Associations Between Thyroid Hormone Levels and Biomarkers of Exposure to DDT and DDE in Mexican-Americans

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P-591 Introduction: Exposure to environmental chemicals has been associated with a range of adverse health effects, including effects on thyroid hormone levels in animals and humans. The organochlorine pesticides, including DDT and its environmental contaminant DDE, are among the chemicals associated with hormonal effects, including thyroid hormones. Thyroid hormone is critical for normal growth and development, and alterations in thyroid hormone levels may have significant health implications. Methods: The U.S. National Health and Nutrition Examination Survey (NHANES) collected blood DDT and DDE concentrations and thyroxin and thyroid stimulating hormone levels from 1999–2002 from a statistical sample of about 4,200 persons in the U.S. We analyzed these data to study the associations between exposure to DDT and DDE and levels of thyroxin and thyroid stimulating hormone in the U.S. population and selected subpopulations defined by country of origin, demographic characteristics, socioeconomic status, and geographic region. Results: DDE was above the limit of detection in the blood of 99.9% of the sampled persons. Mexican- born Americans have an arithmetic mean of 2310 ng/g (95% confidence interval 1814–2807), while the U.S. born have an arithmetic mean of 473 ng/g (417–528). Older persons have higher DDE levels, reflecting the history of the use of DDT. Pearson and Spearman correlations between DDE and thyroid hormone levels were computed for selected subsets of the U.S. population. Most of the correlations were low in magnitude, although some were statistically significant. In this type of study a causal association cannot be established. Discussion: While most of these factors exhibited little influence on the association between DDE and hormone levels, county of origin exibited a significant association. Specifically, U.S. residents born in Mexico had substantially higher levels of DDT and DDE than any other group, including Mexican-Americans born in the U.S. The findings and conclusions in this presentation have not been formally disseminated by the U.S. Environmental Protection Agency and should not be construed to represent any Agency determination of policy.