Improved physiologically based kinetic (PBK) matrix for biotransfer modeling of pesticides in birds: The role of feather dynamics

Pesticides can transport via food webs and bioaccumulate in birds. Feathers can be used as a biomarker to investigate the bird's pesticide exposure, but there are no modeling methodologies that can link the bird's daily intake of pesticides to their amounts in feathers. To fill this gap, we propose a physiologically based kinetic modeling approach that takes into account the feather compartment and feather growth dynamics to estimate pesticide biotransfer potentials in the bird's body. In comparison with the non-feather model, the feather compartment acted as an additional elimination pathway for pesticides from the bird's body, resulting in a decrease in the overall simulated pesticide concentrations in the bird's body. High-lipophilic or high-volatile pesticides had exceptionally poor biotransfer potentials in feathers due to thermodynamics (e.g., partitioning potentials) or kinetics (e.g., elimination rates). As a result, legacy pesticides (such as persistent organic pollutants) will have limited biotransfer potentials in feathers, and the presence of legacy pesticides in feathers could imply relatively high daily pesticide consumption rates, which could affect bird reproductive health. The sensitivity and variability tests revealed that the metabolic (or biotransformation) kinetics of pesticides in avian livers influenced the biotransfer potential of pesticides in feathers significantly. Given the lack of information on pesticide metabolic kinetics in avian livers, we strongly suggest that future research (e.g., in vivo or in vitro studies) determine the metabolic or biotransformation rates of pesticides in avian livers in order to improve the performance of models. Furthermore, the use of additional biomarkers such as blood and uric acid could be valuable in assessing birds' exposure to pesticides. Hopefully, this study will help ecologists comprehend the fate, transport, and biotransfer of pesticides in bird feathers from a modeling point of view.