Mobility and ecological risk assessment of trace metals in polluted estuarine sediments using a sequential extraction scheme F. A. B. Canuto & C. A. B. Garcia & J. P. H. Alves & E. A. Passos Received: 14 April 2012 / Accepted: 20 November 2012 / Published online: 7 December 2012 # Springer Science+Business Media Dordrecht 2012 Abstract The three-stage sequential extraction proce- dure for the fractionation of Cd, Cr, Cu, Ni, Pb, and Zn, proposed by the Commission of the European Communities Bureau of Reference, was applied to sed- iment five samples collected from the Sal estuary, Sergipe State, northeast Brazil, in September 2009. The method showed satisfactory recoveries, detection limits, and standard deviations for determinations of trace metals in the sediments. Cd and Pb were the metals most prevalent in the bioavailable fractions (carbonates, Fe and Mn oxides, organic matter, and sulfides), while Ni, Zn, Cu, and Cr showed higher percentages in the inert fraction. The order of mobility of the metals was Cd (66 %) > Pb (65 %) > Zn (59 %) > Ni (57 %) = Cr (57 %) > Cu (56 %). Possible toxicity related to these metals was examined using the risk assessment code, and by comparing the chemical data with sediment quality guideline ERL-ERM values. Results obtained using the two methods were in agreement, and showed low to medium risk for all metals, indicating that ad- verse effects on aquatic biota should rarely occur. Keywords Trace metal . Sediment . Sequential extraction . Risk assessment code (RAC) . Sediment quality guidelines (SQG) Introduction Estuarine and coastal areas are often regions of high population density and intensive human activity. As a result, elevated levels of trace metals in sediments can reflect the impacts of industrial activities and urban development (Fang et al. 2005). Metal accumulation in sediments poses an environmental problem due to possible metal transfer from the sediments to aquatic media (Filgueiras et al. 2002). The total sediment concentration of a metal does not provide information concerning its mobility, avail- ability, or toxicity (Rauret et al. 1999). Toxicity is dependent on the amount of metal available for bio- accumulation (accumulation by biological organisms), and is determined by those sediment properties that affect its bioavailability (Ure et al. 1993). Hence, it is possible for a sediment to be metal-contaminated (to have a metal content higher than the natural back- ground), but not manifest any toxic effects, depending on the geochemical processes that control the avail- ability of the metal in the sediment (Passos et al. 2011; Silva et al. 2012). Sequential extraction is a well-established approach for the investigation of different forms of trace metals in soils and sediments. Several sequential fractionation procedures have been suggested to identify element distributions in operationally defined pools that in- clude water-soluble species and recalcitrant forms immobilized in mineral lattices (Rauret et al. 1999). Many of these are variants on the scheme proposed by Environ Monit Assess (2013) 185:6173–6185 DOI 10.1007/s10661-012-3015-0 F. A. B. Canuto : C. A. B. Garcia : J. P. H. Alves : E. A. Passos (*) Laboratório de Química Analítica Ambiental, Departamento de Química, Universidade Federal de Sergipe, 49.100-000 São Cristóvão, SE, Brazil e-mail: elisapassos@gmail.com