A model for the bioaccumulation and elimination of Niobium-95 in freshwater biota

Niobium-95 was released into an experimental pond as an acute (6 day) input to investigate its uptake and elimination kinetics in six species of freshwater organisms--snails (Helisoma sp.), clams (Corbicula sp.), crayfish (Cambarus sp.), carp (Cyprinus carpio), bluegill (Lepomis macrochirus). and mosquito fish (Gambusia affinis).

Uptake and elimination parameters were estimated using a three compartment linear model, one compartment representing the environment ex ternal to the organism (water column) and the other two compartments representing the organism's G.I. tract and body tissues. This model was then used to calculate the following bioconcentratior factors of 95-Nb: 3.4 for bluegill, 115.4 for crayfish, 114.9 for clams and 224.8 for snails. Also, the following biological half-times of 95-Nb were calculated: 1.6 days for bluegill, 12.4 days for crayfish, 6.1 days for clams, 1.6 days for snails, and 0.6 days for mosquito fish.

Predictions were made to simulate a chronic (30 day) 95-Nb input and comparisons were made with experimental data. Predicted values and measured values were within the same order of magnitude for the crayfish while predicted values for the snails and bluegill were one to two orders of magnitude below the measured concentrations. The prediction in accuracies may be reduced by including a food source compartment in the snail and bluegill models.

A Monte Carlo error analysis shows that a model which represents the organism by only one compartment is adequate for modelling the cray fish, while significant error may be introduced when a single compart ment model is utilized for organisms obtaining 95-Nb through the food chain, such as bluegill and snails.