PFAS are a large family of manufactured chemicals that have been used for decades in consumer and industrial products because of their remarkable resistance to heat, water, and grease. Nonstick cookware, stain-resistant carpets and fabrics, water-repellent clothing, and grease-resistant food packaging all rely on these compounds, and the same properties that make them useful in manufacturing also make them extraordinarily persistent in the environment and in the human body. Because certain PFAS break down extremely slowly, they can accumulate over years of repeated exposure, entering the body through contaminated drinking water, food, household dust, and air. This persistence has earned them the popular nickname of forever chemicals, and biomonitoring surveys have detected them in the blood of nearly all residents of industrialized countries.

The health stakes of early-life exposure are considerable. Previous research has linked certain PFAS in childhood with weaker responses to routine vaccines, an increased risk of asthma, and measurable changes in metabolism and thyroid function, both of which play central roles in growth and development. Some members of the chemical family are also considered carcinogens, meaning that reducing exposure during childhood, when the body is still developing, is widely regarded by public health researchers as a priority. The George Mason study did not set out to measure health effects in the children themselves. Instead, its value lies in identifying where the exposure may be coming from and, crucially, which everyday circumstances appear to protect against it, information that can guide practical interventions for families and communities.

To pursue those questions, the research team analyzed blood samples from 106 Hispanic children between the ages of four and eleven, all living in Prince William County, Virginia. Most of the children had obesity and were taking part in a family lifestyle program, which provided the opportunity to collect both biological samples and detailed information about diet, language use, and family history. Among the mothers who reported their birthplace, roughly two-thirds had been born in El Salvador, reflecting the distinctive demographic profile of the local Central American community. This combination of blood measurements and richly detailed household data allowed the researchers to look for patterns linking specific foods, school meal participation, and immigration-related factors to the concentrations of individual PFAS compounds detected in the children’s blood.

One of the most striking and consistent findings concerned school meals. Children who received free or reduced-price lunches had lower blood concentrations of five different PFAS compounds, and participation in school breakfast programs was associated with lower levels of another. The authors suggest that the meals provided through these federal programs may reduce families’ reliance on individually packaged foods, which are a recognized potential route of PFAS exposure because grease-resistant packaging can transfer chemicals into food. The researchers are careful to note that they did not directly test that explanation, so it remains a plausible hypothesis rather than a demonstrated mechanism. Even so, the consistency of the association across multiple compounds suggests that school meal programs, which serve tens of millions of American children every day, may play an unappreciated protective role in limiting exposure to environmental contaminants.

Dietary patterns beyond the school cafeteria also left their mark on the children’s chemical profiles, although the relationships varied depending on the specific compound. Greater consumption of cheese was linked to higher levels of one PFAS, while eating more fish was associated with a higher likelihood of detecting another, a pattern consistent with the broader scientific literature, since fish and other animal-based foods can accumulate certain PFAS from contaminated water and feed. Greater consumption of burritos was associated with higher total PFAS, an intriguing result that the authors suggest could reflect the packaging and preparation methods associated with such foods, although the study design cannot pin down the exact pathway. Overall, eating more animal-based foods was associated with higher levels of some PFAS, reinforcing the idea that dietary composition is a meaningful determinant of body burden in children.

Perhaps the most novel dimension of the study concerns the social and immigration-related factors that shaped exposure. Children with stronger English skills had lower levels of one PFAS compound, and for another chemical known as PFBS, the differences were even more pronounced. Hispanic children born in the United States had 75 percent lower odds of PFBS being detected in their blood compared with Hispanic children born elsewhere. Moreover, each additional year that a child’s mother had lived in the United States was associated with an 8 percent lower odds of detecting PFBS. These findings suggest that the circumstances surrounding immigration, including the foods available to families before and after arrival, the neighborhoods they live in, and the resources they can access, may all influence how much of these chemicals children absorb. The researchers emphasize that understanding what families eat and the resources available to them is essential if interventions are to work, and Mohsin argues that the study highlights the necessity of community-informed approaches, such as those targeting dietary habits, to mitigate exposure.

