Portions of sediment were sequentially treated with: 0.11 M CH3COOH solution (exchangeable fraction) and 0.5 M NH2OHHCl solution(fraction bound to Fe and Mn oxy-hydroxides), being the metal analysed in solution as described in Section 2.6.2. Metal levels in organic plus residual fractions was calculated by the difference between total metal levels and the sum of metal levels in fractions exchangeable and bound to Fe and Mn oxy-hydroxides. Percentage of each fraction was calculated relatively to total metal levels.More details can be found in Almeida et al.