Prenatal Heavy Metal Exposure and Neurodevelopmental Outcomes in a Thai Agricultural Birth Cohort Open Access

Schenk, Jamie Erica (2015)

Permanent URL: https://etd.library.emory.edu/concern/etds/6969z139x?locale=en
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Abstract

Current research indicates that low-level prenatal exposure to heavy metals can have increasing neurotoxic effects, especially when exposure is during critical windows of development. Heavy metals can enter the environment through the use of synthetic products, such as pesticides, soldering materials, and paints. Heavy metals can also occur naturally, but rarely at toxic levels or with little bioavailability. The present study aimed to assess the relationship between in utero heavy metal exposure from maternal pesticide application and neurologic integrity at birth. Neurobehavioral function was measured using the Brazelton Neonatal Behavioral Assessment Scale (BNBAS), which utilizes seven clusters (Habituation, Orientation, Motor, Range of State, Regulation of State, Autonomic Stability, and Abnormal Reflex). Trimester-resolved concentrations of five heavy metals (chromium, arsenic, cadmium, mercury, and lead) were measured in blood to assess exposure to the fetuses of tangerine farmworkers in Northern Thailand. These farmworkers are participating in a pilot birth cohort called the Study of Asian Women And their offSpring's Development and Environmental Exposures (SAWASDEE). Results from the SAWASDEE cohort demonstrate that these infants are more highly exposed in utero to heavy metals and perform less optimally on the BNBAS. Significant associations were seen between arsenic levels and diminished Orientation (β=-1.06, 95% CI: -1.65, -0.48) and Motor (β=-1.13, 95% CI: -1.61, -0.64) clusters of BNBAS. For the Abnormal Reflexes cluster of BNBAS, it was demonstrated that there is a significant association between increased heavy metal levels and increased abnormal reflexes for each metal analyzed. The greatest significances were seen in arsenic in enrollment samples (β=1.06, 95% CI: 0.60, 0.85), cadmium in second timepoint samples (β=1.60, 95% CI: 0.54, 4.75), cadmium in third timepoint samples Cd: β=1.32, 95% CI: 0.56, 3.10), and arsenic in cord blood samples (β=1.07, 95% CI: 0.90, 1.28). Ultimately, these results are suggestive of a negative association between prenatal heavy metal exposure and neurobehavioral functioning at birth. This study is one of the first to examine the impact of trimester-specific exposure to heavy metals on neurodevelopment using several measures of exposure biomarkers in a highly exposed agricultural population.

Table of Contents

Table of Contents

I. BACKGROUND & SIGNIFICANCE................................................................................ 1

Heavy Metals................................................................................................................... 1

Prenatal Exposure.......................................................................................................... 5

SAWASDEE Birth Cohort................................................................................................. 7

Brazelton Neonatal Behavioral Assessment Scale........................................................ 9

Dialkyl Phosphate Metabolites (DAPs)......................................................................... 9

II. Methods...................................................................................................................... 10

Participants and Recruitment..................................................................................... 10

Questionnaire and Medical Record Abstraction Data................................................ 12

Exposure Assessment.................................................................................................. 12

Outcome Assessment................................................................................................... 13

Aims and Hypotheses.................................................................................................. 14

Data Analysis................................................................................................................ 14

III. Results....................................................................................................................... 15

Demographic Data....................................................................................................... 15

Exposure Distribution................................................................................................. 16

Outcome Distribution.................................................................................................. 18

Logistic Regression Analysis........................................................................................ 19

Linear Regression Analysis.......................................................................................... 20

Poisson Regression Analysis........................................................................................ 21

IV. DISCUSSION............................................................................................................... 22

Interpretation of Results............................................................................................. 22

Limitations.................................................................................................................... 26

V. CONCLUSION.............................................................................................................. 28

Summary...................................................................................................................... 28

Recommendations for Future Research..................................................................... 28

Policy Recommendations............................................................................................ 29

VI. REFERENCES............................................................................................................ 31

VII. TABLES AND FIGURES.......................................................................................... 34

VIII. APPENDICES........................................................................................................... 48

A. Methods for Scoring BNBAS..................................................................................... 48

1. BNBAS Items................................................................................................................................................................. 48

2. BNBAS Scoring Form............................................................................................................................................... 49

3. Seven Cluster Scoring Method........................................................................................................................... 53

B. Logistic Regression Analysis.................................................................................... 54

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