Methylmercury in the breast milk of Japanese mothers and lactational exposure of their infants

Miyuki Iwai-Shimada, Hiroshi Satoh, Kunihiko Nakai, Nozomi Tatsuta, Katsuyuki Murata, Hirokatsu Akagi

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24 Citations (Scopus)


The human fetus is known to be exposed to methylmercury (MeHg), but little is known about the risk of infant exposure via breast milk. To evaluate the lactational exposure to MeHg via breast milk in Japanese infants, the levels of total mercury (THg) and MeHg were determined in breast milk and maternal blood using samples from a birth cohort study at the Tohoku Study of Child Development. Maternal blood and breast milk were collected one day postpartum and one month after delivery, respectively. The median THg (and MeHg) concentrations in maternal RBCs, plasma and breast milk were 17.8ngg-1 (17.8ngg-1), 1.51ngg-1 (1.33ngg-1) and 0.81ngg-1 (0.45ngg-1), respectively (n=27). The median percentage of MeHg in THg was 54% in breast milk. Breast milk contained substantial amounts of MeHg, which was strongly associated with the internal accumulation of MeHg and the lipid content of the milk (r=0.684). The range of lipid contents in milk varied widely from 0.50 to 6.60g/100g of milk, with a median of 3.60g/100g. The median (range) weekly average intake of MeHg via breast milk was estimated to be 0.63μgkg-1 (0.08-1.68μgkg-1) BW/week. Because the MeHg and lipid contents in milk substantially fluctuate, an investigation of the variations of MeHg and lipid content in breast milk may be required for a more precise risk assessment.

Original languageEnglish
Pages (from-to)67-72
Number of pages6
Publication statusPublished - 2015 May 1


  • Inorganic mercury
  • Lactational exposure
  • Mercury
  • Methylmercury
  • Milk


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