The Fukushima Dai-ichi Nuclear Power Plant accident in 2011 has released a large amount of radionuclides to the atmosphere, and the radioactive plume has been dispersed to a large area in Europe and returned to Asia. To explore long-term trend of the Fukushima-derived radioactive plume and the behavior of harmful radioiodine in the atmosphere, long-term precipitation samples have been collected over 2010–2012 at Fukushima, Japan for determination of long-lived 129I. It was observed that 129I concentrations of 1.2 × 108 atom/L in 2010 before the accident dramatically increased by ∼4 orders of magnitude to 7.6 × 1011 atom/L in March 2011 immediately after the accident, with a 129I/127I ratio up to 6.9 × 10–5. Afterward, the 129I concentrations in precipitation decreased exponentially to ∼3 × 109 atom/L by October 2011 with a half-life of about 29 days. This declining trend of 129I concentrations in precipitation was interrupted around October 2011 by a new input of 129I to the atmosphere following a second exponential decrease. Such a cycle has occurred three times until the present. This temporal variation can be attributed to alternating 129I dispersion and resuspension from the contaminated local environment. A 129I/131I atomic ratio of 16 ± 1 obtained from rainwater samples is comparable with a value estimated for surface soil samples. 129I results from Denmark suggest an insignificant effect of 129I released from Fukushima to the 129I levels in Europe.
Environmental Science and Technology, 2013, Vol 47, Issue 19, p. 10851-10859