This study aimed at understanding the background concentration level of tritium in precipitation in southern Japan, where precipitation samples were collected monthly in 2022 in Okinawa and Kagoshima. Tritium concentration in monthly precipitation collected in Okinawa since 2014 ranged from 0.05 to 0.39 Bq per L with the mean value (2015–2022) of 0.15 ± 0.06 Bq per L. That of Kagoshima since 2022 ranged from < 0.11 to 0.58 Bq per L with the mean value of 0.30 ± 0.13 Bq per L. Our observed values were summarized with reported values, from which a clear latitude effect for tritium concentration was found in precipitation of southern Japan.

The combustion process of the organically bound tritium (OBT) analysis method is difficult and requires sophisticated techniques. For ease, safety, and reproducibility a semi-automatic combustion system was developed. An arbitrary combustion program that prevents sudden ignition was devised and combustion tests were conducted. Analytical test runs were conducted using fish standard samples to confirm the validity of the developed system. The test values were compared with values obtained with another analysis method, and the recovery rate of the combustion water was evaluated. The results confirmed that the analytical values obtained with this combustion system were equivalent to those obtained with another analytical method and were valid for OBT analysis.

This article mainly discusses tritium concentrations in monthly precipitation at Hiroshima City during 2021. The tritium concentrations, which were measured with a low background liquid scintillation counter, fluctuated from 0.16 to 0.78 Bq L−1. Additionally, hydrogen and oxygen stable isotopes and ionic species were measured in order to characterize precipitation, and their trends including tritium concentrations were compared with data collected in other regions of Japan in previous studies. Although the results showed the characteristics of precipitation were similar to those observed in the other regions, the tritium concentrations were found to be contrary to behavior expected from the latitude effect and some of the observed ionic components were suggested to be continental in origin. Since these results are not common at other sites in Japan, the tritium concentration in the westernmost region of Honshu, including Hiroshima City, may be influenced by Asian continental influences.

Granitic soils in the Highlands support the cultivation of Arabica coffee in northern Thailand; however, their geochemical and radiological properties are inadequately defined. This study examined major oxides, trace elements, natural radionuclides, and extractable phosphorus in granitic-derived coffee soils from the Agricultural Innovation Research, Integration, Demonstration, and Training Center (AIRID) in Chiang Mai. Twenty soil samples were obtained from 10 locations at two depth intervals (0–30 cm and 30–60 cm). Major and trace elements were analyzed via X-ray fluorescence (XRF), natural radionuclides were analyzed through high-purity germanium (HPGe) gamma spectrometry, and extractable phosphorus was determined using the Bray II method. The soils demonstrate remarkably high ⁴⁰K activity concentrations (1.2–1.9 kBq kg⁻¹) and increased K₂O contents (4.9–7.8 wt%), about three to five times more than worldwide soil averages according to Reimann & de Caritat, indicating enrichment from potassium-rich granitic rocks. Major oxide compositions suggest extensive tropical weathering, characterized by elevated SiO₂ (>60 wt%) and Al₂O₃ (>14 wt%), alongside significant depletion of CaO and MgO (<1 wt%). In topsoil, Bray II–extractable phosphorus constitutes 10–25% of total phosphorus and has a robust positive connection with P₂O₅ (R² = 0.95, p < 0.001), signifying surface accumulation and restricted vertical mobility. Multivariate analysis indicates lithogenic grouping of trace elements with negligible vertical redistribution. These findings establish a geochemical and radiological baseline for highland coffee soils in northern Thailand, with implications for soil fertility assessment, soil–plant transfer research, and evaluations of natural radioactive exposure related to coffee production.

The concentration of the radioactive cesium (134Cs and 137Cs) in soils and in atmospheric fallouts has been measured at the Koriyama campus, Nihon University, after the Fukushima Dai-ichi Nuclear Power Plant accident for 13 y, from October 2011 till September 2023 and now ongoing. The concentration of them decreased very rapidly due to decontamination activities and weathering effects, with an environmental half-life of 1.21 and 2.82 y in soils, with those of 1.58 and 2.08 y in atmospheric fallouts for 134Cs and 137Cs, respectively. The behavior of the decrease was not simple, due to particles raised from the surface soil in wooded areas that had not been thoroughly decontaminated or that had been accumulated due to the re-release of radioactive cesium by trees after decontaminated activity.