Universal bioaccumulation, biomagnification, and toxicokinetic metrics based on equivalent aqueous concentration

Diverse bioaccumulation and toxicokinetic parameters present a Babel-Tower challenge for cross-disciplinary researchers and various stakeholders alike as they struggle to formulate a holistic understanding of bioaccumulation phenomena from laboratory to field. This work attempts to resolve the challenge by proposing a universal framework for bioaccumulation, trophic magnification, and toxicokinetic metrics. The framework converts different concentrations and toxicokinetic parameters to aqueous equivalent concentration C^⁎ and first-order toxicokinetic constant k^⁎ using equilibrium distribution coefficients. The dimensionless bioaccumulation factor (B), evaluated as biota-to-exposure medium C^⁎-ratio, can represent all bioaccumulation and biomagnification scenarios. When applied to fish bioaccumulation data, B reveals that hydrophilic and low-hydrophobicity organics (log K_OW < 3) accumulate similarly as hydrophobic (log K_OW > 3) organics. Such results suggest that existing regulatory bioaccumulative thresholds (e.g., BCF > 5000 as very bioaccumulative) is self-inconsistent. Further B analyses also show that bioaccumulation is the highest in field environment, followed by modeled ecosystem, and the lowest in laboratory aqueous-only system. k^⁎ facilitates the evaluation of fractional contribution of specific routes/pathways to chemical uptake (F_i), and the timescale comparison of these uptake pathways with those of other biogeochemical processes (e.g., biodegradation, transport) and physical mechanisms (e.g., resuspension, porewater flushing), thus supporting an integrated, grand-scale chemical fate assessment. The universal framework will likely clarify the knowledge landscape on bioaccumulation and trophic transfer of chemicals.