Date of Award

2017

Document Type

Open Access Thesis

Department

Environmental Health Sciences

Sub-Department

Norman J. Arnold School of Public Health

First Advisor

Sarah Rothenberg

Abstract

Objectives: Methylmercury is a neurotoxin that has the ability to cross the placenta and adversely affect the developing fetus. Our primary objective was to investigate whether prenatal methylmercury exposure varied longitudinally, and whether differences were associated with maternal characteristics.

Methods: Pregnant mothers were recruited in Charleston, South Carolina (8-17 weeks gestation) (n=78). Blood samples were collected during both early (11.8 ± 1.7 weeks) and late (35.3 ± 2.0 weeks) gestation. Blood total mercury and methylmercury concentrations were analyzed. Upon enrollment in the study, mothers filled out a sociodemographic questionnaire that included questions regarding maternal age, race/ethnicity, and education level. Additionally, 47 mothers completed a semi-quantitative food frequency questionnaire of 161 items, which included five questions on seafood consumption.

Results: The mean maternal blood total mercury concentration (n=156) was 0.88 ± 0.78 μg/L (range: 0.02-4.0 μg/L), and the mean maternal blood methylmercury concentration (n=156) was 0.54 ± 0.53 μg/L (range: 0.01-2.7 μg/L). Blood total mercury was positively correlated with blood methylmercury in early and late pregnancy (Spearman’s rho=0.89-0.92, p<0.01, n=78). The average number of fish meals consumed was 0.84 ± 0.79 meals/wk (range: 0-3.5 meals/wk). In unadjusted bivariate analyses, blood total mercury and methylmercury were positively correlated with the number of fish meals consumed per week in both early and late pregnancy (Spearman’s rho=0.41-0.63, p<0.01 for all, n=47), and blood total mercury and methylmercury were not significantly correlated with other covariates, including race/ethnicity (Spearman’s rho=-0.04, 0.19, p=0.11-0.98; Kruskal-Wallis, p=0.09-0.86, n=73-78). Using a paired t-test, blood methylmercury decreased from early to late pregnancy (paired t-test, p=0.04, n=78), while total mercury did not change (paired t-test, p=0.29, n=78). When normalized by hematocrit, the decrease in blood methylmercury was slightly attenuated (paired t-test, p=0.16, n=66). The reduction in blood methylmercury was not correlated with maternal characteristics, including race/ethnicity and education level (Spearman’s rho=-0.13, 0.10, p=0.28-0.76; Kruskal-Wallis, p=0.33-0.96, n=73-78). In the mixed model for repeated measures, adjusted for hematocrit, race/ethnicity, and time (early or late pregnancy), the association between blood mercury and race/ethnicity was strengthened, where African Americans had higher blood total mercury and methylmercury than Caucasians and Hispanics (t-test, p=0.02-0.04).

Conclusions: Blood methylmercury, but not total mercury, decreased significantly between early and late pregnancy in unadjusted models. This highlights the importance of mercury speciation, because often methylmercury is not measured. In adjusted models, African American mothers had significantly higher blood mercury compared to Caucasian and Hispanic mothers. Although nearly all values were low-level, there are still uncertainties regarding the health impacts due to prenatal methylmercury exposure.

Share

COinS