Like all cross-sectional research, the study offers a snapshot rather than a moving picture, and the authors are explicit about its limits. Because the measurements were taken at a single point in time, the analysis cannot show whether particular foods or family circumstances actually caused the differences in PFAS levels, only that they were associated. The sample was also small and drawn from a single county, so the findings may not generalize to Hispanic communities elsewhere in the country or to children of other backgrounds. The dietary questionnaire, like most such instruments, may not have captured culturally specific foods that are important in Central American households, potentially leaving some exposure sources unmeasured. The researchers call for larger studies that follow children over time, and for future work to examine drinking water, household products, and the culturally specific foods missing from the current questionnaire.

Even with those caveats, the study opens an important window onto a population that environmental health research has rarely examined in detail. It suggests that the same institutions designed to support low-income families, such as school meal programs, may simultaneously be shielding children from chemical exposure, and that the health of immigrant children may be shaped in part by the environmental conditions of their countries of birth and the length of their families’ residence in the United States. For public health practitioners, the message is that reducing PFAS exposure is not simply a matter of individual choices but of understanding the full context of family life, from the grocery aisle to the classroom cafeteria. As regulators continue to tighten limits on PFAS in drinking water and consumer products, studies like this one demonstrate that exposure is woven into the fabric of daily routines, and that culturally informed, community-based strategies will be essential to untangle it.

The research was a collaborative effort involving multiple departments at George Mason University and beyond. Mohsin and Bloom’s coauthors include faculty members Jenna R. Krall and alum Lameck Chiwaka of the Department of Global and Community Health, Allison J. McKay of the Department of Nutrition and Food Studies, Margaret T. Jones of the College of Education and Human Development, and Robyn Mehlenbeck of the Department of Psychology, along with Virginia Espina and Veronica G. Sanchez of the Center for Applied Proteomics and Molecular Medicine. Additional researchers included Roy R. Gerona and Daniel Tomer of the University of California, San Francisco, and Sina Gallo of the University of Georgia. Mohsin, who earned her PhD in public health with a concentration in epidemiology, is now a postdoctoral research associate at Washington University in St. Louis, where she continues to build on the kind of community-centered exposure science that this study exemplifies. As forever chemicals remain a fixture of the modern environment, work like this makes clear that the path to safer childhoods runs through kitchens, classrooms, and communities alike.

Subject of Research: Dietary and social predictors of PFAS exposure in Hispanic children

Article Title: Study finds diet and culture influences Hispanic children’s exposure to 'forever chemicals'

Article References: Study finds diet and culture influences Hispanic children’s exposure to 'forever chemicals'. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: PFAS, forever chemicals, Hispanic children, school meals, diet, environmental epidemiology, Central American families, immigration, PFBS, George Mason University, exposure science, public health

The research team, led by Simon R. Evans with Henri Bouwmeester, Arie J. van Noordwijk, Marcel E. Visser and Erik Postma, took advantage of one of the longest-running and most intensively monitored wild bird study systems in the world. Great tits breeding in nest boxes across Dutch study populations have been recorded in extraordinary detail for generations, allowing researchers to link individual birds to their reproductive output, their genetic pedigree and their origins. Clutch size, the number of eggs a female lays, is a classic life-history trait: it is heritable, it varies consistently among females, and it is under persistent natural selection, making it an ideal trait for testing whether evolutionary predictions hold in the wild.

The paradox of stasis arises because standard quantitative genetic models make a clear prediction. If a trait is heritable and selection consistently favours particular values, the breeding values of the population, meaning the average genetic propensity of individuals, should shift generation after generation in the direction favoured by selection. Yet in study after study, from birds and mammals to plants, measurable genetic change in fitness-related traits falls far short of these expectations. The new study is unusual in that it does not merely observe stasis after the fact. Instead, it quantifies interannual genetic change in clutch size directly and compares it against explicit adaptive forecasts, distinguishing absolute stasis, where no directional genetic change occurs at all, from relative stasis, where change occurs but is weaker than predicted.

