the ocean floor off Fukushima. Blair Thornton, an associate professor the university, said in 2013 that radiation levels remained hundreds of times as high as in other areas of the sea floor, suggesting ongoing contamination (at the time) from the plant. A monitoring system operated by the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) tracked the spread of radioactivity on a global scale. Radioactive isotopes were picked up by over 40 monitoring stations. On 12 March, radioactive releases first reached a CTBTO monitoring station in Takasaki, Japan, around away. The radioactive isotopes appeared in eastern Russia on 14 March and the west coast of the United States two days later. By day 15, traces of radioactivity were detectable all across the northern hemisphere. Within one month, radioactive particles were noted by CTBTO stations in the southern hemisphere. Estimates of radioactivity released ranged from 10 to 40% of that of Chernobyl. The significantly contaminated area was 10–12% of that of Chernobyl. In March 2011, Japanese officials announced that "radioactive iodine-131 exceeding safety limits for infants had been detected at 18 water-purification plants in Tokyo and five other prefectures". On 21 March, the first restrictions were placed on the distribution and consumption of contaminated items. , the Japanese government was unable to control the spread of radioactive material into the nation's food supply. Radioactive material was detected in food produced in 2011, including spinach, tea leaves, milk, fish, and beef, up to 320 kilometres from the plant. 2012 crops did not show signs of radioactivity contamination. Cabbage, rice and beef showed insignificant levels of radioactivity. A Fukushima-produced rice market in Tokyo was accepted by consumers as safe. In the first half of September 2011, TEPCO estimated the radioactivity release at some 200 MBq (megabecquerels, 5.4 millicuries) per hour. This was approximately one four-millionth that of March. According to the French Institute for Radiological Protection and Nuclear Safety, the release from Fukushima represents the most important individual oceanic emissions of artificial radioactivity ever observed. The Fukushima coast has one of the world's strongest currents (Kuroshio Current). It transported the contaminated waters far into the Pacific Ocean, dispersing the radioactivity. As of late 2011 measurements of both the seawater and the coastal sediments suggested that the consequences for marine life would be minor. Significant pollution along the coast near the plant might persist, because of the continuing arrival of radioactive material transported