Effects of Perfluorobutane Sulfonate (PFBS) on Female Reproduction, Pregnancy, and Birth Outcomes.

Per- and polyfluoroalkyl substances (PFAS) encompass thousands of chemicals composed of fluorinated carbon chains with different functional groups. They can be broadly categorized into two main classes: perfluoroalkyl substances, where all carbon chains are fully fluorinated, and polyfluoroalkyl substances, which contain partially fluorinated chains. Industries have been using PFAS compounds for several reasons, primarily due to their unique chemical properties. PFAS compounds are known for repelling water and oil, making them ideal for products that resist stains, spills, and moisture. This property is advantageous for fabrics, carpets, and paper products. Additionally, PFAS compounds are highly stable and resistant to heat, chemicals, and degradation. This durability makes them valuable for industrial applications, including coatings for cookware, firefighting foams, and various industrial processes. Moreover, the strong carbon-fluorine bonds in PFAS make them resistant to environmental breakdown, which raises concerns about their persistence and potential accumulation in ecosystems and living organisms. Growing concerns surrounding the ecological and health impacts of PFAS have led to increased scrutiny and calls for regulation and alternatives. Each PFAS compound exhibits distinct physicochemical properties and behaviors in the environment, influencing their toxicity and bioaccumulation potential. Perfluorobutane sulfonic acid (PFBS, C 4 F 9 SO 2 F) was first introduced in 2002 as a replacement for perfluorooctane sulfonate (PFOS, C 8 F 17 SO 3 − ) after PFOS was phased out due to ecological and human health concerns. 1 , 2 Given its shorter chain length than PFOS, PFBS was assumed to have a lower potential for accumulation in the environment and biota. However, after only two decades of use, PFBS is now among the most frequently detected PFAS compounds in wastewater and drinking water throughout the United States and China. 3 PFBS levels in water and soil vary depending on geography, industrial practices, and disposal methods, which are influenced by the specific cultural, social, and regulatory contexts of different countries. PFBS can enter water systems through discharges from manufacturing facilities, industrial applications, fire control and crash training areas, wastewater treatment plants, and the disposal of contaminated biosolids. 4 PFBS is highly soluble in water (52.6 g/L at 22.5–24°C for the potassium salt) but is not considered volatile. 4 , 5 A comprehensive review by Podder et al. (2021) provides a detailed analysis of the occurrences and sources of both short- and long-chain PFAS in surface water matrices, including rivers, lakes, canals, and precipitation. They present the first systematic review of global PFAS contamination trends from the 1990s to 2021, highlighting the increasing use of short-chain PFAS like PFBS, which may pose similar toxicological risks to their long-chain counterparts. 6 The authors emphasize the importance of understanding the spatiotemporal distribution of PFAS, including PFBS, to design effective management strategies. Their summary is a crucial resource for future PFBS research and regulation. Investigations conducted in Europe, Asia, and the United States have confirmed the presence of PFBS in drinking water samples over a wide range of concentrations and highlighted that PFBS is more mobile than other PFAS, such as PFOS, and exhibits lower removal efficiency from water. 7 – 16 Using contaminated water in agriculture also increases the accumulation of PFBS in soil and crops, particularly root vegetables, as reported by Xu et al. (2022). 17 It has been suggested that even upon repeated exposure to PFBS, its short chain length would allow for more rapid elimination from the body than other perfluorinated compounds like PFOS. Despite the proposed efficient excretion, PFBS exposure leads to undeniable accumulation in serum and tissues. 4 , 18 Studies comparing PFAS levels in different regions of Sweden indicate that high exposure to PFBS from drinking water results in significantly elevated serum concentrations. 19 , 20 Elevated serum PFBS levels were also detected in pediatric and adult populations exposed to highly contaminated water in Germany. 21 Interestingly, serum PFBS levels declined after reducing consumption of contaminated drinking water. 22 Moreover, a study focusing on childhood exposure through placental transfer, breastfeeding, and contaminated drinking water demonstrated a strong association between serum PFBS concentrations from 4-, 8- and 12-year-old children and cumulative drinking water exposure, increasing by 207% per month of exposure. 23 Additionally, a study from Spain evaluated PFAS concentrations in human tissues from 20 individuals. It showed that PFBS is one of the predominant compounds detected in the brain, liver, lungs, kidney, and bones. 24 The increasing detection of PFBS in human serum and tissues is likely due to consistent daily exposure to PFBS through drinking water. Thus, these findings emphasize the importance of drinking water as a key route of PFBS exposure, especially for children who may already face additional exposure from other sources. PFBS was detected in fishmeal samples collected from the most important fishmeal-producing countries, contributing 0.22 ng/g to the total PFAS concentrations, and was present in 26.1% of the samples, with salmon showing higher levels (19.4 ng/g) than shrimp(5.55 ng/g). While long-chain PFAS, like PFOS, were more prevalent in fishmeal, short-chain PFAS, including PFBS, were also commonly found and contributed 15.7% to the total PFAS detected. 25 The PFBS levels in this study were higher than those reported in a previous study conducted a decade ago, 26 suggesting an increasing presence of short-chain PFAS in the environment. Moreover, PFAS concentrations in fishmeal were highest in North America (29.7 ng/g), followed by Europe (25.8 ng/g) and China (24.4 ng/g), with coastal Chinese residents showing elevated PFBS exposure, highlighting the global nature of PFAS contamination and the ongoing risk to public health. Interestingly, PFBS was detectable in plasma samples of women of reproductive age, with a median concentration of 0.24 ng/mL, which was significantly associated with dietary seafood intake (eg, fish, shellfish, shrimp, and crab). In contrast, the consumption of soy products was inversely associated with PFAS concentrations. Importantly, this study also found that women who drank bottled water had lower plasma levels of PFBS than those who drank tap water, with a 9% reduction in observed exposure. 27 These results highlight that environmental and dietary factors play a role in PFBS exposure levels. Hence, PFBS persistence in the environment and its bioaccumulation potential have raised significant public health concerns. Studies have shown that PFBS can adversely impact liver function, disrupt hormonal systems, and be linked to various health issues, including developmental and reproductive problems. Hence, this review aims to highlight the adverse effects of PFBS on reproduction and development and encourage both industrial practices and medical care systems to take proactive steps to limit exposure, monitor affected populations, and address long-term health consequences. By combining regulatory action, public health interventions, and scientific research, we can begin to mitigate the risk posed by PFBS and improve overall public health outcomes.

