Bioconcentration of perfluorinated alkyl acids: how important is specific binding?

Perfluorinated alkyl acids (PFAAs) are important global pollutants with unique pharmacokinetics. Evidence is accumulating that their behavior within organisms is affected by interaction with a number of proteins. In mammals, serum albumin, fatty acid binding proteins (FABPs) and organic anion transporters (OATs) have been identified as important to the tissue distribution, species-specific accumulation, and species- and gender-specific elimination rates of perfluoroalkyl carboxylates and perfluoroalkane sulfonates. Similar pharmacokinetics has been identified in fish. Yet, no mechanistic model exists for the bioaccumulation of PFAAs in fish that explicitly considers protein interactions. In this work, we present the first mechanistic protein-binding bioconcentration model for PFAAs in fish. Our model considers PFAA uptake via passive diffusion at the gills, association with serum albumin in the circulatory and extracellular spaces, association with FABP in the liver, and renal elimination and reabsorption facilitated by OAT proteins. The model is evaluated using measured bioconcentration and tissue distribution data collected in two previous studies of rainbow trout (Oncorhynchus mykiss) and common carp (Cyprinus carpio). Comparing our model with previous attempts to describe PFAA bioconcentration using a nonspecific (partitioning-type) approach shows that inclusion of protein interactions is key to accurately predicting tissue-specific PFAA distribution and bioconcentration.