Xenoestrogens earn their name from their structural resemblance to endogenous estrogens, the natural hormones that guide far more than reproduction. In the brain, estrogen signaling shapes neuronal differentiation, synaptic plasticity, neurotransmitter release, and the organization of sexually dimorphic circuits. Because xenoestrogens can bind estrogen receptors and hijack these pathways, they can mimic, amplify, or scramble hormonal instructions at concentrations far below those traditionally used in toxicological testing. The review emphasizes that these compounds frequently display non-monotonic dose-response curves, meaning that low doses can produce effects that are different, or even opposite, to those seen at high doses. That property upends a foundational assumption of classical toxicology, which has long held that the dose makes the poison.

The chemicals in question are everywhere. Bisphenol A, or BPA, leaches from plastic containers, food-can linings, and thermal receipts. Phthalates, added to plastics to make them flexible and durable, shed from personal care products, building materials, and countless household items. Polychlorinated biphenyls, or PCBs, were banned decades ago yet persist in soil, water, and animal tissue, bioaccumulating as they move up the food chain. Natural xenoestrogens such as phytoestrogens, found in certain plants, add a further layer of complexity. The result, the authors note, is chronic, low-dose, real-world exposure to a shifting cocktail of compounds whose combined effects remain poorly understood.

At the molecular level, the review describes several converging mechanisms of harm. BPA and certain PCBs bind estrogen receptors ERα and ERβ, triggering both genomic and rapid non-genomic signaling through pathways such as MAPK and PI3K/AKT, which govern cell proliferation, apoptosis, and differentiation. Xenoestrogens also disrupt the synthesis, transport, and metabolism of endogenous hormones by interfering with the hypothalamic-pituitary-gonadal axis, tilting the hormonal milieu that the developing brain depends on. Beyond receptor binding, these compounds perturb calcium signaling and glutamatergic neurotransmission by modulating NMDA receptor expression, a shift that can push neurons toward excitotoxicity and impair the precise wiring of synaptic connections.

Perhaps the most unsettling mechanism is epigenetic. Xenoestrogen exposure can induce aberrant DNA methylation and histone modifications, chemically rewriting the instructions that govern gene expression without changing the underlying DNA sequence. Among the genes affected are BDNF, SHANK3, and RELN, all of which are central to synaptic function and have been implicated in neurodevelopmental disorders such as autism spectrum disorder and attention-deficit/hyperactivity disorder. The downstream consequences include defects in synaptic pruning, neuronal migration, and myelination, the very processes that sculpt a mature, functional brain. Because epigenetic marks can be inherited, the review raises the possibility that today’s exposures may predispose future generations to neurodevelopmental vulnerability, a transgenerational shadow that conventional risk assessments have barely begun to address.

The behavioral evidence spans the laboratory and the wild. In rodent models, perinatal exposure to BPA, PCBs, and the synthetic estrogen diethylstilbestrol disrupts mating behavior by deranging the hypothalamic-pituitary-gonadal axis and altering estrogen and testosterone levels. Male rodents exposed to BPA early in life show reduced mounting and intromission frequencies, while females display altered estrous cyclicity and diminished lordosis responses. The sexually dimorphic nucleus of the preoptic area, normally larger in males, shrinks following early-life exposure to estrogenic disruptors, accompanied by disturbances in dopamine and oxytocin signaling that underpin sexual and affiliative behavior. In aquatic species, estrogenic pollutants have feminized male fish and amphibians, collapsing courtship behavior and reproductive success, with one landmark study documenting the collapse of an entire fish population after exposure to a synthetic estrogen.

Cognitive and emotional effects are equally well documented. The review links xenoestrogen exposure to impairments in learning, memory, and executive function, with implications for academic and professional performance, and to heightened anxiety, depression, and mood dysregulation, likely reflecting disruption of the limbic system. Social behavior is also affected, with altered social recognition, interaction, and communication observed across studies. Critically, many of these effects are sex-specific. Estrogen receptor subtypes are distributed differently in male and female brains, particularly in the hypothalamus, hippocampus, and amygdala, and male neurodevelopment depends heavily on the aromatization of testosterone into estradiol, creating distinct points of vulnerability. Prenatal BPA exposure, for example, has been associated with hypomethylation of the estrogen receptor alpha gene in the prefrontal cortex of female rodents but not males, correlating with increased anxiety-like behavior in females. The authors call for sex-stratified analyses to become standard practice in this field.

