Neurodevelopmental associations of prenatal and postnatal methylmercury exposure among first-grade children in the Kinan region, Japan

Masaaki Nakamura; Nozomi Tatsuta; Katsuyuki Murata; Kunihiko Nakai; Toyoto Iwata; Takayuki Otobe; Mineshi Sakamoto; Megumi Yamamoto; Mina Itatani; Yoko Miura; Chihaya Koriyama

doi:10.1016/j.envres.2023.116688

Neurodevelopmental associations of prenatal and postnatal methylmercury exposure among first-grade children in the Kinan region, Japan

Environ Res. 2023 Oct 15:235:116688. doi: 10.1016/j.envres.2023.116688. Epub 2023 Jul 17.

Authors

Affiliations

¹ Department of Clinical Medicine, National Institute for Minamata Disease, 4058-18 Hama, Minamata City, Kumamoto, 867-0008, Japan. Electronic address: MASAAKI_NAKAMURA@env.go.jp.
² Development and Environmental Medicine, Tohoku University Graduate School of Medicine, Sendai City, Miyagi, 980-8575, Japan. Electronic address: nozomi@med.tohoku.ac.jp.
³ Department of Environmental Health Sciences, Akita University Graduate School of Medicine, 1-1 Hondo, Akita City, Akita, 010-8543, Japan. Electronic address: winesteem@yahoo.co.jp.
⁴ Development and Environmental Medicine, Tohoku University Graduate School of Medicine, Sendai City, Miyagi, 980-8575, Japan. Electronic address: nakai-k@tokaigakuen-u.ac.jp.
⁵ Department of Environmental Health Sciences, Akita University Graduate School of Medicine, 1-1 Hondo, Akita City, Akita, 010-8543, Japan. Electronic address: iwata@med.akita-u.ac.jp.
⁶ Department of Child Education, Jin-ai University, Echizen City, Fukui, 910-0124, Japan. Electronic address: otb@jindai.ac.jp.
⁷ Department of Environment and Public Health, National Institute for Minamata Disease, 4058-18 Hama, Minamata City, Kumamoto, 867-0008, Japan. Electronic address: MINESHI_SAKAMOTO@env.go.jp.
⁸ Department of Environment and Public Health, National Institute for Minamata Disease, 4058-18 Hama, Minamata City, Kumamoto, 867-0008, Japan. Electronic address: MEGUMI_YAMAMOTO@env.go.jp.
⁹ Department of Clinical Medicine, National Institute for Minamata Disease, 4058-18 Hama, Minamata City, Kumamoto, 867-0008, Japan. Electronic address: MINA_ITATANI@env.go.jp.
¹⁰ Department of Clinical Medicine, National Institute for Minamata Disease, 4058-18 Hama, Minamata City, Kumamoto, 867-0008, Japan. Electronic address: YOKO_MIURA@env.go.jp.
¹¹ Department of Epidemiology and Preventive Medicine, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima, 890-8544, Japan. Electronic address: fiy@m.kufm.kagoshima-u.ac.jp.

PMID: 37467938
DOI: 10.1016/j.envres.2023.116688

Abstract

The most severe effects of methylmercury (MeHg) exposure during child development are thought to result from exposure during fetal life and childhood. However, comparing the neurodevelopmental effects of prenatal and postnatal MeHg exposure (PreMeHg and PostMeHg, respectively) remains unclear. We aimed to investigate the associations between neurodevelopmental indicators and PreMeHg or PostMeHg. The participants were 134 children in the first grade of elementary schools aged 7-8 years from the Kinan region, an area with high consumption of MeHg-rich whales and tunas in Japan. We measured MeHg levels in preserved umbilical cord tissues and total mercury (T-Hg) levels in children's hair to estimate PreMeHg and PostMeHg levels, respectively. Neuropsychological (intelligence quotient testing and Boston Naming Test) and neurophysiological (brainstem auditory evoked potential [BAEP], visual evoked potential [VEP], and color vision tests) studies were performed to evaluate the neurodevelopmental status. Multiple regression analyses were conducted according to sex. The geometric mean MeHg levels in preserved umbilical cord tissues and T-Hg levels in children's hair were 0.11 μg/g and 2.94 μg/g, respectively. Neither PreMeHg nor PostMeHg was related to neuropsychological indicators. Some associations between MeHg exposure and neurophysiological results were observed only in boys. N145 latency in VEPs was significantly prolonged with increasing PreMeHg (β: 12.01, 95% confidence interval [CI]: 0.648, 23.38). The III-V interpeak intervals in BAEP were significantly prolonged with increasing PreMeHg or PostMeHg (β [95% CI]: 0.142 [0.041, 0.243] and 0.159 [0.052, 0.265], respectively). After adjusting for PreMeHg, the association between PostMeHg and BAEP latencies disappeared. In conclusion, the latency in the auditory and visual pathways was significantly prolonged with increasing PreMeHg in boys. These findings suggest that male fetuses may be more susceptible to MeHg exposure.

Keywords: Child development; Childhood; Fetal life; Kinan region; Sex; Whales.

MeSH terms

Child Development
Evoked Potentials, Visual
Female
Humans
Japan
Male
Mercury* / analysis
Methylmercury Compounds* / analysis
Pregnancy
Prenatal Exposure Delayed Effects* / chemically induced
Prenatal Exposure Delayed Effects* / epidemiology

Substances

Methylmercury Compounds
Mercury