Probing Mechanisms for the Tissue-Specific Distribution and Biotransformation of Perfluoroalkyl Phosphinic Acids in Common Carp (Cyprinus carpio)

Abstract

This study investigated the tissue-specific accumulation and biotransformation of 6:6 and 8:8 perfluoroalkyl phosphinic acids (PFPiA) in common carp (Cyprinus carpio) during 90 d exposure and 30 d depuration in water in the laboratory. Both 6:6 and 8:8 PFPiAs could quickly accumulate in the carp, and 6:6 PFPiA displayed higher bioaccumulation potential than 8:8 PFPiA. The highest concentrations of PFPiAs were observed in the blood, while the lowest were found in the muscle. The equilibrium dialysis experiment indicated that both PFPiAs had higher binding affinities with the proteins in the fish serum than in liver, which was supported by the molecular docking analysis. The results also indicated that 6:6 PFPiA had higher binding affinities with the serum and liver proteins than 8:8 PFPiA. These results suggested that the tissue-specific distribution of PFPiAs was highly dependent on the binding affinities with the specific proteins. Both in vivo and in vitro experiments consistently indicated that PFPiAs experienced biotransformation and produced perfluoroalkyl phosphonic acids (PFPAs), and biotransformation of 8:8 PFPiA was more active than 6:6 PFPiA. It was worth noting that perfluorohexanonate and perfluorooctanoic acids were identified in fish as metabolites after long-term exposure to PFPiAs for the first time.

PFAS Biotransformation Pathways: A Species Comparison Study

“…The maps for C6/C6 and C8/C8 PFPiA resulted in similar metabolic patterns. The pathway for rainbow trout [ 16 ], rat [ 17 ], carp [ 18 ], and wheat [ 19 ] is shown in Figure 7 . The rainbow trout samples were whole animal homogenates, while blood and liver were analyzed in the rat from in vivo chemical exposures.…”

“… Metabolic map for bis(perfluorooctyl)phosphinic acid (C8/C8 PFPiA) as found in rainbow trout [ 16 ], rat [ 17 ], carp [ 18 ], and wheat [ 19 ]. Structures as shown within the dotted box were assumed by the authors but were not actually observed metabolites in the studies.…”

Novel Insight into the Mechanisms of Neurotoxicity Induced by 6:6 PFPiA through Disturbing the Gut–Brain Axis

“…11,20 PFPiAs have longer carbon chain lengths (≥12 carbon atoms) than PFOS and are similar to PFOS in the chemical structure; thus, it is hypothesized that they may also cause neurotoxicity. 21 Liu et al 22 found that PFPiAs were able to accumulate in the brain of Cyprinus carpio, and the concentrations increased steadily with time during the 90-day exposure duration. 22 This implies that PFPiAs might cross the blood−brain barrier (BBB) and enter the brain, where they may bind with target receptors and then cause adverse effects.…”

“…21 Liu et al 22 found that PFPiAs were able to accumulate in the brain of Cyprinus carpio, and the concentrations increased steadily with time during the 90-day exposure duration. 22 This implies that PFPiAs might cross the blood−brain barrier (BBB) and enter the brain, where they may bind with target receptors and then cause adverse effects. 22 It is well known that BBB is a dynamic and dense barrier between the blood circulatory system and the brain central nervous system (CNS) to maintain homeostasis of the brain internal environment and protect the brain from external stimuli.…”

“…22 This implies that PFPiAs might cross the blood−brain barrier (BBB) and enter the brain, where they may bind with target receptors and then cause adverse effects. 22 It is well known that BBB is a dynamic and dense barrier between the blood circulatory system and the brain central nervous system (CNS) to maintain homeostasis of the brain internal environment and protect the brain from external stimuli. 23 The tight junction (TJ) is the functional basis of BBB, and its structure is susceptible to the pressure of external stimuli, resulting in increased BBB permeability.…”