Effects of humus concentrations on benzo[a]pyrene accumulation from water to Daphnia magna: comparison of natural waters and standard preparations.

The bioaccumulation of benzo[a]pyrene (BaP) into Daphnia magna from two natural humic waters (one lake water and one bog water), and two humus preparations (Nordic Reference fulvic acid (Nordic FA) and a lyophilized concentrate) of the same aquatic origin was measured by using several dissolved organic carbon (DOC) concentrations for each sample. The partition coefficient (Kp) of BaP to the humus content of the water was determined by an equilibrium dialysis technique. In all four samples, an increase in humus concentration decreased the bioavailability of BaP in a logarithmic manner. The Nordic FA and the natural untreated humic water, from the same source as the water used for isolation of Nordic FA, gave a similar DOC bioaccumulation response and similar Kp values. The difference between the two natural humic waters was obvious, both in the accumulation experiments and the Kp values. The assumption that the total bound fraction of organic pollutant is not available for D. magna is not fully supported by this study.