Summary
A medRxiv preprint links the timing of early-life exposure to mixtures of nine metals with risk-taking, reward sensitivity and task-related brain activity in adolescents from a Mexico City birth cohort. The observational findings come from tooth biomarkers and functional MRI data.
A medRxiv preprint reports that the timing of early-life exposure to a mixture of metals was associated with risk-taking, reward sensitivity and task-related brain activity in early adolescents from a Mexico City birth cohort. The study used chemical measurements in deciduous teeth to estimate exposure from 19 weeks before birth through 43 weeks after birth, then compared those measurements with behavioural and functional MRI data collected at ages 8 to 14.
The findings, posted on 14 September 2026, come from an observational study and are presented as a preprint rather than a peer-reviewed journal article. They suggest that prenatal and postnatal exposure periods may have different relationships with the neural systems involved in adolescent decision-making.
How the study measured exposure and decision-making
The researchers analysed weekly concentrations of nine metals in children's deciduous teeth: barium, copper, lithium, magnesium, manganese, lead, tin, strontium and zinc. Because tooth dentine forms in layers over time, the measurements can be used as a timeline of exposure during fetal development and early infancy.
Participants were drawn from the Programming Research in Obesity, Growth, Environment and Social Stressors longitudinal birth cohort in Mexico City. The group was 45% female. During a functional MRI gambling task, the researchers measured brain activity while participants made risky decisions and processed rewards. They also estimated three behavioural measures from those decisions: risk-taking tendency, risk sensitivity and reward sensitivity.
To examine whether associations changed across development, the analysis used lagged weighted quantile sum regression, a statistical method for evaluating mixtures of correlated exposures across time windows. The models were adjusted for child age, child sex and socioeconomic status.
Exposure timing was associated with different patterns
The analysis associated higher metal-mixture exposure during the early-to-late postnatal period with increased risk-taking tendency and risk sensitivity.
Exposure during prenatal development and the late postnatal period was associated with increased reward sensitivity. The same exposure windows were associated with reduced activation in the angular gyrus and inferior parietal lobule during risky decision-making. These brain regions are involved in integrating information relevant to attention, evaluation and decision-making; in this study, the result describes task-related activation rather than a clinical diagnosis.
Late postnatal exposure was also associated with increased activation in the insula and rolandic operculum during reward processing. The researchers reported that postnatal associations involving risk-related neural activation were driven primarily by strontium, while the reward-related neural association was driven primarily by magnesium. The behavioural associations—risk-taking tendency, risk sensitivity and reward sensitivity—were linked to multiple metals in the mixture rather than one dominant element.
What the findings mean
The study's main contribution is its focus on exposure timing. Instead of treating childhood metal exposure as a single cumulative measure, the analysis used tooth biomarkers to examine whether different developmental periods were associated with different behavioural and neural correlates in adolescence.
Because this was an observational cohort analysis, exposure was not experimentally assigned. The findings therefore support association-level interpretation: they identify patterns connecting metal-mixture measurements with later task performance and brain activity. They do not establish that a particular metal or exposure window directly caused the observed decision-making patterns, or that the patterns represent lasting clinical impairment.
The supplied abstract does not report the number of participants or effect sizes, which limits assessment of the study's statistical precision from the available record. Its results also come from one Mexico City birth cohort and may not represent exposure patterns or outcomes in other populations. The longer-term significance of the task-related neural differences is not addressed in the abstract.
The authors report that all study procedures received approval from institutional review boards in the United States and Mexico. The source also discloses that Manish Arora is an officer of Linus Biotechnology Inc., a Mount Sinai start-up that undertakes tooth metal analysis; the company was not involved in the study, and the conflict is managed under Mount Sinai Health System policy.