Aqueous characteristics and radionuclides in Peito Hot Spring Area

Aqueous characteristics and activity concentrations of U/Th-series radionuclides were investigated in the birthplace of hokutolite – the Peito Hot Spring Area in Taiwan. Water samples were taken in 12 locations from the hot spring pond and the Peito Creek in this study. Temperature, acidity and redox potential exhibited similar trends decreasing from the hot spring pond toward downstream Peito Creek. The aqueous environment of this area existed in an acidic and oxidative state and was found influenced by hot spring water drawing and wastewater discharge. Major ions in water were Fe3+, Ca2+, Sr2+, Ba2+, Pb2+, Cl− and SO42−, which (except for Ba2+) generally varied with sampling locations in a tendency similar to those of temperature, acidity and redox potential. U/Th-series radionuclides were examined by α spectrometry while 226Ra were determined with ICP-QMS. Th-series was found predominant over U-series in this area. Activity concentrations of 238U (0.09 ± 0.02 to 2.69 ± 0.13 pCi/L) and 234U (0.10 ± 0.02 to 2.64 ± 0.13 pCi/L) were similar and the activity ratios for 234U/238U were greater than unity. For 230Th and 226Ra, the activity concentrations were respectively 0.07 ± 0.03 to 0.86 ± 0.06 pCi/L and 0.17 ± 0.02 to 1.49 ± 0.06 pCi/L, which led to activity ratios of 230Th/234U lower than unity while those of most 226Ra/230Th greater than unity. In Th-series, the activity concentrations of 232Th (0.06 ± 0.02 to 0.90 ± 0.06 pCi/L) and 230Th were similar at the sampling area. Apparent disequilibria were discovered between 228Ra and 232Th resulting from abundant 228Ra (6.01 ± 0.41 to 10.5 ± 0.8 pCi/L). The variation for activity concentration of 228Th (0.43 ± 0.06 to 9.26 ± 0.18 pCi/L) with sampling locations was similar to that of 232Th. However, significant disequilibria were discovered between 228Th and 232Th. The reported data contribute to the assessment of radionuclides distribution and the investigation of hokutolite recovery in the studied area.