Industrial emission of cadmium in Japan.

Direct emission of cadmium into air and water in Japan has been controlled on the basis of the Emission and Effluent Standards. Environmental quality in these media has been improved, but delayed effects of these emissions in the past are now manifest by contamination of agricultural acreage in various parts of this country. Special land improvement projects are therefore required, and cost allocation should be made on the basis of scientific assessment of natural background. An impact assessment on accidental release of potential sources of cadmium dispersed in the water system should be made on the basis of inventory surveillance. Assessment of natural background can practically be made by two means. One is to examine the vertical distribution of cadmium in a soil profile and to search for a subsurface layer in which there can be no contamination. Another is the use of the Zn/Cd ratio as an index of pollution, a value of 400 being suggested as a screening level. The transport of cadmium was found to occur principally in particulate form, and sampling and analysis of water together with suspended solid after a heavy rainfall is suggested as a useful means for assessing the character of a catchment area and for planning the improvement of land surface in mining districts.