Research on tree trunk bark pocket as pollution time capsules

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The concentration of lead in bark pockets of tree trunks was investigated for its potential use as an archival indicator of pollution. The bark pocket investigated were those of a conifer, Cryptomeria japonica, formed around 1760-1780 (235-255 years ago) at Nikko about 100 km north of Tokyo, and around 1786-1809 (186-209 years ago) on Yakushima Island, located in a remote southern region of Japan. The lead concentrations in these C.japonica bark prockets, repesenting the total lead accumulation during a period of about 20 years at each site, were 0.1 mug Pb g^<-1> at Nikko and 0.22 mug Pb g^<-1> at Yakushima. In contrast, the lead concentration in the outer bark of C.japonica at the present time is about 150 mug Pb g^<-1> at Nikko (1990) and 1.4mug Pb g^<-1> at Yakushima (1992). The use of leaded gosoline, the main source of lead in atmosphere, was initiated in Jaan in 1949 and reached a maximum during 1960-1965. As the production of leaded gosoline was stopped in 1987, the lead concentration in the outer bark represents the total for a period of about 40 years. Therefore, these results suggest an increase in lead pollution of about three orders of magnitde at Nikko, which is relatively close to Tokyo, and one order of magnitde at Yakshima, which is relatively remote.