ABSTRACT

Rainwater has been sampled on a monthly basis at the University of Tsukuba, Japan, since 2009. The serious accident at the Fukushima Daiichi Nuclear Power Plant in March 2011 resulted in the atmospheric emission of large quantities of radionuclides. Monthly ¹²⁹I deposition was monitored for 19 months before and 41 months after the accident to estimate its influence at Tsukuba. Before the accident, ¹²⁹I concentration in rainwater was in the range (0.19–2.6) × 10⁸ atoms L^–1. There was a rapid increase after the accident, with the highest ¹²⁹I concentration recorded in March 2011 as (5.4 ± 0.8) × 10¹⁰ atoms L^–1. It took approximately 1 y for the ¹²⁹I concentration to return to pre-accident background levels, due to continuing resuspension and deposition. Measured decreases in ¹²⁹I concentration in rainfall showed good agreement with double-exponential modeling.