Outdoor air pollution and brain development in childhood and adolescence

Commentary: Air pollution and neurodevelopmental disorders: a cause for concern in an urbanising world

The world's population is rapidly urbanising, especially in low- to middle-income countries. However, urban living is associated with an increased risk of neurodevelopmental disorders (NDD) like autism spectrum disorders (ASD) and schizophrenia. Exposure to urban air pollutants like particulate matter has been positively associated with both ASD and schizophrenia diagnosis rates. Mechanistic studies have shown that particulate matter exposure leads to brain inflammation and white matter pathologies consistent with these disorders. Children are especially susceptible to these effects due to their rapidly developing nervous systems. Despite this, few reviews on the subject recommend future steps to mitigate the teratogenic effects of particulate air pollution. This commentary both synthesises evidence and recommends research and policy goals to protect children, both present and future, from the neurodevelopmental consequences of particulate air pollution. These steps include further study of the relationship between air pollution and equitable resource distribution to address the coming global rises in NDD. Furthermore, capacity building in urbanising nations is essential to overcome barriers erected by resource extraction and pollution outsourcing by wealthy nations. With such an integrated approach, progress can be made in protecting the developing nervous systems of children and future generations in both affluent and resource-strained nations.

A systematic review of air pollution exposure and brain structure and function during development

OBJECTIVES

Air pollutants are known neurotoxicants. In this updated systematic review, we evaluate new evidence since our 2019 systematic review on the effect of outdoor air pollution exposure on childhood and adolescent brain structure and function as measured by magnetic resonance imaging (MRI).

METHODS

Using PubMed, Web of Science, and Scopus we conducted an updated literature search and systematic review of articles published through January 2025, using key terms for air pollution and functional and/or structural MRI. Two raters independently screened all articles using Covidence and implemented the risk of bias instrument for systematic reviews used to inform the World Health Organization Global Air Quality Guidelines.

RESULTS

We identified 29 relevant papers, and 20 new studies met our inclusion criteria. Including six studies from our 2019 review, the 26 publications to date include study populations from the United States, Netherlands, Spain, and United Kingdom. Studies investigated exposure periods spanning pregnancy through early adolescence, and estimated air pollutant exposure levels via personal monitoring, geospatial residential estimates, or school courtyard monitors. Brain MRI occurred when children were on average 6-14.7 years old; however, one study assessed newborns. Several MRI modalities were leveraged, including structural morphology, diffusion tensor imaging, restriction spectrum imaging, arterial spin labeling, magnetic resonance spectroscopy, as well as resting-state and task-based functional MRI. Air pollutants were associated with widespread brain differences, although the magnitude and direction of findings are largely inconsistent, making it difficult to draw strong conclusions.

CONCLUSION

Prenatal and childhood exposure to outdoor air pollution is associated with structural and functional brain variations. Compared to our initial 2019 review comprised of only cross-sectional studies, the current literature now includes longitudinal studies and more advanced neuroimaging methods. Further research is needed to clarify the effects of developmental timing, along with the downstream implications of outdoor air pollution exposure on children's cognitive and mental health.

Early life exposure to fine particulate matter and fine motor function, attentional function, and working memory among Spanish school-aged children

Background

Evidence of the association between fine particulate matter (PM2.5) exposure and child neuropsychological function is equivocal. We examined early life PM2.5 exposure in relation to fine motor function, attention, and working memory in early childhood.

Methods

We used data from the Spanish INfancia y Medio Ambiente Project, 2003-2008. Exposure to PM2.5 (μg/m3) was assessed using spatiotemporal land-use random forest models and assigned based on residential address histories. Around age six, children completed the finger tapping test, attentional network test (ANT), and n-back task to evaluate fine motor speed, attention, and working memory, respectively. A total of 1,310 children had data from at least one neuropsychological assessment. General linear models were applied to assess associations between average prenatal and postnatal PM2.5 with each outcome. Distributed lag nonlinear models were used to explore refined periods of susceptibility to PM2.5. We reported β estimates and 99% credible intervals (CrI) representing the change in each outcome per 5-μg/m3 increase in PM2.5.

