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. 2023 Sep;131(9):96001.
doi: 10.1289/EHP11750. Epub 2023 Sep 27.

Disparities in Toxic Chemical Exposures and Associated Neurodevelopmental Outcomes: A Scoping Review and Systematic Evidence Map of the Epidemiological Literature

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Disparities in Toxic Chemical Exposures and Associated Neurodevelopmental Outcomes: A Scoping Review and Systematic Evidence Map of the Epidemiological Literature

Devon C Payne-Sturges et al. Environ Health Perspect. 2023 Sep.

Abstract

Background: Children are routinely exposed to chemicals known or suspected of harming brain development. Targeting Environmental Neuro-Development Risks (Project TENDR), an alliance of >50 leading scientists, health professionals, and advocates, is working to protect children from these toxic chemicals and pollutants, especially the disproportionate exposures experienced by children from families with low incomes and families of color.

Objective: This scoping review was initiated to map existing literature on disparities in neurodevelopmental outcomes for U.S. children from population groups who have been historically economically/socially marginalized and exposed to seven exemplar neurotoxicants: combustion-related air pollution (AP), lead (Pb), mercury (Hg), organophosphate pesticides (OPs), phthalates (Phth), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs).

Methods: Systematic literature searches for the seven exemplar chemicals, informed by the Population, Exposure, Comparator, Outcome (PECO) framework, were conducted through 18 November 2022, using PubMed, CINAHL Plus (EBSCO), GreenFILE (EBSCO), and Web of Science sources. We examined these studies regarding authors' conceptualization and operationalization of race, ethnicity, and other indicators of sociodemographic and socioeconomic disadvantage; whether studies presented data on exposure and outcome disparities and the patterns of those disparities; and the evidence of effect modification by or interaction with race and ethnicity.

Results: Two hundred twelve individual studies met the search criteria and were reviewed, resulting in 218 studies or investigations being included in this review. AP and Pb were the most commonly studied exposures. The most frequently identified neurodevelopmental outcomes were cognitive and behavioral/psychological. Approximately a third (74 studies) reported investigations of interactions or effect modification with 69% (51 of 74 studies) reporting the presence of interactions or effect modification. However, less than half of the studies presented data on disparities in the outcome or the exposure, and fewer conducted formal tests of heterogeneity. Ninety-two percent of the 165 articles that examined race and ethnicity did not provide an explanation of their constructs for these variables, creating an incomplete picture.

Discussion: As a whole, the studies we reviewed indicated a complex story about how racial and ethnic minority and low-income children may be disproportionately harmed by exposures to neurotoxicants, and this has implications for targeting interventions, policy change, and other necessary investments to eliminate these health disparities. We provide recommendations on improving environmental epidemiological studies on environmental health disparities. To achieve environmental justice and health equity, we recommend concomitant strategies to eradicate both neurotoxic chemical exposures and systems that perpetuate social inequities. https://doi.org/10.1289/EHP11750.

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Figures

Figure 1 is a flowchart titled Identification of Studies via Databases and Other Methods, which has three steps: Identification, Screening, and Inclusion. Step 1: Identification: Records identified through database searching include 6,117 records from PubMed, 926 cases from CINAHL with full text (EBSCO), 155 records from GreenFILE (EBSCO), 16,820 records from Web of Science, and 25 additional records identified through gray literature. The total number of records is 24,043, of which 9,333 duplicate records were removed. Step 2: Screening: There are 14,710 records screened at the title or abstract level, of which 12,982 records were excluded. There are 1,728 full-text records assessed for eligibility, of which 1,516 full-text records were excluded. The excluded full-text records included 127 records of the wrong study type, 376 records of the wrong population, 233 records of the wrong exposure, 580 records of the wrong or no comparator, and 200 records of the wrong outcome. Step 3: Included: There are 212 records of articles included in the review, of which 74 records examined interaction or effect modification.
Figure 1.
PRISMA flowchart of study inclusion (included articles: n=212). Note: PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.
Figure 2 is a bar graph, plotting study counts, ranging from 0 to 70 in increments of 10 (y-axis) across air pollution, environmental tobacco smoke, lead, mercury, organophosphate pesticides, phthalates, polychlorinated biphenyls, polybrominated diphenyl ethers, and chemical mixtures (x-axis).
Figure 2.
Frequencies of TENDR exemplar contaminants examined by the studies. Some studies are counted more than once if they examined multiple exemplar neurotoxicants separately. Note: AP, air pollution; ETS, environmental tobacco smoke; Hg, mercury; mixtures, chemical mixtures; OP, organophosphate pesticides; Pb, lead; PBDE, polybrominated diphenyl ethers; PCB, polychlorinated biphenyls; Phth, phthalates; TENDR, Targeting Environmental Neuro-Development Risks.
Figure 3 is a line graph, plotting proportion of all studies, ranging from 0.00 to 100.00 percent in increments of 20.00 percent (y-axis) across decade, ranging from 1970 to 1979, 1980 to 1989, 1990 to 1999, 2000 to 2009, 2010 to 2019, and 2020 to 2023 (x-axis) for comparator, including race, ethnicity, geography, socioeconomic status, adversity indices, language, and HOME scores.
Figure 3.
Proportion of studies that included social comparators by decade. Data for the graph can be found in Excel Table S10. Number of publications per decade=3, 8, 17, 39, 117, and 28 for 1970–1979; 1980–1989; 1990–1999; 2000–2009; 2010–2019; and 2020–2023, respectively. Note: SES, socioeconomic status.

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