Timing magnifies the danger. The developing brain passes through tightly choreographed windows, spanning prenatal life, infancy, early childhood, and adolescence, when hormonal signals orchestrate the construction of neural circuits. Exposure during these periods can permanently alter brain structure, neuronal connectivity, and neurotransmitter systems, and the review links prenatal and early-childhood exposures to neurodevelopmental disorders, cognitive deficits, and behavioral abnormalities that persist into adulthood. Fetuses and infants are especially susceptible because their detoxification systems are immature and their brains are maximally plastic, while adolescents face risks during the extensive cortical reorganization of that stage. Regulatory frameworks, the authors argue, have lagged badly behind the science. Agencies such as the United States Food and Drug Administration and Environmental Protection Agency have restricted some compounds, and the European Union and World Health Organization have taken steps of their own, but critics contend these measures are insufficient. Most regulations still test chemicals one at a time and at high doses, missing the low-dose and mixture effects that define real-world exposure, and industry-conducted safety assessments raise conflicts of interest. The pattern of regrettable substitution is a case in point: when BPA was phased out, structurally similar analogs such as BPS and BPF moved in, potentially carrying comparable endocrine-disrupting activity. Legacy pollutants like DDT and PCBs continue to circulate decades after their bans.

What can be done? The review outlines a prevention agenda that spans individual action and structural reform. Reducing exposure means choosing products free of known xenoestrogens, improving manufacturing practices, and strengthening waste management. Public education can empower families, clinicians, and policymakers to make informed choices, while targeted interventions, including dietary modifications and environmental remediation, may help protect the most vulnerable. On the research frontier, the authors identify priorities that include characterizing emerging xenoestrogens, deploying sensitive tools such as neuroimaging and epigenetic profiling, testing whether pharmacological or nutritional therapies can mitigate harm, and untangling the synergistic effects of chemical mixtures. They also flag persistent methodological hurdles: non-monotonic dose responses that defy standard modeling, species differences that complicate extrapolation to humans, and the difficulty of sustaining longitudinal studies long enough to capture chronic and transgenerational outcomes. The bottom line, the authors conclude, is that safeguarding the neurological health of current and future generations demands a coordinated, precautionary response, one that combines rigorous independent research, evidence-based policymaking, international collaboration, and honest public engagement with the invisible chemical landscape that now surrounds every developing brain.

Subject of Research: Neurobehavioral and developmental toxicity caused by xenoestrogen endocrine-disrupting chemicals

Article Title: An overview of neurobehavioral and developmental toxicity induced by xenoestrogens

Article References: Shaw, R., Kamath, A. S., & Chaube, R. (2025). An overview of neurobehavioral and developmental toxicity induced by xenoestrogens. Discover Toxicology, 2(1), Article 10. https://doi.org/10.1007/s44339-025-00025-x

Image Credits: AI Generated

DOI: 10.1007/s44339-025-00025-x

Keywords: xenoestrogens, endocrine-disrupting chemicals, bisphenol A, phthalates, PCBs, estrogen receptors, neurodevelopment, epigenetics, developmental toxicity, neurobehavioral effects, brain development, public health

The research, led by Shimao Xiong, Naiyi Yin, and Yanshan Cui of the College of Resources and Environment at the University of Chinese Academy of Sciences, together with colleagues at Peking University People’s Hospital, set out to answer a deceptively simple question: does arsenic encountered before or shortly after birth program the gut microbial community in ways that persist or even amplify later in life? To find out, the team built a carefully staged exposure model in C57BL/6J mice, one of the most widely used strains in biomedical research. Pregnant females were given drinking water laced with arsenic at an environmentally relevant concentration of 0.10 milligrams per liter, with exposure beginning either on gestational day zero, before embryos had even implanted, or on gestational day fourteen, during late organogenesis. Exposure then continued through lactation, meaning that pups were dosed both in the womb and through their mother’s milk.

The consequences for growth were immediate and, crucially, dependent on when exposure began. Pups whose mothers started drinking arsenic-contaminated water on gestational day zero showed markedly reduced body weight at weaning, while pups exposed only from gestational day fourteen onward actually gained weight significantly faster than controls. That divergence is more than a curiosity. It implies that the earliest embryonic window, when the foundations of metabolism and organ development are being laid, may be uniquely sensitive to arsenic, whereas later prenatal exposure can steer growth in the opposite direction. Because both groups received the same dose, the timing of exposure, not the amount, was the decisive variable, a conclusion with uncomfortable implications for regulatory standards that typically treat a contaminant as a uniform hazard regardless of developmental stage.