Results

Prenatal PM2.5 exposure was associated with decreased mean hit reaction time (HRT) (β = -21.82; 99% CrI = -64.1, 20.4) and HRT-standard error (β = -9.7; 99% CrI = -30.3, 10.9) on the ANT but estimates were imprecise. Postnatal PM2.5 was associated with reduced mean HRT on the n-back task (β = -39.4; 99% CrI = -115.1, 26.3). We observed sensitive periods of exposure in the postnatal period associated with both better and worse performance on the finger-tapping test and ANT.

Conclusions

We found limited evidence to support an association between PM2.5 exposure and fine motor function, attentional function, or working memory in school-aged children.

Sources and components of fine air pollution exposure and brain morphology in preadolescents

Air pollution is an emerging novel neurotoxicant during childhood and adolescence. However, little is known regarding how fine particulate matter (PM2.5) components and its sources impact brain morphology. We investigated air pollution exposure-related differences in brain morphology using cross-sectional magnetic resonance imaging data from 10,095 children ages 9-11 years-old enrolled in the United States' Adolescent Brain Cognitive Development Study [2016-2018]. Air pollution estimates included fifteen PM2.5 constituent chemicals and metals, and six major sources of PM2.5 (e.g., crustal materials, biomass burning, traffic) identified from prior source apportionment, as well as nitrogen dioxide (NO2) and ozone (O3). After adjusting for demographic, socioeconomic, and neuroimaging covariates, we used partial least squares analyses to identify associations between simultaneous co-exposures and morphological differences in cortical thickness, surface area, and subcortical volumes. We found that greater exposure to PM2.5 and NO2 was associated with decreases in frontal and increases in inferior temporal surface area. PM2.5 component and source analyses linked cortical surface area and thickness to biomass burning (e.g., organic carbon, potassium), crustal material (e.g., calcium, silicon), and traffic (e.g., copper, iron) exposures, while smaller subcortical volumes were linked to greater potassium exposure. This is the first study to show differential effects of several air pollution sources on development of children's brains. Significant associations were found in brain structures involved in several cognitive and social processes, including lower- and higher-order sensory processing, socioemotional behaviors, and executive functioning. These findings highlight differential effects of several air pollution sources on brain structure in preadolescents across the U.S.

Ambient air pollution and hospitalisation for epilepsy in China: A nationwide, individual-level case-crossover study

Emerging evidence has indicated the detrimental effects of air pollutants on the central nervous system (CNS). However, few studies have examined the impact of air pollution on epilepsy morbidity at a nationwide scale in China. To address this gap, we conducted an individual-level, nationwide case-crossover study to investigate the association between air pollutants and epilepsy-related hospitalisations. Daily air pollution concentrations were estimated using high-resolution (1 km) satellite-based exposure models, and hospitalisation data were collected from 153 hospitals across 20 provinces in China between 2005 and 2020. Analysing data from 14,747 patients, we observed increased risks of epilepsy hospitalisations associated with exposure to nitrogen dioxide (NO2) and ozone (O3), with significant increases of 4.5 % (95 % confidence interval [CI]: 0.9 %, 8.4 %) and 4.9 % (95 % CI: 0.8 %, 9.3 %) per interquartile range (IQR) increment in lag 0 day exposure, respectively. The exposure-response curve for NO2 was approximately linear at low concentrations but plateaued above 30 μg/m3. For O3, the curve was flat at lower levels and steeper at higher concentrations. Female patients and children were more susceptible to NO2 exposure, with 10.5 % and 9.1 % increases in hospitalisations per IQR increment, respectively. O3-related risks were more pronounced among patients in northern regions and during the warm season. This individual-level, nationwide case-crossover study provides the first evidence that short-term exposure to NO2 and O3 elevates the risk of epilepsy-related hospitalisations. These findings underscore the need for stricter air quality standard to mitigate the detrimental effects of air pollution on CNS diseases.

