Early-Life Arsenic Exposure Reshapes the Gut Microbiome in Sex-Specific Ways

Arsenic is one of the most widespread environmental contaminants on Earth, seeping into groundwater across large swaths of Asia, South America, and the United States, and reaching millions of people through the water they drink and the rice and other crops they eat. While the element’s links to cancer, cardiovascular disease, and developmental problems have been documented for decades, the biological machinery that translates exposure into harm remains only partially understood. Now, a team of researchers in China has added a striking new piece to that puzzle, showing that the timing of arsenic exposure early in life can leave sex-specific fingerprints on body weight, arsenic metabolism, and the stability of the gut microbiome in laboratory mice. The findings, published in the journal Microbiome, suggest that the trillions of microbes inhabiting the intestine are not passive bystanders in arsenic toxicity but active participants whose behavior diverges sharply between males and females.

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