Concentration-dependent toxicokinetics of novel PFOS alternatives and their chronic combined toxicity in adult zebrafish.

The increasing use of perfluorooctanesulfonate (PFOS) alternatives has led to their release into the aquatic environment. This study sought to determine the effects of exposure concentration on the toxicokinetics of PFOS and its alternatives, including perfluorobutanesulfonic acid (PFBS), perfluorohexanesulfonic acid (PFHxS), chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p-perfluorous nonenoxybenzenesulfonate (OBS) in adult zebrafish by exposure to mixtures of the five per- and polyfluoroalkyl substances (PFAS) at 1, 10, and 100 ng/mL for 28-day, followed by a 14-day depuration. PFAS predominantly accumulated in the blood and liver, and the bioconcentration factor (BCF) decreased in the order of F-53B > PFOS > OBS ≫ PFHxS > PFBS in whole-fish homogenates. The uptake rate constants and BCF of the short-chain PFAS (≤C6) positively correlated with increasing exposure concentration, while the long-chain PFAS (≥C8) exhibited a pattern of first increasing and then decreasing. A consistent increase in the elimination rate constants of short- and long-chain PFAS was observed with increasing exposure concentration. All PFAS form tight conformations with ZSA and ZL-FABP via hydrogen bonding as revealed by molecular docking analysis. Furthermore, chronic combined exposure to PFAS induced the occurrence of vacuolation and oxidative stress in the zebrafish liver. Our findings uniquely inform the concentration-dependent bioconcentration potential and health risks to aquatic organisms of these PFOS alternatives in the environment.

Developmental toxicity of the novel PFOS alternative OBS in developing zebrafish: An emphasis on cilia disruption.

In recent years, sodium p-perfluorous nonenoxybenzene sulfonate (OBS) has emerged as a substitute for PFOS with large demand and application in the Chinese market. However, little is known about potential developmental effects of OBS. In this study, zebrafish embryos were acutely exposed to different concentrations of OBS and the positive control PFOS for a comparative developmental toxicity assessment. OBS caused hatching delays, body axis curvature, neurobehavioral inhibition and abnormal cardiovascular development. These organismal effects were accompanied by change of development related genes expression profile, in which some cases were similar to PFOS. Overall, the toxic effects induced by OBS were generally milder than that of PFOS. Further investigation suggested that both OBS and PFOS disrupted ciliogenesis, evidenced by the ciliary immunostaining, changes in gene expression of kinesin family, dynein arm family and tubulin family members, as well as downregulation of the abundance of motor proteins including KIF3C, DYNC1H1 and DYNC1LI1. The influence of PFOS was stronger than that of OBS on ciliary genes and proteins. Molecular docking analysis revealed that both OBS and PFOS fitted into the motor proteins tightly, but binding affinity between OBS and motor proteins was lower than PFOS. Collectively, OBS and PFOS may act on ciliary motor proteins to interfere with ciliogenesis, leading to ciliary dysfunction and providing a novel probable action mode linked to developmental toxicity. This raises concerns regarding the health risks of the novel PFOS alternative OBS.

Exploring the Impact of a Low-Protein High-Carbohydrate Diet in Mature Broodstock of a Glucose-Intolerant Teleost, the Rainbow Trout.

