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Various approaches to clean contaminated aquatic environments have been proposed. In recent years, natural attenuation has received increasing attention and it is generally accepted that microorganisms are the principal mediators of the natural attenuation of many pollutants. However, the complexity of environmental systems such as sediments requires a multifaceted approach to understand microbial processes and their potential. This is even more so under in situ conditions, where the activity of pollutant degrading microorganisms is generally slow, partial and constrained spatially and/or temporally. Recent developments in molecular biology and genomics are offering tools to explore microbial processes at a level that encompasses the genetic characteristics of the local microbial players, culturable or not, as well as their organization into complex communities and their interactions both with each other and with the target chemicals. It is now possible to study microbes directly in their environments at the population level as well as at the single cell level and to link biology to geochemistry. Integrative knowledge from culture independent studies based on functional characters and assessment of the diversity and quantity of catabolic genes in response to pollution, will allow a deeper understanding of and a rational intervention in environmental processes. Moreover, the use of genomic libraries to retrieve genes from natural bacterial communities without cultivation will allow a breakthrough in accessing new microbial capabilities. In this chapter, the main features, advantages and limitations of these innovative approaches to the biomonitoring and analysis of intrinsic bioremediation potential of polluted environments and sediments are critically reviewed. Then, the potential of the same strategies in the integrated chemical, physical and biological monitoring and characterization of polluted sediments subjected to natural decontamination is shown through the description of the main results of case studies performed on a) polychlorinated biphenyl (PCB)-contaminated marine sediments of the Porto Marghera area of Venice Lagoon (Italy) in which the occurrence of PCB-reductive dechlorination processes has been demonstrated for the first time in the literature, b) sediments contaminated by chlorinated aliphatic hydrocarbons (CAHs) collected from different positions of the eutrophic river Zenne (Vilvoorde, Belgium), where they have been found to act as a natural biobarrier for the CAHs occurring in the groundwater that is passing through the sediment zone, hereby reducing the risk of surface water contamination, and c) other environmental contaminated systems subjected to ex-situ and in situ active bioremediation, where these processes are described on the basis of the experience accumulated in pilot and real-life systems. [ABSTRACT FROM AUTHOR]

Several approaches to the containment and treatment of contaminated sediment were evaluated, including the efficacy of adding activated carbon to sediment as an in-situ stabilization method and the use of conventional and innovative treatment caps. The applicability of phytoremediation for dredged sediments and sediments in shallow water or wetlands was also explored. The effectiveness of any treatment relies on successful application in the field and the emphasis herein is on evaluation of these approaches in the field. A demonstration at Hunters Point, San Francisco Bay, California strives to prove the efficacy of activated carbon treatment, and stands as an example for applications elsewhere. Simultaneous containment and treatment of sediment contaminants is being demonstrated in the Anacostia River, Washington, DC using both organic and metal sequestering agents incorporated into a cap. Both conventional placement and placement in a laminated mat were demonstrated to provide an array of placement approaches. The laminated mat allowed placement of thin layers of high value material at specific location, enabling the use of high value “active” capping materials such as activated carbon and microscale iron. Phyto- and rhizoremediation using plants and related bacteria is a promising approach for treatment of contaminated sediments, but has its inborn limitations. To overcome the slow performance of the process, transgenic plants were evaluated that express the bacterial gene responsible for cleaving PCBs, or metal binding proteins to provide additional metal binding capacity. Continued development of cap and sediment treatments, and approaches to assess effectiveness and long-term reliability are encouraged. [ABSTRACT FROM AUTHOR]

Physicochemical and biological processes that influence contaminant fate and transport in sediments are diverse, and include physical chemical behaviour, biological processes at microbial and macro scales, as well as pore water and solid phase transport. Spatial and temporal variability in these environmental characteristics and processes are large, and can be difficult to portray and predict. We herein present a series of case studies that evaluate environmental processes and properties that must be assessed with respect to studies of contaminated sediments. These topics are: chemical behaviour of metals in the environment; biological processes and sediment properties influencing contaminant release from sediments; the biogeochemistry and adsorptive capacity of ambient organic compounds in aquatic environments; and new approaches to modeling and scaling the spatial distribution of relevant processes and sediment properties. In a concluding assessment of our state of understanding for these processes and properties, we find that significant knowledge gaps remain in terms of both causal and statistical uncertainty, and these uncertainties should be the focus of new research and development in assessment and characterization of contaminated sediments. [ABSTRACT FROM AUTHOR]

Sediment is an essential, integral and dynamic part of the hydrologic system. In natural and agricultural basins, sediment is derived from the weathering and erosion of minerals, organic material and soils in upstream areas and from the erosion of river banks and other in-stream sources. As surface-water flow rates decline in lowland areas, transported sediment settles along the river bed and banks by sedimentation. However, because sediments are the ultimate reservoir for the numerous potential chemical and biological contaminants that may be contained in effluents originating from urban, agricultural, and industrial lands and recreational activities, contaminated sediments in rivers and streams, lakes, coastal harbors, and estuaries have the potential to pose ecological and human health risks. The management of sediment quality and quantity in support of ecological and socioeconomic goals is a cause of extensive research, investment and regulatory and public scrutiny, both in Europe and internationally. This chapter examines the management of sediment from a European perspective. The first section discusses the role of sediment management in achieving European ecosystem objectives. Section two summarizes the findings of the EC-funded, demand driven European Sediment Research Network (SedNet). Section three describes a framework risk assessment and management in a major European region, the Venice Lagoon. The next three sections describe aspects of sediment management in an EC accession country, and the host country for this workshop - Slovakia. Section four describes river and lake sediment contamination and related legislation in Slovakia. Section five discusses the assessment and management of Persistent Organic Pollutants (POPs), a major risk driver in Slovakia. Section six discusses a specific class of POPs - PCBS in sediments of a specific region of Slovakia. Finally, Section seven discusses some barriers to successful sediment risk assessment and management, and lists science and infrastructure needs to address these barriers. Whilst all the authors of this chapter are living and/or working in Europe, and the focus is on European perspectives, much work has benefited from international collaborations and we feel that many of the observations and recommendations will have relevance to a broader audience. [ABSTRACT FROM AUTHOR]