Copper speciation in aqueous solutions of fulvic acid and related molecular weight distributions

Potentiometric and fluorescence measurements of aqueous solutions of fulvic acid containing Cu(NO3)(2) or Cu(ClO4)(2), respectively, were carried out at 25 degrees C and pH 5.5 to determine naturally occurring Cu species. The fulvic acid used was isolated by XAD-8 from filtrated (0.3 mu m) water of a peat bog in the Dachauer Moos near Munich. From the results an operationa l molecular weight of fulvic acid of about 750 Si mol was estimated, which was confirmed by molecular weight distributions determined by high-performa nce size-exclusion chromatography (HPSEC), gel permeation chromatography (G PC) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Using th is molecular weight and assuming that mainly 1:1 Cu-fulvic acid complexes a re formed, a conditional stability constant of the Cu-fulvic acid complex o f 10(5,9) could be calculated. These data are essential for the assessment of organic carrier-mediated migration of Cu as well as of the toxicological risk potential of Cu in aqueous environment and can be used as input param eters fur geochemical modeling of the Cu species distribution in aqueous so lutions.