Interactions Between Humic Acid and the Forms and Bioavailability of Copper in Water

There is widespread concern about pollution of freshwater ecosystems caused by heavy metals. The aim of this study was to determine how humic acid affected the bioavailability of Cu at a range of Cu concentrations in water. The concentrations of selected Cu species were characterized by spectroscopic methods and multiple regression models. The results showed that the dissolved Cu concentration decreased by an average of 13.4% for every 5-mg/l increase in the humic acid concentration in the Cu-treated water, indicating that humic acid could reduce the Cu bioavailability. Tests to show how DOM fluorescent components affected the Cu species concentrations showed that the Cu species were significantly correlated with five fluorescent components of DOM (P<0.01, linear goodness of fit: R-min(2)=0.8374). We then examined how the pH and DOM fluorescent components together affected the concentrations of the Cu forms. When 3 <= pH <= 7, both tryptophan and fulvic acid promoted the transformation of dissolved Cu forms to suspended Cu forms. The Cu forms were significantly correlated with the pH and DOM fluorescence (P<0.01, linear regression goodness of fit: R-min(2)=0.8898). However, tryptophan and fulvic acid had contrasting effects when the pH was less than, or greater than, 7. The influences on the migration ability and bioavailability of Cu therefore varied, depending on the water conditions. We conclude that it may be possible to identify the substances that have most effect on the bioavailability of Cu in water environments from the pH range of the water body, and that the bioavailability of heavy metals in water environments may be controlled by adding substances with specific properties.