The influence of pulp and paper mill effluents on the composition of the humic fraction of aquatic organic matter

The humic fraction of dissolved organic matter was isolated from three sites of River Vouga (Portugal) and its lagoon, corresponding to unpolluted water and water contaminated with pulp mill effluent. Humic substances were characterized by elemental analysis, Fourier transform infrared spectroscopy, CPMAS-13C-NMR spectroscopy and potentiometric titration. The fulvic acids isolated from the most contaminated site exhibit several structural features characteristic of lignosulphonic acids, such as a high sulphur content, the presence of sulphonic groups, higher phenol and methoxyl contents, higher aromaticity and lower carboxyl content than the fulvic acids upstream of the discharge from the pulp mill effluent. The humic substances further downstream still show some of those structural characteristics but they are preferentially shown in the humic acids than in the fulvic acids. These results highlight the importance of the contribution of anthropogenic sources of organic matter to the composition of humic substances from surface waters.