Lead isotope ratios in Tokyo Bay sediments and their implications in the lead consumption of Japanese industries.

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Abstract
The annual lead accumulation and the change of the isotope ratios of sediments in the Tokyo Bay are discussed in relation to the development of the Japanese industrial activities. Lead had been spread out from the north western part of the bay, showing a part of concentric circles. The total lead accumulation rate in the bay was calculated to be 17t/y in 1880, which was regarded as the non-artificial lead input rate, and increased gradually with time reflecting increase in the consumption of lead in Japanese industries. In 1920, the isotope ratios changed extraordinarily, which was estimated to be caused by the introduction of the Broken Hill lead of Australia. The annual lead accumulation has been accelerated since 1950 and the isotope ratios have also been affected by the change in the varieties of the sources. It reached a maximum, 110t/y, in 1970 and was reduced to 71t/y in 1980. Although the sources of anthropogenic lead are complicated, the gasoline additives would be one of the major sources for the lead pollution until 1970. Although the consumption of gasoline additives in 1980 was reduced to 1/20 of the 1970 value in Japan, the decrease of the gasoline lead seems not yet clearly observed isotopically in the sediments of the bay. The lead in the cored sediments did not move vertically, but showed a systematic difference horizontally after anthropogenic lead was introduced into the by. The systematic difference of the isotope ratios indicates the difference of the pollution sources.

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