During meiosis, the process by which sperm are made, chromosomes must sort themselves with extraordinary precision. Each mature sperm cell is supposed to carry exactly 23 chromosomes: one sex chromosome, either X or Y, and 22 others. When the sorting goes wrong, a sperm ends up with an extra chromosome, sometimes two sex chromosomes instead of one, sometimes none at all. Most of the time this matters little; aneuploid sperm rarely fertilise successfully. But when they do, the consequences can include Klinefelter syndrome, Turner syndrome, or, more often, miscarriage. The causes of this chromosomal mis-sorting have remained largely mysterious. Now, a study following 96 men from birth into their early twenties suggests part of the answer was already written into their bodies before they drew their first breath.
The men grew up in the Faroe Islands, an archipelago in the North Atlantic where traditional diets heavy in pilot whale and contaminated seafood exposed residents to some of the highest levels of persistent organic pollutants ever documented in a general population. Their mothers had enrolled in a birth cohort study back in 1986 and 1987, providing blood samples during pregnancy. Those samples, and later blood samples taken from the boys themselves at ages 7, 14, and again in early adulthood, captured a detailed chemical record spanning decades. What the researchers found when they examined the men’s sperm in 2009 and 2010 was, by any measure, unsettling.
What the Chromosomes Revealed
Higher concentrations of polychlorinated biphenyls (PCBs) in cord blood at birth were associated with a significant increase in the proportion of sperm carrying an extra Y chromosome, a pattern that persisted and extended across the childhood years. The connection was dose-dependent: the more PCB exposure, the worse the chromosomal sorting appeared to be. PFAS chemicals (perfluorinated alkyl substances, the so-called forever chemicals that coat non-stick pans, food packaging, and waterproof clothing) showed a somewhat different pattern. Rather than concentrating their signal in the fetal period, PFAS levels in adulthood were most strongly associated with sperm carrying extra copies of either sex chromosome. The researchers, led by Melissa Perry, dean of the College of Public Health at George Mason University, describe the findings as, in Perry’s words, “new evidence that fetal and subsequent chemical exposures can have an enduring influence into adulthood on the genetic integrity of sperm.”
That phrase, “enduring influence,” is doing a lot of work here. The implication is that damage inflicted on the developing testis, in utero, does not resolve or reset. It compounds.
The study is believed to be the first in humans to directly link prenatal organochlorine exposure to chromosomal abnormalities in sperm produced twenty-odd years later. Animal work had pointed in this direction for some time: prenatal PCB exposure in mice caused sperm damage that persisted across at least two subsequent generations, and rodent studies with individual PCB congeners produced similar results. But translating that picture to humans required a cohort study long enough, and detailed enough, to bridge fetal life and young adulthood. The Faroese cohort, which has been running for nearly four decades, was one of very few that could do it.
Why These Chemicals Are So Difficult to Escape
PCBs were industrial chemicals, widely used in electrical equipment and building materials, formally banned in most countries in the late 1970s. The bans helped; concentrations in the Faroese men fell measurably between ages 7 and 22. But “fell” is relative. These compounds persist in fat tissue, accumulate up the food chain, and cross the placenta. A mother who ate contaminated whale meat in 1986 passed her chemical burden to her fetus. That fetus, now a man in his mid-twenties, carries the biological signature of a meal his mother ate before he was born. PFAS chemicals are, if anything, worse: roughly 15,000 variants exist, many still in active production, and the name “forever chemicals” reflects the fact that they do not meaningfully break down in the environment or the body.
Perry’s team found that PFAS exposure in early childhood, likely transferred via breast milk in addition to in utero exposure, showed independent effects from PCBs on chromosomal disomy rates. The two chemical classes appear to act through partially overlapping but distinct mechanisms, both involving disruption of endocrine signalling in the developing testis. PCBs, in particular, can interfere with androgen and thyroid hormone pathways, both critical for the early differentiation of sperm-producing cells called Sertoli cells. Damage to Sertoli cells during fetal development, the hypothesis goes, subtly impairs the machinery of meiosis for life.
The study was not designed to, and cannot, establish causation. The Faroe Islands population is ethnically homogenous and their chemical exposures are higher than what most people encounter, which limits how directly the findings generalise. The sample of 96 men is also relatively small, though the statistical associations across multiple chromosome types and multiple time points give the results a robustness that numbers alone might not convey. A previous study by some of the same researchers found similar associations between adult PCB exposure and sperm disomy among men attending a US fertility clinic, where chemical levels were much lower, and on par with the general American population. That parallel matters.
The Longer Shadow
Aneuploidy in sperm is the leading cause of the chromosomal abnormalities that account for roughly half of all preterm pregnancy losses. The conditions it can produce when fertilisation succeeds, Klinefelter syndrome (XXY) most commonly, are being diagnosed at rising rates in some countries. Whether that reflects better detection, genuinely increasing incidence, or both remains disputed. What is increasingly less disputed is that male reproductive health has been declining across Western populations for at least 50 years. Sperm counts, by most analyses, have roughly halved over that period. Chromosome quality, far less studied than count or motility, may be part of that picture in ways research is only beginning to capture.
The Faroese data, if it holds up in larger and more diverse populations, would suggest that the chemical environment a man encountered before he was born helps determine how accurately his sperm sort chromosomes decades later. “Chemical exposure is a public health issue,” Perry said, “and there are strong associations with declining sperm concentration and quality. We really need to look toward policy solutions that prevent these chemicals from entering our environment and prevent related harms.” What those policies would look like for PFAS, a class still in widespread production and use, remains one of the more pressing unsettled questions in environmental health. The chemicals are in the water, in the packaging, already in the blood. The children who will one day provide their own sperm samples are being exposed right now.
Source: Perry MJ et al. “In utero and childhood exposure to organochlorines and perfluorinated chemicals in relation to sperm aneuploidy in adulthood.” Environmental Health (2026). https://doi.org/10.1186/s12940-026-01303-w
Frequently Asked Questions
Does this mean men whose mothers ate contaminated fish can’t have children?
Not necessarily. The study found an increased proportion of chromosomally abnormal sperm among men with higher chemical exposures, not that all their sperm were affected or that fertility was eliminated. Most sperm in any man are chromosomally normal, and many men with elevated disomy rates will still conceive without difficulty. The concern is about risk at a population level, and about what happens when aneuploid sperm do succeed in fertilising an egg.
Are PFAS chemicals in non-stick pans a serious exposure route?
Cookware is one source, but probably not the dominant one for most people. PFAS compounds enter the body primarily through contaminated drinking water, food packaging, and certain consumer products, with drinking water being the most significant route in areas where PFAS contamination has been documented. The chemicals accumulate in the body over time, so cumulative lifetime exposure matters more than any single source.
Could improving diet during pregnancy actually reduce this kind of risk in future generations?
In principle, yes, though it depends heavily on which chemicals are involved. Reducing consumption of large predatory fish during pregnancy does lower PCB and mercury exposure, and public health advisories in the Faroe Islands have moved in that direction since 1998. For PFAS, dietary changes help at the margins, but the chemicals are so pervasive that meaningful exposure reduction likely requires regulatory action to remove them from production and remediate contaminated water supplies.
Why does fetal exposure matter more than adult exposure for this kind of damage?
The cells that will eventually produce sperm, called primordial germ cells, are established and begin differentiating during fetal life. If the chemical environment disrupts that early development, the effects on how those cells handle chromosomes during meiosis may be permanent, because the foundational biology was already set. This is broadly analogous to how fetal alcohol exposure can affect brain development in ways that persist despite no further alcohol exposure after birth.
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