Blood total mercury and methylmercury among pregnant mothers in Charleston, South Carolina, USA

Background Maternal blood total mercury (THg) is a biomarker for prenatal methylmercury (MeHg) exposure. Few studies have quantified both blood THg and MeHg during pregnancy, and few studies have reported longitudinal trends. Objectives We analyzed blood THg and MeHg in a cohort of pregnant mothers in Charleston, South Carolina (n = 83), and investigated whether blood THg or MeHg changed between early and late gestation. Methods THg and MeHg were analyzed in blood samples from early (12 +/- 1.7 weeks) and late (35 +/- 2.2 weeks) gestation. Results Blood %MeHg (of THg) averaged 63% (range: 10-114%) and 61% (range: 12-117%) during early and late gestation, respectively. In unadjusted analyses, blood MeHg decreased from early to late pregnancy (paired t-test, p = 0.04), while THg did not change (paired t-test, p = 0.34). When blood MeHg was normalized by the hematocrit, this decrease was no longer statistically significant (paired t-test, p = 0.09). Conclusions In unadjusted analyses, blood MeHg, but not THg, decreased significantly between early and late gestation; this decrease was due in part to hemodilution. Percent MeHg (of THg) varied by up to one order of magnitude. Results highlight the importance of Hg speciation in maternal blood samples to assess prenatal MeHg exposure.