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 KOW < 3) accumulate similarly as hydrophobic (log KOW > 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 (Fi), 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.