Significance of fingernail and toenail mercury concentrations as biomarkers for prenatal methylmercury exposure in relation to segmental hair mercury concentrations

Objective: To investigate the appropriateness of mercury (Hg) concentrations in fingernails and toenails at parturition for detecting prenatal exposure to methylmercury (MeHg). Methods: Total Hg concentrations were measured in 54 paired samples of fingernails, toenails, maternal blood, and maternal hair (1 cm incremental segments from the scalp toward the tip) collected at 4th weeks of (early) pregnancy, and the same specimens and cord blood collected at parturition. Results: Strong correlations were observed between Hg concentrations in fingernails and toenails at early pregnancy (r=0.923, p <0.01) and at parturition (r=0.895, p <0.01). At early pregnancy, Hg concentrations in fingernails and toenails showed the strongest correlations with those in hair 3-4 cm from the scalp (r=0.818 and r=0.747, p <0.01, respectively) among the 1 cm incremental hair segments. Mercury concentrations in fingernails and toenails at parturition represented strong correlations with those in cord blood (r=0.803, p <0.01 for fingernails and r=0.792, p <0.01 for toenails, respectively). At parturition, Hg concentrations in fingernails had the highest correlation with those in hair 0-1 cm from the scalp (r=0.918, p <0.01), and Hg concentrations in toenails showed the highest correlation with those in hair at 2-3 cm from the scalp (r=0.872, p <0.01). In addition, Hg concentrations in both finger and toe nails at parturition had equally high (p < 0.01) correlation coefficients with hair segments at 0-1, 1-2, and 2-3 cm from the scalp. Conclusions: Mercury in fingernails and toenails at early pregnancy reflected the maternal Hg body burden level approximately 5 months retroactively. At parturition, Hg levels in fingernails and toenails also showed strong correlations with those in cord blood. In addition, Hg levels in fingernails and toenails at parturition reflected more recent MeHg exposure, compared with those at early pregnancy. These results suggest that fingernails and toenails at parturition are useful biomarkers for prenatal MeHg exposure for mothers and fetuses, especially during the third-trimester of gestation. (C) 2014 Elsevier Inc. All rights reserved.