GC-MS/MS Links Tooth-Layer Pollutant Traces to Autism Risk

Being exposed to certain long-lasting environmental pollutants while still in the womb may raise the risk of autism, but earlier research mostly relied on testing pregnant mothers' blood or other samples as a stand-in for what the baby was exposed to, rather than measuring it directly. A team of researchers were inspired to take a more direct approach: they examined baby teeth that had naturally fallen out from children with autism and typically developing children, all born in California between 1998 and 2014, as part of a larger research project studying genetic and environmental causes of autism. Using gas chromatography-tandem mass spectrometry (GC-MS/MS), the team measured pollutant levels captured in different layers of the teeth corresponding to the second trimester, third trimester, and the period after birth. A paper based on this research was published in the journal Environmental Research.¹

How Do Baby Teeth Record a History of Chemical Exposure During Fetal and Early Childhood Development?

Baby teeth grow in layers, similar to tree rings, with each layer capturing a snapshot of what a baby was exposed to, even before birth.^2,3 This is because these teeth start forming while a baby is still in the womb, around the second trimester, and new layers keep building up over time. As each layer forms, it locks in traces of chemicals that were circulating in the bloodstream at that exact moment. The research team was able to develop a way to carefully separate these layers and test them individually, which lets them look back in time and figure out what a child was exposed to during specific stages of early development.^4,5

Does Pollutant Exposure During Pregnancy Actually Raise Autism Risk?

Participants in this study came from the CHARGE study, a long-running California-based research project comparing children with autism to typically developing peers, matched by age, sex, and location. Autism diagnoses were confirmed through standard clinical assessments, while comparison cases were confirmed as typically developing through learning and behavior tests. Families mailed in naturally shed baby teeth, and only children with at least one available tooth were included in this analysis. The study was approved by university ethics boards.¹

Researchers measured levels of 13 different man-made chemicals, including PCBs, pesticides, and flame retardants, that had built up in the teeth representing 213 autism cases and 124 typically developing controls. They then compared children who had been diagnosed with autism to their typically developing peers, first looking at each chemical individually, then looking at how the chemicals might act together as a group. They found that when looking at chemical exposure during the third trimester of pregnancy, higher levels of this chemical mixture were linked to a higher likelihood of autism (children with higher exposure were roughly one and a half times more likely to have autism). When the researchers looked separately at boys and girls, this link held up for boys, who showed close to a 75% higher likelihood of autism with higher exposure, but the connection for girls was much weaker and not statistically meaningful. Exposure during the second trimester or after birth wasn't clearly linked to autism risk either way.¹

“Direct fetal and early-life measures of POPs,” write the authors of the paper,¹ “indicate the third trimester as a potential high-risk biological window for POPs exposures that increase autism risk, particularly in males.”

In the opinion of the research team, future studies should investigate how exposure to these chemicals late in pregnancy might affect the body biologically, to find possible ways to intervene and lower the risk of autism.¹

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References

1. Petrick, L. M.; Dassanayake, P. S.; Gennings, C. et al. Fetal Exposure to Persistent Organic Pollutants and Childhood Autism Risk. Environ Res. 2026, 125179. DOI: 10.1016/j.envres.2026.125179
2. Papakyrikos A. M.; Arora, M.; Austin C. et al. Biological Clocks and Incremental Growth Line Formation in Dentine. J. Anat. 2020, 237 (2), 367-378. DOI: 10.1111/joa.13198
3. Arora, M.; Reichenberg, A.; Willfors, C. et al. Fetal and Postnatal Metal Dysregulation in Autism. Nat Commun. 2017, 8, 15493. DOI: 10.1038/ncomms15493
4. Andra, S. S.; Austin, C.; Wright R. O. et al. Reconstructing Pre-Natal and Early Childhood Exposure to Multi-Class Organic Chemicals Using Teeth: Towards a Retrospective Temporal Exposome. Environ. Int.2015, 83, 137-145. DOI: 10.1016/j.envint.2015.05.010
5. Yu, M.; Tu, P.; Dolios, G. et al.Tooth Biomarkers to Characterize the Temporal Dynamics of the Fetal and Early-Life Exposome. Environ. Int.2021, 157, 106849. DOI: 10.1016/j.envint.2021.106849