Mercury speciation in preserved sludge which is estimated to be remaining under the reclaimed land area of Minamata Bay Japan.

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K00533
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Environmental dynamic analysis
• Research Institution: National Institute for Minamata Disease
• Principal Investigator: Sakamoto Mineshi 国立水俣病総合研究センター, その他部局等, 主任研究員 (60344420)
• Co-Investigator(Kenkyū-buntansha): 板井 啓明 東京大学, 大学院理学系研究科(理学部), 准教授 (60554467) ; 冨安 卓滋 鹿児島大学, 理工学域理学系, 教授 (60217552) ; 児玉谷 仁 鹿児島大学, 理工学域理学系, 助教 (30434468)
• Research Collaborator: Marumoto Koji ; Marumoto Masumi ; Matsuyama Akito
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 水俣湾 / 汚泥 / 総水銀 / メチル水銀 / 硫化水銀

Outline of Final Research Achievements

We conducted the mercry speciation of current sediment and historical preserved sludge from the Minamata Bay area, Japan to evaluate potential risks of mercury pollution from sludge leakage. Total mercury (THg) dry basis was 0.18 μg/g for the control (n = 1), 6.1 μg/g for the current Minamata sediment (0.83-12.2, n = 5), and 241 μg/g for the preserved sludge (22.4-3620, n = 4). In turn, MeHg concentrations were 0.41%, 0.12% (0.051-0.21), and 0.031% (0.014-0.049), respectively. The main chemical form of the mercury in the preserved sludge was confirmed to be stable β-mercury sulfide via X-ray absorption fine structure (XAFS）analysis. The results of the present study, suggest that although THg is extremely high in the preserved sludge, the risk of MeHg pollution due to accidental leakage from the reclaimed land into Minamata Bay is low.

Free Research Field

環境科学

Academic Significance and Societal Importance of the Research Achievements

水俣湾の埋立地の下に閉じ込められた汚泥中水銀の化学形態別評価は、水俣湾における埋立地からのメチル水銀曝露リスク推定に重要である。今研究で、保存汚泥中のメチル水銀含有量は0.05％未満であり、保存汚泥中の主要水銀は、比較的不溶性で生物に取り込まれにくいβ-硫化水銀であることが示唆された。そこで、自然災害や鋼矢板の老朽化による埋立地からの汚泥流出は、湾内への直接のメチル水銀流出やその後の大幅なメチル水銀の増加に繋がらないと推察された。