The sediment samples were air-dried, disaggregated using a mortar and pestle to pass through a 2 mm mesh sieve, dried at 105 °C for 24 h and digested as following: 15 ml concentrated ultrapure nitric acid (Fluka, TraceSELECT®, for trace analysis ≥ 69%) were added to the sample (2.0 g) and heated to 160 °C for 1 h, using an aluminium block heating digester (VELP Scientific, Inc.); then, the vessel was cooled to room temperature and 10 ml ultrapure concentrated hydrochloric
acid (Fluka, TraceSELECT®, for trace analysis ≥ 37%) were added and