The results reveal a nuanced picture. Interannual genetic changes in clutch size were directionally consistent with the direction of selection, which refutes the idea of absolute stasis: the population was not frozen in evolutionary time. However, the magnitude of those genetic changes was consistently smaller than adaptive evolutionary models predicted, supporting relative stasis. In other words, evolution was happening, but it was happening more slowly than the textbook equations suggested it should. This tendency toward overprediction is precisely the pattern that has fuelled decades of debate, and the great tit data now provide a direct, quantified example of it in a free-living vertebrate population.

The breakthrough came from recognising a distinction that is often blurred in evolutionary studies: the difference between adaptation and evolution. Adaptation refers to populations becoming better matched to their environments, which can occur through selection on the individuals already present. Evolution, in the genetic sense, refers to changes in the genetic composition of the population, and that composition is shaped not only by selection but also by which individuals arrive, survive and breed. When new immigrants enter a population after selection has acted on the resident birds, they carry genes that were not filtered by local selection. The researchers term this post-selective immigration, and explicitly accounting for it dramatically improved the accuracy of their forecasts of genetic change.

By decomposing the interannual genetic change in clutch size into its contributing demographic processes, the team showed that immigration was the key variable explaining periods of both evolutionary stasis and evolutionary change. In years when many immigrants arrived, the genetic composition of the breeding population was reshuffled, diluting or reversing the genetic changes that selection had produced among residents. In years when immigration was low, selection’s signature could express itself more fully in the population’s genetic makeup. The evolutionary impact of gene flow therefore varied across time and space in a manner directly analogous to the well-known dynamism of natural selection itself, which fluctuates in strength and direction from year to year and from place to place.

This finding has profound implications for how evolutionary biologists interpret long-term monitoring data. Most studies of contemporary evolution in the wild estimate selection and genetic change within a defined study area, treating the population as a closed system. But real populations are rarely closed. Individuals disperse, and in a species such as the great tit, with its strong natal dispersal and its patchy distribution across habitat fragments, the arrival of first-time breeders from outside the study plots can constitute a substantial fraction of each new generation. If those immigrants differ genetically from residents, and if their numbers fluctuate, then gene flow becomes a dynamic evolutionary force in its own right rather than a static background parameter.

The study also helps resolve why the paradox of stasis has proved so stubborn. If stasis is identified a posteriori, simply as the gap between predicted and observed change, then any number of explanations can be invoked, from fluctuating selection to unmeasured environmental covariance between trait and fitness. The great tit study shifts the framing: rather than asking why selection fails to produce change, it asks how the demographic processes that build the breeding population each year transform selection into evolution. When post-selective immigration is included, the apparent mismatch between adaptive prediction and genetic reality shrinks, suggesting that much of the paradox may be an artefact of treating populations as closed and of conflating the response of residents to selection with the evolution of the population as a whole.

The experimental component of the study deserves particular emphasis. Because the researchers examined the populations before, during and after an experimental evolutionary perturbation, they could observe how the system responded to a deliberate disturbance in the selective regime, rather than relying solely on natural variation. This before-during-after design strengthens causal inference in a field where experiments on wild populations are rare and where most evidence is correlational. It allowed the team to test whether the contribution of gene flow changed predictably as the evolutionary dynamics of the population were perturbed, and the answer was that immigration’s role remained pivotal throughout, modulating the pace of genetic change in every phase.

Clutch size is not an incidental choice of trait. It is a key determinant of life history, shaping how many offspring a female attempts to raise and, ultimately, her contribution to the next generation. That gene flow is crucial to explaining the contemporary evolution and stasis of such a central fitness component suggests the same processes may operate broadly across wild populations and across many traits. For conservation biologists, the message is equally significant: fragmented populations connected by dispersal are not simply reservoirs of variation, they are dynamic evolutionary systems in which the timing and magnitude of movement can determine whether adaptation keeps pace with environmental change or falls behind. As climates shift and habitats transform, understanding how gene flow interacts with selection will be essential for predicting which populations can evolve quickly enough to survive. This study, grounded in decades of meticulous fieldwork on a familiar backyard bird, demonstrates that the answer to one of evolution’s oldest puzzles may lie not in the strength of selection alone, but in the constant traffic of individuals moving across the landscape.

