Elevated levels of tritium in surface water collected in the immediate aftermath of the Fukushima accident

Abstract

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011, triggered by the Tohoku earthquake and tsunami, released a substantial amount of radionuclides into the environment, including approximately 2.7 PBq of ¹³⁷Cs and 200–210 TBq of tritium (³H). While extensive research has reported ¹³⁷Cs concentrations across various environmental media, data on ³H levels in water resources immediately following the accident remain limited. This study examines ³H concentrations in terrestrial surface water collected from one week to 100 days post-accident. ³H concentrations ranged from 0.3 to 267.8 Bq L⁻¹, with the highest levels exceeding typical background concentrations (0.5–2 Bq L⁻¹) by a factor of 200. The highest ³H concentration (267.8 Bq L⁻¹) was measured in snowmelt collected 100 km from the FDNPP one week after the accident, suggesting that snowfall effectively deposited atmospheric ³H. By one-month post-accident, all surface water samples showed ³H levels consistent with natural background concentrations, indicating rapid dispersion and dilution. No correlation was found between ¹³⁷Cs and ³H concentrations, likely due to their differing deposition mechanisms and environmental behaviors. An annual effective dose estimation, based on the ingestion of the most contaminated sample (snowmelt), was 3.5 × 10⁻³ Sv y⁻¹—286 times lower than the 1 mSv annual dose limit for the general public.