The extractions were performed using Nalgene (40 ml PPCO Oak Ridge) centrifuge tubes, with 20 ml extractant added in each step, except in step 5, where 15 ml of H2O2 and later 5 ml NH4Ac solution was added. Due to the high organic matter content in the sediments it was necessary to perform extraction step 5 very carefully, with gradual addition of H2O2. The sediments were washed with de-ionized water between each extraction step. Three parallel samples consisting of 2 g of the homogenized sediments were extracted in order to get representative results.
All equipment used for the experiment was acid washed prior to use. Reagents of analytical grade or better were used throughout, and all water was de-ionized (>18 MΩ cm−1).