This dissertation focuses on young children’s exposures to pesticides in indoor environmentsfrom dust. Research shows that young children, particularly in California, are exposed to pesticides
in their environment, including in their homes and child care / early care and education (ECE)
settings. Children are uniquely vulnerable to chemical exposures due to their exposure-prone
behaviors and rapidly developing bodies and systems. Chemical exposures during critical windows
of development put children are at higher risk since their respiratory, reproductive, digestive,
immunological, and central nervous systems are not fully developed and are vulnerable to
disruption.
Most children in the U.S. spend a significant amount of time in environments other than their
home, but few studies have characterized exposures to pesticides in child care programs. Likewise,
there are few studies that derive potential intake doses and characterize risk, despite the effort over
the past three decades make risk assessments more protective of vulnerable populations, including
young children. In this dissertation, we take a mixtures approach to assessing potential health
impacts from early childhood exposures to pesticides in indoor dust, both in assessing cumulative
risk for children in ECE settings, and assessing exposures to pesticide mixtures among children in
an agricultural community and potential impacts on child cognition.
Chapter 1 reviews literature on determinants of pesticide exposure to young children in indoor
environments and their potential health impacts. We present a brief introduction to the pesticides
that will be discussed throughout this dissertation, key concepts related to measuring pesticides in
dust, as well as the two study populations used in this dissertation.
Chapter 2 aims to identify determinants of pesticide levels in carpet dust samples collected
from 51 licensed child care centers in Northern California and analyzed for 14 structural and
agricultural pesticides. The most frequently detected pesticides were cis-permethrin (98%), transpermethrin (98%), bifenthrin (94%), fipronil (94%), and chlorpyrifos (88%). Higher bifenthrin
levels were correlated with agricultural applications within 3 kilometers, and higher fipronil levels
were correlated with professional pesticide applications in the prior year. In multivariable models,
higher Integrated Pest Management (IPM) Checklist scores were associated with lower loading of
chlorpyrifos and permethrin. Placement of the sampled area carpet was also a predictor of
chlorpyrifos loading. The strongest predictor of higher pesticide loading for the most frequently
detected pesticides was location in California’s San Joaquin Valley.
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Chapter 3 aims to determine if children’s exposures to pesticides in child care via non-dietary
ingestion and dermal absorption exceed health-protective reference values, and compares
traditional risk calculations to methods that account for uncertainty and cumulative risk. Estimated
exposures did not exceed EPA-established RfDs or approximated probabilistic RfDs. While
potential pesticide exposures in licensed child care centers are unlikely to cause neurotoxic or
hepatotoxic effects, these estimates represent only a portion of the total daily exposure. Our tiered
approach to producing a comprehensive risk assessment for multiple pesticides in children’s ECE
settings is an important application of available methods for improved health risk assessment.
Chapter 4 examines the relationship between early life exposure to pesticide mixtures in house
dust and children's neurodevelopment, accounting for co-exposures and potential interactions with
social factors. We used Bayesian Hierarchical Modeling to evaluate the association between levels
of common pesticide classes detected in the dust and neurodevelopmental outcomes assessed by
the Wechsler Intelligence Scale for Children at age seven years. A 10-fold increase in pesticide
loading was associated with a 3-point deficit on the Processing Speed subscale at age seven years
for the organophosphate oxydemeton-methyl (median of posterior: -3.3 (95% CrI: -6.4, -0.2)), but
higher iprodione loading was associated with higher Verbal Comprehension subscale scores (2.5
(0.3, 4.6)). Results were null for pyrethroids, herbicides (individual or class effects), and for
interaction with the quality of the home environment. Early childhood exposure to pesticide
mixtures, especially organophosphates, in indoor environments may negatively impact children’s
cognition. Our findings support further research into pesticide mixtures effects potentiated by sex
of the child and quality of the home environment.
Chapter 5 concludes the dissertation with a summary of the results from each chapter, the
strengths and limitations of the current work, and a discussion of future directions for research on
children’s exposures to pesticides in early childhood environments.
