Samples of sea, river and pond water of different absorbance were exposed to artificial radiation resembling sunlight in the UV range. A statistically significant increase in ammonium concentration was detected in pond water of the highest absorbance after 5 h of irradiation. In sea and river water a corresponding increase (< 0.5 μM) was recorded after an exposure time of 25 hours. The bulk characteristics of the analysed samples were insufficient to explain the observed differences.
The complexation of cadmium and lead with humic substances was studied using differential pulse anodic stripping voltammetry and a standard addition technique. The titration was done for humic substances of different molecular weight that had been isolated from seawater and subsequently redissolved in organic-free seawater. The different molecular weight fractions were obtained by ultrafiltration using 1000 D (Dalton), 5000 D and 10 000 D pore size filters. Comparison of the calculated stability constants suggests that the strengths of lead complexes in the analysed fractions are similar and that cadmium is complexed by the fraction smaller than 1000 D.