Utilization of tracer techniques in investigation and control of environmental pollution

General description of the tracer techniques in environmental problems is first given, then, the instances of three techniques, i.e. radioactive tracer, activable tracer, and environmental radioactivity tracer, are explained. In a salt electrolysis plant, the quantity of mercury is monitored by the isotope dilution method with radiomercury. In activable-tracer technique applied to the measurements of air pollutant, river water, etc., there are peculiar conditions to be considered in the chemical form of tracers. In the utilization of environmental radioactivity tracers, 222Rn is effectively used to know leakage of natural gas to ground surface and to observe the artificial turbulence of circulating water. (Mori, K.)