Cited by 268Autism Spectrum Disorder ResearchEffects and risks of endocrine disrupting chemicalsHealth, Environment, Cognitive Aging

The DOI matches its Crossref record; 235 of the 240 references it cites were found in a registry or an index; 2 of the 150 sources its claims cite were checked for support.

Environmental Chemical Exposures and Autism Spectrum Disorders: A Review of the Epidemiological Evidence

Open access
Kalkbrenner, Amy E., Schmidt, Rebecca J., Penlesky, Annie C.·2014·Current Problems in Pediatric and Adolescent Health Care

Abstract

In the past decade, the number of epidemiological publications addressing environmental chemical exposures and autism has grown tremendously. These studies are important because it is now understood that environmental factors play a larger role in causing autism than previously thought and because they address modifiable risk factors that may open up avenues for the primary prevention of the disability associated with autism. In this review, we covered studies of autism and estimates of exposure to tobacco, air pollutants, volatile organic compounds and solvents, metals (from air, occupation, diet, dental amalgams, and thimerosal-containing vaccines), pesticides, and organic endocrine-disrupting compounds such as flame retardants, non-stick chemicals, phthalates, and bisphenol A. We included studies that had individual-level data on autism, exposure measures pertaining to pregnancy or the 1st year of life, valid comparison groups, control for confounders, and adequate sample sizes. Despite the inherent error in the measurement of many of these environmental exposures, which is likely to attenuate observed associations, some environmental exposures showed associations with autism, especially traffic-related air pollutants, some metals, and several pesticides, with suggestive trends for some volatile organic compounds (e.g., methylene chloride, trichloroethylene, and styrene) and phthalates. Whether any of these play a causal role requires further study. Given the limited scope of these publications, other environmental chemicals cannot be ruled out, but have not yet been adequately studied. Future research that addresses these and additional environmental chemicals, including their most common routes of exposures, with accurate exposure measurement pertaining to several developmental windows, is essential to guide efforts for the prevention of the neurodevelopmental damage that manifests in autism symptoms.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

This review synthesizes epidemiological research on environmental chemical exposures and autism, focusing on exposures during conception, pregnancy, and the first postnatal year. It concludes that some traffic-related air pollutants, metals, and pesticides show associations with autism, with suggestive evidence for certain volatile organic compounds and phthalates, but causality remains unproven.

Key findings

  • Among 32 included publications, associations were most consistent for traffic-related and criteria air pollutants (e.g., PM2.5, PM10, NO2), some metals, and several pesticides; associations were often stronger for late pregnancy and the first year of life.
  • Direct maternal smoking during pregnancy showed no strong causal link with autism overall, though a possible signal for higher-functioning autism was complicated by sociodemographic confounding.
  • Thimerosal-containing vaccines showed mostly null results, with most odds ratios between 0.9 and 1.2 and confidence intervals crossing the null; exceptions were imprecise or inconsistent with biologic plausibility.
  • Some volatile organic compounds (methylene chloride, trichloroethylene, styrene) had consistently elevated associations, and phthalates were suggestive; evidence for PCBs, flame retardants, non-stick chemicals, and bisphenol A was inconclusive.

Methods

  • The authors reviewed human population-based epidemiological studies published in English-language peer-reviewed journals before March 1, 2014, requiring individual-level autism data, exposure during conception/pregnancy/first postnatal year, valid comparison groups, confounder control, and adequate sample size or precision.
  • Searches used PubMed, Google Scholar, personal libraries, and citation tracking; 58 publications met initial inclusion criteria, 26 were excluded for validity or precision concerns, leaving 32 included publications, some reporting multiple chemicals.
  • Included designs were cohort, nested case–control, and case–control studies; autism measures included clinical diagnoses and continuous autism phenotype measures, while exposure measures included biomarkers, residential proximity, air pollution models, questionnaires, and registries.

Limitations

  • The paper states that exposure measurement error is common and likely attenuates observed associations, and that many chemicals and common exposure routes remain inadequately studied.
  • The paper notes that small samples, wide confidence intervals, residual confounding (e.g., socioeconomic status, season, traffic noise, co-pollutants, genetics), and etiologic heterogeneity may dilute or mask true effects, and that causal conclusions cannot yet be drawn.
  • Evident from the text: this is a narrative review rather than a systematic meta-analysis, with subjective decisions about including one estimate per chemical–autism question and no formal assessment of publication bias.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1016/j.cppeds.2014.06.001

Cites

235 of 235 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

88 Not checked yet · 53 No basis given · 39 Own interpretation · 18 Own method · 5 Own result · 1 Partly supported · accuracy not yet measured

Verify all 148 references — free account

Show all 102 claims

  • It may state two separate claims as one. 89
  • Probably not a substantial claim. 35
102 of 102
  • The paper relies on this without support.

    Community-level exposure estimates are reasonable proxies for individual-level exposure.

    “Community-level exposures (e.g., an air toxic pollutant estimated for a census tract) often serve as reasonable proxies of individual-level exposure, although they include some degree of exposure measurement error.”
  • The paper relies on this without support.

    Environmental chemical exposures can be reduced, opening avenues for primary prevention of autism.

    “exposure to these factors can be reduced, opening up viable avenues for the primary prevention of autism”
  • The paper relies on this without support.

