Chronological trends in trace metals recorded by a tree bark pocket in Yakushima Island, Japan

Abstract

Bark included within the trunk of a 200-year-old Japanese cedar tree harvested in Yakushima Island, Japan, a World Natural Heritage Site located 150 km south of mainland Japan and 800 km east of Shanghai, China, was analysed for trace metals by ICP-MS providing a chronology of atmospheric pollution. The concentration of V, As and Pb in decadal sections of the bark pocket increased 30 to 50 fold from 1900–09 to 1960–69, indicating increased atmospheric deposition of these metals. The trend coincided with the establishment and expansion of heavy industries in Kyushu, Japan, resulting in locally high levels of air pollution. V, As and Pb subsequently declined, reflecting lower industrial emissions following air pollution control legislation from the late 1960’s and decline in heavy industries. Ni, Cu and Zn showed a relatively small, 7 to 10 fold increase over time. Lead isotope ratios in the bark pockets shifted from about 0.84 to 0.86 for ²⁰⁷Pb/²⁰⁶Pb and from 2.04 to 2.10 for ²⁰⁸Pb/²⁰⁶Pb, showing that the origin of atmospheric lead changed over time from coal to more diverse sources.