PFBS, like other PFAS compounds, has been shown to disrupt the hormonal systems essential for reproduction and pregnancy, such as estrogen (E2), progesterone (P4), and thyroid hormones (TH), which may impair fertility, disrupt menstrual cycles, and alter pregnancy outcomes. Understanding these effects is crucial for assessing the potential risks of PFBS exposure on human reproductive health. Menstruation is viewed as a proxy for female fecundity. Irregular and long cycles have been related to lower fecundity. 28 Menstrual cycle dysfunction is accepted as a common co-occurrence with infertility. 29 , 30 Several studies in Chinese and Taiwanese populations examined the associations between PFBS exposure and female fecundity. One cohort study examined the association between PFAS levels and menstrual cycle regularity, duration, and volume of blood loss in women planning to become pregnant. No significant relationship was found between PFBS exposure and menstrual cycle characteristics. 31 Steroid hormones are vital in follicle growth, endometrial maturation, and metabolism regulation in reproductive-aged women. 32 One low-confidence case-section study investigated PFBS exposure in adolescents. No clear associations were found between PFBS levels and reproductive hormone levels across the entire study population. 33 A study involving 433 women of reproductive age found that exposure to certain PFAS alternatives was associated with altered levels of total testosterone. However, this association was not significant in the PFBS exposure group. 34 Infertility rates are rising globally, reaching 16.5–25%. This makes infertility the third most prevalent health condition, following cancer and cardiovascular diseases. 35 , 36 There are several predominant causes of infertility, including polycystic ovary syndrome (PCOS), endometriosis, primary ovarian insufficiency (POI), and exposure to endocrine-disrupting chemicals (EDCs). 37 In vitro fertilization-embryo transfer (IVF-ET) is the most effective infertility treatment. During IVF-ET, oocytes are retrieved, fertilized, and subsequently monitored in vitro to observe embryo development. This provides an opportunity to study the effects of reproductive pathologies or EDC exposure on embryonic development. A case-control study enrolled 180 infertile women with PCOS and 187 healthy controls, evaluating PFBS levels in whole blood specimens. No significant relationship was observed between PCOS-attributed infertility and PFBS exposure. 38 In another study, plasma PFBS levels were measured in 120 Chinese women with POI and 120 healthy controls. No association was found between PFBS exposure and an increased odds of having POI. 39 To examine the association between PFAS and endometriosis-related infertility among Chinese reproductive-age women, Wang et al. collected blood specimens from 157 infertile women (surgically confirmed endometriosis cases) and 178 fertile women (controls seeking infertility treatment because of male reproductive dysfunction). They revealed that elevated plasma PFBS concentrations were associated with an increased risk of endometriosis-related infertility. 40 Some studies have explored the effect of PFBS exposure on embryonic development using IVF-ET patient cohorts from China. The concentrations of PFAS in blood samples from 96 couples 41 and 259 women 42 who underwent IVF-ET treatment were measured. Poisson and Bayesian kernel machine regression models with log link were used to evaluate the association between the tertiles of PFAS concentrations and numbers of retrieved oocytes, mature oocytes, two-pronuclei (2 PN) zygotes, and good-quality embryos. The results suggested a potential inverse relationship between PFBS and the number of high-quality embryos, 2 PN zygotes, and cleavage embryos. 42 The reproductive toxicity of PFBS has also been evaluated using rodents, Caenorhabditis elegans (C. elegans) , amphibians , and fish. For instance, a mouse study evaluating the effects of PFBS exposure on ovarian function showed a reduction in the number of secondary, early antral, and antral follicles and an increase in the atretic follicles in PFBS-exposed mice. 43 These changes were recovered by the replacement of L-thyroxine or the treatment with PPARa antagonist GW6471. PFBS-induced hypothyroxinemia decreased Akt, mTOR, and p70S6K phosphorylation levels in ovarian granulosa and cumulus cells, which suppressed cellular proliferation while promoting autophagy. The results indicate that PFBS exposure (200 mg/kg/day) causes downregulation of Akt-mTOR signaling in granulosa and cumulus cells by TH homeostatic disruption, leading to deficits in follicular development and biosynthesis of ovarian hormones. 43 In a study with African clawed frog ( Xenopus laevis ) tadpoles, exposure to PFBS (0.1, 1, 100, and 1,000 μg/L) did not alter gonadal histology but upregulated the expression of E2 and androgen receptors (ER and AR) in the brain, posing a potential pathway for impacts on sexual development. 44 Two C. elegans studies focused on the influence of PFBS exposure on reproduction. Egg production and brood number in C. elegans decreased significantly following exposure to 1000 or 1500 μM of PFBS. In addition, germ cell apoptosis and reactive oxygen species (ROS) production increased significantly following exposure to 500 or 1000 μM PFBS. Expression of the antioxidant genes sod-3 , ctl-2 , and gst-4 and the pro-apoptotic genes egl-1 and ced-13 was significantly up-regulated, caused by elevated ROS levels following PFBS exposure. These findings indicate that PFBS exerts reproductive toxicity in C. elegans , likely attributable to germ-cell apoptosis from elevated ROS levels. 45 The other study demonstrated that PFBS (≥1000 μM) significantly reduced brood size (total egg number) and progeny number (hatched offspring number) without affecting hatchability. Several studies found that PFBS exposure impairs oocyte development rhythm with in vitro fish models. PFBS life cycle exposure of marine medaka at environmentally relevant concentrations (0, 1.0, 2.9, and 9.5 μg/L) shifted the sex ratio toward male dominance, while reproductive functions of female fish were significantly impaired, as characterized by extremely small ovaries, blocked oocyte development, and decreased egg production. 46 Endocrine disruption through the hypothalamus-pituitary-gonad axis was induced by PFBS exposure, showing antiestrogenic activity in females but estrogenic activity in males. 46 When adult zebrafish were exposed to 10 μg/L PFBS for 28 days, the concentration of maturation-inducing hormones was increased in the ovary, and ovary histological observation showed that oocyte growth was significantly promoted after PFBS exposure. Despite the enhanced hormonal signals, gene transcription of ovarian local autocrine and paracrine factors was consistently decreased in PFBS exposure groups, suggesting the blocked transition from the oocyte growth phase toward the oocyte maturation phase. Overall, the present study provided more mechanistic evidence about the impacts of PFBS on egg production rhythm through oocyte growth and maturation phases. 