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Effects of methylmercury on neurodevelopment in Japanese children in relation to the Madeiran study

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Abstract

Objectives: A cross-sectional study was carried out to assess the effects of methylmercury exposure on neurodevelopment in Japanese children, in relation to the Madeiran cross-sectional study, and to estimate benchmark dose (BMD) levels using the data of two studies. Methods: Mercury levels in hair samples obtained from 327 Japanese mothers and their 7-year-old children, and methylmercury levels in the umbilical cord, were determined. Neurodevelopmental examinations, including the brainstem auditory evoked potential (BAEP), were performed on the children. Results: The medians of hair mercury were 1.63 (0.11–6.86) μg/g for mothers and 1.65 (0.35–6.32) μg/g for children, and a significant correlation was seen between the hair mercury levels in mothers and children. The maternal hair mercury was significantly correlated with the methylmercury in the umbilical cords obtained from 49 children. In 210 children whose mothers had not changed their dietary habits since pregnancy, most of the neurodevelopmental variables were not significantly related to hair mercury levels. The BAEP latencies were significantly shorter in the Japanese children than in the 113 Madeiran 7-year-old children, whose mothers had hair mercury of 1.12–54.5 (median 10.9) μg/g. Significant relationships between the maternal hair mercury level and BAEP latencies (peaks III and V, and interpeak I–III) were found only in the merged data of Japanese and Madeiran children. When the lower 95% confidence limit of BMD (BMDL) was calculated, the BMDLs of mercury exposure for BAEP latencies in the merged data were between 6.9 and 10.5 μg/g, and lower than those in the Madeiran children. Conclusions: It is suggested that Japanese children may ingest similar doses per body weight of methylmercury to their mothers. If maternal hair mercury was used as a proxy for mercury exposure at birth, no significant dose–effect associations with the BAEP latencies were observed in Japanese children with exposure levels below 6.9 μg/g of hair mercury, but only when higher-level exposures from Madeiran children were included. The BMDL was lower for the merged data than for Madeiran children alone.

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Acknowledgments

We thank Prof. Philippe Grandjean for his valuable comments, and Dr. Satoshi Terui and the Akita and Tottori Prefectural Education Boards for their cooperation in collecting the study population. This research was supported by a grant from the Ministry of the Environment, Japan, and partly by grants-in-aid for scientific research from the Nissan Science Foundation and the Ministry of Education, Culture, Science and Technology, Japan.

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Authors and Affiliations

  1. Division of Environmental Health Sciences, Department of Social Medicine, Akita University School of Medicine, 1-1-1 Hondo, Akita, 010-8543, Japan

    Katsuyuki Murata, Miwako Dakeishi, Toyoto Iwata, Tomoko Ohno & Tomoko Kurosawa

  2. Department of Epidemiology, National Institute for Minamata Disease, Minamata, Japan

    Mineshi Sakamoto & Xiao-Jie Liu

  3. Environmental Health Sciences, Tohoku University Graduate School of Medicine, Sendai, Japan

    Kunihiko Nakai & Hiroshi Satoh

  4. Department of Occupational and Public Health, Faroese Hospital Systems, Faroe Islands

    Pal Weihe

  5. Environmental Health Department, Ministry of the Environment, Tokyo, Japan

    Kazuko Kamiya

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  1. Katsuyuki Murata
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Correspondence to Katsuyuki Murata.

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Murata, K., Sakamoto, M., Nakai, K. et al. Effects of methylmercury on neurodevelopment in Japanese children in relation to the Madeiran study. Int Arch Occup Environ Health 77, 571–579 (2004). https://doi.org/10.1007/s00420-004-0542-1

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