Record of lead pollution in sediments of the Tokyo Bay, Japan

Lead concentration and 210Pb activity profiles of 8 core samples from the inner Tokyo Bay were determined. The lead profiles showed a typical lead pollution pattern by human activities. Generally the lead concentration increased gradually from the background level of about 15 ppm before 1900 A.D. to the level in 1940's and then grew up rapidly until 1970. The pollution lead went up as high as about 7 times the natural value in around 1970 in some cores. Since 1970, lead concentration has been decreasing clearly up to date. The average lead accumulation rates in the bay were estimated to be 7.1μg/cm2/y in 1980 and 13μg/cm2/y in 1970. The value of 2.2μg/cm2/y in around 1880 seems close to the natural input rate. More than 75% of the accumulated lead during 1945–1980 was contributed by the pollution lead. Even before that time, 1900–1945, a half of the accumulated lead resulted from the human activities. The values indicate that the Tokyo Bay has been exposed to severe lead pollution for a long time.