Fukushima's Tap and Groundwater a Decade after the Nuclear Accident with Radiocesium, Tritium, and Radon

More than 13 years after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, concerns remain about drinking water contamination from artificial radionuclides and the ongoing discharge of tritiated water into the Pacific Ocean. However, natural radionuclides unrelated to FDNPP releases can also contribute to human radiation exposure. Here, we measured radionuclides in Fukushima tap and groundwater to assess exposure from ²²²Rn (natural); ¹³⁷Cs (artificial); and ³H (both artificial and natural). Ten years after the accident, all drinking water samples had ¹³⁷Cs levels below detection limits (<0.02 Bq L^-1), while only groundwater had elevated ²²²Rn (<3-399 Bq L^-1). Trace amounts of ³H (0.07-0.55 Bq L^-1) were measured in both sources, with tap water generally exhibiting higher levels. ³H levels in drinking water did not increase after several discharges of tritiated water into the Pacific Ocean. Estimated annual effective doses from tap water were 0.57 μSv (¹³⁷Cs), 0.0058 μSv (³H), and 20 μSv (²²²Rn). For groundwater, doses were 0.57 μSv (¹³⁷Cs), 0.0072 μSv (³H), and 1020 μSv (²²²Rn). The primary radiation exposure source is naturally occurring ²²²Rn from rock formations. Boiling well water in a vented area reduced radon levels by 95%, significantly mitigating exposure.