Dynamics of Hydrophobic Organic Chemical Bioconcentration in Fish

158

241

Abstract-A mechanistic mass balance bioconcentration model is developed and parameterized for ionogenic organic chemicals (IOCs) in fish and evaluated against a compilation of empirical bioconcentration factors (BCFs). The model is subsequently applied to a set of perfluoroalkyl acids. Key aspects of model development include revised methods to estimate the chemical absorption efficiency of IOCs at the respiratory surface (E W ) and the use of distribution ratios to characterize the overall sorption capacity of the organism. Membranewater distribution ratios (D MW ) are used to characterize sorption to phospholipids instead of only considering the octanol-water distribution ratio (D OW ). Modeled BCFs are well correlated with the observations (e.g., r 2 ¼ 0.68 and 0.75 for organic acids and bases, respectively) and accurate to within a factor of three on average. Model prediction errors appear to be largely the result of uncertainties in the biotransformation rate constant (k M ) estimates and the generic approaches for estimating sorption capacity (e.g., D MW ). Model performance for the set of perfluoroalkyl acids considered is highly dependent on the input parameters describing hydrophobicity (i.e., log K OW of the neutral form). The model applications broadly support the hypothesis that phospholipids contribute substantially to the sorption capacity of fish, particularly for compounds that exhibit a high degree of ionization at biologically relevant pH. Additional empirical data on biotransformation and sorption to phospholipids and subsequent incorporation into property estimation approaches (e.g., k M , D MW ) are priorities with respect to improving model performance. Environ. Toxicol. Chem. 2013;32:115-128. # 2012 SETAC

Section: Absorptionmentioning

confidence: 99%

Development and evaluation of a mechanistic bioconcentration model for ionogenic organic chemicals in fish

Armitage

Arnot

Wania

et al. 2012

158

241

“…Compartments may or may not represent a physical entity. The mathematical formalism for the compartment models takes three forms: rate constant or rate coefficient (RC) models [25], clearance volume (CV) models [26], and fugacity models [27]. Each of these forms is mathematically equivalent for exposures with a single uptake route, but differs in the conceptual basis that produces its formalism [27,28].…”

Section: Kinetic Modelsmentioning

confidence: 99%

“…Scaling these models to invertebrates will require collection of additional physiological data and may well require adding additional processes, such as accumulation and loss across the integument, that are unimportant for most vertebrates. The ability to scale models has been better investigated with PBPK models than compartment models, but some efforts have been examined with the compartment-based models [27].…”

Section: Physiological-and Energetics-based Modelsmentioning

confidence: 99%

“…However, as has been pointed out by Barron et al [26], the RCs in CV models may have little physiological meaning, making it difficult to extrapolate to other species or toxicants. However, compartment-based models have had limited success in scaling data to different size organisms that are closely related [27]. Multiple compartments within an organism can also be accommodated in the RC- [59] and fugacity-based formats [67].…”

Section: Utilizing Kinetic Models In Exposure Assessmentmentioning

confidence: 99%

See 1 more Smart Citation

Toxicokinetics in aquatic systems: Model comparisons and use in hazard assessment

Landrum

Lydy

Lee

1992

348

247

-Toxicokinetic models are not constrained by assumptions of equilibrium as are thermodynamic (equilibrium-partitioning) models and are more accurate predictors of toxicant accumulation for non-steady-state exposures and multiple uptake routes. Toxicokinetic models -compartmentbased models, physiological-based models, and energetics-based models-are reviewed and the different mathematical formalisms compared. Additionally, the residue-based toxicity approach is reviewed. Coupling toxicokinetic models with tissue concentrations at which toxicity occurs offers a direct link between exposure and hazard. Basing hazard on tissue rather than environmental concentrations avoids the errors associated with accommodating multiple sources, pulsed exposures, and non-steady-state accumulation. Keywords-Kinetic models Bioaccumulation Tissue residue effects Sediment contaminationHazard assessment INTRODUCTlONAssessment and prediction of toxicant effects on aquatic organisms require evaluation of the extent of organism exposure. Exposure assessment establishes the relationship between environmental toxicant concentrations and organism accumulation while accounting for environmental and biological factors that modify exposure. If the relationships between the amount of toxicant accumulated and the resulting effects are known, then the hazard for a particular exposure regime can be established.Aquatic exposure assessments and predictions have employed mainly steady-state and equilibriumpartitioning models. Early efforts, using simple kinetic models, were designed to provide estimates of steady-state accumulation from water exposures [1,2]. These steady-state estimates were then utilized in hazard assessments based on thermodynamic limits (chemical equilibrium). Such models have been employed with good success for evaluation of general conditions, describing toxicant distribution among ecosystem components and *To whom correspondence may be addressed.identifying components dominating toxicant mass balance. This approach has been best refined using the fugacity concept and applied to describe the importance of sediment as a toxicant source [3] and toxicant distributions within ecosystems [4,5].Although there is a continued focus on equilibrium-partitioning models within regulatory agencies, it is clear that the environment is complex and variable. Therefore, to obtain more accurate predictions and assessments, kinetic models are needed to predict non-steady-state, nonequilibrium accumulation from temporally and spatially varying exposures when the simplifying assumptions of the equilibrium-partitioning models are inappropriate, for example, when multiple sources contribute significantly to accumulation.Kinetic models have been used successfully in pharmacology for decades. Such models permit prediction of the onset of drug action and allow the monitoring of drug clearance and termination of effects. Further, these kinetic models describe changes in tissue concentrations resulting from absorption, distribution, metabolism, a...

“…Processes such as gill uptake and food uptake are considered diffusive processes and are expressed as D( f i -fi), where ( f l -f2) is the fugacity difference or driving force [54].…”

Section: Food-chain Transportmentioning

confidence: 99%

Modeling mobility and effects of contaminants in wetlands

Dixon

Florian

1993

-Early efforts at modeling wetland ecosystems were aimed primarily at reflecting biomass or nutrient dynamics. A number of models have been developed for different wetland types, including coastal salt marshes, mangrove wetlands, freshwater marshes, swamps, and riparian wetlands. The early ecosystem models were mostly simple compartment models with linear, constant-coefficient differential equations used to simulate biomass or nutrient dynamics. Practically no contaminant flux was incorporated into these models. With few exceptions, the ecosystems were considered spatially homogeneous. At the same time that the ecosystem models were being developed, considerable effort was given to modeling various wetland processes, such as circulation and sediment transport. Other process-level modeling included plant and animal uptake and elimination of both organic chemicals and heavy metals. The level of detail in these process models, however, has not been applied to most ecosystem models. There has been a recent trend, however, to increase the complexity of ecosystem-level models and to incorporate spatial dynamics. These developments should greatly enhance the ability to simulate contaminant transport and effects in wetlands.