Geochemical Journal, Vol. 47 (No. 1), pp. 79-82, 2013
Yutaka Kanai,1 Yoshiki Saito,1 Toru Tamura,1 Van Lap Nguyen,2 Thi Kim Oanh Ta2 and Akio Sato3
1Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba, Ibaraki 305-8567, Japan
2HCMC Institute of Resources Geography, VAST, 1 Mac Dinh Chi St., 1 Dist., Ho Chi Minh City, Vietnam
3Department of Natural Environmental Studies, Graduate School of Frontier Science, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8563, Japan
(Received June 20, 2012; Accepted November 8, 2012)
Deltaic sediments of the Mekong River delta sampled from a tidal beach in Vietnam during the wet season (late October 2011) showed strong 137Cs and 134Cs activities reflecting radionuclides released from the Fukushima Dai-ichi nuclear power plant (FDNPP) after the March 2011 Tohoku-oki earthquake and tsunami, but samples from the same site taken about three months later during the dry season (early February 2012) showed weak activities. This finding indicates that soil from the Mekong drainage basin was deposited along the delta front in the wet season and then removed in the dry season during the winter monsoon. Thus, seasonal changes in the sedimentary environment of sediment supply and accumulation were elucidated by Cs isotopes from the FDNPP accident. This finding may expand the usefulness of radionuclides for obtaining important information about geochemical events.
Key words: Fukushima Dai-ichi nuclear power plant accident, Cs isotopes, erosion, Vietnam, mega-delta