Modeling pesticide and PFAS bioaccumulation in amphibians: integration of biphasic ecology and route specific uptake

Amphibians are sensitive indicators of environmental contamination due to their permeable skin and dual aquatic-terrestrial life cycle. A physiologically based kinetic (PBK) model was developed to quantify the bioaccumulation of pesticides and per- and polyfluoroalkyl substances (PFAS) in amphibians, linking two chemical classes with contrasting environmental behaviors. The model integrates multiple exposure routes and connects aquatic and terrestrial phases within a unified framework. Simulations show that PFAS exhibit greater accumulation potential than herbicidal pesticides. Pesticide uptake occurs mainly via terrestrial ingestion and aquatic dermal absorption, while PFAS accumulation is dominated by aquatic dermal uptake. Pesticide residues are largely controlled by metabolic clearance, whereas PFAS retention depends on physicochemical partitioning, chain length, and protein-binding affinity. Short-chain PFAS penetrate skin readily but are rapidly cleared, whereas long-chain congeners persist in tissues. Model evaluation against empirical data showed good agreement for both chemical groups, with higher accuracy for pesticides. This PBK framework provides a route- and species-specific tool for predicting contaminant kinetics in amphibians and offers new insights into how biphasic ecology and chemical persistence shape bioaccumulation risk.