A food web bioaccumulation model for organic chemicals in aquatic ecosystems

Abstract

The present study examines a new bioaccumulation model for hydrophobic organic chemicals in aquatic food webs. The purpose of the model is to provide site-specific estimates of chemical concentrations and associated bioconcentration factors, bioaccumulation factors, and biota-sediment accumulation factors in organisms of aquatic food webs using a limited number of chemical, organism, and site-specific data inputs. The model is a modification of a previous model and incorporates new insights regarding the mechanism of bioaccumulation derived from laboratory experiments and field studies as well as improvements in model parameterization. The new elements of the model include: A model for the partitioning of chemicals into organisms; kinetic models for predicting chemical concentrations in algae, phytoplankton, and zooplankton; new allometric relationships for predicting gill ventilation rates in a wide range of aquatic species; and a mechanistic model for predicting gastrointestinal magnification of organic chemicals in a range of species. Model performance is evaluated using empirical data from three different freshwater ecosystems involving 1,019 observations for 35 species and 64 chemicals. The effects of each modification on the model's performance are illustrated. The new model is able to provide better estimates of bioaccumulation factors in comparison to the previous food web bioaccumulation model while the model input requirements remain largely unchanged.

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

“…These processes have successfully been described for neutral organic chemicals using mechanistic models (e.g., based on either first-order rate constant [16] or fugacity-based approaches). For this model application, test organisms (fish) are assumed to be fed ''clean'' food throughout the duration of the exposure period (i.e., the concentration of chemical in diet is negligible and the related uptake term can be omitted) and only uptake from water needs to be considered.…”

“…As outlined below, we have modified the existing Arnot and Gobas bioaccumulation model [16] for neutral organic chemicals. Readers are directed to the original publication for complete details on the development, parameterization, and evaluation of the previous model.…”

“…The uptake rate constant for neutral organic chemicals from the water column at the respiratory surface (k U ) is estimated in the original model [16] using the following expression…”

“…Generic methods for estimating the tissue-plasma partitioning of IOCs have also been described in the literature [14,15]. Characterizing the sorption capacity of an organism (and of its diet and fecal egesta) is a central element of mechanistically based bioaccumulation models [16]. The key task is then to integrate chemical partitioning and distribution information with uptake and elimination kinetics.…”

“…The model is based on an existing approach for neutral organic chemicals [16] but was modified to account for dissociation of IOCs. Empirical bioconcentration factors (BCFs, in L/kg) for various IOCs in fish, including some PFAAs, were compiled and evaluated for general quality.…”