A site-specific bioaccumulation model for aquatic food webs

AQUAWEB v1.1 provides site-specific estimates of chemical concentrations in organisms of aquatic food webs from chemical concentrations in the water and the sediment (Arnot and Gobas 2004). The model is presented in rate constant format for assessing the bioaccumulation of non-ionic hydrophobic organic chemicals at steady-state. For zooplankton, aquatic invertebrates and fish the model calculates rates of chemical uptake from the water and the diet and rates of chemical elimination to the water, feces and the pseudoTM loss mechanism of growth dilution. Reliable metabolic transformation rate data can also be included as a mechanism of chemical elimination. AQUAWEB v1.1 is a modification of a previous model (BIO v1.1; Gobas 1993). Key revisions include: (i) a new model for the partitioning of chemicals into organisms, (ii) kinetic models for predicting chemical concentrations in algae, phytoplankton and zooplankton, (iii) new allometric relationships for predicting gill ventilation rates in a wide range of aquatic species, and (iv) a mechanistic model for predicting gastrointestinal magnification of organic chemicals in a range of species. Both AQUAWEB v1.1 and BIO v1.1 models have been evaluated using empirical data from three different freshwater ecosystems involving 1019 observations for 35 species and 64 chemicals. Both models are coded in one Microsoft EXCEL® workbook that is freely available for download.

The following table summarizes the limited number of site-specific data inputs required by AQUAWEB v1.1.

Chemical properties:
    • octanol-water partition coefficient (KOW)

Site-specific environmental properties:
    • mean water temperature
    • concentration of particulate organic carbon in the water
    • concentration of dissolved organic carbon in the water
    • concentration of suspended solids in the water
    • organic carbon content of the sediment
    • chemical concentration in the water
    • chemical concentration in the sediment

Site-specific biological properties:
    • organism wet weight
    • organism lipid content
    • organism feeding preferences

Intended Uses
The site-specific models are intended to estimate chemical concentrations and associated bioconcentration factors (BCF), bioaccumulation factors (BAF) and biota-sediment accumulation factors (BSAF) of non-ionic hydrophobic organic chemicals. The models are useful for assessing exposure and risks of chemicals in the water and sediment to organisms in aquatic ecosystems and higher trophic level organisms that eat aquatic species (i.e., shellfish and fish) including humans. The models are limited in calculating chemical concentrations in species of aquatic macrophytes, algae, phytoplankton, zooplankton, invertebrates, and fish of different trophic levels. Site-specific measurements can be included to evaluate model performance.