Chemical factors (including pH, redox potential, content of total organic compound (TOC) and major ions) and U/Th-series radionuclides in the hot-spring water environment of Peito were determined to investigate the impact of environmental change and migration of radionuclides in water on conserving the precious mineral, hokutolite, in Peito (Taiwan). The activity concentrations of U/Th increased with Eh and those of Cl− and SO42−. 234U/238U ratios were nearly >1 ascribed to Szilárd–Chalmers effect and α-recoil. 230Th/234U ratios were <1 resulting from complexation with chloride and sulfate ions. 228Ra and 226Ra activities were governed by pH, Eh and SO42− concentration. Disequilibria of 228Th/228Ra and 228Ra/232Th were evident attributed to complexation of Th with major anions and co-precipitation of radium with (Ba,Pb)SO4. Alpha-recoil caused the enrichment of 228Ra and apparent disequilibrium of 232Th/228Th. A mechanism illustrating the radiochemistry involving the formation of hokutolite in Peito was derived accordingly. The water environment of the studied area was found apparently changed in light of the variation of temperature, TOC and concentration ratio of Ba/Pb, which resulted from the channeling of hot spring water and the release of household waste water. The water environmental change can thus hinder the migration of radionuclides as well as the formation of hokutolite so that the performance of hokutolite conservation can be decreased. Immediate enactment of regulations for conserving hokutolite in Peito was therefore suggested in this research.