Subject of Research: The role of gene flow in evolutionary stasis and change of clutch size in wild great tit populations

Article Title: Gene flow drives periods of both evolutionary stasis and change in a wild bird population

Article References: Evans, S. R., Bouwmeester, H., van Noordwijk, A. J., Visser, M. E., & Postma, E. (2026). Gene flow drives periods of both evolutionary stasis and change in a wild bird population. PLOS Biology, 24(9), e3004004. https://doi.org/10.1371/journal.pbio.3004004

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004004

Keywords: great tits, gene flow, paradox of stasis, clutch size, evolutionary biology, natural selection, immigration, life history, quantitative genetics, wild populations, PLOS Biology, long-term study

The research, led by Oguzhan Ekizoglu together with Marine Dario, Maxime Pastor, Catherine Cyteval, and Laurent Martrille, focused on a bone that has been comparatively neglected in the MRI-based age estimation literature: the proximal humerus, the ball-shaped top of the upper arm bone. While the hand-wrist region and the knee have been extensively mapped with MRI for forensic purposes, the shoulder has received far less systematic attention, particularly in Western European populations. The team retrospectively analyzed 346 shoulder MRI examinations drawn from a French cohort spanning the ages of 7.18 to 33.82 years, comprising 204 males and 142 females. Because the scans had been acquired for clinical reasons and were fully anonymized, the ethics committee of CHU Montpellier approved the study and waived the need for individual informed consent, an approach consistent with the Declaration of Helsinki.

The technical backbone of the study is the combined Schmeling–Kellinghaus staging system, a widely used framework originally developed for the medial end of the collarbone. In this system, ossification of the epiphysis, the secondary growth center that fuses to the main bone shaft after puberty, is graded in discrete stages, from an entirely cartilaginous growth plate through progressive partial fusion to complete union, with an optional subdivision for the earliest signs of fusion. On T1-weighted MRI sequences, the developing bone and the cartilaginous plate between epiphysis and metaphysis produce distinct signal intensities, allowing a trained observer to assign each shoulder to a stage. Two independent raters, blinded to each subject’s age and sex, staged all 346 scans, providing a direct test of how reproducible the method is when applied to the humeral head.

The results were strikingly consistent. The correlation between chronological age and ossification stage was strong and statistically significant across the whole sample, with a Spearman’s rank correlation coefficient of 0.878, and nearly identical values of 0.880 in males and 0.878 in females, all with p-values below 0.001. In practical terms, this means that as the humeral epiphysis progresses through its developmental stages, age increases in a tight, predictable relationship, and that this relationship holds equally well for both sexes. Statistical testing with the Mann–Whitney U method found no significant difference between males and females in the ages associated with any given stage, a finding that simplifies the application of the system, since a single set of stage descriptions may suffice for both sexes in this population.

Reliability, the measure of whether different observers reach the same conclusion from the same image, was equally impressive. Cohen’s kappa, a statistic that quantifies agreement beyond what would be expected by chance, reached 0.911 within observers rating their own scans twice and 0.890 between the two independent raters. Values above 0.8 are conventionally considered to indicate very good agreement, and these figures place the proximal humerus staging on par with, or better than, many established forensic imaging indicators. For a method that might one day inform legal decisions with life-changing consequences, this level of observer agreement is not a technical nicety but an essential prerequisite, because inconsistent readings between experts would undermine the credibility of any age estimate offered in court.

The most legally consequential finding concerns the age of majority, the threshold at 18 years that separates minors from adults in most jurisdictions. In this cohort, the youngest individual showing stage 4, defined by the presence of a visible epiphyseal scar after fusion, was 18.33 years in males and 18.06 years in females. In other words, once the epiphyseal scar is visible on the proximal humerus, the data suggest the person has very likely passed their eighteenth birthday. Notably, stage 5, the final stage of the amplified scheme, was never observed despite the cohort including individuals up to nearly 34 years of age, an observation the authors interpret in light of the persistent visibility of the epiphyseal scar in adult shoulders and the anatomical characteristics of trabecular bone in this region.

