Risk assessments of Arsenic in tsunami sediments from Iwate, Miyagi and Fukushima Prefectures, Northeast Japan, by the 2011 off the Pacific coast of Tohoku Earthquake

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The Pacific coast of Tohoku District in Northeast Japan (Iwate, Miyagi, and Fukushima Prefectures) was seriously damaged by a violent tsunami resulting from the 2011 off the Pacific coast of Tohoku Earthquake on March 11 2011. The disaster area was covered by tsunami sediments, which are mainly marine sediments. We collected 137 tsunami sediments from Kuji City, Iwate Prefecture through to Minamisoma City, Fukushima Prefecture (40°11′N, 141°58′E to 37°43′N, 140°51′E). Analysis of bulk sediment chemistry and leaching test by pure water and seawater were carried out to access arsenic contamination. In addition, chemical forms of arsenic in different size fractions (<3 kDa, 3 kDa to 0.2 μm, 0.2 μm to 0.45 μm, and ≥0.45 μm) from the leachates were investigated by filtering techniques.Arsenic concentrations in the pure water leachates of 45 samples had higher arsenic levels than the Japanese Environmental Quality Standards for Soil Pollution (10 μg/l). In particular, tsunami sediments from the Ohya area in Kesen-numa City, Miyagi Prefecture, had arsenic levels 39 times greater than this threshold, reflecting the influence of gold mines in this region. The fraction of arsenic species < 3 kDa in size in leachates of the high arsenic samples was ca. 70%, indicating that most of the arsenic in the leachates is present as fine colloidal particles and/or dissolved species.