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| 1. Introduction and outline |
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| Polychlorinated biphenyls (PCBs) are a group of halogenated organic substances that are frequently assigned to the larger group of persistent organic pollutants (POPs). PCBs and the other POPs are of great environmental concern because they are lipophilic (bioaccumulative), occur to a significant extent in the gas phase and condensed states (semi-volatile), and are toxic as well as persistent. PCBs have been commercially produced for various applications since the 1930s. The known global mass production of PCBs virtually ceased in 1984, except for the production in the former Soviet Union, which ended in 1993. Worldwide, more than 1.3 million tonnes of PCBs have been intentionally produced (Breivik et al., 2002a). Dated sediment core studies have indicated that the temporal contamination pattern has mirrored the production and use of these contaminants (e.g. Christensen & Lo, 1986 & Gevao et al., 1997). The environmental occurrence of these compounds in coastal zones and elsewhere are thus believed to be a direct result of the historical intentional production, consecutive use and disposal or accidental releases from products or materials containing PCBs (Breivik et al., 2002b). In addition, incidental or unwanted formation (de novo synthesis) is also reported to contribute to the environmental burden of PCBs (e.g. Brown et al., 1995). Even though global mass production has ended, PCBs are still frequently detected in environmental samples. This may in part be attributed to the long environmental half-lives of PCBs (Sinkkonen and Paasivirta, 2000) and in part caused by the potential long lifetime of products or materials containing PCBs (resulting in a significant time delay between production and emissions).
The environmental concerns caused by PCBs in coastal zones are primarily a result of the affinity for PCBs to partition into the organic phases of suspended particles and bottom sediments as well as into the lipids of aquatic biota. This is problematic for several reasons. A primary issue of concern is that human exposure to PCBs tends to be significantly controlled by consumption of seafood, such as fatty fish. A second issue of long-term concern is the potential remobilisation of PCBs from contaminated sediments (Larsson, 1985), representing a potential threat for further uptake in biota for decades to come because of the long response time of sediments to loading reductions. In this document, a brief overview is presented on key issues and research results related to PCBs in coastal zones (Figure 1). A particular emphasis is on results that have emerged from the ELOISE and IMPACTS projects. |
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| Figure 1. General chemical structure of the PCBs. |
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| Figure 2. Estimated cumulative usage of PCBs in tonnes (Breivik et al., 2002a). |
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| 2. Sources and pathways of PCBs to the coastal environment |
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| It is of considerable interest to understand contemporary sources and pathways of PCBs to the coastal environment. Although there is still limited quantitative understanding of the relative importance of the sources and pathways into the aquatic environment, it is generally considered that atmospheric inputs are of key significance on a regional scale, whilst direct discharges may be of key significance on the local scale (e.g. Maldonado and Bayona, 2002). Sources and pathways of PCBs to the aquatic environment have been key issues within the POPCYCLING (Wania et al., 1998; Haugen et al., 1999; Pacyna et al., 1999), EROS-21 (Maldonado & Bayona, 2002) and ADIOS projects (Mandalakis et al., 2003; Mandalakis & Stephanou, 2004) with particular emphasis on atmospheric behaviour and fate. Haugen et al. (1999) studied processes affecting the occurrence of PCBs in air at a coastal site in Norway from long-term monitoring data, whilst Mandalakis et al. (2003) conducted pioneering filed studies on the degradation of PCBs in air at a remote site of the eastern Mediterranean. Additional field studies have focussed on the transfer of PCBs from the atmosphere to the aquatic environment (Mandalakis & Stephanou, 2004). Finally, theoretical approaches used to describe air-sea exchange of such compounds have been reviewed (Wania et al., 1998). |
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| Figure 3 . The POPCYCLING-Baltic project aimed to quantify the pathways of POPs including PCBs from the terrestrial environment to the marine environment via atmosphere and rivers (Wania et al., 2000). |
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| 3. Environmental cycling and fate of PCBs in the coastal environment |
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Various aspects regarding the environmental cycling and fate of PCBs in the coastal environment have been studied within several projects (ADIOS, EROS-21, POPCYCLING). These studies include both process-oriented field studies (Maldonado & Bayona, 2002) as well as modelling studies (Sinkkonen & Paasivirta, 2000; Wania et al., 2000; 2001). Maldonado & Bayona (2002) studied the sources, fate and transformation of PCBs in the north-western Black Sea. They found that PCBs introduced to surface waters tend to be taken up by phytoplankton, with consecutive rapid sinking in sorbed state and degradation or solubilization along the water column. Wania et al. (2001) developed a multi-compartmental model to describe the fate of PCBs in the Baltic Sea. The POPCYCLING-Baltic model is believed to provide invaluable insight into the complex set of interactions that determine the overall fate of POPs in the Baltic Sea drainage basin, but which are inaccessible to measurements.
Sorbed
A substance taken into and retained in another substance.