Beyond the conventional minimum-age approach, the team applied an ordinal probit transition analysis, a statistical framework borrowed from paleodemography that models the probability of moving from one ossification stage to the next as a function of age. Rather than relying on the single youngest individual observed at a stage, a figure that is highly sensitive to how many older or younger people happen to be in the sample, transition analysis yields sex-specific ages at which the probability of progression to the next stage reaches 50 percent. This provides a more statistically robust characterization of the timing of skeletal maturation and has been increasingly advocated in forensic age research, including recent work on third molars and other skeletal indicators. The authors are careful, however, to stress that both minimum-age and transition-age estimates derived from any single cohort should not be applied as forensic thresholds without independent, population-specific validation, a caution that reflects the well-documented variation in skeletal maturation across populations and socioeconomic conditions.

Perhaps the most original contribution of the study is the description of a previously unreported interpretive pitfall. The authors identified a trabecular hypointense pattern, a dark appearance of the internal bone architecture on T1-weighted images, that can potentially mimic a persistent gap between the epiphysis and the metaphysis, the appearance that would normally indicate an unfused, and therefore juvenile, growth plate. Mistaking this normal variant for an open growth plate could lead an examiner to underestimate a person’s age, with serious implications in asylum or criminal proceedings. The paper includes recommendations for recognizing this pattern, underscoring that even a highly reliable staging system depends on the examiner’s ability to distinguish true developmental landmarks from imaging artifacts and anatomical variants of the cancellous bone in the proximal humerus.

The broader context of this work is a slow but decisive shift in forensic practice. European radiation protection directives and international basic safety standards from bodies such as the International Atomic Energy Agency have sharpened the ethical and legal scrutiny applied to X-ray-based age assessments in healthy young people, pushing researchers toward MRI as a non-ionizing alternative. Previous MRI studies of the proximal humeral epiphysis, including earlier work by Ekizoglu and colleagues on Turkish cohorts and studies from China and Turkey using both 1.5 and 3.0 Tesla scanners, have demonstrated the promise of the approach, but population-specific data remained sparse for Western Europe. By extending the combined Schmeling–Kellinghaus system to a French cohort for the first time, the Montpellier team has filled an important geographic gap and shown that the staging framework travels well across populations, at least in terms of correlation strength and observer reliability.

What remains before shoulder MRI can enter routine forensic use is a matter of validation and standardization rather than proof of concept. Large, independently collected cohorts from different populations will be needed to confirm the minimum ages and transition probabilities reported here, and the newly described trabecular pitfall will need to be characterized across scanner types and imaging protocols. Cost and scanner availability also remain practical constraints, since MRI is more expensive and less widely accessible than plain radiography. Nevertheless, the study offers a compelling vision of the field’s future: a radiation-free, highly reproducible, and anatomically well-characterized method for answering one of forensic science’s most sensitive questions. For the hundreds of thousands of young people whose ages are contested each year in legal systems worldwide, the humeral head, imaged safely with magnets rather than X-rays, may soon become a key witness.

Subject of Research: Non-ionizing forensic age estimation using T1-weighted MRI of the proximal humeral epiphysis in a French cohort

Article Title: T1-Weighted MRI of the proximal humerus: Toward a non-ionizing approach to forensic age estimation in a French cohort

Article References: Ekizoglu, O., Dario, M., Pastor, M., Cyteval, C., & Martrille, L. (2026). T1-Weighted MRI of the proximal humerus: Toward a non-ionizing approach to forensic age estimation in a French cohort. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-03996-7

Image Credits: AI Generated

DOI: 10.1007/s00414-026-03996-7

Keywords: forensic age estimation, MRI, proximal humerus, epiphyseal fusion, Schmeling-Kellinghaus staging, age of majority, transition analysis, non-ionizing imaging, forensic medicine, immigration, radiation protection, French cohort