47 Overall, evidence from studies on the reproductive toxicity of PFBS suggests that PFBS disrupts hormonal homeostasis, including hypothyroxinemia, decreased serum E2 and P4 levels, and elevated luteinizing hormone (LH) levels. These effects may lead to reduced numbers of follicles and corpora lutea, disrupted menstrual cycle regularity, infertility associated with endometriosis, and adverse impacts on oocyte development and embryo quality. However, current mechanistic studies are limited, highlighting the need for further research to confirm these effects. Studies have investigated PFBS exposure in relation to various pregnancy complications, including hypertensive disorders of pregnancy (HDP), gestational diabetes mellitus (GDM), and preterm birth (PTB), providing insight into possible mechanisms by which PFBS affects maternal health. HDP are among the most common pregnancy complications and are typically classified into four categories: 1) chronic hypertension, 2) gestational hypertension, 3) preeclampsia-eclampsia, and 4) preeclampsia (PE) superimposed on chronic hypertension. 48 Huo et al. conducted a large prospective cohort study enrolling 3,220 women in early pregnancy. They measured ten PFAS compounds, including PFBS, and did not find an association between PFBS levels and an increased risk of gestational hypertension. 49 However, in a cross-sectional study involving 687 women delivering at two large hospitals in Shanghai, Huang et al. analyzed umbilical cord blood for eight PFAS, including PFBS. They found that PFBS levels were positively associated with an increased risk of HDP. 48 Similarly, in a prospective nested case-control study, Liu et al. investigated the impact of PFBS on HDP among 136 cases and 408 controls in China. They reported a positive association between maternal serum PFBS levels and HDP. 50 Moreover, Pang et al. performed a meta-analysis examining prenatal exposure to PFAS and the risk of pregnancy complications. Their computational data analysis indicated that PFBS was positively associated with HDP. However, no significant association was found between PFBS and gestational hypertension or preeclampsia alone. 51 The current consensus is that PE is closely linked to abnormal placental development. The placenta, a transient but crucial organ, connects the mother and fetus, facilitating the exchange of nutrients, oxygen, blood, waste, and xenobiotics. In an uncomplicated pregnancy, placental cytotrophoblasts begin to invade the maternal uterine wall around gestation week 13, remodeling the maternal spiral arteries to support blood flow to the developing embryo. 52 Disruptions in this process can impair placental vascularization, leading to pregnancy complications, including PE. Thus, studies investigated whether PFBS exposure interferes with placental development and function, which may underlie the association between PFBS exposure and the increased risk of PE. In New Zealand White rabbits, PFBS exposure significantly changed blood pressure markers, as seen through increased pulse pressure and renal resistive index measures. In addition, transcriptome in placentas identified a dysregulation of angiotensin (AGT) by PFBS exposure in these rabbits, which might contribute to the hypertension observed in this study. However, these results were only found in the high-dose PFBS (100 mg/L) group, making it less translational. 53 Marinello et al. conducted in vitro studies using HTR-8/SVneo, a human placental invasive trophoblast cell line exposed to PFBS. At a concentration of 100 μM, PFBS significantly increased cell proliferation while decreasing cell migration and invasion. Interestingly, at a low concentration (0.1 μM), PFBS promoted cell invasion without affecting migration. 54 RNA sequencing revealed dysregulation of genes regulated by HIF-1α involved in cell proliferation and invasion, indicating that HIF-1α signaling may play a key role in the potential impacts of PFBS on PE development. 54 Furthermore, PFBS exposure in the BeWo human placenta trophoblast cell line significantly reduced human chorionic gonadotropin (hCG) secretion and its corresponding gene, CGB7, expression in a dose-dependent manner. These findings suggest that PFBS may disrupt endocrine functions critical for pregnancy maintenance and contribute to the development of PE. 55 Research suggests that PFAS compounds may contribute to HDP through mechanisms involving placental dysfunction, lipid metabolism disruption, immunotoxicity, and oxidative stress. 52 Although studies specifically focusing on PFBS are limited, an association between PFBS exposure and HDP has been indicated. In the Shanghai Birth Cohort, Yu et al., investigated the association between PFBS exposure and GDM risk by analyzing blood samples from 2,747 pregnant women. Their findings indicated that each log-unit increase in PFBS concentration during early pregnancy was associated with a higher risk of developing GDM. 56 Furthermore, Xu conducted a nested case-control study within a prospective cohort of 2,460 pregnant women, finding that PFBS levels were significantly higher in women who developed GDM than controls. The highest quartile of PFBS exposure was associated with more than double the risk of developing GDM, even after adjusting for maternal age, sampling time, parity, and body mass index (BMI). 22 A study involving 874 pregnant women in China found that each doubling of PFBS levels in umbilical cord blood was linked to an increase in 1-hour and 2-hour blood glucose levels during an oral glucose tolerance test (OGTT). This suggests a dose-dependent relationship with impaired glucose tolerance. 57 Pang et al. conducted a meta-analysis, aggregating results from multiple studies on prenatal exposure to perfluorinated compounds, and found that higher PFBS exposure was associated with an increased risk of GDM. 51 In an experimental study, Yu et al. administered PFBS to pregnant Sprague Dawley rats at different dosages (5 or 50 mg/kg/day PFBS) and found that high doses led to significantly lower 1-hour glucose levels and impaired glucose tolerance, as evidenced by OGTT outcomes. Transcriptomic analysis revealed alterations in critical metabolic pathways, including genes involved in glutathione metabolism and bile acid secretion in the maternal rat liver. Additionally, changes in metabolites, such as fumaric acid and L-lactic acid, suggest their potential role in modulating glucose and lipid metabolism. 58 Liu’s research in zebrafish ( Danio rerio ) demonstrated that PFBS exposure increased blood glucagon levels, disrupted insulin receptor expression, and depleted hepatic glycogen, which impaired glucose metabolism. 59 Additionally, PFBS exposure in male zebrafish affected fatty acid β-oxidation pathways in the liver, suggesting that PFBS may contribute to energy balance disruption through alteration in lipid metabolism. 50 Hence, research has consistently shown an association between elevated PFBS exposure and an increased risk of GDM. However, mechanistic insights into the effects of PFBS on glucose metabolism are limited, though some studies provide valuable clues. Studies have explored the effects of PFBS exposure on PTB risk. In a prospective analysis of the Guangxi Zhuang Birth Cohort, Liao et al. enrolled 1,341 pregnant Chinese women and examined the relationship between PFBS exposure and PTB. 60 Using restricted cubic splines, Liao observed an inverse U-shaped relationship between PFBS levels and PTB risk, suggesting that low and high PFBS levels may increase the likelihood of PTB. 60 Mechanistic studies are beginning to clarify how PFBS may contribute to PTB. Du et al. conducted in vitro experiments and found that PFBS exposure promotes trophoblast invasion through the ERK-dependent iNOS/NO signaling pathway, a mechanism that could contribute to adverse pregnancy outcomes, including PTB. 61 Another study by Chen et al. suggested that PFBS exposure disrupts sex hormone homeostasis, potentially creating an antiestrogenic environment that interferes with pregnancy maintenance by altering crucial signaling pathways. 