    Measurement error in environmental exposure measurement is non-differential with respect to autism and therefore attenuates observed associations.

    “Despite the inherent error in the measurement of many of these environmental exposures, which is likely to attenuate observed associations”
    “measurement error that would be expected to attenuate findings”
  • The paper relies on this without support.

    Exposure measurement error in the reviewed studies is nondifferential and biases observed associations toward the null.

    “which would be expected to attenuate observed ORs”
  • The paper relies on this without support.

    Adjustment for socioeconomic status and maternal age is sufficient to make residual confounding an unlikely explanation for the metal-autism associations.

    “confounding not highly likely given that all of these studies adjusted for socioeconomic status and maternal age, but possible”
  • The paper relies on this without support.

    A pattern of small odds ratios around the null with confidence intervals spanning the null indicates no causal association for thimerosal.

    “results were most consistent with a pattern due to chance, demonstrated by ORs of small magnitude (most between 0.9 and 1.2), above and below the null, and with confidence intervals spanning the null, suggesting that thimerosal does not increase autism risk”
  • The paper relies on this without support.

    The included thimerosal studies' validity criteria are adequate to support the conclusion of no association despite minor flaws.

    “Although the studies we included met our validity criteria, some minor flaws may have created such an influence.”
  • The paper relies on this without support.

    Autism is common enough that using an odds ratio may overestimate association in one pesticide study.

    “the study used an OR, which is best suited for rare diseases, for a common outcome”
  • The paper relies on this without support.

    Beneficial nutrients in fish can counteract mercury toxicity enough to explain the null Seychelles result.

    “the impacts of brain-enhancing nutrients contained in fish may have counteracted any toxic impact of mercury”
  • The paper relies on this without support.

    The comparison group of children with speech and language impairment in one metal study may have a stronger association with lead or manganese, causing inverse findings.

    “which could have been caused by a stronger association with the comparison group in this design: children with speech and language impairment”
  • The paper relies on this without support.

    Children given autism diagnoses vary widely in symptoms, disability level, and co-occurring conditions.

    “children diagnosed under the autism umbrella exhibit a very wide range of symptoms, level of disability, and co-occurring conditions.”
  • The paper relies on this without support.

    The environment is not a single entity.

    “The environment is not one entity”
12 of 12

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Self-check

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Each contradiction between two passages listed here was confirmed by an independent check.

1 of 1

Citations

Cites

1 retracted

Research works printed but not linked: 4

  1. Institute of Medicine (US) Immunization Safety Review Committee, 2004
  2. De Cock, 2012, Does perinatal exposure to endocrine disruptors induce autism spectrum and attention deficit hyperactivity disorders? Review, Acta Paediatr, 101, 811, 10.1111/j.1651-2227.2012.02693.x · DOI · Paper page
  3. Volk, 2011, Residential proximity to freeways and autism in the CHARGE study, Environ Health Perspect, 119, 873, 10.1289/ehp.1002835 · DOI · Paper page
  4. Volk, 2013, Traffic-related air pollution, particulate matter, and autism, J Am Med Assoc Psychiatry, 70, 71

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Metadata

Authors
Kalkbrenner, A. E., Schmidt, R. J., & Penlesky, A. C.
Affiliations
  • University of Wisconsin–Milwaukee (US)
  • University of California Davis Medical Center (US)
Venue
Current Problems in Pediatric and Adolescent Health Care
Publisher
Elsevier BV
Published
2014-11
Volume
44
Issue
10
Pages
277-318
ISSN
  • 1538-3199 (ISSN-L)
  • 1538-5442
OpenAlex
W2064675231
Cited by
268
References
240
Citations by year
2026: 4 · 2025: 11 · 2024: 14 · 2023: 16 · 2022: 26 · 2021: 25 · 2020: 29 · 2019: 34 · 2018: 34 · 2017: 27 · 2016: 32 · 2015: 16
FWCI
13.95
Type
journal article
Language
en
Open access
Locations
  • Current problems in pediatric and adolescent health care (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
  • eScholarship (California Digital Library) (submittedVersion)
Funders
  • Autism Speaks (AS9038)
  • Eunice Kennedy Shriver National Institute of Child Health and Human Development (K12HD051958)
Topics
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Autism Spectrum Disorder Research
  • Physical Sciences › Environmental Science › Health, Toxicology and Mutagenesis › Effects and risks of endocrine disrupting chemicals
  • Physical Sciences › Environmental Science › Health, Toxicology and Mutagenesis › Health, Environment, Cognitive Aging
Keywords
autism spectrum disorder, environmental chemical exposure, prenatal exposure, early childhood exposure, tobacco smoke exposure, air pollutants, traffic-related air pollution, volatile organic compounds, solvents, metals, dental amalgam, thimerosal-containing vaccines, pesticides, endocrine disruptors, flame retardants, phthalates, bisphenol A, autism prevention, neurodevelopmental damage
MeSH terms
Child Development Disorders, Pervasive, Environmental Pollutants, Female, Humans, Pesticides, Pregnancy, Prenatal Exposure Delayed Effects, Risk Factors, Nicotiana, Vaccination, Maternal Exposure, Metals, Heavy

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