Electronic Cigarette-Derived Metals: Exposure and Health Risks in Vapers

Despite the popularity of electronic cigarettes (e-cigs) among adolescent and youth never-smokers and adult smokers seeking a less harmful substitute for tobacco cigarettes, the long-term health impact of vaping is largely unknown. Biochemical, molecular, and toxicological analyses of biospecimens from e-cig users as well as assays in relevant in vitro models and in silico studies can identify chemical constituents of e-cig emissions that may contribute to the disease-causing potential of vaping. E-cig aerosol contains a wide range of toxic and carcinogenic compounds, of which metals are of particular concern. This is due to the known or suspected role of various metals in the pathogenesis of numerous diseases. Many metals and metalloids (herein referred to as "metals") have been detected in e-cig liquid (e-liquid) and aerosol and/or in cells, tissues, biofluids, or other specimens from e-cig users. Metals can contaminate the ingredients of e-liquid or corrode from the internal components of the e-cig device. Metals may also be directly aerosolized from the surface of the heating element or other parts of the device. Inhalation of e-cig metal emissions in habitual vapers and nonusers through secondary exposure may increase the body burden of toxic and carcinogenic chemicals. This review summarizes the state of research on e-cig-derived metals and their contributions to the estimated health risks of vaping. Highlighting the chemical composition of e-cig liquid and aerosol, it focuses on the metal contents of the inhaled aerosol and the health risks associated with this exposure. Emphasis is placed on adolescents and youth who are vulnerable populations and bear a disproportionate burden of risk and harm from tobacco products. The gaps in knowledge, methodological challenges, and opportunities ahead are discussed. The importance of translating research findings into actionable information that can be used for the regulation of the manufacturing of tobacco products is underscored.

Sleep and Arousal Hubs and Ferromagnetic Ultrafine Particulate Matter and Nanoparticle Motion Under Electromagnetic Fields: Neurodegeneration, Sleep Disorders, Orexinergic Neurons, and Air Pollution in Young Urbanites

Air pollution plays a key role in sleep disorders and neurodegeneration. Alzheimer's disease (AD), Parkinson's disease (PD), and/or transactive response DNA-binding protein TDP-43 neuropathology have been documented in children and young adult forensic autopsies in the metropolitan area of Mexico City (MMC), along with sleep disorders, cognitive deficits, and MRI brain atrophy in seemingly healthy young populations. Ultrafine particulate matter (UFPM) and industrial nanoparticles (NPs) reach urbanites' brains through nasal/olfactory, lung, gastrointestinal tract, and placental barriers. We documented Fe UFPM/NPs in neurovascular units, as well as lateral hypothalamic nucleus orexinergic neurons, thalamus, medullary, pontine, and mesencephalic reticular formation, and in pinealocytes. We quantified ferromagnetic materials in sleep and arousal brain hubs and examined their motion behavior to low magnetic fields in MMC brain autopsy samples from nine children and 25 adults with AD, PD, and TDP-43 neuropathology. Saturated isothermal remanent magnetization curves at 50-300 mT were associated with UFPM/NP accumulation in sleep/awake hubs and their motion associated with 30-50 µT (DC magnetic fields) exposure. Brain samples exposed to anthropogenic PM pollution were found to be sensitive to low magnetic fields, with motion behaviors that were potentially linked to the early development and progression of fatal neurodegenerative diseases and sleep disorders. Single-domain magnetic UFPM/NPs in the orexin system, as well as arousal, sleep, and autonomic regions, are key to neurodegeneration, behavioral and cognitive impairment, and sleep disorders. We need to identify children at higher risk and monitor environmental UFPM and NP emissions and exposures to magnetic fields. Ubiquitous ferrimagnetic particles and low magnetic field exposures are a threat to global brain health.

