No detectable impact of ALPS-treated water discharge on tritium levels in terrestrial waters of the upper Ota River catchment, Fukushima, Japan.

Tritium (3H) is the principal radionuclide remaining in ALPS-treated water discharged from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), and its potential environmental impact has drawn considerable attention. To evaluate possible terrestrial effects, 3H concentrations were monitored in precipitation, groundwater, and river water in the upper Ota River catchment in Fukushima Prefecture. Monthly samples were collected before and after the initiation of oceanic discharge in August 2023. Time-series comparison showed no discernible increase in 3H concentrations after the start of discharge for any water type. Non-parametric statistical analysis further confirmed the absence of significant differences for groundwater and river water. Observed variations were consistent with natural background levels and known seasonal patterns in precipitation in Japan. These results indicate that ALPS-treated water discharge has had no detectable impact on terrestrial waters in the study area.