The behavior of pollutant lead in a river is discussed. The River Tamagawa which flows through Tokyo Metropolitan district in the lower stream was selected for this study. The lead concentration of the river water increased from 20 at the river head to 500 ng/kg at the middle and then increased to 2400 ng/kg at the lower stream. Although natural level of lead concentration in the lower stream is estimated to be around 200 ng/kg, the observed value is about 10 times as high as the value owing to nonnatural origin. Sediments showed the similar increasing pattern of lead to the water from 11 to 81 μg/g. The patterns are relative to the cumulative population in the drainage basin of the river, so that the introduction of pollutant lead by human activities is suggested. It seems that main source of pollutant lead is not conclusively attributed to automobiles from the consumption of lead alkyls in Japan in 1980. Suspended substance contained 30-60% of total lead in water at the normal flow. During the flood more than 95% of lead was carried out by particulate matter but the amounts of lead in the dissolved state remained rather constant. Approximately 80% of lead in sediments was considered to be contained in hydroxides of iron and others and organic matter.
