The Forestry and Forest Products Research Institute, a quasi-governmental "independent administrative agency" in Japan, has demonstrated how a cedar forest ecosystem functions to filter and collect lead from polluted air and prevent efflux back into the environment, according to its report released on October 23, 2007.
Researchers first measured and analyzed lead levels in Japanese cedar trees and soil in forests in Japan's Kanto region. As a result, in addition to finding direct absorption of lead in the soil, it identified a forest mechanism that prevents lead runoff through a cyclical process in which lead in the air is first washed to the earth by precipitation, taken up by tree roots, accumulates in the leaves and branches, and eventually returns to the surface soil when leaves fall to begin the cycle again.
Even a small amount of lead is harmful to living organisms, and it is retained for a long time once released into the environment. By the late twentieth century, a large amount of lead had been used as a gasoline additive and released into the air through emissions. Although most Japanese assume that the problem of lead-polluted air was solved with the introduction of a lead-free gasoline policy in Japan, various other human activities continue as sources of lead emissions even now.
The institute plans to further assess the impact of lead accumulation on forest plants and animals, as well as track the effects of lead on forest soil surfaces.