Early childhood education and handgun carrying, serious fighting, and assault charges: a retrospective cohort study

High-quality early childhood education may buffer against social and structural drivers of interpersonal violence. We examined the association of Head Start-a large-scale early childhood education program for low-income children, launched in 1965 as part of the War on Poverty-with handgun carrying, serious fighting, and assault charges among 4281 individuals born between 1980 and 1984 in the National Longitudinal Survey of Youth 1997. We found that attending Head Start vs other childcare was associated with 0.77 times the risk of handgun carrying by age 31 (95% CI: 0.60, 0.99) and 0.79 times the risk of serious fighting by age 24 (95% CI: 0.64, 0.98) among Black males. No reduction in the risk of outcomes was observed among other subpopulations or when comparing Head Start with solely parental childcare. Expanding access to high-quality early childhood education programs may reduce later-life handgun carrying and serious fighting among those at highest risk, thus reducing racialized disparities. Results suggest that early-life investments in the social, economic, and human capital of structurally disadvantaged children and families may be effective and equitable tools to prevent violence and firearm-related harms.

Neurodevelopment and climate change

OBJECTIVE

This article aims to assess the impact of climate change, a reality already present on the neurodevelopment of both neurotypical and atypical children.

DATA SOURCES

A narrative review of the literature was carried out based on articles available in the PubMed database, published in the last five years using the keywords neurodevelopment and climate change, as well as websites of organizations dedicated to childhood such as UNICEF, the American Academy of Pediatrics and the Center for Developing Childhood at Harvard University.

SUMMARY OF FINDINGS

Children and adolescents are more directly affected by the effects of climate change due to their developmental stage and greater vulnerability. Prolonged exposure to air pollutants can affect brain development, resulting in cognitive and behavioral problems. Extreme weather events, such as floods, cyclones, and heat waves, can destroy essential infrastructure such as schools and hospitals, interrupting the educational process and access to health care. Changes in rainfall patterns and extreme droughts can affect food production, leading to malnutrition and food insecurity. Direct experience of natural disasters can cause stress and psychological trauma, affecting children's emotional and mental well-being.

CONCLUSIONS

Studies clearly demonstrate the potential impact of climate change on the neurodevelopment and mental health of children and adolescents. This topic should be part of the current agenda of pediatricians, not only treating the resulting illnesses but mainly acting on the front line and supporting proposals to attenuate the environmental disaster that has already occurred.

Air pollution and cortical myelin T1w/T2w ratio estimates in school-age children from the ABCD and NeuroSmog studies

Air pollution affects human health and may disrupt brain maturation, including axon myelination, critical for efficient neural signaling. Here, we assess the impact of prenatal and current long-term particulate matter (PM) and nitrogen dioxide (NO2) exposure on cortical T1w/T2w ratios - a proxy for myelin content - in school-age children from the Adolescent Brain Cognitive Development (ABCD) Study (United States; N = 2021) and NeuroSmog study (Poland; N = 577), using Siemens scanners. Across both samples, we found that NO2 and PM were not significantly associated with cortical T1w/T2w except for one association of PM10 with lower T1w/T2w in the precuneus in NeuroSmog. Superficially, ABCD Study analyses including data from all scanner types (Siemens, GE, Philips; N = 3089) revealed a negative association between NO₂ exposure and T1w/T2w ratios. However, this finding could be an artifact of between-site sociodemographic differences and large scanner-type-related measurement differences. While significant associations between air pollution and cortical myelin were largely absent, these findings do not rule out the possibility that air pollution affects cortical myelin during other exposure periods/stages of neurodevelopment. Future research should examine these relationships across diverse populations and developmental periods using unified analysis methods to better understand the potential neurotoxic effects of air pollution.

Associations between residential segregation, ambient air pollution, and hippocampal features in recent trauma survivors

Background

Residential segregation is associated with differential exposure to air pollution. Hippocampus structure and function are highly susceptible to pollutants and associated with posttraumatic stress disorder (PTSD) development. Therefore, we investigated associations between residential segregation, air pollutants, hippocampal neurobiology, and PTSD in recent trauma survivors.