The gut microbiome told an equally nuanced story. When the researchers sequenced the 16S ribosomal RNA genes of bacteria in pup feces at three weeks of age, they found that maternal arsenic exposure had elevated gut microbial diversity in the offspring, a counterintuitive result given that reduced diversity is usually framed as a hallmark of a stressed or dysbiotic gut. Arsenic, it appears, does not simply poison the microbial community; it restructures it, opening ecological space for different species. Whether that restructuring is beneficial, harmful, or neutral depends on which microbes move in, and the study’s longer-term experiments suggest the answer differs between the sexes.

To probe those long-term effects, the team extended the experiment beyond weaning. Some pups received only a five-week high-dose arsenic exposure of 10.0 milligrams per liter during adolescence, a level designed to test the impact of a concentrated later-life hit. Others carried the legacy of early-life low-dose exposure from their mothers and then received the same adolescent high dose. Comparing these groups at eight weeks of age revealed that early-life exposure fundamentally changed how the body and its microbes handled the later arsenic assault, and that the changes ran in opposite directions in males and females.

In female pups with the early-life exposure history, the adolescent high dose promoted gut microbial diversity and strengthened the network of interactions among bacterial species, indicating a more interconnected and, in ecological terms, more complex community. At the molecular level, the researchers measured the abundance of arsenic biotransformation genes using a high-throughput quantitative PCR chip that targeted eighty genes involved in arsenic reduction, oxidation, methylation, and transport. In females, genes responsible for reducing arsenate, the pentavalent and generally more toxic form of arsenic, into arsenite were downregulated. Because arsenite is more readily taken up by cells, dampening this reduction pathway coincided with a meaningful outcome: less arsenic accumulated in the females’ kidneys. In other words, the microbial community sculpted by early exposure appeared to blunt the internal dose of the toxin in females, potentially softening the blow of later-life contamination.

Male pups responded in nearly mirror-image fashion. Their gut microbial diversity and network interactions declined under the combined exposure, and instead of retaining arsenic, their bodies excreted more of it in feces, which corresponded with reduced arsenic bioaccumulation in the liver. On the surface, more fecal excretion might sound protective, and for the liver it plausibly was. But the accompanying loss of microbial diversity and the weakening of interaction networks hint at a community under strain, and the study’s authors emphasize that the divergent arsenic metabolic profiles of males and females represent genuinely different biological strategies rather than simply better or worse outcomes. The sex-specific nature of these responses is consistent with a growing body of literature showing that the gut microbiome is shaped by sex hormones and that males and females metabolize xenobiotics differently, but few studies have traced those differences back to exposures occurring before birth.

The technical apparatus behind these conclusions was considerable. The team used inductively coupled plasma mass spectrometry to quantify total arsenic in blood, liver, kidney, and fecal samples, and paired high-performance liquid chromatography with the same detector to separate and measure individual arsenic species, including inorganic arsenate and arsenite and the methylated metabolites monomethylarsonic acid and dimethylarsinic acid. Speciation matters because the toxicity and mobility of arsenic depend entirely on its chemical form, and the gut microbiome is a major site of arsenic methylation and reduction. The researchers also examined histopathology of the ileum and measured the expression of pro-inflammatory cytokines such as IL-8, IL-1 beta, and TNF-alpha, along with transport-related proteins including NaPi-IIb, OATP2B1, and MRP4, which govern how arsenic and its metabolites move across the intestinal barrier. Ecological network analyses of the sequencing data mapped which bacterial groups tended to co-occur or exclude one another, revealing that the architecture of the microbial community, not just its composition, shifted with exposure history and sex.

What emerges from the full dataset is a picture of arsenic as a developmental programming agent whose effects ripple through a biological network spanning metabolism, immunity, and microbial ecology. The authors frame their work as highlighting both the short-term and long-term impacts of arsenic exposure on gut microbiome stability and arsenic metabolic characteristics under different exposure conditions, offering what they call novel insights into the developmental toxicity of early-life exposure. The practical implications are hard to ignore. If the timing of exposure during gestation determines whether offspring grow slower or faster, and if early-life exposure determines whether a later arsenic burden lands in the kidneys or the liver, then risk assessments built on steady-state exposure assumptions may systematically misjudge the hazard, particularly for girls and boys whose responses diverge from the very start.

