Long-range transport of heavy metals from the Asian continent contributes to surface sediments in Lakes Shinji and Nakaumi in western Japan

Evaluation of sources of metal contamination in freshwater and short-neck clams marketed in Japan based on lead isotope ratios

“…Such high Pb isotope ratios have never been observed in Japanese aquatic regions such as Tokyo Bay and Lake Shinji. Additionally, they cannot be explained by the discharge of domestic waste waters, including treated water from sewage treatment plants (Sakata et al, 2018) and mining or smelting effluent associated with Pb ores in Japan. The Japanese Pb ores have relatively low Pb isotope ratios because the formation age of Pb ores is considerably young.…”

“…3 Pb isotope ratios ( 207 Pb/ 206 Pb and 208 Pb/ 206 Pb) in freshwater (F-1-F-19) and short-neck (S-1-S-7) clam samples. These values are compared with those in the surface (polluted by Pb) and background (unpolluted by Pb) sediments in Tokyo Bay (Hirao et al, 1986;Sakata et al, 2018) and Lake Shinji (Kusunoki et al, 2012) 2 4). This supports the hypothesis that the Pb in those freshwater clam samples F-14, F-15, F-16, and F-18 originates predominantly from effluent and exhaust from mining or smelting associated with old Pb ores formed in countries such as China and North Korea.…”

“…Thus, the Pb ore deposits (primarily galena, PbS) formed in the ancient times of Earth have relatively high Pb isotope ratios. The Pb isotope ratios in the clam samples were compared with those in the surface (polluted by Pb) and background (unpolluted by Pb) layers of sediment cores in Tokyo Bay (Hirao et al, 1986;Sakata et al, 2018) and Lake Shinji (Kusunoki et al, 2012). Anthropogenic Pb in surface sediments were observed to be enriched in Tokyo Bay and Lake Shinji probably owing to the discharge of river bottom sediments polluted by Pb (Sakata et al, 2018) and the longrange transport of Pb from the Asian continent (Kusunoki et al, 2012;Kusunoki and Sakata, 2018), respectively.…”

“…The Pb isotope ratios in the clam samples were compared with those in the surface (polluted by Pb) and background (unpolluted by Pb) layers of sediment cores in Tokyo Bay (Hirao et al, 1986;Sakata et al, 2018) and Lake Shinji (Kusunoki et al, 2012). Anthropogenic Pb in surface sediments were observed to be enriched in Tokyo Bay and Lake Shinji probably owing to the discharge of river bottom sediments polluted by Pb (Sakata et al, 2018) and the longrange transport of Pb from the Asian continent (Kusunoki et al, 2012;Kusunoki and Sakata, 2018), respectively. It is noteworthy that the Pb isotope ratios in the background sediments in Tokyo Bay and Lake Shinji are almost identical to those in Japanese background soils ( 207 Pb/ 206 Pb = 0.846 ± 0.004; 208 Pb / 206 Pb = 2.093 ± 0.011; Sakata et al, 2021).…”