Methods

Participants (N = 278; 34% non-Hispanic white, 46% Non-Hispanic Black, 16% Hispanic) completed multimodal neuroimaging two weeks after trauma. Yearly averages of air pollutants (PM2.5 and NO2) and racial/economic segregation (Index of Concentration at the Extremes) were derived from each participant's address. Linear models assessed if air pollutants mediated associations between segregation and hippocampal volume, threat reactivity, or parahippocampal cingulum fractional anisotropy (FA) after covarying for age, sex, income, and 2-week PTSD symptoms. Further models evaluated if pollutants or segregation prospectively predicted PTSD symptoms six months post-trauma.

Results

Non-Hispanic Black participants lived in neighborhoods with significantly greater segregation and air pollution compared to Hispanic and non-Hispanic white participants (ps<.001). There was a significant indirect effect of NO2 between segregation and FA values (β = 0.08, 95% CI[0.01, 0.15]), and an indirect effect of PM2.5 between segregation and threat reactivity (β = -0.08, 95% CI[-0.14, -0.01]). There was no direct effect of segregation on hippocampal features. Pollutants and segregation were not associated with PTSD symptoms .

Conclusion

Residential segregation is associated with greater air pollution exposure, which is in turn associated with variability in hippocampal features among recent trauma survivors. Further research is needed to assess relationships between other environmental factors and trauma and stress-related disorders.

An ex vivo model of systemically-mediated effects of ozone inhalation on the brain

Air pollution is associated with increased risk of neurodegenerative and neuropsychiatric conditions. While animal models have increased our understanding of how air pollution contributes to brain pathologies - including through oxidative stress, inflammatory, and stress hormone pathways - investigation of underlying mechanisms remains limited due to a lack of human-relevant models that incorporate systemic processes. Our objective was to establish an ex vivo approach that enables assessment of the roles of plasma mediators in pollutant-induced effects in the brain. As a proof-of-concept for application in the human context, we assessed whether such effects reproduced in vivo responses to pollutant exposure. Primary rat hippocampal neurons and microglia were each treated with plasma collected from rats immediately or 24 h after ozone inhalation (0 or 0.8 ppm) ± pre-treatment with the glucocorticoid synthesis inhibitor metyrapone. Microglia were further challenged with lipopolysaccharide to evaluate modification of inflammatory responses. Plasma from the ozone-exposed group produced transcriptional changes (inflammatory, antioxidant, glucocorticoid-responsive) in neurons, some of which were glucocorticoid-dependent. Ex vivo and hippocampal responses were strongly correlated, establishing the in vivo relevance of the model. Plasma from the ozone-exposed group modified inflammatory responses to lipopolysaccharide challenge in microglia, demonstrating the model's utility to assess functional changes resulting from pollutant exposure. This study establishes that an ex vivo approach can reproduce ozone-induced effects in the brain. The model was sensitive to specific plasma mediators and temporal effects, and enabled assessment of functional responses. This approach may serve to investigate mechanisms underlying effects of pollutants on the human brain.

Adolescent brain maturation associated with environmental factors: a multivariate analysis

Human adolescence marks a crucial phase of extensive brain development, highly susceptible to environmental influences. Employing brain age estimation to assess individual brain aging, we categorized individuals (N = 7,435, aged 9-10 years old) from the Adolescent Brain and Cognitive Development (ABCD) cohort into groups exhibiting either accelerated or delayed brain maturation, where the accelerated group also displayed increased cognitive performance compared to their delayed counterparts. A 4-way multi-set canonical correlation analysis integrating three modalities of brain metrics (gray matter density, brain morphological measures, and functional network connectivity) with nine environmental factors unveiled a significant 4-way canonical correlation between linked patterns of neural features, air pollution, area crime, and population density. Correlations among the three brain modalities were notably strong (ranging from 0.65 to 0.77), linking reduced gray matter density in the middle temporal gyrus and precuneus to decreased volumes in the left medial orbitofrontal cortex paired with increased cortical thickness in the right supramarginal and bilateral occipital regions, as well as increased functional connectivity in occipital sub-regions. These specific brain characteristics were significantly more pronounced in the accelerated brain aging group compared to the delayed group. Additionally, these brain regions exhibited significant associations with air pollution, area crime, and population density, where lower air pollution and higher area crime and population density were correlated to brain variations more prominently in the accelerated brain aging group.