The study also carries a broader message for microbiome science. The gut microbiome is increasingly recognized as a mediator between environmental chemicals and human health, and this work demonstrates that its mediating role is calibrated by developmental timing and biological sex. For the hundreds of millions of people worldwide whose drinking water exceeds recommended arsenic limits, and for the fetuses and infants exposed in utero and through breast milk, the findings suggest that the microbial consequences of contamination may be set in motion long before symptoms appear, and that protecting the earliest stages of development may be the most effective intervention point. As the researchers and their funders, including the National Natural Science Foundation of China, continue to untangle the mechanisms, the humble gut microbes of laboratory mice have delivered an unmistakable warning: the health effects of arsenic are written differently in males and females, and the writing begins before birth.

Subject of Research: Sex-specific effects of early-life arsenic exposure on body weight, arsenic metabolism, and gut microbiome stability in mice

Article Title: Sex-specific effects of early-life arsenic exposure on body weight, arsenic metabolism, and gut microbiome stability in C57BL/6J mice

Article References: Xiong, S., Jiang, X., Wu, Y., Li, R., Zhao, F., Xiao, P., Yang, Y., Li, Z., Xie, B., Xu, X., Cai, X., Yin, N., & Cui, Y. (2026). Sex-specific effects of early-life arsenic exposure on body weight, arsenic metabolism, and gut microbiome stability in C57BL/6J mice. Microbiome. https://doi.org/10.1186/s40168-026-02535-1

Image Credits: AI Generated

DOI: 10.1186/s40168-026-02535-1

Keywords: arsenic exposure, gut microbiome, developmental toxicity, C57BL/6J mice, sex differences, arsenic metabolism, microbial diversity, prenatal exposure, environmental toxicology, arsenic biotransformation genes, body weight, kidney bioaccumulation

The study, led by Aline Pompermaier of the Federal University of Fronteira Sul in Brazil with collaborators at Purdue University, focused on a commercial premix fungicide containing two active ingredients: azoxystrobin, a strobilurin compound that blocks mitochondrial respiration in fungi, and tebuconazole, a triazole that inhibits sterol biosynthesis in fungal cell membranes. These dual mechanisms, belonging to Fungicide Resistance Action Committee Groups C3 and G1, make the product highly effective against a broad range of crop diseases, from soybean rust to wheat stripe rust. It is registered for use on more than two dozen crops, including cotton, rice, corn, coffee, sugarcane, and grapes, and is sold in countries including Brazil, Australia, Argentina, Canada, Spain, and Germany.

What makes the new work particularly significant is that the researchers tested the product exactly as it is sold—as a ready-made formulation containing 120 grams per liter of azoxystrobin, 200 grams per liter of tebuconazole, and a substantial fraction of undisclosed excipients. Most previous ecotoxicology studies have either tested single active ingredients or combined pure compounds in the laboratory. Commercial premixes, by contrast, enter waterways as complete formulations, and the inert ingredients they contain can modify how the active substances are absorbed and how toxic they become. The authors argue this distinction matters, and their results suggest it does.

The exposure regime was designed around environmental reality. Zebrafish embryos were placed in solutions containing 30, 100, or 180 micrograms per liter of the fungicide, with concentrations benchmarked against the highest dose of the mixture component, tebuconazole. The two lower levels correspond to tebuconazole concentrations actually measured in surface and groundwaters in Brazil and elsewhere, while the highest matches Brazil’s maximum allowable limit for tebuconazole in drinking water. Notably, all three levels fall well below concentrations of azoxystrobin recorded in some Brazilian agricultural watersheds, where average detections have reached 1,055 micrograms per liter and peaks of 6,672 micrograms per liter—values that dwarf the experimental doses.

Embryos were exposed from 3 to 120 hours post-fertilization, a window covering the critical organogenesis phase when the nervous system, heart, and other organs take shape. The zebrafish is an ideal model for such work: its embryos are transparent, develop externally, and within days display species-specific behaviors that can be quantified with simple video recording. The team monitored 110 embryos per group for survival and hatching, tracked spontaneous movement in 20 embryos per group under a stereomicroscope at 24 hours post-fertilization, and counted heartbeats at 72 hours. Later, they filmed shoaling behavior at five days and tested antipredator responses at seven days using a moving red sphere displayed on a monitor beneath the test plates.

