Robustness, metabolic states modeling

Figure 47. The robustness of metabolic states. Shown is the probability that a randomly chosen state is unstable. Starting with initially 100% stable models, the parameters are subject to increasing perturbations of strength p, corresponding to a random walk in parameter space. (A) The initial states are chosen randomly from the parameter space. (B) The initial states are confined to a small region with 0.01 < < 0. Note that the state Catp exhibits a rapid decay in stability. The data...

Landrum et al. (1992) developed a kinetic bioaccumulation model for PAHs in the amphipod Diporeia, employing first-order kinetic rate constants for uptake of dissolved chemical from the overlying water, uptake by ingestion of sediment, and elimination of chemical via the gills and feces. In this model, diet is restricted to sediment, and chemical metabolism is considered negligable. The model and its parameters, as Table 9.3 summarizes, treat steady-state and time-variable conditions. Empirically derived regression equations (Landrum and Poore, 1988 and Landrum, 1989) are used to estimate the uptake and elimination rate constants. A field study in Lake Michigan revealed substantial differences between predicted and observed concentrations of PAHs in the amphipod Diporeia. Until more robust kinetic rate constant data are available for a variety of benthic invertebrates and chemicals, this model is unlikely to provide accurate estimates of chemical concentrations in benthic invertebrates under field conditions. 

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