Total mercury levels in hair of children aged 7 years before and after the Great East Japan Earthquake

The Great East Japan Earthquake on March 11, 2011 caused severe damage to the Sanriku coastal area, where we have been conducting a birth cohort study. The disaster occurred in the middle of 7-year-old examination. The mother-child pairs who participated in our study were compulsorily divided into two groups: the examination was finished for 157 children before the disaster, and for 335 after the disaster. We examined whether the disaster affected total mercury (THg) levels of the cohort, as well as a relationship between the THg levels at birth and at present. Although there was no significant difference between the predisaster and postdisaster groups for THg levels in cord blood (16.3 and 16.1 ng g^− 1, respectively) or maternal hair at parturition (2.57 and 2.55 μg g^− 1, respectively), the THg in hair of the 7-year-old children was significantly lower in the postdisaster group (1.79 μg g^− 1) than in the predisaster group (2.51 μg g^− 1). The difference remained significant after adjusting for the prenatal exposure level of THg. In the 492 mother-child pairs, the cord-blood THg was significantly correlated with the THg in maternal hair at parturition (r = 0.846) and in hair of the 7-year-old children (r = 0.147). In conclusion, the 29% decrease in hair THg after the disaster appears to have been due to the fact that children in the affected area could not consume fish/seafood as usual, probably because of destructive damage to the fishery. Nevertheless, the THg levels at 7 years of age reflected the prenatal exposure levels to some extent.