Research on tree trunk bark pocket as pollution time capsules

研究了树干树皮袋中铅的浓度，以期将其作为污染的档案指标。被调查的树皮袋是一种针叶树，日本Cryptomeria japonica，大约形成于1760-1780年（235-255年前）在东京以北100公里的日光，以及大约1786-1809年（186-209年前）在日本南部偏远地区的屋久岛。日兴地区和屋久岛地区的铅浓度分别为0.1 mg Pb g^<-1>和0.22 mg Pb g^<-1>。相比之下，目前日本金银花外皮的铅浓度在Nikko（1990）约为150杯Pb g^<-1>，在屋久岛（1992）约为1.4杯Pb g^<-1>。含铅汽油是大气中铅的主要来源，于1949年在Jaan开始使用，并在1960-1965年达到最大值。由于含铅gosoline的生产于1987年停止，因此外层树皮中的铅浓度代表了大约40年的总铅浓度。因此，这些结果表明，在距离东京相对较近的日光，铅污染增加了约3个数量级，而在距离东京相对较远的屋岛，铅污染增加了1个数量级。

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.