62 Studies in both humans and animals have shown that PFAS compounds, including PFBS, readily transfer from maternal blood to the fetus through the placenta. Placental transfer efficiency (PTE), measured by the ratio of PFBS concentration between cord blood and maternal blood, is a critical indicator of fetal PFBS exposure. Several studies have investigated PFBS transplacental transfer efficiency (TTE). In 2022, Bao and colleagues analyzed PFAS concentrations in 50 paired maternal serum, cord blood, and placental samples from pregnant women in Fuxin, China, finding a high TTE for PFBS, with a TTE of 1.9. 63 Similarly, Gao and colleagues examined 132 paired maternal and cord serum samples from residents in Beijing, China, reporting a PFBS PTE of 97%. 64 Together, these studies provide strong evidence that PFBS can cross the placental barrier to reach fetal circulation, potentially impacting fetal development during pregnancy. 65 – 67 It was also found that PFBS exhibited higher TTE and lactation transfer than PFOS, likely due to its hydrophilic properties and low molecular weight, facilitating its passage through both the placenta and mammary epithelium. Notably, postnatal exposure to PFBS through breastfeeding (lactational exposure = 435 ng) was significantly higher than prenatal exposure (body burden of prenatal exposure = 9 ng), indicating that lactation may pose a greater exposure risk. 66 Given the potential for increased neonatal exposure to PFBS, further research is needed to evaluate its health implications, especially considering evolving exposure guidelines and the lack of a specific Tolerable Daily Intake (TDI) for PFBS.

The studies highlighted in this review demonstrate that significant adverse effects from PFBS exposure are evident after only twenty-two years of use, suggesting that caution should be exercised in its management, similar to the regulatory approaches taken for PFOS and PFOA. However, even with the eventual phaseout of PFBS, its persistence in the environment remains a major concern. Due to its chemical stability, PFBS can remain detectable in water for extended periods, potentially indefinitely. This long-term environmental presence, coupled with the co-occurrence of other PFAS compounds, may exacerbate ecological and human health risks. From a clinical perspective, the potential for trans-generational effects through epigenetic mechanisms raises additional concerns. Like other PFAS, PFBS has been shown to alter gene expression and cellular function, which may affect not only directly exposed individuals but also their offspring. These epigenetic changes could influence disease susceptibility and developmental disorders across generations, compounding the long-term public health impact of PFBS contamination. The conclusions regarding the reproductive toxicity of PFBS are inconsistent. Animal model studies suggest that PFBS exposure may affect hormone synthesis and oocyte development. However, epidemiological studies in human populations are limited, and some research indicates that PFBS has little association with hormone synthesis or diseases such as PCOS and POI. This discrepancy may stem from selection bias within the study populations. Further clinical studies are needed to explore the reproductive toxicology of PFBS, along with more mechanistic research to validate its effects on reproductive health. The current research on PFBS exposure during pregnancy reveals significant associations with pregnancy complications, such as HDP, GDM, and PTB, despite some inconsistencies in the epidemiological evidence. Human and animal studies indicate that PFBS may affect maternal and fetal health by disrupting placental function, glucose metabolism, and endocrine regulation. Future studies should focus on elucidating the molecular mechanisms underlying PFBS-induced disruptions in placental development, glucose metabolism, and endocrine regulation. Longitudinal studies in both human cohorts and animal models will be crucial in establishing causal relationships and understanding the long-term impacts of PFBS exposure on maternal and fetal health. Regarding regulatory action, significant efforts are underway globally to address PFBS and other PFAS compounds. While regulations for PFBS use are still evolving, countries in Europe, Asia, and the United States have started implementing measures to limit its presence in the environment. Denmark, Sweden, and Germany, particularly, have taken proactive stances on regulating PFAS, including PFBS, with a focus on water contamination and environmental pollution. Denmark, for example, has set limits for certain PFAS in drinking water, creating pressure for other European countries to adopt similar regulatory approaches. In the United States, the Environmental Protection Agency (EPA) has initiated actions to monitor and regulate PFBS alongside other PFAS compounds, particularly in relation to drinking water safety. Two primary technologies in the United States have proven to effectively reduce PFBS levels in drinking water are activated carbon and reverse osmosis filtration. These technologies have become essential tools in mitigating PFBS contamination, although their efficiency and widespread adoption remain ongoing research topics. However, there is a noticeable gap in our understanding of the use and regulation of PFBS in many African and Latin American countries. Limited data and research on PFBS exposure, contamination, and regulation in these regions highlight the urgent need for further investigation into its environmental and public health impacts. The absence of comprehensive regulatory frameworks and monitoring efforts in many of these countries underscores the importance of expanding research and establishing guidelines to address potential PFBS contamination with a focus on protecting vulnerable populations. Given these regulatory advancements, future research should prioritize developing effective strategies for removing and remediating PFBS and other PFAS from environmental systems. Notably, a project funded by the National Institutes of Health in 2024 is focused on developing innovative treatment technologies for PFAS contamination. 115 Several promising studies are also underway to improve PFBS degradation and removal from water sources. These include advanced techniques, such as vacuum-ultraviolet treatments with iodide involvement, plasma-assisted degradation, and novel filtration techniques like nanofiltration combined with foam fractionation. 116 – 120 Other studies are investigating the role of the air-water interface in adsorbing PFAS from drinking water. These efforts are crucial for addressing the persistent challenge of PFAS contamination. Furthermore, understanding the mechanisms underlying PFBS toxicity across different organisms and tissues, including its potential epigenetic effects, is essential for informing accurate risk assessments and developing effective mitigation strategies. A comprehensive approach to studying PFBS will be vital for addressing the long-term and transgenerational impacts of PFBS contamination, minimizing its detrimental effects on public and environmental health.

