A mechanistic model for the uptake of waterborne strontium in the common carp (Cyprinus carpio L.)

The release of radioactive strontium to the environment is of concern due t o the strong accumulation of this calcium resembling element in the bone an d other tissues. To predict the effects of changes in environmental conditi ons on the uptake of Sr2+ and Ca2+ by freshwater fish, a Michaelis-Menten t ype model is introduced that accounts far the effects of chemical speciatio n, hydrogen ion activity, and metal ion competition. The-uptake kinetics we re characterized in vivo from short-term exposure experiments using the com mon carp (Cyprinus carpio) as the model organism. Fish were exposed to a wi de range of waterborne Sr2+ (0.2-10 000 muM) and Ca2+ (10-10 000 muM) conce ntrations and water pH (5.0-8.5). Strontium uptake by the whole body of fis h increased with increasing Sr2+ activity, displaying saturation kinetics, but decreased significantly with increasing Ca2+ and H+ activities in the w ater. Likewise, calcium uptake by the fish decreased with increasing Sr2+ a nd H+ activities in the water. The model fitted to the pealed data explains 97.5% of the variation in Sr2+ uptake and 86% in Ca2+ uptake over the wide range of exposure conditions and reveals that Sr2+ and Ca2+ inhibit each o ther completely competitively, while Hf inhibits the uptake of both metal i ons in a partially noncompetitive way. This model can be used as a mechanis tic tool to predict the uptake of these metals in carp under variable condi tions.