Th-230/Th-232 activity ratios as a chronological marker complementing Pb-210 dating in an estuarine system affected by industrial releases

The main purpose of this research is to show the usefulness of the Th-230/T h-232 activity ratios as a chronological marker that can be helpful in the dating of sediment cores collected from an estuarine system located in the south west of Spain highly polluted by wastes from fertilizer plants. These wastes, being released for 30 years, and enriched in radionuclides from th e uranium series including Pb-210, invalidate the application of the Pb-210 dating technique in full extent to the sediment cores collected in this es tuary. However, the evaluation and the interpretation of both Pb-210 and Th -230/Th-232 profiles allows the determination of average sedimentation rate s in different parts of the cores, contaminated and noncontaminated zone, t hat agree in the case analysed in this research. Through this approach, a c onfident chronology covering the last century, which is essential to analys e and reconstruct the historical evolution of other pollutants in this heav ily contaminated system can be established. (C) 2001 Elsevier Science Ltd. All rights reserved.