UC Berkeley

Protecting children's environmental health is a significant public health challenge given children's unique exposure pathways and special vulnerabilities to environmental contaminants compared to adults. This dissertation focused on topics surrounding children's environmental health research with an emphasis on exposure assessment and application in an epidemiologic investigation. The environmental contaminants that this work focused on included pesticides and polybrominated diphenyl ether (PBDE) flame retardants.

Chapter 1 provides a general introduction to children's environmental health and highlights the background and significance and specific aims for each study/chapter.

Chapter 2 focuses on children's residential exposures via house dust to pesticides and PBDEs in low-income homes. House dust was used to assess indoor residential exposures to these environmental contaminants given that for young children this medium serves as a reservoir for contaminants tracked-in or used indoors and a source of non-dietary ingestion. Additionally, the contaminants of interest have been routinely measured in this medium. In this study, concentrations for 24 pesticides, one pesticide synergist, and three PBDE congeners (major constituents of the pentaBDE flame retardant commercial mixture commonly used on furniture) were measured in house dust samples from farmworker and urban homes in California. Pesticides frequently detected in most homes included: organophosphates (chlorpyrifos and diazinon) which were voluntarily phased-out for residential uses prior to this study by the urging of the United States Environmental Protection Agency (EPA); pyrethroids such as permethrins, allethrins, cypermethrins; and the synergist piperonyl butoxide. Interestingly, chlorthal-dimethyl was detected solely in farmworker homes, suggesting contamination due to regional agricultural use. All three PBDE congeners were detected in all homes and maximum concentrations for each of these congeners are the highest reported to date in house dust (BDE-47: 125 632 ng/g, BDE-99: 218 768 ng/g, BDE-100: 41 149 ng/g). Possible explanations for the high PBDE concentrations observed include California's stringent flammability standards and the presence of poorly constructed or deteriorating furniture treated with PBDEs as previously hypothesized by other researchers. Additionally, diazinon and chlorpyrifos concentrations in Salinas farmworker homes were lower than concentrations reported in samples from Salinas farmworker homes studied between 2000-2002, suggesting a temporal reduction after the U.S. Environmental Protection Agency's voluntary residential phase-out. Lastly, for some resident children, estimated non-dietary PBDE but not pesticide intake exceeded U.S. EPA recommended chronic reference doses (RfDs).

In chapter 3 the presence in the environment of dialkylphosphates (DAPs), non-specific urinary OP pesticide metabolites, and their relation to children's urinary DAP metabolites was investigated. Although DAPs were found to be present in the environment, as assessed in house dust, this medium may not play a significant contribution to the DAPs observed in children's urine. The non-dietary ingestion exposure route for environmental DAPs was estimated to be <5% of the dose calculated from DAP levels in children's urine. The distribution of concentrations of diethyl and dimethyl DAPs in dust differed from those observed in children's urine, a finding suggesting that DAPs behave differently in the environment and in the body. However, if humans excrete DAPs unchanged then it is possible for urinary DAPs to reflect exposure to both OP pesticides and DAPs present in one's environment and/or food. Results from this study indicate other sources and pathways, such as DAPs in food, may impact urinary DAP levels more significantly than DAPs in dust. More research is needed on the pharmacokinetics and toxicodynamics of preformed DAPs and other specific OP metabolites to determine the extent of their contribution to urinary biomarkers in humans.

In chapter 4 the effects of early life exposures to OP pesticides, as assessed by urinary DAP metabolites, on children's autonomic dysregulation (concomitant sympathetic activation and parasympathetic withdrawal) were assessed at several time points (i.e., when children were 6 months and 1, 3 ½ and 5 years of age). This is the first study to use ANS response measures as outcomes to investigate the association between OP pesticide exposures in children and ANS regulation. The study population was part of the Center for Children's Environmental Health Research longitudinal birth cohort study (CHAMACOS). Children in this cohort live in the Salinas Valley, an agricultural region in California with intense OP pesticide use and were predominantly from Mexico or Mexican-American. Children's autonomic nervous system (ANS) function was assessed using resting and reactivity measures of respiratory sinus arrhythmia (RSA), pre-ejection period (PEP), and heart rate (HR), while OP pesticide exposures were assessed in utero and postnatally by using urinary DAPs. Although the results suggest that OP pesticides at the exposure levels observed are not associated with children's ANS dysregulation, the study focused on a relatively demographically and ethnically homogeneous study population; thus, the results may not be generalizable to other populations. Future investigations in this population will involve evaluating what factors predict ANS regulation and whether ANS resting and reactivity measures of HR, RSA, and PEP are related to later physical and mental problems as observed in prior studies.

Finally, chapter 5 highlights the major findings, public health implications and future directions for each chapter/study.