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This review describes applications of inductively coupled plasma mass spectrometry (ICP-MS) to the determination of long-lived radionuclides in environmental samples. Simultaneous determination of 232Th and 238U in biological samples is described in detail; in this procedure an internal standard, Tl or Bi, is adopted for correction of the matrix effect. Determination of 237Np in soil samples by ICP-MS is also described. It is chemically separated to ensure no interference from matrix elements. The detection limits are several mBq (several pg) for the case of radionuclides having a half life of thirty or forty thousand years.

Tritium, deuterium and chloride concentrations in the Arima hot spring waters were measured as a clue to their origin and subsurface behavior. T-D-Cl relationships clearly indicate that the saline brine of deep origin (T=O TR, SD=-30%o and C1-=43 g/1) is mixed with young meteoric water having T=30 TR, SD= -50 %o and Cl-= Og/l in varying proportions to form a group of high chloride hot spring waters. The young meteoric water in a shallow aquifer is also mixed with the older meteoric water in a deeper aquifer characterized by high tritium concentration (^-100TR), forming another group of low chloride waters. The mixing ratio of the two meteoric waters varies with season.

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