Estimating the Equilibrium Distribution of Perfluoroalkyl Acids and 4 of Their Alternatives in Mammals

Abstract

Perfluoroalkyl acids (PFAAs) mostly exist as ionic compounds that are of major concern because of their accumulative behavior. The discussion about their risk is ongoing considering the increasing production of structurally similar alternatives. We conducted model calculations based on equilibrium distribution coefficients that allow studying the distribution of PFAAs and their alternatives in various mammalian organs through comparison to empirical measurements in humans and rats. The calculations rely on experimentally determined distribution coefficients of a series of PFAAs and 4 of their alternatives to physiological matrices such as structural proteins, storage lipids, membrane lipids, albumin, and fatty acid binding protein (FABP). The relative sorption capacities in each organ were calculated from the combination of distribution coefficients and physiological data. The calculated distribution of PFAAs and alternatives within the organs showed that albumin and membrane lipids and, to a lesser extent, structural proteins have the highest relative sorption capacities for the compounds. Sorption to FABP is only relevant in the distribution of short‐chain PFAAs. Storage lipids play a minor role in the distribution of all studied compounds. Our calculated distribution of PFAAs was evaluated by comparison to reported PFAA concentrations in various organs. Environ Toxicol Chem 2021;40:910–920. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Developing Methods for Assessing Trophic Magnification of Perfluoroalkyl Substances within an Urban Terrestrial Avian Food Web

“…Unlike most legacy POPs, such as polychlorinated biphenyls, PFAS typically exhibit negligible solubility in storage lipids (i.e., neutral lipids). 39,47,48 Instead, PFAS predominately partition into phospholipids in cell membranes (i.e., polar lipids) and nonstructural proteins (specifically albumin) and to a lesser extent into structural proteins (e.g., collagen, myosin, and actin). 39,40,47−49 Thus, to account for the differing sorptive capacities of polar and neutral lipids and albumin and structural proteins, the sorptive capacity of organisms for PFAS can be expressed as…”

“…Normalized concentrations of PFAS were expressed as total protein equivalent concentrations (C P ); albumin equivalent concentrations (C AL ); and polar lipid equivalent concen-trations (C PL ) and account for the predominant sorption of PFAS to protein content in the organism, and more specifically to albumin, but also recognize the high sorption of PFAS to polar lipids. 39,40 We also investigated if frequently used total lipid normalized concentrations or wet weight concentrations generated TMFs that were different from TMFs determined with chemical activities. TMFs based on wet weight concentrations do not account for differences in biochemical composition between species or samples.…”

“…Unlike most legacy POPs, such as polychlorinated biphenyls, PFAS typically exhibit negligible solubility in storage lipids (i.e., neutral lipids). ,, Instead, PFAS predominately partition into phospholipids in cell membranes (i.e., polar lipids) and non-structural proteins (specifically albumin) and to a lesser extent into structural proteins (e.g., collagen, myosin, and actin). ,,− Thus, to account for the differing sorptive capacities of polar and neutral lipids and albumin and structural proteins, the sorptive capacity of organisms for PFAS can be expressed as S organism = ( φ NL × S NL + φ PL × S PL + φ ALB × S ALB + φ SP × S SP + φ W × S W ) where φ NL represents the fraction of neutral or storage lipids in the organism or sample; φ PL is the fraction of polar or membrane lipids; φ ALB is the fraction of albumin; φ SP is the fraction of structural protein; φ W is the fraction of water; and S NL , S PL , S ALB , S SP , and S W represent the solubilities of the substance in neutral lipids, polar lipids, albumin, structural proteins, and water, respectively. Since the relative partitioning of PFAS between neutral lipid, polar lipid, albumin, and structural proteins is typically measured as distribution coefficients relative to water, it may be simpler to express the solubilities S NL , S PL , S ALB , and S SP relative to that in water ( S W ). ,, Therefore, eq may be modified as S organism = ( φ NL × D NLW + <...…”

“…Using measured wet weight concentrations ( C ww ) of PFAS, we derived concentrations normalized to total protein, albumin, or polar lipids as C normalP = C ww φ normalP C AL = C ww φ ALB C PL = C ww φ PL where φ P , φ ALB , and φ PL represent the relative fractions of total protein, albumin, and polar lipid content, respectively, in the organism on a mass basis (i.e., g of tissue/g of sample). Normalized concentrations of PFAS were expressed as total protein equivalent concentrations ( C P ); albumin equivalent concentrations ( C AL ); and polar lipid equivalent concentrations ( C PL ) and account for the predominant sorption of PFAS to protein content in the organism, and more specifically to albumin, but also recognize the high sorption of PFAS to polar lipids. , …”

“…However, this practice cannot be applied to many PFAS because they do not preferentially accumulate in neutral or storage lipids; instead, they exhibit high affinities for protein and membrane or polar lipids. 39,40 Currently, there is no agreed-upon method for determining whether PFAS biomagnify in terrestrial food webs or not. Hence, there is a need to develop robust approaches to accurately assess bioaccumulation of PFAS in terrestrial and air-breathing organisms.…”