Fig. 2. Cadmium (a) and copper (b) concentrations, corrected for mixing, in the percolate collected from different standard-size suction cups at pH 7.5. For the conditions at Steps 1 to 4 of the experiment refer to the Materials and Methods section and Table 3. Volumes are given in multiples of the pore volume (V₀) of the respective cup. The reference lines show the expected metal concentrations if no interaction with the cup materials occurred (i.e., the concentration measured in the initial solution). Copper concentrations in the percolates from polytetrafluorethylene (PTFE), ceramic, and glass cups in Steps 1, 2, and 3 were all below the detection limit of 0.004 µmol L^–1 and are plotted at this value.