See Glossary for a complete list of all terms. |
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| 4. Closing remarks |
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| It is recognized that the IMPACTS and ELOISE projects that addressed PCBs in coastal zones are very diverse in terms of key objectives. A simple overview of relevant projects (ADIOS, AIRWIN, BIOCET, EROS-21, FAMIZ, POPCYCLING) is therefore included in Table 1 below to highlight the unique features of each project. Websites of selected projects (where available) are furthermore included for which more detailed information can be obtained. |
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| Projects |
Project Features |
| ADIOS (IMPACTS) |
The key incentive of the ADIOS project was to assess the impact of atmospheric deposition on the open Mediterranean Sea with respect to natural processes and anthropogenic activities. Organic pollutants were among the target compounds considered in the project. ADIOS did not only include studies related to the basin-wide characterisation of atmospheric deposition, but also the determination of anthropogenic compounds in the ecosystem of the open Mediterranean Sea . Methodologies used included environmental (air, water, sediments) and ecotoxicological monitoring, laboratory experiments, remote sensing and modelling. |
| AIRWIN (IMPACTS) |
The AIRWIN project aimed to characterize processes occurring in the sea surface microlayer (SML) and their relevance to global change and effects on the marine environment and its living resources.
Key objectives included;
(i) To define the role of the SML in the entry and loss of organic and inorganic pollutants in the marine environment (ii) To identify those pollutants which are preferentially transferred to humans through marine food webs
(iii) To identify and to isolate micro-organisms that could be used for bioremediation and as cosmetic products to improve human's health
(iv) To provide potential bioindicators of atmospheric pollution.
Examples of fieldwork carried out within the project with regards to organic contaminants demonstrated the enrichment of such substances (e.g. PCBs, PAHs, etc.) in the SML, as an organic carbon driven process, both in the dissolved and particulate phases. In this respect, the trophic status of the coastal waters will determine the partitioning of xenobiotics between the particulate, colloidal and truly dissolved phases, which has important implications in assessing the corresponding bioavailability. The fieldwork, in combination with the modelling task, has also evidenced that coastal regions are characterized by important net volatilization fluxes of POPs such as PAHs and PCBs. Conversely, net absorption fluxes are observed at open sea. |
| BIOCET (IMPACTS) |
The BIOCET project aimed to quantify and model the transport pathways and impact on reproduction of bioaccumulation of persistent organic pollutants (POPs) in four species of small cetaceans (harbour porpoises and dolphins) in European Atlantic waters. The geographical scope of the project encompassed the Irish, Scottish (UK) and Dutch coasts, as well as the Atlantic coasts of France and Spain . The organic contaminants studied included the PCBs and DDE as representatives of the ‘classical’ POPs as well as selected brominated flame retardants (PBDEs). |
| EROS-21 (ELOISE) |
The key objective of EROS-21 was to develop an integrated framework of coupled biogeochemical models on the basis of field and laboratory studies, in order to provide a management tool for eutrophication reduction scenarios in the Black Sea . This project additionally included research on the sources, distribution and water column processes of selected POPs (PAHs, PCBs and selected organochlorine pesticides) in the study area. |
| FAMIZ (IMPACTS) |
FAMIZ aimed to study the food web uptake of POP in the Barents Sea . The main incentive for carrying out the project relied on the observation that the ratio between the concentration of POPs in higher organisms and the concentration of POPs in seawater appeared to be higher in the Arctic than in other marine ecosystems. The objectives of FAMIZ was to understand this phenomenon by developing mechanistic models of the introduction of POPs into food webs in the highly productive marginal ice zone of Barents Sea.
The studies were directed towards two main hypothetical mechanisms: (1) Effects of microhabitats - locally elevated exposure to POPs, in particular to ice-algae microhabitats caused by ice rafted sediment, brine formation and/or melting deposited snow; and (2) Effects of food webs - more efficient POP accumulation due to slower growth, higher lipid content and longer life cycles of plankton and sympagic organisms. The project included laboratory and field studies as well as model development. |
| POPCYCLING-BALTIC (ELOISE) |
The overall goal of the project POPCYCLING-BALTIC was to develop a comprehensive, multicompartmental model to study the fate and behaviour of POPs in the Baltic Sea environment. Specific objectives of the project were to (1) understand and quantify the major sources, pathways and loss processes of the contaminants, (2) establish a link between contaminant loadings and environmental concentrations (3) estimate the time response to loading reductions (4) interpret spatial patterns and temporal trends of the contamination. The project also included the development of emission inventories for POPs (HCHs, PCBs, DDT, HCB, PAHs, PCDD/Fs) across Europe , as well as a database on environmental levels of selected POPs in various environmental compartments of the Baltic Sea drainage basin. |
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| Table 1. List of projects (both IMPACTS and ELOISE) that addressed PCBs in coastal zones. |
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