Dietary kinetics of a PFAS mixture in the American toad (<i>Anaxyrus americanus</i>): laboratory insights into trophic transfer of PFAS

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in environmental media and are a concern for food web-driven exposure to ecological receptors. Terrestrial life stage amphibians concurrently represent taxa that have high potential for exposure but are generally data-poor in comparison to their aquatic life stages. Adult American toads (Anaxyrus americanus) likely have high dermal exposure to soil and eat terrestrial organisms that are likely to accumulate chemicals from soil. To better understand the relationship between dietary PFAS and toads in a trophic transfer context, toads were fed earthworms (Eisenia andrei) exposed to PFAS-spiked soil for 28 days and then were fed clean earthworms for 28 days-a 28-day uptake phase and 28-day elimination phase. Toad blood, liver, and remaining tissues were sampled weekly. Concentrations of PFAS were quantified in soil, earthworm diet, and toad tissues. Toxicokinetics of PFAS in toad livers, remainder, and estimated whole animal were evaluated using the methods of Organisation for Economic Co-operation and Development Test Guideline #305, a nonlinear regression approach, and a physiologically-based method. Definitive models were selected via a leave-one-out cross validation method and model parameters were used to determine kinetic trophic transfer coefficients (TTCs). Our TTC approach indicates perfluorooctane sulfonate, perfluoroundecanoic acid, and perfluorodecanoate are likely to magnify and 8:2 fluorotelomer sulfonate and perfluoroheptane sulfonic acid are likely to transfer or dilute in the worm-toad transition. Most PFAS have similar uptake rates, but elimination rates are clustered, suggesting that kinetics are driven by elimination mechanisms. These laboratory data use field-representative exposure approaches and provide inference about internal kinetics of individual PFAS as well as the potential for trophic transfer from soil invertebrates to terrestrial life stage amphibian predators.