The ability of PFBS to cross the placenta raises concerns about its potential to disrupt fetal growth and development, including effects on organ formation and reproductive health. Its high PTE further exacerbates concerns regarding fetal exposure and the risk of interference with critical developmental pathways during pregnancy. However, given the recent use of PFBS as an alternative to legacy PFAS compounds like PFOS, there is a significant gap in longitudinal data on its effects on human offspring development. Most research has relied on animal models, including fish and rodents, to investigate potential developmental impacts. These studies have typically modeled human gestational exposures by administering PFBS to pregnant rodents via gavage or drinking water or by directly exposing fish, C. elegans , and amphibian embryos. We present the findings of these studies in order of relevance to human health, beginning with cohort studies and followed by in vivo investigations. When PFBS was examined in conjunction with other PFAS compounds in mixture analyses, several cohort studies found no association between PFBS and birth weight. 68 – 70 One examination of 214 mother-child pairs revealed a strong positive relationship between umbilical cord serum PFBS and birth weight in female infants. 67 PFBS displayed the strongest positive correlation out of the 23 PFAS measured, which the authors attributed to its short chain length that gives rise to highly TTE. 67 However, the limited human studies cannot definitively confirm or rule out the effects of PFBS on infant size. First, as an emerging contaminant, PFBS concentrations in drinking water are typically lower than those of PFOS and perfluorooctanoic acid (PFOA), which are the most frequently detected PFAS compounds in the United States and China. 71 The effects of these low concentrations may take longer to manifest or could be challenging to distinguish from the impacts of other PFAS compounds. Furthermore, birth weight is an important albeit single time point for assessing offspring development. Studies that examine birthweight alone may overlook the long-term consequences of exposure. For instance, in a study of 2395 mother-child pairs from the Shanghai birth cohort, elevated maternal plasma concentrations of PFBS during pregnancy were associated with lower weight-for-length scores and BMI-for-age scores at 42 days, 6 months, and 1 year. 72 This effect was not sex-specific. Similarly, a study of 887 mother-child pairs from birth to 10 years of age found a negative relationship between cord blood PFBS and BMI from birth to 3 years of age. The effect was largely sex-specific to males and did not persist later in childhood. 73 A consensus has yet to be reached regarding the impact of PFBS on weight alone. A major confounding factor in these studies, which may account for the variability in findings, is the lack of longitudinal monitoring of PFBS levels in childhood serum to correlate with changes in size. Moreover, BMI is not an ideal metric because it does not directly measure adiposity and has been shown to be a poor indicator of adiposity for children. 74 , 75 Therefore, it is essential to consider the validity of adiposity metrics when evaluating cohort studies. Other observational studies have observed positive relationships between maternal PFBS levels and body fat in children, using closer proxies for adiposity such as waist circumference or direct measures like body fat percentage. For example, in a study of 404 children, girls with higher PFBS levels in cord plasma exhibited larger waist circumferences and higher waist-to-height ratios at 5 years of age. 76 Girls in the highest tertile for cord PFBS levels also demonstrated higher fat mass and body fat percentage than those in the lowest. 76 An analysis of 783 live births with available cord blood samples showed a positive relationship between short-chain PFAS, including PFBS, and neonatal adiposity as measured by MRI at birth. 77 These changes were transient, disappearing by 6 years of age. 77 However, seemingly opposite trends have been observed depending on the population and exposure levels. The variability in results across these studies may be attributed to differences in study design, population characteristics, and environmental factors, which complicate generalizability. Researchers collected umbilical cord blood, maternal blood, or both from participants. Although maternal and cord blood are related, cord blood provides a more direct measure of fetal pollutant exposure. Cord blood is also considered a preferred indicator, as maternal blood can sometimes overestimate exposure to pollutants, including PFAS. 78 Although some studies use serum while others use plasma, the difference in measured PFAS levels is generally negligible. 79 Regardless of the type of blood samples used, the sampling time can influence the strength and direction of the observed relationships. The authors collected blood at specific gestational ages, ranging from early to late pregnancy, often using a single time point. Given the relatively short half-life of PFBS, a single concentration snapshot may not accurately reflect temporal trends or overall gestational exposure. There are also confounding factors that extend beyond gestational exposure studies. Each population group has unique lifestyle and social factors that may influence outcomes. As noted by Chen et al. 2024, trends can vary between ethnic groups, and the composition of participants can affect results. Thus, it is essential to include a diverse range of ethnic groups in study populations. It is also important to note that all cohort studies examining maternal PFBS exposure and body size in this review originate from China, which may limit the generalizability of the findings to other global communities. On a smaller scale, individual factors such as processed food or seafood consumption and drinking water sources can impact both immediate and long-term exposure. Finally, in addition to the unique PFAS exposure scenarios represented by different populations, the studies do not account for co-exposures to other unmeasured pollutants that could influence the outcomes. 80 It is impossible to account for all known and unknown variables inherent in observational human studies, which is why animal model studies are necessary for understanding the effects of PFBS. Subtle but diverse developmental effects have been uncovered with chronic low-dose developmental exposure to PFBS. In a study of New Zealand White Rabbits, chronic prenatal PFBS exposure resulted in sex-independent growth restriction, as measured by crown-to-rump length. 