| The technologic and economic development of human society, based on high industrialization, requires an increase in metallic mineral supplies. However, these supplies require exploration of ore deposits and beneficiation of minerals, which frequently release different kinds of contaminants in soils, water and air. Mining and industrial wastes are environmental sources of heavy metals, also known as trace metals. Metal contamination of soils and waters is reported around the world and may have a severe impact of human health (Förstner, 1998), due to persistence and inherent toxicity of some trace metals. Metal fate and bioavailability in water resources and tailings dams are dependent of some aspects of water quality. The presence of binding phases like organic matter, carbonates, sulfides and iron and manganese oxides may retain trace metals in the sediments and reduce the toxicity to aquatic organisms. On the other hand, solubilization of these phases under specific conditions may transfer trace metals into the dissolved fraction, which is considered to be the most mobile and most bioavailable form of trace metals (Salomons, 1998). The distribution of trace metals in the different phases of the sediments determines their mobility, bioavailability and toxicity (Szefer et al., 1995). The knowledge of the physic-chemical forms in which trace metals exist in the sediments, rather than total quantification, is a tool to precisely locate the origin of metals (i.e., if they are related to anthropogenic sources or to background levels) and to understand their geochemical cycles and mobility. In spite of some limitations, sequential extraction techiniques are commonly used to study the speciation of sediment bound trace metals (Tessier et al., 1979; Tessier et al. 1985, Loring and Rantala, 1992, Quevaullier et al. 1997, Haese et al. 1997, Haese et al. 2000, Gómez-Ariza et al. 2000a, Gómez-Ariza et al. 2000b). Some trace metals have the capacity to enter and remain in food webs for a long time (Szefer et al., 1998). Some species of organisms that accumulate and concentrate heavy metals in high levels can be used as biomonitors to reflect the extent of metal pollution and to assess their potential impacts in human health. Various species of mollusks and fish are commonly used as monitors. Geochemical studies assessing the bioavailability of trace metals related to m |
