Conical terracotta containers (43 cm upper diameter, 40 cm height), filled with artificial soft sediment (sand-Benthonit mixture), exposed subsequently since 2002 at 20 m depth, sampled and refilled for one-year, two-year and three-year exposure plus ambient samples. Sampled with core (diameter 4.5 cm; area 15.9 cm**2), upper 3 cm of sediment. Extraction by Levasil flotation method with centrifugation (40 µm mesh size).