Hydrobiologia 392: 81–88, 1999. H.L. Golterman (ed.), Sediment–Water Interaction 9. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 81 Arsenic and antimony release from sediments in a Mediterranean estuary Christophe Migon 1 & Christophe Mori 2 1 Laboratoire de Physique et Chimie Marines, Universit´ e de Paris 6, CNRS INSU, La Darse, BP 8, 06238 Villefranche sur mer Cedex, France 2 CEVAREN, Universit´ e de Corse, Grossetti, BP 52, 20250 Corte, France Key words: arsenic, antimony, release, estuary Abstract An ancient realgar mine is responsible for the contamination of a riverine system in central Corsica. Nearby the mine, high As and Sb concentrations are found (up to 2–3 mg l -1 and 2–3 μgl -1 respectively). A significant increase of the As and Sb concentrations in water is found in the water of the mixing zone of river and sea (Bravona estuary; chlorinity 7000–7800). In the same area, a decrease of As and Sb concentrations in sediments is observed. Fe and Mn exhibit the same behaviour. The possible involvement of redox processes is discussed. However, owing to insufficient reducing capacity and insignificant variation of redox potential values along the various estuarine sites (from 320 down to 280 mV), this scenario is rather doubtful. Desorption from FeOOH particles is the most likely process in the Bravona estuary. The impact of these contaminated waters on the marine environment is discussed. Owing to decrease by dilution, as well as the reduced water flow of the estuary, the net supply of As and Sb to the Tyrrhenian Sea is approximately 5 and 1.5 t y -1 for As and Sb respectively. The possible harmful influence of the Bravona river should be of local concern only, and the emphasis of this study is, therefore, on a better knowledge of in situ processes. Introduction Mining activities are responsible for high concen- trations of heavy metals in natural waters (Johnson & Thornton, 1987; Duzzin et al. 1988; Mok & Wai, 1990; Caboi et al., 1993; Migon et al., 1995), which can cause severe environmental harm. Many studies have been undertaken in order to determine the toxicity, the chemical speciation (and thus the bioavailability) and the possible removal mechanisms of heavy metals in freshwaters. In estuaries, which have specific physical and chemical characteristics, various metal transfers occur between dissolved and particulate phases, as well as uptake by phytoplankton (Windom et al., 1988; Dorten et al., 1991; Gadd, 1991; Martin et al., 1993; Migon, 1993). Many authors have discussed the impact of metals on natural ecosystems: e.g., Burrows & Whitton (1983) have observed that high concentrations of Cd, Pb and Zn in water and sed- iment generally lead to high metal concentrations in animals; Romeo (1991) reviewed physiological sub- lethal effects (respiration, growth, reproduction, beha- viour) of Cd, Cu, Hg, Pb and Sn on marine organisms; Mori et al. (1999) studied the bioaccumulation of As and Sb and its effects on freshwater macroinvertebrate populations. In certain cases, processes of metal remobiliza- tion from sediment to the overlying water may occur, which may increase the significance of the pollutant threat. Such a behaviour can be due to (i) the formation of soluble chloro-metal complexes (e.g., cadmium; Elbaz-Poulichet et al., 1987); (ii) regeneration or re- cycling from degrading organic matter (Church, 1986; Windom et al., 1988); (iii) ionic exchange during the transfer from freshwater to saltwater; (iv) redu- cing conditions, which may favour the dissolution of reduced forms and the release of free ionic species. Among potentially harmful elements, As and Sb are known to be highly toxic. A realgar (As 4 S 4 ) de- posit was found in central Corsica, close to the village of Matra, between 1880 and 1890. In 1913, the ore production reached its highest value, more than 4000 tonnes per year. After a production of 30,000 tonnes of ore at 30% of As, the mine was abandoned in 1945. A minor river (Presa) crosses the ancient mine and then runs into the Bravona river, which reaches the