53 In zebrafish, chronic low-dose PFBS exposures were also associated with offspring defects. After 28 days of parental exposure to low PFBS doses, zebrafish embryos exhibited reduced body weight and other adverse developmental effects, including increased mortality, delayed hatching, slower heart rate, reduced body weight, and neurobehavioral disorders. 81 The authors suggest that these effects may be linked to disturbances of maternal transcript transfer, although it remains unclear if these changes alter transcription within the zygotic genome. 82 Acute exposures to PFBS in zebrafish have yielded mixed findings. In a 6-day embryonic exposure study, doses from 0.0002–400 μM of PFBS did not cause significant birth defects or increased mortality. 83 In contrast, when embryos were exposed to 2–200 μM of PFBS for just under 5 days, the acute exposure led to dose-dependent reductions in hatch rates, increased mortality, and malformations to the pericardium, yolk sac, swim bladder, body size, and eyes. However, exposure to 0.2 μM of PFBS for the same period yielded no effects. 84 Differential expression of 2,471 genes suggests that a generalizable mechanism of toxicity, such as ROS production, could underlie the broad range of observations. Gong et al. highlighted the importance of detailed assessments of developmental effects. While Menger et al. found no gross morphological changes or mortality, Gong et al. identified system-specific changes beyond obvious acute toxicity. Some authors assert that compared to long-chain PFAS, short-chain PFAS, like PFBS, exerts less potent developmental effects, particularly in acute exposures. In C. elegans , a 48-hour exposure to PFBS resulted in mild effects on worm length and mortality, with these effects being less pronounced than those observed with legacy and long-chain compounds. 85 The effect was relatively consistent across C. elegans strains presumably due to a lack of the sulfonamide in the functional group. 85 Because a single short-term exposure was used, it is difficult to extrapolate if this trend holds true when in chronic exposure scenarios. Moreover, all the animal studies presented here are impacted by interspecies differences in PFBS kinetics, making it challenging to directly compare exposure timeframes across different animal models. Significant changes in animal size following PFBS exposure have primarily indicated neonatal growth restriction. However, metabolic changes at the molecular level could lead to excess weight later in life, even if not during infancy. In rats, low-dose maternal PFBS exposure altered gene expression and the presence of molecules involved in lipid metabolism in offspring. 86 The authors found differential expression of pantetheine 4′-phosphate, which is negatively associated with low-density lipoproteins (LDL) and total cholesterol. Additionally, upregulation of several metabolites correlated with lipid metabolism disorders was observed. 86 Alteration of these metabolic pathways could lead to a hyperlipidemia phenotype, which may not manifest immediately in offspring during early life but could emerge later in development. In C. elegans , transgenerational metabolic disturbances were observed through the fourth generation following gestational PFBS exposure. 87 Increased fat content was stimulated via disturbances in lipid metabolism and the insulin and insulin-like signaling pathway. 87 However, in a similar single-generation larval study, gene expression related to lipid composition and accumulation remained unchanged. 88 In leopard frog tadpoles, PFBS-exposed at low concentrations resulted in sex-independent increases in hepatosomatic indexes for PFBS-exposed embryos. However, expected corresponding changes in fatty acid profiles were not observed. 89 Taken together, these studies highlight that PFBS exposure can disrupt offspring metabolic homeostasis and growth dynamics, with ramifications for later-in-life obesity and related metabolic disruption, but the specific outcomes may vary across species and exposure scenarios. In addition to changes in gross morphology, neurobehavioral and neurodevelopmental changes have been observed with gestational PFBS exposure. However, few human studies have linked neurotoxic effects to PFAS compounds other than PFOA and PFOS, including PFBS. Moreover, PFBS is often either not measured or present in relatively low concentrations in studies, as it is an emerging contaminant. Although there is evidence that PFOS and PFOA readily enter the developing brain, 90 – 92 no studies have specifically examined PFBS ability to cross the blood-brain barrier (BBB) following developmental exposure. Adult rat studies have shown low brain-to-plasma PFBS ratios, suggesting limited BBB penetration compared to other compounds like PFOS, possibly due to the high binding affinity of PFBS for serum albumin. 93 Females eliminated PFBS from all tissues, including the brain, faster than their exposed male counterparts. 93 Both human and rodent studies indicated that the liver and kidneys are the primary sites of PFBS accumulation in adults rather than the brain. 24 , 94 While PFBS may not accumulate significantly in the brain due to its low BBB permeability or rapid serum elimination, developmental studies are needed to explore potential differences in BBB function during fetal and neonatal stages. Moreover, PFBS may affect the nervous system through mechanisms beyond direct toxicity, such as changes in neurotransmitter levels, synaptic ion homeostasis, epigenetic modifications, and endocrine disruption. Several studies have reported the neurodevelopmental effects of PFBS in early childhood, particularly in adaptive and motor developmental domains. In the Laizhou Wan Birth Cohort of 274 mother-infant pairs, elevated prenatal PFBS levels in cord blood were associated with considerable decrements in the developmental quotient for gross motor and adaptive domains at 1 year of age. 95 Similarly, in the Sheyang Mini Birth Cohort, low developmental scores on two screening tests from birth to 6 years of age were associated with increased PFBS levels in cord serum in 716 children. 96 In contrast, a study of 2,257 mother-child pairs from the Shanghai Birth Cohort found a positive relationship between PFBS exposure and adaptive behavior scores in 2-year-old children in the highest exposure quartile. 