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 Please tell us about your educational background and early research experiences.  

My first contact with the research activity was during my Ph.D. on the synthesis and identification of natural products from pine resins through a contract with the US Department of Agriculture. During the mid-seventies, several well-known scientists moved from the study of biogenic natural products to those of geological origin, namely petroleum, to understand the geochemical processes involved in its formation.

A meeting with Prof. Guy Ourisson from the University of Strasbourg, France, one of the pioneers of the organic geochemistry, and a stage in his laboratory, were the source of my enthusiasm to work in this field.

Finally, in 1979, I established the Department of Environmental Chemistry at the CSIC in Barcelona, Spain, where research activities on environmental organic geochemistry started to develop.

 What first drew your interest to oil spills?

Photo 1

A view of an oiled beach after the Prestige oil spill.

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The starting of off-shore oil production in the Spanish Mediterranean coastal waters in the '70s worried the Spanish authorities about the possible impact of an oil spill on the coast, which might have significant consequences for tourism. As a result, I was responsible for implementing a surveillance system for the identification of marine oil spills. My geochemical background was quite useful in this task. In this respect, we were one of the first to use GC-MS techniques for oil spill fingerprinting.

Since then, I combined the basic research on environmental organic geochemistry, mainly focused on the marine environment, with the study of oil spills. I followed several spills, e.g. Ixtoc (Mexico) and Metula (Argentina), and, more recently, the Aegean Sea and the Prestige (Spain). At the same time, as a consultant for the UNEP Regional Seas Program, I kept a personal engagement in promoting technical cooperation for the development of marine pollution monitoring programs with developing countries, particularly in Latin America.

 Your most-cited paper in our analysis is the 2006 Marine Pollution Bulletin article, "Spatial and temporal distribution of dissolved/dispersed aromatic hydrocarbons in seawater in the area affected by the Prestige oil spill." Would you please tell us about this paper—your methods and findings, and the implications for the field?

A detailed understanding of the fate of an oil spill is essential in order to foresee the extension of the environmental damage and to develop effective restoration strategies. As the first processes affecting the spilled oil are dispersion and dissolution, the determination of the composition and concentration of the soluble fraction is important for assessing the early impact of the spilled product on marine biota. In this respect, aromatic hydrocarbons are of special concern as they exhibit higher solubility and toxicity in the aquatic environment.

Therefore, taking into account the large extension covered by the heavy fuel oil discharged by the Prestige during its towing away from the coast, and after its sinking 240 km off the northwest coast of Spain, and the fact that the coastal area was sustaining an intensive mariculture activity, it was imperative to carry out a complete survey of dissolved/dispersed petroleum hydrocarbons in the water column.

This survey started immediately after the accident, in December 2002, and was continued in February-March and September 2003. Seawater samples collected at three depths from 68 stations along the Northern Spanish coast were analyzed for dissolved/dispersed petroleum aromatic hydrocarbons (PAHs) by UV-fluorescence and for 25 individual compounds by GC-MS.

Although higher concentrations of total aromatic hydrocarbons were found at all depths in the samples collected during December 2002 off the Galicia coast, in the area more heavily affected by the spill, surprisingly, the concentrations were not as high as the values reported in other accidents (e.g., Exxon Valdez, Baltic Carrier, and North Cape) in spite of the amount of the spilled oil (near 60.000 tons).

This was attributed to the heavy nature of the fuel, which was barely dispersed in the seawater and mainly stranded on the shoreline or deposited in the form of patches or tar aggregates. Three months after the spill the PAH levels in the water column showed a 50% decrease in the most affected area and three months later returned to background levels.  

Photo 2

Satellite picture of the Prestige oil spill - 2002 (ESA).

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Besides the extensive oiling of beaches and costal areas, the apparently low incidence of the oil on the continental shelf was also confirmed by the monitoring of more than 80 sediment stations established along the Spanish coast, just after the accident, and in 2003, 2004, and 2005 (Mar. Pollut. Bull., 53: 260, 2006; Environ. Pollut., 158: 1551, 2010).

More than 40 coastal stations were also selected for sampling wild bivalves and PAH levels declined to background values about six months after the spill (Sci. Total Environ., 370: 80, 2006; J. Environ. Monitor., 9: 1018, 2007). 

 Earlier this year, you and your co-authors published a paper in Environmental Pollution: "Sources and distribution of polycyclic aromatic hydrocarbons in sediments from the Spanish northern continental shelf. Assessment of spatial and temporal trends." Please sum up this paper for our readers.

The oil discharged from the Prestige rapidly reached the adjacent Galician coast; but drifting northeast, arrived by early December 2002 to Asturias, and, in early summer 2003, to Cantabria and the Basque Country, thereby affecting the entire northwestern coast of Spain, along more than 800 km. In order to assess the impact of the oil on the coast, an extensive survey of sediments was carried out, constituting the most comprehensive study up to date on PAH pollution in the northern Iberian continental shelf.

The information obtained indicated a low-to-moderate pollution, with hotspots corresponding to some coastal urban-industrial areas. This was reflected in the ecotoxicological assessment, using sediment quality guidelines (SQGs), where most of the stations were below the toxicity thresholds, with few of them (6%) above probable effect concentration (PEC).

The combined assessment of PAH profiles and main drivers in the studied area provided useful information for the source apportionment and the study of transport and accumulation processes of PAHs in the coastal/marine environment. The detailed study of diagnostic ratios suggested a rather uniform mixture of petrogenic and pyrolytic PAH sources along the continental shelf, reflecting the chronic inputs of hydrocarbons in the area, with a decrease of the combustion signature moving westwards and away from the potential coastline sources. Moreover, the effect of the Prestige oil spill was not observed.

On the other hand, the study was used to assess the field variance of the values obtained in using sediments for monitoring marine pollution by hydrocarbons. Thus, repeated sampling of several stations every six months, during 2003, 2004, and 2005, allowed the determination of a variance in the range of 12–33% (average 31%), providing a guideline for interpreting spatial and temporal trends. This mean variance decreased to 23% when sediment morphology parameters, notably TOC, were considered for data normalization.

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