Interaction of humic acid with selected trace metals: Influence on bioaccumulation in daphnids

Abstract The influence of humic acid (HA) on the bioaccumulation of Cd, Cr VI and two forms of Cr III was evaluated using a common freshwater cladoceran, Daphnia magna. HA (0.5, 5 and 50 mg/L) had a much greater influence on the bioaccumulation of Cd and Cr III than of Cr VI. At only one time point (96 h) did the 50 mg/L HA significantly decrease the bioaccumulation of Cr VI. The remaining concentrations of HA (0.5 and 5 mg/L) had no influence on Cr VI bioaccumulation. However, with both forms of Cr III, 50 mg/L HA significantly decreased bioaccumulation, while 0.5 and 5 mg/L HA concentrations either decreased or had no influence on bioaccumulation. The results of the Cd-HA interaction were much more variable than those obtained with Cr VI or Cr III. The bioaccumulation of Cd was increased, decreased or not influenced by HA, depending on the concentration of HA and the exposure period examined.