las concentraciones de PAHs y PFASs en la capa de mezcla superficial de la columna de agua. Los procesos examinados para PAHs incluyen los flujos verticales asociados con la sedimentación de materia orgánica (bomba biológica), la biodilución, la degradación planctónica, y el equilibrio aire-agua-partícula. Para las PFASs, la bomba biológica y los flujos difusivos turbulentos (basados en medidas de los coeficientes de difusión turbulenta simultáneas con el muestreo de PFASs) fueron medidos empíricamente por primera vez en la literatura. El análisis de los complejos efectos retroactivos establecidos entre los flujos de deposición y los procesos de degradación, difusión y la bomba biológica a escala global también ha sido abordado. De la misma forma, un amplio espectro de parámetros ambientales se ha revisado para dilucidar posibles factores que pudieran afectar al destino de los COP en el Océano Abierto, y se proponen una serie de líneas de investigación y necesidades prioritarias para su futura investigación.