Record of mercury pollution in sediments of lakes Nakaumi and Shinji in Japan
Two sediment core profiles from lakes Shinji and Nakaumi were studied in order to understand the level of mercury (Hg) pollution in lakes in northwestern Japan. The sedimentation rates were established on the basis of the activity of [210Pb] and [131Cs] in the sediments. In Lake Shinji, the highest level of Hg (130 ng g–1) in the sediment was found at a depth of 20–22 cm, while 195 ng g–1 was found at a depth of 10–12 cm in the core profiles from Lake Nakaumi. The relative increase in Hg concentration in lake sediments started after 1960 and significant contamination events occurred in the early 1960s. Mercury profiles in lake sediments from lakes Shinji and Nakaumi are found to reflect the anthropogenic Hg released into the environment in the 1950s and 1960s. A pronounced maximun concentration of Hg is found in both lakes, where sediment accumulation rates differ.