Bioavailability of Cd to the common carp, Cyprinus carpio, in the presenceof humic acid

The uptake of cadmium by the common carp, Cyprinus carpio, was studied in c hemically defined freshwater in the absence and presence of commercial humi c acid. This was done to evaluate whether the cadmium uptake by carp in the presence of humic acid was related to the ambient Cd2+-ion activity or whe ther the complexed metal also contributed to the uptake. Uptake of Cd durin g a 3-h period of exposure was used as a measure of the biological availabi lity of the metal. The uptake rate data for Cd in total fish and gills obta ined in the absence (control) and presence (treatment) of humic acid were a nalyzed using a Michaelis-Menten model for mediated transport. The Michaeli s-Menten parameters K-M and V-max obtained in the control and the treatment experiment were compared for each of the two investigated carp compartment s (total fish and gills). The model parameter estimates for Cd uptake by to tal carp in the treatment experiment (K-M = 0.41 +/- 0.11 mu mol l(-1); V-m ax = 0.66 +/- 0.13 mu mol kg(-1) h(-1)) were not significantly different fr om the model parameters in the control experiment (K-M = 0.34 +/- 0.06 mu m ol l(-1); V-max = 0.58 +/- 0.07 mu mol kg(-1) h(-1)) on the basis of Welch' s approximate t-test. Similarly, the Michaelis-Menten model parameter estim ates for Cd uptake by carp gills in the treatment experiment (K-M = 0.15 +/ - 0.06 mu mol l(-1); V-max = 5.14 +/- 1.07 mu mol kg(-1) h(-1)) were not si gnificantly different from the model parameters derived from the control ex periment (K-M = 0.27 +/- 0.09 mu mol l(-1); V-max = 7.63 +/- 1.38 mu mol kg (-1) h(-1)). This indicated that the Cd uptake rate by total carp and in ca rp gills in the presence of commercial humic acid followed the measured var iations in Cd2+-ion activity as predicted by the control experiment. (C) 20 01 Elsevier Science B.V. All rights reserved.