Associations between Fine Particulate Matter Components, Their Sources, and Cognitive Outcomes in Children Ages 9-10 Years Old from the United States

BACKGROUND

Emerging literature suggests that fine particulate matter [with aerodynamic diameter ≤ 2.5 μ m (PM 2.5 )] air pollution and its components are linked to various neurodevelopmental outcomes. However, few studies have evaluated how PM 2.5 component mixtures from distinct sources relate to cognitive outcomes in children.

OBJECTIVES

This cross-sectional study investigated how ambient concentrations of PM 2.5 component mixtures relate to neurocognitive performance in 9- to 10-year-old children, as well as explored potential source-specific effects of these associations, across the US.

METHODS

Using spatiotemporal hybrid models, annual concentrations of 15 chemical components of PM 2.5 were estimated based on the residential address of child participants from the Adolescent Brain Cognitive Development (ABCD) Study. General cognitive ability, executive function, and learning/memory scores were derived from the NIH Toolbox. We applied positive matrix factorization to identify six major PM 2.5 sources based on the 15 components, which included crustal, ammonium sulfate, biomass burning, traffic, ammonium nitrate, and industrial/residual fuel burning. We then utilized weighted quantile sum (WQS) and linear regression models to investigate associations between PM 2.5 components' mixture, their potential sources, and children's cognitive scores.

RESULTS

Mixture modeling revealed associations between cumulative exposure and worse cognitive performance across all three outcome domains, including shared overlap in detrimental effects driven by ammonium nitrates, silicon, and calcium. Using the identified six sources of exposure, source-specific negative associations were identified between ammonium nitrates and learning & memory, traffic and executive function, and crustal and industrial mixtures and general cognitive ability. Unexpected positive associations were also seen between traffic and general ability as well as biomass burning and executive function.

DISCUSSION

This work suggests nuanced associations between outdoor PM 2.5 exposure and childhood cognitive performance, including important differences in cognition related both to individual chemicals as well as to specific sources of these exposures. https://doi.org/10.1289/EHP14418.

A Systematic Review of Air Pollution Exposure and Brain Structure and Function during Development

Objectives

Air pollutants are known neurotoxicants. In this updated systematic review, we evaluate new evidence since our 2019 systematic review on the effect of outdoor air pollution exposure on childhood and adolescent brain structure and function as measured by magnetic resonance imaging (MRI).

Methods

Using PubMed and Web of Science, we conducted an updated literature search and systematic review of articles published through March 2024, using key terms for air pollution and functional and/or structural MRI. Two raters independently screened all articles using Covidence and implemented the risk of bias instrument for systematic reviews informing the World Health Organization Global Air Quality Guidelines.

Results

We identified 222 relevant papers, and 14 new studies met our inclusion criteria. Including six studies from our 2019 review, the 20 publications to date include study populations from the United States, Netherlands, Spain, and United Kingdom. Studies investigated exposure periods spanning pregnancy through early adolescence, and estimated air pollutant exposure levels via personal monitoring, geospatial residential estimates, or school courtyard monitors. Brain MRI occurred when children were on average 6-14.7 years old; however, one study assessed newborns. Several MRI modalities were leveraged, including structural morphology, diffusion tensor imaging, restriction spectrum imaging, arterial spin labeling, magnetic resonance spectroscopy, as well as resting-state and task-based functional MRI. Air pollutants were associated with widespread brain differences, although the magnitude and direction of findings are largely inconsistent, making it difficult to draw strong conclusions.

Conclusion

Prenatal and childhood exposure to outdoor air pollution is associated with structural and functional brain variations. Compared to our initial 2019 review, publications doubled-an increase that testifies to the importance of this public health issue. Further research is needed to clarify the effects of developmental timing, along with the downstream implications of outdoor air pollution exposure on children's cognitive and mental health.