Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul Silver and copper as pollution tracers in Neogene to Holocene estuarine sediments from southwestern Spain Francisco Ruiz a,f,1,∗ , Joaquín Rodríguez Vidal a,1 , Luis Miguel Cáceres a,1 , Manuel Olías a , María Luz González-Regalado a,1 , Juan Manuel Campos b,1 , Javier Bermejo b,1 , Manuel Abad c,d , Tatiana Izquierdo d , María Isabel Carretero e , Manuel Pozo f , Guadalupe Monge e , Josep Tosquella a,1 , Maria Isabel Prudencio g , Maria Isabel Dias g , Rosa Marques g , Paula Gómez a,1 , Antonio Toscano a,1 , Verónica Romero a,1 a Departamento de Ciencias de la Tierra, Universidad de Huelva, 21071 Huelva, Spain b Departamento de Historia, Geografía y Antropología, Universidad de Huelva, 21071 Huelva, Spain c Departamento de Biología y Geología, Física y Química Inorgánica, ESCET, Universidad Rey Juan Carlos, c/ Tulipán s/n, 28933 Móstoles, Spain d Instituto de Investigaciones Científicas y Tecnológicas de la Universidad de Atacama (IDICTEC-UDA), Avenida Copayapu 485, Copiapó, Chile e Departamento de Cristalografía, Mineralogía y Química Agrícola, Universidad de Sevilla, 41012 Sevilla, Spain f Departamento de Geología y Geoquímica, Universidad Autónoma de Madrid, 28049 Madrid, Spain g Centro de Ciências e Tecnologias Nucleares (C2TN), Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela LRS, Portugal ARTICLE INFO Keywords: Silver Copper Natural pollution Anthropic impacts Miocene-recent Tinto-odiel estuary Guadalquivir estuary SW Spain ABSTRACT Estuaries are very sensitive ecosystems to human activities and the natural evolution of their drainage basins located upstream. Pollution derived from human activities, such as historical mining or recent industrial wastes, can significantly affect their environmental quality. This paper analyzes the silver and copper contents of four cores extracted in two estuaries of SW Spain. Its chronology and vertical evolution allow to differentiate the effects of several pollution episodes (natural, Roman, 19th-20th centuries) on its different sedimentary en- vironments in the last 6 million years. Possible future applications are included in the fields of environmental management or even education. 1. Introduction Estuaries are ecosystems highly vulnerable to anthropogenic pres- sure, because they are the intermediate or definitive containers of nu- merous polluting actions that occur in the drainage basins located up- stream or at their margins. These polluting inputs can come from agricultural activities (Longphuirt et al., 2015), fish farming (Fowles et al., 2018), urban wastes and sewages (Brand et al., 2018), mining (Gomez et al., 2017) or industrial discharges (Irabien et al., 2018). Re- sults are the contamination of waters and sediments (Elias et al., 2018; Nguyen, 2019), the deterioration of flora and fauna (Kosyan et al., 2017; Rigaud et al., 2019) and risks for human health (Chiesa et al., 2018). One of the most used techniques to define the environmental quality of an estuary is the geochemical analysis of its bottom sediments. Heavy metal contents (e.g. Cu, Zn, Pb) provide a direct reference to their degree of contamination, as well as the sources (Liu et al., 2018; Hossain et al., 2019). Silver is an unusual element in this evaluation, although it has been used to delimite the impact of mining or agri- cultural activities (e.g. Vallejo et al., 2016). Different methods have been developed to reflect the degree of pollution of a sample. The geoaccumulation index (I geo ; Müller, 1981) is frequently used for this purpose (Harikrishnan et al., 2017; Kim et al., 2018), although other indices are also applied (e.g. enrichment factor –EF-; contamination factor –CF-; pollution load index; see Tholkappian et al., 2018 for a review). If possible, it is desirable to obtain previously a regional or local background for the finer grain sizes (silt, clay) and for the thicker ones (sand, gravel) before applying the geoaccumulation index (e.g. Ruiz, 2001). This paper analyzes the silver content of Neogene and Holocene sediments from two estuaries in southwestern Spain, with the https://doi.org/10.1016/j.marpolbul.2019.110704 Received 22 April 2019; Received in revised form 30 October 2019; Accepted 31 October 2019 ∗ Corresponding author. Facultad de Ciencias Experimentales, Universidad de Huelva, Avda. 3 de marzo, s/n, 21071, Huelva, Spain. E-mail address: ruizmu@uhu.es (F. Ruiz). 1 Centro de Investigación en Patrimonio Histórico, Cultural y Natural (CIPHCN), Universidad de Huelva, 21071 Huelva, Spain Marine Pollution Bulletin 150 (2020) 110704 Available online 16 November 2019 0025-326X/ © 2019 Elsevier Ltd. All rights reserved. T