Bioavailability of Cd to the common carp, Cyprinuscarpio, in the presence of humic acid

Abstract

The uptake of cadmium by the common carp, Cyprinus carpio, was studied in chemically defined freshwater in the absence and presence of commercial humic acid. This was done to evaluate whether the cadmium uptake by carp in the presence of humic acid was related to the ambient Cd 2+-ion activity or whether the complexed metal also contributed to the uptake. Uptake of Cd during a 3-h period of exposure was used as a measure of the biological availability of the metal. The uptake rate data for Cd in total fish and gills obtained in the absence (control) and presence (treatment) of humic acid were analyzed using a Michaelis–Menten model for mediated transport. The Michaelis–Menten parameters K M and V max obtained in the control and the treatment experiment were compared for each of the two investigated carp compartments (total fish and gills). The model parameter estimates for Cd uptake by total carp in the treatment experiment ( K M=0.41±0.11 μmol l −1; V max=0.66±0.13 μmol kg −1 h −1) were not significantly different from the model parameters in the control experiment ( K M=0.34±0.06 μmol l −1; V max=0.58±0.07 μmol kg −1 h −1) on the basis of Welch's approximate t-test. Similarly, the Michaelis–Menten model parameter estimates for Cd uptake by carp gills in the treatment experiment ( K M=0.15±0.06 μmol l −1; V max=5.14±1.07 μmol kg −1 h −1) were not significantly different from the model parameters derived from the control experiment ( K M=0.27±0.09 μmol l −1; V max=7.63±1.38 μmol kg −1 h −1). This indicated that the Cd uptake rate by total carp and in carp gills in the presence of commercial humic acid followed the measured variations in Cd 2+-ion activity as predicted by the control experiment.