INTERACTION OF HUMIC SUBSTANCES WITH HYDROPHOBIC METAL-COMPLEXES - A STUDY BY ANODIC-STRIPPING VOLTAMMETRY AND SPECTROPHOTOMETRY

The interaction of humic substances [humic acid (HA) and fulvic acid (FA)] with stable hydrophobic copper(II) complexes Cu(PAN)2 and Cu(oxine)2 has been studied at pH 8.2 by DC-anodic stripping voltammetric measurements at a Nafion-coated thin mercury film electrode [PAN = 1-(2-pyridylazo)-2-naphthol; oxine = 8-quinolinol]. The apparent lability of the copper(II) complexes decreased in the presence of both humic substances. The association capacity, the capacity for strong binding to these complexes, was greater for humic acid than for fulvic acid [ca. 2.8 x 10(-7) mol l-1 Cu(oxine)2 at 10-mu-g/ml-1 HA, or 50-mu-g ml-1 FA]. Combined with spectrophotometric measurements, the data were interpreted in terms of a hydrophilic interaction involving displacement of ligand from the hydrophobic copper(II) complex and formation of a ternary complex HS-Cu-L (HS = humic substance). Such reactions could be effective in moderating the toxicity of hydrophobic copper(II) complexes in river and estuarine systems.