Evaluation of the effects of natural dissolved and colloidal organic ligands on the electrochemical lability of Cu, Pb and Cd in the Arran Deep, Scotland

The physicochemical speciation of Cu, Pb and Cd was determined by voltammetric titration procedures on filtered (F; 0.4-μm) and cross-flow filtered (CFF; 3000 Da) fractions of 15 samples collected at three sites in the Firth of Clyde, on Scotlandʹs west coast. The colloidal material — defined on the basis of size (size <0.4 μm) and molecular weight (NMW>3000 Da) — was characterized by dynamic light scattering in terms of its electrophoretic behaviour with changing pH in a 0.01 M NaCl medium. The particulate material (size >0.4 μm) was analysed for its total metal content (Cu, Pb, Cd, Mn, Fe) by atomic absorption spectrometry. The top 20 m of the water column in the Arran Deep was influenced by freshwater inputs (32.9