Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul Multi-annual survey of health status disturbance in the Bilbao estuary (Bay of Biscay) based on sediment chemistry and juvenile sole (Solea spp.) histopathology T. Briaudeau a , I. Zorita b , N. Cuevas b , J. Franco b , I. Marigómez a, ⁎ , U. Izagirre a a CBET Research Group, Dept. Zoology and Animal Cell Biology, Faculty of Science and Technology and Research Centre for Experimental Marine Biology and Biotechnology PIE, University of the Basque Country UPV/EHU, Basque Country, Spain b AZTI, Herrera Kaia, Portualdea z/g, 20110 Pasaia, Spain ARTICLE INFO Keywords: Bilbao Pollution monitoring Sediment Solea spp. Histopathology ABSTRACT The Bilbao estuary (SE Bay of Biscay) is a recovering ecosystem whose sediments are still contaminated. They represent a potential risk for the biota including benthic and demersal species living in direct contact with the sediment. In this context, the present study aims to survey trends of the health status of the Bilbao estuary based on sediment chemistry and sole (Solea spp.) histopathology. Monitoring campaigns were carried out every au- tumn from 2011 to 2017 along the estuary. Contaminant levels were measured in sediments; liver, gills and gonads of juvenile fish were collected for histopathology. Overall, contaminant levels fluctuated throughout the years, with highest values recorded in the earlier years of the study period. Sole histopathology showed al- terations of mild severity. Results permitted to assess the environmental health status of the Bilbao estuary during 7 years, although no clear temporal trend was detected. Longer-term monitoring programmes are ne- cessary to confirm the ecosystem recovery. 1. Introduction The marine environment is exposed to a large variety of persistent chemicals, which even at low levels can cause adverse effects to the ecosystem (Bernet et al., 1999; Haynes and Johnson, 2000; Moore et al., 2004). Pollution monitoring programmes are therefore developed to survey status and trends of the affected aquatic environments over time. In the Bay of Biscay and the Atlantic Iberian coast, chemical long-term data were recorded for the past years in offshore, coastal and estuarine areas (Besada et al., 2011, 2014; Borja et al., 2011, 2016; Legorburu et al., 2013, 2014). Amongst these areas, the Bilbao estuary (SE Bay of Biscay) attracted great interest for its industrial past and its recent re- covery processes (Borja et al., 2006, 2010, 2016; Cajaraville et al., 2016; Irabien et al., 2018). This estuary suffered from intense industrial and domestic pollution of the Bilbao metropolitan area since the 19th century and was consequently highly contaminated (Soto et al., 1995; González-Oreja and Saiz-Salinas, 1998; Orbea and Cajaraville, 2006; Fernández-Ortiz de Vallejuelo et al., 2010; Gredilla et al., 2013). Over the last decades, the industrial decline and improvement of wastewater- treatment in the area enhanced the recovery of both water and sedi- ment quality, as well as the diversity and abundance of the planktonic and benthic communities and fish populations (Saiz-Salinas and González-Oreja, 2000; Cearreta et al., 2004; Borja et al., 2006; García- Barcina et al., 2006; Díez et al., 2009; Fernández-Ortiz de Vallejuelo et al., 2010; Villate et al., 2013; Pouso et al., 2018a, 2018b). Nevertheless, the recovery of sediment quality is a slow process and thus, some areas of the estuary were still considered moderately toxic (Borja et al., 2015; Cajaraville et al., 2016). Based on sediment analysis, the estuary was chronically impacted by metals, PCBs and PAHs con- tamination (Montero et al., 2013; Borja et al., 2015). These sediments represented a potential source of pollutants for the surrounding biota (Eggleton and Thomas, 2004). A particular interest has been drawn towards the use of flatfishes as sentinel species for biomonitoring programmes (Köhler et al., 1992; Myers et al., 1994; Stehr et al., 2003; Dabrowska et al., 2012; Fricke et al., 2012). This is mainly related to their benthic behaviour, which links their general health status to sediment quality (Feist et al., 2004; Lang et al., 2006; Jimenez-Tenorio et al., 2008). In this respect, the common sole (Solea solea) and the Senegalese sole (Solea senegalensis) are two frequent flatfishes found along the coast of Southern European countries (Quéro et al., 1986). Their suitability as sentinel species for biomonitoring programmes has been proposed in many works. They https://doi.org/10.1016/j.marpolbul.2019.05.034 Received 24 January 2019; Received in revised form 13 May 2019; Accepted 15 May 2019 ⁎ Corresponding author. E-mail address: ionan.marigomez@ehu.eus (I. Marigómez). Marine Pollution Bulletin 145 (2019) 126–137 Available online 23 May 2019 0025-326X/ © 2019 Published by Elsevier Ltd. T