The survival results were stark. Kaplan-Meier analysis revealed that larvae exposed to 100 and 180 micrograms per liter died at significantly higher rates than controls. In the 100 microgram per liter group, the hazard ratio indicated a 70 percent lower probability of survival compared with unexposed animals; at 180 micrograms per liter, survival probability dropped by 63 percent. These are not laboratory extremes—they are concentrations of tebuconazole documented in real waterways and legally permitted in Brazilian tap water. Hatching, remarkably, was unaffected, meaning the fungicide killed embryos after they emerged rather than preventing emergence itself. The authors point out that azoxystrobin, unlike tebuconazole, has no established regulatory limit in drinking water in Brazil, a regulatory gap they describe as a genuine threat to aquatic life.

Equally troubling were the sublethal effects on developing physiology. At the highest concentration, embryos showed significantly reduced spontaneous movement, the early wriggling behavior controlled by the nascent nervous system. Because this reflexive coiling is orchestrated by developing neural circuits, its suppression is widely interpreted as an early warning sign of neurotoxicity or broader developmental impairment. Heart rate told a stranger story: exposure to 30 micrograms per liter slowed larvae heartbeats, while 100 micrograms per liter sped them up. This non-monotonic, potentially biphasic pattern mirrors hormetic responses documented in fish embryos exposed to other contaminants, and the authors caution that the underlying mechanism—whether adaptive compensation, direct cardiotoxicity, or oxidative stress—remains unresolved and warrants dedicated investigation.

The behavioral findings may be the most ecologically provocative. In the shoaling test, larvae exposed to 100 and 180 micrograms per liter bunched significantly closer together than controls, with reduced average distance between individuals. Zebrafish are intensely social animals, and tight shoaling is their primary defense against predators. But abnormally heightened cohesion can signal an anxiety-like state—a baseline perception of danger that persists even when no threat exists. The researchers suggest the exposed larvae behaved as though a predator were always present. Intriguingly, when the team later confronted the animals with an actual simulated threat in the aversive stimulus test, the exposed larvae responded normally, dodging away from the moving sphere just like controls. This dissociation is telling: it indicates the fungicide did not paralyze the animals or destroy their motor capacity, but rather shifted their default behavioral state, plausibly through dysregulation of cholinergic neurotransmitter pathways that govern anxiety and sociability.

The mechanistic picture drawn from prior literature is consistent with this interpretation. Azoxystrobin has been shown to disturb acetylcholinesterase activity, elevate reactive oxygen species, and disrupt dopaminergic signaling in zebrafish brains, while tebuconazole is known to inhibit acetylcholinesterase in larvae, induce oxidative stress in carp and zebrafish, and cause neurochemical and behavioral alterations. A mixture combining a mitochondrial respiratory inhibitor with a sterol biosynthesis inhibitor may therefore impose a dual burden—neural and oxidative—on embryos whose defenses are still under construction, potentially overwhelming redox homeostasis and cardiac regulation simultaneously. The authors are careful to note that they did not measure biochemical biomarkers directly, framing these pathways as plausible hypotheses grounded in the literature rather than confirmed mechanisms, and they call for follow-up work measuring acetylcholinesterase activity, antioxidant enzymes, lipid peroxidation, and gene expression.

The ecological and regulatory implications are difficult to overstate. A fish larva locked in a perpetual state of vigilance burns energy that should fuel growth and reproduction, and an abnormally cohesive shoal may become easier for predators to spot or less efficient at finding food. Reduced larval survival at environmentally realistic concentrations, meanwhile, can ripple through food webs and disrupt trophic cascades. The study’s central message is that environmental risk assessment must evolve beyond testing isolated active ingredients and counting corpses. Sublethal endpoints—heart function, embryonic movement, social behavior—capture harms that mortality statistics miss entirely, and commercially formulated mixtures must be evaluated as the integrated chemical systems they are. As the authors conclude, premix fungicides entering the environment as ready-made cocktails may act additively or synergistically on aquatic fauna, and regulatory frameworks that ignore this reality leave ecosystems—and potentially drinking water supplies—protected by standards built for a simpler chemical age.

Subject of Research: Toxicological effects of a commercial azoxystrobin-tebuconazole fungicide mixture on zebrafish physiology and behavior

Article Title: Beyond mortality: A fungicide mixture alters physiology and causes impaired behavior in zebrafish

Article References: Beyond mortality: A fungicide mixture alters physiology and causes impaired behavior in zebrafish. (n.d.). https://doi.org/10.1007/s10646-026-03147-z

Image Credits: AI Generated

DOI: 10.1007/s10646-026-03147-z

Keywords: zebrafish, fungicide mixture, azoxystrobin, tebuconazole, ecotoxicology, pesticides, shoaling behavior, developmental toxicity, heart rate, neurotoxicity, water contamination, environmental risk assessment