*Structure and role of biological communities involved in the transport and transformation of persistent pollutants at the marine AIR-Water INterface.

Problems to be solved :

    The sea surface micro-layer (SML)which represents not more than a few hundred micrometers is perhaps one of the most important but also most poorly characterised regions of the marine environment. The biology and chemistry of the SML are sufficiently different from the subsurface waters that they can be regarded as an important and distinct ecological compartment of the marine environment. The SML is generally enriched in metals, organic matter and pollutants, hydrocarbons, pesticides and PCBs. The SML is also exposed to strong UV radiation which photo-chemically alters the dissolved organic matter leading to the formation of photo-oxidants. Therefore because biological activity at the SML is generally high, organisms living in this layer may have developed resistance mechanisms to overcome oxidative stress and more generally to grow in the presence of toxic compounds. Oxidants may also lead to a more rapid oxidative turnover of materials at the SML and, potentially, to reactions and processes not observed in the bulk waters. Despite this, little is known on the structure of biological communities inhabiting the SML, on biological processes occurring at this layer, and on interactions between chemical and biological compartments. In this respect, there is an urgent need to investigate the structure of biological communities living and growing in the SML, and their role in the transport and cycling of natural organic matter and xenobiotics, including lipids, metals and persistent organic pollutants (POPs). It is also urgent to determine the role of the SML in the transfer of pollutants to the underlying waters and food webs and/or to the atmosphere, as well as the synergistic or antagonistic effects of metals and UV radiation on these processes.

Scientific objectives and approach :

    The AIRWIN project proposes a multidisciplinary approach to characterise processes occurring in the SML and their relevance to global change on the marine environment and its living resources. This project brings together chemists, biologists and engineers who will help (a) to define the role of the SML in the entry and loss of organic and inorganic pollutants in the marine environment, (b) to identify those pollutants which are transferred to humans through marine food webs, (c) to identify and to isolate micro-organisms that could be used for bioremediation and as cosmetic products to improve human health and lastly, (d) to provide bio-indicators of atmospheric pollution.

Appropriate sets of three different sampling and analytical techniques will be used to investigate the chemical and biological components of the SML in both oligotrophic and highly industrialized coastal areas. Cell sorting techniques will be used to isolate and to identify organisms able to live in the presence of toxic compounds and UV radiation. The role of resistant organisms in the accumulation and/or transformation of toxic compounds and metals, in modifying the air-seawater exchanges, and in the transfer of contaminants to underlying waters will be investigated. Special attention will be given to compounds responsible for accumulation, aggregation and polymerisation processes mediated by UV radiation and microbial activity. Petrogenic and pyrolytic (PAHs) hydrocarbons, chlorinated pesticides, PCBs, surfactants and trace metals will be analysed in marine samples (SML, underlying waters, surface particulate matter, neuston and sinking particles) to model the cycle of pollutants in the SML.

Expected impacts :

    Understanding the role of the SML in the air-water exchange of persistent pollutants as well as in the transformation and/or concentration of toxic compounds such as metals, hydrocarbons, chlorinated pesticides, PCBs and surfactants will help (a) to better estimate the impact of different pollutants on marine ecosystems, (b) to define what pollutants may be transferred to humans through the marine food webs and more generally, (c) to model the cycle of pollutants in the SML. The isolation of a wide diversity of micro-organisms able to produce organic compounds such as antioxidants or to transform pollutants will provide a collection of organisms that could be used for biotechnological applications. This is also why end users including industrials, participate in the AIRWIN project. The potential use of neuston organisms as bio-indicators of atmospheric pollution will also be investigated depending on the sensitivity and specificity to different toxic compounds and trace elements.