97 However, median gestational maternal plasma PFBS concentrations were the lowest of the 10 PFAS measured, 97 which may explain the null or nonintuitive associations with behavioral outcomes. Relatively low PFBS exposures may contribute to these mixed results, highlighting the need for repeated neurodevelopmental assessments, particularly with follow-up extending beyond toddler years, to confirm the findings from these observational studies. The neurodevelopmental effects of PFBS are more pronounced in animal studies, particularly concerning locomotor activity. In one study, exposing zebrafish embryos to high concentrations of PFBS (3332–6664 μM) for 5 days increased locomotor activity, as measured in the visual motor response assay. This effect was more potent than observed with the short-chain emerging PFAS compound GenX. 98 In the same animals, a decrease in whole-organism dopamine levels was observed, suggesting a potential mechanism for neurotoxicity and possibly linked to hyperactivity observed in humans. 98 However, a mixed phenotype was observed at slightly lower PFBS exposure concentrations of (1,000–3,332 μM) for 6 days 99 ; larvae displayed higher active swimming speeds but reduced overall locomotor activity. 99 In contrast, no significant locomotor effects were observed in studies using lower concentrations of PFBS, such as0.0002–400 μM for 6 days 83 or 5.5–100.0 μM of PFBS for 6 days. 100 This inconsistent trends in locomotor activity and the limited neurodevelopmental data available, underscores the need for further investigation using a broader range of exposure scenarios and neurobehavioral assays. Parental exposure to PFBS, rather than direct embryonic exposure, appears to play a significant role in altering activity phenotype in offspring through epigenetic changes. Adult parental chronic low-dose exposure to 3.3 mg/L PFBS for 28 days resulted in offspring zebrafish displaying increased locomotor activity, measured by distance traveled. 82 The authors assert that developmental impacts at low concentrations could be attributed to altered histone-DNA packaging in the nucleosome and disordered transfer of maternal factors, such as protein and mRNA. 82 Interestingly, in a crossbreeding study on marine medaka ( Oryzias melastigma ) commonly known as rice fish exposure found that exposure to environmentally relevant concentrations of PFBS (0, 1, 3, and 10 μg/L) throughout the F0 paternal life cycle led to hyperactive swimming behavior in offspring. 62 The authors suggested that epigenetic modifications incurred from paternal exposure may significantly impact developmental impairment more than maternal exposure alone. 62 In another study on C. elegans , chronic parental exposure to 1.0mM PFBS led to diminished locomotor activity in the F0 and F1 generations but not the F2 generation. 101 Transferable behavioral toxicity was only noted at relatively high doses, not concentrations below 0.0005 mM. 101 However, these studies, and most others, lack a comprehensive exploration of the molecular links between altered pathways and behavioral endpoints. Further, they provide a limited perspective of tissue-specific methylome changes, as most sampling was restricted to a single tissue type or wholebody larvae. 46 Despite these limitations, examining parental exposures, especially in paternal versus maternal contexts, remains valuable for understanding the broader impacts of PFBS on offspring development. In addition to behavioral phenotypes, developmental exposures to PFBS can lead to physical neurotoxicity manifestations. Abnormal swimming movements were observed in zebrafish larvae exposed to concentrations of PFBS up to 9,996 μM for 3 days, resulting from malformations and uninflated swim bladders. 102 Notably, PFBS exposure led to craniofacial abnormalities, which represent a new dimension and were previously only seen in the context of PFOS exposure. 103 , 104 In marine medaka, exposure to environmentally relevant concentrations of PFBS (0.0033–0.0317 μM) across an entire life cycle resulted in decreased eye weight but increased water content, a likely indicator of increased intraocular pressure. 105 Multiple neural signaling pathways were disturbed, including cholinergic, glutamatergic, GABAergic, and monoaminergic pathways. The differential expression of proteins involved in visual perception and oculomotor activity confirmed ocular toxicity following chronic low-dose PFBS exposure. 105 Finally, a rare co-exposure study highlighted that developmental toxicities of PFBS could be modulated by concurrent environmental stressors such as hypoxia. While chronic PFBS exposure alone resulted in mild effects in marine medaka larvae, its toxicity became significantly more potent when combined with hypoxia. 81 Co-exposure to 10 μM PFBS and hypoxia for 15 days resulted in disruptions to the phototransduction pathway in the larvae, with downregulation of cyclic nucleotidegated cation channels and components involved in retinol metabolism. In contrast, PFBS alone disrupted a separate sensory group, specifically olfactory and gustatory receptors. The combined effects of PFBS and hypoxia were linked to shared epigenetic modifications, including chromatin deacetylation, methylation, and remodeling, which likely underpinned the observed sensory perception disturbances. 81 Overall, developmental exposure to PFBS, at both environmentally relevant and high doses, exhibited toxicity to multiple neurological systems. These effects may be strengthened or altered entirely by co-exposures, underscoring the need for more interaction models to understand the complex dynamics of PFBS-induced toxicity better. Endocrine disruption, notably TH disruption, has been implicated as a key mechanism underlying both neurotoxicity and general developmental toxicity associated with PFBS. Both human and animal studies have observed TH disruption following increasing gestational PFBS exposure. However, the directionality and sex-specificity of these effects remain varied. Understanding how PFBS disrupts TH hormone homeostasis during early life is essential, as such disruption can result in increased risks of growth and neurodevelopmental delays later in childhood. A prospective cohort study involving 1,015 mother-child pairs showed a negative association between cord PFBS levels and TSH in infancy, a relationship not seen with other studied PFAS compounds. 106 The effect was particularly pronounced in males, in contrast to findings from animal studies, which will be discussed. The Laizhou Wan Birth Cohort study with 274 mother-child pairs corroborated this negative association between cord serum PFBS and TSH in offspring. 95 However, the Sheyang Mini Birth Cohort study with 490 mother-infant pairs found no association between PFBS and offspring TSH. 107 These large-scale cohort studies must be interpreted with caution, especially given the poorly understood mechanism of thyroid signaling disruption. In addition, the limitations of cohort studies, including potential confounding by co-exposures, lifestyle factors, and population characteristics, should be considered when evaluating these results. The first study was conducted on marine medaka, identifying PFBS as a TH disruptor. In this study, F0 fish were exposed to 0.0033–0.033 μM of PFBS for 6 months. 