Sustainable aquaculture production requires a greater reduction in the use of marine-derived ingredients, and one of the most promising solutions today is the augmentation in the proportion of digestible carbohydrates in aquafeed. This challenge is particularly difficult for high trophic level teleost fish as they are considered to be glucose-intolerant (growth delay and persistent postprandial hyperglycemia observed in juveniles fed a diet containing more than 20% of carbohydrates). It was previously suggested that broodstock could potentially use carbohydrates more efficiently than juveniles, probably due to important metabolic changes that occur during gametogenesis. To investigate this hypothesis, 2-year old male and female rainbow trout (Oncorhynchus mykiss) were either fed a diet containing no carbohydrates (NC) or a 35%-carbohydrate diet (HC) for an entire reproductive cycle. Zootechnical parameters as well as the activities of enzymes involved in carbohydrate metabolism were measured in livers and gonads. Fish were then reproduced to investigate the effects of such a diet on reproductive performance. Broodstock consumed the HC diet, and in contrast to what is commonly observed in juveniles, they were able to grow normally and they did not display postprandial hyperglycemia. The modulation of their hepatic metabolism, with an augmentation of the glycogenesis, the pentose phosphate pathway and a possible better regulation of gluconeogenesis, may explain their improved ability to use dietary carbohydrates. Although the HC diet did induce precocious maturation, the reproductive performance of fish was not affected, confirming that broodstock are able to reproduce when fed a low-protein high-carbohydrate diet. In conclusion, this exploratory work has shown that broodstock are able to use a diet containing digestible carbohydrates as high as 35% and can then grow and reproduce normally over an entire reproductive cycle for females and at least at the beginning of the cycle for males. These results are highly promising and suggest that dietary carbohydrates can at least partially replace proteins in broodstock aquafeed.

Polystyrene microplastics decrease F-53B bioaccumulation but induce inflammatory stress in larval zebrafish.

There is growing concern that microplastics (MPs), which act as carriers of other organic contaminants, are mistakenly ingested by aquatic organisms, consequently causing unpredictable adverse effects. In this study, zebrafish larvae (6 d post fertilization) were exposed to either 6:2 chlorinated polyfluorinated ether sulfonate (F-53B), polystyrene microplastics (PS-MPs) or their combination for 7 d to evaluate the effects of the presence of PS-MPs on the bioaccumulation and immunomodulation of F-53B. PS-MPs greatly promoted the sorption of F-53B, which reduced the bioavailability and bioaccumulation of F-53B in zebrafish larvae. F-53B, PS-MPs, or their mixture significantly reduced the body weight of zebrafish larvae. Combined exposure of PS-MPs and F-53B resulted in a significant reduction in superoxide dismutase (SOD) and lysozyme activity, indicating the occurrence of oxidative stress and inflammatory response in zebrafish larvae. The content of malondialdehyde (MDA) and immunoglobulin M (IgM) was not affected by F-53B or PS-MPs, but significantly increased in their combined exposure. Furthermore, co-exposure of F-53B and PS-MPs significantly upregulated the transcripts of pro-inflammatory cxcl-clc and il-1ß genes and increased the levels of iNOS protein in zebrafish larvae. In addition, enhanced protein expression of NF-κB paralleled the upregulation in the expression of most immune-related genes, suggesting NF-κB pathway was mechanistically involved in these responses. Collectively, the presence of MPs decreased F-53B bioaccumulation, but induced inflammatory stress in larval zebrafish. These findings highlight the health risks of co-contamination of MPs and F-53B in aquatic environments.

Bioconcentration and Metabolic Effects of Emerging PFOS Alternatives in Developing Zebrafish.

The novel PFOS alternatives, 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p-perfluorous nonenoxybenzenesulfonate (OBS), are emerging in the Chinese market, but little is known about their ecological risks. In this study, zebrafish embryos were exposed to PFOS, F-53B, and OBS to evaluate their bioconcentration and acute metabolic consequences. Per- and polyfluoroalkyl substances (PFASs) accumulated in larvae in the order of F-53B > PFOS > OBS, with the bioconcentration factors ranging from 20 to 357. Exposure to F-53B and PFOS, but not OBS, increased energy expenditure, and reduced feed intake in a concentration-dependent manner and the expression of genes involved in metabolic pathways at the transcriptional and translational levels. Molecular docking revealed that the binding affinities of PFASs to glucokinase were decreased in the following order: F-53B > PFOS > OBS. Finally, the results of Point of Departure (PoD) indicate that metabolic end points at the molecular and organismal level are most sensitive to F-53B followed by PFOS and OBS. Collectively, F-53B has the highest bioconcentration potential and the strongest metabolism-disrupting effects, followed by PFOS and OBS. Our findings have important implications for the assessment of early developmental metabolic effects of PFOS alternatives F-53B and OBS in wildlife and humans.