Socioeconomic and racial-ethnic disparities in flame retardant exposure and executive function skills in preschool children
Does socioeconomic status affect children's exposure to flame retardant chemicals and do these exposures impact cognitive development during the critical preschool years?
College of Health researcher(s)
College unit(s)
Abstract
Background
Polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs) are commonly used as flame retardants. Limited research exists on socioeconomic and racial/ethnic disparities in exposure to these compounds and their impact on executive functioning (EF) in early childhood. The present study examined independent and joint effects of income and race/ethnicity on flame retardant exposure in early childhood and investigated associations between flame retardant exposure and children's EF.
Methods
This cross-sectional study used data from 349 preschool children recruited in Oregon. Children wore silicone wristband samplers for seven days, with exposures to 41 flame retardant compounds analyzed by gas chromatography mass spectrometry. We focused on exposure to 6 compounds (BDE 47, BDE 99, BDE100, TCPP, TDCPP, TPP) and two composite indices (ΣPBDE, ΣOPE). Wilcoxon rank-sum tests examined exposure differences by race/ethnicity and income (low income = below federal poverty level). Multiple linear regression models, nested within classrooms, assessed the association between PBDE and OPE exposure and EF, measured by the Head-Toes-Knees-Shoulders-Revised (HTKS-R) and Dimensional Change Card Sort (DCCS) tasks.
Results
Children were 5.1 years old (SD = 0.3), 29.9% were from underserved racial/ethnic backgrounds, and 27.8% of families were low income. Compared with higher income families, children from low income families were exposed to 83.4% greater ΣPBDE exposures and 36% greater TDCPP exposures. There was no evidence of racial/ethnic disparities in PBDE or OPE exposures. Controlling for age, sex, income, race/ethnicity, and disability or cognitive delay, neither PBDE nor OPE exposures were consistently related to EF, but children from lower income families scored 28.6% lower on the HTKS-R, and children from underserved races/ethnicities scored 25.9% lower on the HTKS-R.
Conclusions
Our findings highlight persistent income disparities in PBDE exposures at a pivotal point in children's development, and reveal similar disparities in TDCPP exposures. Furthermore, socioeconomic disadvantage was more strongly associated with reduced EF than either PBDE or OPFR exposures. These findings underscore the need to address structural social inequities, and also highlight the need for greater representation of children from underserved backgrounds in research that seeks to characterize chemical and social exposures within neighborhood and preschool environments.
Frequently Asked Questions about Flame Retardant Exposure and Child Development
What are flame retardants and why are they a concern for children's health?
Flame retardants, such as polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs), are chemicals added to consumer goods and building materials to meet flammability standards. While PBDEs were largely phased out in the US by 2005, their persistence in older products means ongoing exposure. OPEs replaced PBDEs, but their health impacts are still being investigated, with some identified as priority chemicals by the U.S. EPA. Children are particularly vulnerable to exposure due to their higher inhalation and ingestion rates per pound of body weight, greater contact with house dust, and frequent hand-to-mouth activity. These chemicals are concerning because they have been linked to various negative health effects, including potential carcinogenicity, disruption of immune, endocrine, and reproductive systems, and negative impacts on neurocognitive development.
What kind of flame retardant exposures were studied in preschool children and how were they measured?
The study focused on exposure to six specific flame retardant compounds: BDE 47, BDE 99, BDE 100 (from the PBDE class), and TCPP, TDCPP, TPP (from the OPE class), as well as two composite indices (ΣPBDE and ΣOPE) representing total exposure to these classes. Exposure was measured non-invasively using silicone wristband passive samplers worn by 349 preschool children in Oregon for seven days. These wristbands absorb chemicals from the environment, and their concentrations were analyzed using gas chromatography mass spectrometry. This method allows researchers to capture personal exposure to multiple flame retardants over time.
Were there socioeconomic or racial/ethnic disparities in flame retardant exposure among the preschool children?
The study found persistent socioeconomic disparities in flame retardant exposures. Children from low-income families (below the federal poverty level) were exposed to 83.4% greater total PBDEs and 36% greater TDCPP compared to children from higher-income families. This disparity is likely due to low-income families residing in older homes and owning older or secondhand furniture and items manufactured before PBDEs were phased out. Contrary to expectations and some previous research, the study did not find evidence of racial/ethnic disparities in PBDE or OPE exposures. This null finding might be due to the study's limited sample size and racial/ethnic diversity.
How was executive function (EF) assessed in the children?
Children's executive functioning was assessed using two validated direct assessment measures:
- Head-Toes-Knees-Shoulders-Revised (HTKS-R): This 30-item task measures inhibitory control, working memory, and cognitive flexibility by asking children to perform the opposite of what they are told (e.g., touch toes when told "touch head"). Higher scores indicate greater EF.
- Dimensional Change Card Sort (DCCS): This task measures inhibitory control, working memory, and cognitive flexibility by requiring children to sort cards based on changing rules (e.g., first by color, then by shape, and later based on a black border). Higher scores indicate greater EF.
What was the relationship between flame retardant exposure and children's executive function?
Contrary to the study's initial hypotheses and some existing literature, neither cumulative PBDE exposure nor individual PBDE compounds were directly related to children's executive function as measured by either task. Interestingly, higher exposure to cumulative OPEs (primarily driven by TCPP) was associated with higher scores on the DCCS. While TPP exposure also showed a positive association with HTKS-R scores, this was not significant after adjusting for multiple comparisons, suggesting it might be a Type I error. The study suspects that unmeasured factors associated with higher socioeconomic status (e.g., newer homes, non-toxic furniture, higher-resourced schools) could confound these findings, as these factors might simultaneously lead to higher OPE exposure and better EF due to greater resources.
What was the impact of socioeconomic factors on children's executive function, independent of flame retardant exposure?
The study strongly emphasized that socioeconomic disadvantage was consistently and significantly associated with reduced executive function, even after controlling for flame retardant exposures and other factors like age, sex, and disability. Children from low-income families scored 28.6% lower on the HTKS-R and 14% lower on the DCCS compared to children from higher-income families. Similarly, children from underserved racial/ethnic backgrounds scored 25.9% lower on the HTKS-R and 16% lower on the DCCS. These findings highlight that structural social inequities have a substantial impact on children's cognitive health.
What are the key implications of these findings for public health and environmental justice?
The study's findings underscore the continued existence of environmental justice issues, with low-income children disproportionately exposed to legacy PBDEs and newer TDCPP flame retardants. While a direct causal link between flame retardants and reduced EF was not consistently established in this study, the profound impact of socioeconomic disadvantage on children's executive function is clear. This emphasizes the critical need to address broader structural social inequities to promote cognitive health and well-being for children from underserved backgrounds. It also highlights the importance of incorporating children from underserved backgrounds in future research.
What are the limitations of this study and future directions for research?
Limitations include a relatively small sample size and limited racial/ethnic diversity, which might have hindered the detection of racial/ethnic disparities in exposure. The study also acknowledged that the COVID-19 pandemic introduced unique challenges to data collection and may have influenced exposure patterns. Future research should aim for larger, more diverse populations and consider longitudinal studies with repeated sampling to better understand the long-term effects of cumulative flame retardant exposure on cognitive development. Additionally, exploring how neighborhood and preschool environments contribute to exposure and incorporating "positive aspects" of underserved communities, such as community connectedness and social support, as potential protective factors against toxic exposure should be considered.