Mechanistic modeling of chemical bioaccumulation in aquatic invertebrates: A shrimp-based demonstration

Understanding the mechanisms of chemical bioaccumulation in aquatic invertebrates is fundamental to ecological toxicology, as contaminant retention in key species shapes exposure pathways and trophic transfer within aquatic ecosystems. In this study, we developed a physiologically based kinetic (PBK) model to quantify the bioaccumulation factors (BAF) of 101 organic contaminants in adult white-leg shrimp (Litopenaeus vannamei). The model subdivides the organism into hemolymph, digestive tract, gills, muscle, shell, and eggs, and simulates uptake through gill respiration and dietary intake, together with elimination via respiratory exchange, fecal excretion, growth dilution, molting, and spawning. Predictions showed overall good agreement with reported BAF, with 50-80 % of chemicals deviating by less than one order of magnitude. Performance was highest for brominated flame retardants (BFRs) and other hydrophobic compounds (Log K_ow 4-6), whereas substantial biases occurred for Per- and polyfluoroalkyl substances (PFAS) and certain pesticides, likely due to unmodeled metabolic processes and sediment-water interactions. Simulations identified gill and egg tissues as major accumulation sites, reflecting their lipid content and direct environmental exposure. Exposure pathways were chemical-specific: gill uptake dominated for most hydrophobic pollutants (>94 %), while dietary intake was the principal contributor to PFAS accumulation in the digestive system (>90 %). The nonlinear relationship between bioconcentration factor (BCF) and Octanol-Water Partition Coefficient (K_ow) suggested a threshold effect in bioavailability. Overall, this shrimp-based PBK model enhances mechanistic understanding of contaminant dynamics in crustaceans and provides a basis for evaluating chemical risks and exposure heterogeneity in aquatic ecosystems.