Bioaccumulation kinetic models

FIGURE 4.2 (a) A bioaccumulation model for terrestrial organisms. A kinetic model for... 

Walker, C.H. (1987). Kinetic models for predicting bioaccumulation of pollutants in eco-sytems. Environmental Pollution 44, 227-240. 

Walker, C.H. (1990b). Kinetic models to predict bioaccumulation of pollutants. Functional Ecology 4, 295-301. 

BIOACCUMULATION OF METALS AS COLLOID COMPLEXES AND FREE IONS A KINETIC MODEL... 

Several models have been developed for a kinetic approach to bioaccumulation that would model the trophic transfer of contaminant in animals from ingested food. A first-order kinetic model has been proposed, which considers uptake from both dissolved and particulate phases [95], A particular application of that model is to separate the pathways for metal uptake in marine suspension and deposit feeders since ... 

Thomann et al. (1992) and Morrison et al. (1997) have developed kinetic models employing rate constants to assess the extent of chemical bioaccumulation in zooplankton, as Tables 9.1 and 9.2 summarize. Thomann et al. (1992) list relationships which incorporate organism physiology, bioenergetics, and chemical characteristics to estimate uptake and elimination rate constants which are used to estimate bioaccumulation. Morrison et al. (1997) rely on physiological information to estimate bioaccumulation. Both models provide a potentially more realistic description of bioaccumulation by zooplankton, although, to date, neither model has been tested independently against field data. 

A number of authors (e.g., Bruggeman et al., 1981 and 1984 Opperhuizen et al., 1985 Gobas et al., 1989) have applied simple kinetic models (i.e., equations (13)-(15), (25)-(27), (29, (30))to fish. In most cases, the models are used in a descriptive sense to describe empirical data derived from bioconcentration or bioaccumulation tests. These models can play an important role in the analysis of the results of bioconcentration tests, but they are generally inapplicable to bioaccumulation under field conditions. 

Physiological Models for chemical bioaccumulation in fish are based on the same mass balance equations as the kinetic models for bioaccumulation, but the rate constants and chemical fluxes that quantify the rates of uptake and elimination of the substance are derived from Kow and a set of physiological parameters. The most well known model in this category is the FGETS (Food and Gill Exchange of Toxic Substances) model Barber et al. (1988, 1991) developed. This is a FORTRAN simulation model that predicts dynamics of a fish s whole body concentration of non-ionic, nonmetabolized, organic chemicals absorbed from the water only, or from water and food jointly. 

Park, S.S., Erstfeld, K.M. (1997) A numerical kinetic model for bioaccumulation of organic chemicals in sediment-water system. Chemosphere 34, 419 -27. 

Bioaccumulation can be estimated by a kinetic model. In kinetic models (sometimes called physiological models or physiologically based pharmacokinetic models), consideration is given to the dynamics of ingestion, internal transport, storage, metabolic transformation, and excretion processes that occur in each type of organism for each type of chemical. In kinetic models,... 

FIGURE 2-29 Schematic representation of a physiologically based kinetic model for bioaccumulation of a chemical that is absorbed through the gills, transported by blood flow, stored in various body tissues, and metabolized by the liver. Such a model requires much more detailed information on the fish than does a partitioning model however, it may be necessary to use this more complex approach for chemicals that are metabolized or excreted by the fish more rapidly than they are exchanged with the water [adapted from Barron (1990). Reprinted with permission. 1990 American Chemical Society]. 

As seen above (equation (5)), the basis of the simple bioaccumulation models is that the metal forms a complex with a carrier or channel protein at the surface of the biological membrane prior to internalisation. In the case of trace metals, it is extremely difficult to determine thermodynamic stability or kinetic rate constants for the adsorption, since for living cells it is nearly impossible to experimentally isolate adsorption to the membrane internalisation sites (equation (3)) from the other processes occurring simultaneously (e.g. mass transport complexation adsorption to other nonspecific sites, Seen, (equation (31)) internalisation). 

Figure 10.6 Illustration of some processes determining bioaccumulation of a chemical in a fish. The various k values can be formulated as first-order rate constants for description of the kinetics dependent on the physiology and behavior of the fish (for more advanced models, see Gobas and Morrison, 2000).

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. 

Thomann et al. (1992) developed a steady-state food web bioaccumulation model that combines kinetic and bioenergetic parameters to quantify chemical uptake and elimination by zooplankton, benthic invertebrates and fish. First-order kinetic rate constants quantify uptake of freely-dissolved chemical from interstitial water and overlying water and total chemical elimination from gills and feces. Various physiological and bioenergetic parameters quantify chemical uptake from diet and growth dilution. 

Risk assessment and sediment quality criteria. Risk assessment does not necessarily represent an ordered sequence of elements involving the recognition of hazards, the measurement of impact and the comparison of the measurements. Rather, all possible combinations of elements exist in practice. Sediment quality criteria, among other approaches (see 6.3) use kinetic bioaccumulation models and bioaccumulation tests (Chapman et al., 1987)... 

Although Neely and Blau (87) used direct laboratory measurements to develop rate constants, there are a few mathematical representations of environmental pathways which provide similar kinetics information (Table XV). Unfortunately, only a few of these pathways can currently be modeled based solely on physical/ chemical properties (e.g., volatilization from water and bioaccumulation). For some pathways (such as those describing atmospheric deposition and washout, biodegradation, and oxidation), adequate mathematical representations are not currently available. Other mathematical representations require either laboratory kinetics data (e.g., photodegradation and hydrolysis) or empirical data for model chemicals or environmental media (e.g., soil evaporation, adsorption, and leaching). Therefore, kinetics/rates models require more data as input than are likely to be available at the time of premanufacture notification. 

Veltman, K., M.A. Huijbregts, and A.J. Hendriks. 2010. Integration of biotic ligand models (BLM) and bioaccumulation kinetics into a mechanistic framework for metal uptake in aquatic organisms. Environ. Sci. Technol. 44 5022-5028. 

Elimination Kinetics. Determination of the rate of elimination is a useful exercise that can be used to calculate the half-life ty and determine the persistence of PAHs in tissue, in addition to modeling steady-state tissue burdens. The balance between uptake and elimination will determine the bioconcentration or bioaccumulation factor, which can be compared to an expected value (for example, see BCFpred in Appendix). Computation of half-life is also a good benchmark for interspecific comparison of the per-... 

Opperhuizen A (1991) Bioaccumulation kinetics experimental data and modelling. In Angeletti G, Bjorseth A (eds) Organic Micropollutants in the Aquatic Environment, Proceedings of the Sixth European Symposium, Lisbon, Portugal. Kluwer Academic Publishers, Amsterdam, pp 61-70. 

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