105 F1 offspring from the exposed fish exhibited symptoms of thyroidal disruption, including decreased body weight and length, low levels of 3,3′, 5-triiodothyronine (T3), and delayed hatching. The F2 generation also demonstrated symptoms of thyroid disruption, with elevated synthesis of thyroxine (T4). 105 Importantly, TH homeostasis was disturbed even without direct larval exposure to PFBS, supporting the well-established knowledge that maternal TH levels during pregnancy predict offspring thyroid function. 108 Similar disruptions have been observed in mammalian animal models. Female offspring showed low perinatal body weights, delayed eye-opening, and altered TH levels in pregnant mice exposed to 200 and 500 mg/kg/day of PFBS from gestational days 1–20. 109 Specifically, offspring demonstrated decreased T4 and T3 levels and increased TSH and thyrotropin-releasing hormone (TRH) at fetal, pubertal, and adult time points. 109 In a previously mentioned study of chronic prenatal PFBS exposure in New Zealand White Rabbits, RNA sequencing revealed diminished expression of SCARB1, a gene involved in placental T4 transport. 53 This finding suggests that PFBS may hinder TH transport across the placenta, contributing to the observed growth restriction, which was sex-independent. Although no statistically significant differences were revealed in T4 levels in exposed dams, a downward trend in T4 was noted, and T3 was undetectable in kit whole blood samples. 53 These initial studies highlight the need for future investigation into TH disruption following PFBS exposure in model organisms. Studies investigating maternal exposure to PFAS compounds, including PFBS, have highlighted their potential as endocrine disruptors, particularly regarding fetal and neonatal hormone levels. In the Shanghai Birth Cohort (752 mother-infant pairs), higher maternal PFBS levels were associated with altered fetal gonadotropin and androgen levels. Specifically, elevated maternal PFBS concentrations were linked to lower levels of fetal follicle-stimulating hormone (FSH), LH, and the free androgen index (FAI) in boys and girls. 110 Furthermore, a study from the Wuhan Birth Cohort (374 neonates) found a positive correlation between PFBS levels and P4 concentrations in boys, while no significant association was observed in girls. 111 A prospective birth cohort study, which included 351 full-term pregnant women, reported lower levels of testosterone and estradiol in the cord blood of male infants with increasing levels of PFBS exposure. However, these differences were not statistically significant. 112 These findings suggest that PFBS interferes with the hormonal regulation of reproductive development in utero , potentially affecting fetal gonadal development and subsequent reproduction. Considering differences in the timing, duration, or dosage of PFBS exposure, the effects observed in these studies may indicate that PFBS exerts complex, dose-dependent, and context-dependent effects on hormone levels. Our current understanding of the effects of PFBS on the reproductive and endocrine systems has focused on its potential anti-estrogenic or estrogenic activity under various exposure conditions. For instance, a study investigating the effects of PFBS on marine medaka embryos exposed to different PFBS concentrations (0, 1, 3.3, and 10 mg/L) under both normoxic and hypoxic conditions revealed intriguing results. When PFBS was administered alone, it exerted anti-estrogenic effects. However, when combined with hypoxic conditions, these effects were reversed, and estrogenic activity was observed instead. This suggests that the co-occurrence of hypoxia and PFBS exposure may influence the toxicity profile of PFBS in aquatic organisms. It underscores the importance of considering environmental stressors, such as hypoxia, when assessing the interactive effects of xenobiotic pollutants like PFBS. 81 Similarly, in a study of pregnant mice, oral administration of PFBS at 200 and 500 mg/kg/day from gestation days 1 to 20 resulted in significant reproductive and hormonal alterations in the F1 offspring. Female offspring in the 200 mg/kg/day exposure group exhibited reduced ovarian and uterine sizes alongside decreased follicular and corpora lutea counts. Hormonal analysis revealed decreased serum levels of E2 and P4, along with increased levels of LH, indicating disrupted endocrine signaling. These findings suggest that PFBS exposure can impair mammalian reproductive organ development and hormonal regulation, particularly at higher doses. 109 In contrast, a study examining the effects of PFBS on F1-generation rats exposed to K + PFBS did not reveal significant changes in reproductive parameters. Offspring sperm motility, sperm count, and morphology remained largely unaffected, with only a slight, non-biologically significant increase in sperm abnormalities observed at the highest dose (1000 mg/kg/day). Likewise, no changes in estrous cycle regularity or fertility in female offspring were observed. Although a minor reduction in seminal vesicle weight was noted in high-dose males, this was attributed to overall body weight reduction rather than a direct effect of PFBS. Histological examination of reproductive organs showed no significant changes, including in ovarian follicle counts. These findings suggest that, at least in this model, K + PFBS exposure does not lead to meaningful disruptions in reproductive or endocrine function. 113 At a molecular level, in vitro studies have shown that PFBS does not significantly affect the expression of ER and AR genes, nor does it influence the secretion of steroid hormones. This lack of receptor-mediated activity further suggests that PFBS may exert its effects through alternative mechanisms or indirect pathways rather than through direct modulation of hormone receptors. 114 Overall, the evidence suggests that PFBS may have complex and dose-dependent effects on reproductive and endocrine function across different species and exposure conditions. While some studies report anti-estrogenic or endocrine-disrupting effects, others suggest minimal or no significant reproductive toxicity, particularly in rodent models. The interaction of PFBS with environmental stressors, such as hypoxia, warrants further investigation, as it may modulate the compound toxicological profile in aquatic systems. These findings underscore the need for more comprehensive studies that consider both the direct and indirect effects of PFBS, including potential synergistic interactions with other PFAS compounds, to better understand its full health impacts.