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Phytoremediation and bioremediation of contaminants in salt marshes: plant – microorganisms interactions

Period: June 2010 till November 2013
Status: Completed

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Estuaries are often considered sinks for contaminants, (e.g. metals and polycyclic aromatic hydrocarbons (PAHs)), receiving important anthropogenic inputs from the upstream catchments and from metropolitan areas and industries located on or near those areas. Temperate salt marshes have an important ecological role since not only are among the most productive ecosystems on Earth, but also because are among the most sensitive ecosystems, and therefore, the most difficult to clean and recover. The development of strategies to clean these ecosystems in order to facilitate their recovery is a tremendous challenge facing the scientific community worldwide.
Phytoremediation and bioremediation are potentially less damaging and cost effective methods for the recovery of contaminated areas compared to alternatives such as soil washing, incineration or disposal to landfill. The potential of plants for phytoremediation of metal can be enhanced by the presence of several microorganisms in its rhizosphere, because plants benefit from the microbial turnover of root exudates and other sediment organic and inorganic substances. In addition, soil/sediment microorganisms are stimulated by plant root exudates and the presence of plants can enhance the potential of microorganisms for bioremediation of soils/sediments contaminated with organic contaminants, like PAHs, by providing specific microenvironments for pollutant-degrading microorganisms. However, very little is known about the complex and varied interactions between plants and microorganisms in the salt marsh rhizosphere. As a result, further research is needed to find suitable combinations of plants, microorganisms and soil/sediment types to improve rhizoremediation processes, particularly in estuarine areas.
The aims of this project are to investigate potential plant-microorganisms associations that could, on one hand, improve metal phytoremediation capacities of the plant and, on the other hand, improve bioremediation of organic compounds, namely PAHs, by microorganisms in estuarine salt marshes.
Following a characterization of the rhizosphere of salt marsh plants, in terms of contaminants (metals and PAHs) and microbial communities, autochthonous microorganisms (AM) with capacity to resist to chosen contaminants will be selected using enrichment cultures, in order to be used in laboratory experiments. Specific experiments are planned to ascertain the influence of microorganisms in the efficiency of plants for the removal of metals (Cd, Cu, and Pb). For that, selected enrichment of AM resistant to metals will be added to the plants rhizosphere, and controls will be used without AM amendments. Another set of experiments will be carried out in order to understand the contribution of plants to bioremediation of PAHs (the 16 EPA priority PAHs). For that, the ability of the selected enrichment of AM resistant to PAHs to degrade these compounds will be tested in the presence and in the absence of salt marsh plants. Later the contribution of the plants/microorganisms system to the rhizoremediation of a mixed contamination of metals and PAHs will be also assayed by testing different combinations of plants with selected microorganisms resistant to metals and/or PAHs. This study will be conducted in River Lima Estuary (North of Portugal), an urban-industrialized estuary with a large salt marsh area, which is the end member of an international watershed. On the shores, a large shipyard and an important commercial sea-port are installed, representing this estuary an optimal study case, not only in terms of diffuse pollution by hydrocarbons (e.g. PAHs) and metals but also in terms of potential risk of accidents associated to the shipping activities.
In brief, recovering of estuarine environments is in need and remediation methodologies using both plants and microorganisms could be a valid option due to the potential synergisms. However, information on the subject is scarce and it is expected that this project could break new ground aiming the validation of the approach and contributing to the development of new strategies for the control and reduction of estuarine pollution in view with the stated in the Water Framework Directive.

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