Relationships between polychlorinated biphenyls in molluscs, hydrological characteristics and human pressures, within Basque estuaries (northern Spain) O. Solaun ⇑ , J.G. Rodríguez, A. Borja, J. Larreta, V. Valencia Marine Research Division, AZTI-Tecnalia Foundation Herrera Kaia, Portualdea, z/g, 20110 Pasaia, Spain highlights  The highest PCBs concentrations were found close to industrial-influenced areas.  Residence time, river flow and ‘pressure index’ were related to PCB concentrations.  Hexachlorinated congeners dominated the PCB profiles. article info Article history: Received 27 June 2013 Received in revised form 17 June 2014 Accepted 20 July 2014 Available online 24 August 2014 Handling Editor: H. Fiedler Keywords: Molluscs Sediments PCBs Hydrological characteristics Human pressures Basque Country abstract Interannual variability of polychlorinated biphenyls (PCBs), measured in the soft tissues of Mytilus galloprovincialis mussels and Crassostrea gigas oysters, collected from estuarine waters within the Basque Country (Bay of Biscay), are investigated. Samples were collected in the autumn, between 2002 and 2011. Sites located within the ports of Bilbao and Pasaia showed the highest PCBs concentrations in molluscs; the lowest were observed in the mouth of the Oka estuary, an area of low population and industrial activ- ity. Congener profiles of PCBs in the tissues of molluscs reveal the predominance of hexachlorobiphenyls (CB153 and CB138). In addition, redundancy analysis has shown that residence time, river flow and a ‘pressure index’ explain 57% of the variability in the PCB congener concentrations (the higher the values of these variables, the higher the concentration). Finally, R7PCB median concentrations in molluscs and sediments, collected from nearby sampling sites, were found to be moderately correlated (r 2 = 0.513, p < 0.01). Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Polychlorinated biphenyls (PCBs) are amongst the contami- nants of particular concern in the marine environment, because of its capacity of bioaccumulation in marine fauna (Magnusson et al., 2006). Comprising 209 structurally-related congeners, PCBs are synthetic substances manufactured and used world-wide, from the 1930s to mid-1970s. Due to their physico-chemical properties (i.e., chemical stability, high heat capacity, low flammability, and insulating properties), they have been used for a variety of indus- trial and commercial applications; these include dielectric fluids in transformers and capacitors, printing ink, adhesives, fire retar- dants and lubricants (Erickson, 2001). Within Europe, although substantial reductions in releases and progress on the phase-out have been achieved between 1998 and 2005, there are widespread locations where concentrations of PCBs in sediments and/or biota pose a risk of pollution (OSPAR, 2009, 2012). Therefore, as historic pollution of river, estuarine and mar- ine sediments can act as a continued source for the release of con- taminants (Magnusson et al., 2006; OSPAR, 2009), environmental monitoring of contamination in different environments should continue (Scarpato et al., 2010). In the above sense, research programmes are considered to be valuable tools for assessing the status and trends within coastal environments, for the identification of potential sources of contam- ination; this is to prevent future problems and the enhancement of the control of pollution, by means of compliance to national/inter- national regulatory limits (e.g., Kimbrough et al., 2008). Therefore, in recent decades, many coastal monitoring networks which include biomonitors (i.e., mussels or oysters) have been http://dx.doi.org/10.1016/j.chemosphere.2014.07.053 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +34 946574000; fax: +34 946572555. E-mail address: osolaun@azti.es (O. Solaun). Chemosphere 118 (2015) 130–135 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere