Preschool-age children’s exposures to pesticides measured in indoor dust in California

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. 2 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.

Advisor: Bradman, Asa
Graham, Jay