The Science of the Total Environment 318 (2004) 143–157 0048-9697/04/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0048-9697(03)00367-X Vertical distribution of Th-isotope ratios, Pb, Ra and Cs in 210 226 137 sediment cores from an estuary affected by anthropogenic releases E.G. San Miguel *, J.P. Bolıvar , R. Garcıa-Tenorio a, a b ´ ´ Dpto Fısica Aplicada, E.P.S. La Rabida, Ctra Palos SyN, Huelva 21819, Spain a ´ ´ Dpto Fısica Aplicada, E.T.S. Arquitectura, Avda, Reina Mercedes, 2, Sevilla 41012, Spain b ´ Received 12 August 2002; received in revised form 22 May 2003; accepted 26 May 2003 Abstract In an estuary system highly polluted by mining and industrial activities, the sections of sediment cores affected by anthropogenic inputs of U-series radionuclides (due to fertilizer plants releases) were determined through the vertical profiles of Th-isotopic ratio ( Thy Th). Also, when possible, a modified version of the Pb dating method was 230 232 210 applied in the uncontaminated sections of these cores. Using the information provided by the Th-isotopic ratio and Pb methods, we were able to establish confident chronologies, covering the last century, in several of the analysed 210 sediment cores. These chronologies will be used in forthcoming research to study the time evolution of pollutant concentrations in the estuary. Additionally, and based on the established chronologies, we have found that sedimentation rates have drastically increased in some zones of the estuary since the commencement of several industrial activities in the surrounding environment and since the construction of two dikes in the area.  2003 Elsevier Science B.V. All rights reserved. Keywords: Th-isotopes; Ra, Cs and Pb dating; Fertilizer factories; Estuarine system 226 137 210 1. Introduction The Tinto and Odiel rivers flow through Huelva province (southwest of Spain) from north to south forming, at their mouth, the Huelva Estuary (Fig. 1). Important metal mining activities (Cu, Fe, Zn) have been carried out around the basin of these rivers for more than twenty centuries (Davis et al., 2000), with a clear peak from 1875 to 1925. However, after 1925 the production fell to 10% of the maximum reached (Pinedo Vara, 1963). *Corresponding author. Tel.: q34-959017584; fax: q34- 959017304. E-mail address: sanmigue@uhu.es (E.G. San Miguel). As a consequence of the mining operations occurring in both watersheds, the waters of these rivers are very acid. This has allowed heavy metals and other pollutants to travel in solution down to the estuary, where ocean and river waters are mixed. Heavy metal precipitation is then produced as a consequence of the abrupt change in the pH. The strong heavy metal contamination caused by mining activities has been shown in different environmental compartments of the whole ecosys- tem: in the Tinto river watershed (Davis et al., 2000); in the Odiel river watershed (Martın et al., ´ 1998) and in the Huelva Estuary (Ruiz Munoz et ˜ al., 1997).