Per- and polyfluoroalkyl substances (PFAS) are a diverse group of man-made chemicals that have been widely used in various industrial applications and consumer products since the 1940s. These substances are characterized by strong carbon–fluorine bonds that confer water-, oil-, and heat-resistance, enabling their widespread use in applications such as non-stick cookware, water-repellent clothing, stain-resistant fabrics, food packaging, firefighting foams, and other consumer products [1]. However, the same chemical stability that makes PFAS so useful also leads to their environmental persistence and widespread contamination, raising significant ecological and health concerns [2,3]. PFAS can persist in the environment for long periods of time, and they have been detected in surface waters (rivers, lakes and oceans), groundwater and drinking water supplies, soils and sediments and even atmospheric dust [[4], [5], [6]]. Environmental concentrations of PFAS can vary widely, typically ranging from parts per trillion (ppt) to parts per billion (ppb), depending on proximity to sources such as industrial sites, firefighting training areas, or wastewater treatment plants [7,8].

The persistence of PFAS in the environment results in their accumulation in the tissues of aquatic organisms, leading to higher concentrations in predators at the top of the food chain. This bioaccumulation poses a risk not only to animals, but also to humans who consume contaminated food [9]. PFAS exposure can result in various toxic effects on aquatic organisms, including developmental and reproductive toxicity, endocrine disruption, immune system effects and behavioral changes, such as altered feeding and avoidance of predators, which can impact survival and reproduction [10,11].

Perfluorooctane sulfonate (PFOS) is a specific type of PFAS, with an eight-carbon chain in which hydrogen atoms have been substituted with fluorine. It has been widely used in various industrial and consumer products due to its hydrophobic and lipophobic properties [12,13]. PFOS readily bioaccumulates in aquatic organisms, leading to higher concentrations in top predators [14]. Exposure to PFOS has been associated with various adverse effects, including developmental and reproductive toxicity, endocrine disruption, liver toxicity, immune system effects and behavioral changes [10]. Its effects on lipid metabolism, as reported in zebrafish embryos, involve several pathways and cellular processes, such as fatty acid oxidation, lipid transport and lipid synthesis, induction of lipid peroxidation and mitochondrial dysfunction [3,15,16].

PFOS interacts with various organic anion transporters (OATs) and organic anion transporting polypeptides (OATPs). These membrane transporters play a crucial role in the uptake, distribution and excretion of PFOS in humans and animals. Research has shown that PFOS can be transported by more than one OAT in humans, including hOAT4 [17] and OATPs such as OATP1B1 and OATP1B3, which are expressed in different tissues including the liver, kidney and intestine [18]. Studies have shown that hOAT4 is involved in the renal clearance of PFOS and facilitates its excretion from the body [17]. Similarly, OATPs in the liver and intestine contribute to the disposition of PFOS by mediating its uptake into hepatocytes and enterocytes [19]. This transport activity affects the bioavailability and toxicity of PFOS, influencing its accumulation in tissues and its potential health effects. An important aspect of PFOS interaction with these transporters is its impact on reproductive toxicity, particularly through OATP3a1 in Sertoli cells, which may lead to adverse effects on male reproductive health [20]. Additionally, the involvement of transporters such as NTCP and ASBT in the liver highlights the complexity of PFOS disposition and its potential impairment of bile acid transport [21].

Internal exposure dynamics are important for understanding PFOS effects in fish. In zebrafish, PFOS reaches steady state within about two weeks, with median whole-body BCFs around 934 L kg−1 (255 – 2.136 L kg−1) [22]. BCF decreases at higher water concentrations and is generally higher in males. PFOS is efficiently transferred from females to eggs, and embryos may not reach steady state during short exposures (Tal and Vogs, 2021). Overall, PFOS bioconcentration in zebrafish depends on concentration and life stage, and it is not stored in fat but binds to proteins [22,23].

The toxicokinetics of PFOS in fish is also determined by its interaction with various transporters, including Oatps and Oats. These interactions can lead to significant changes in the bioconcentration and tissue distribution of PFOS, e.g., in rainbow trout [9]. Likewise, zebrafish Oats play an important role in modulating the transport activity of PFOS. Specifically, zebrafish Oat1 and Oat3 exhibit interactions with environmental contaminants, including PFOS, affecting their bioavailability and toxicity [24]. In addition, Oatp1d1 has a high affinity for PFOS in vitro, indicating potential role for Oatp1d1 in mediating the uptake and possible toxic effects of PFOS in zebrafish [25]. Oatp1d1 transporter is predicted to span the membrane with 12 transmembrane helices, forming the single active site, with a bicarbonate antiport mechanism like that of mammalian OATPs/Oatps [26]. Additionally, the functional conservation of OATPs/Oatps in vertebrates suggests that zebrafish Oatp2b1 might serve as a functional ortholog to human OATP2B1, showing strong interactions with PFOS and impacting its toxicity [27]. PFOS also showed the effect on expression of transporter genes in downstream pathways of developing zebrafish embryos, indicating the crucial role of these transporters in mediating toxic effects of PFOS [28].

In this study, we investigated the impact of PFOS exposure on both wild-type (WT) and Oatp1d1 mutant zebrafish embryos, focusing on mortality rates, developmental abnormalities, oxidative stress, apoptosis, and gene expression changes. Our results demonstrated that PFOS exposure led to disruptions in normal embryonic development, with distinct differences observed between WT and mutant embryos. Reported effects defined the characteristic phenotype of Oatp1d1 mutant embryos under the PFOS exposure. We also confirmed PFOS-induced phenotype with silencing of Oatp1d1 by specific morpholinos. Additionally, using specific uncompetitive inhibitors of Oatp1d1, we simulated characteristic phenotypes of embryos that are more sensitive to deleterious effects of PFOS. We believe these findings offer valuable additional insights into the toxicological effects of PFOS and the role of Oatp1d1 in the associated defense mechanisms.