Tokyo Electric Power Co. confirmed Tuesday that radioactive cesium had again been detected about one kilometer offshore from the Fukushima nuclear plant, crippled in March 2011 by the Great East Japan Earthquake and the tsunami that it triggered.
The tests identified 1.6 becquerels of Cesium-137 per liter of seawater on October 18, slightly higher than the level at the same point on October 8, but the operator of the plant said the readings were far below the legal limit of 90 becquerels per liter and that therefore the impact on the environment was "little."
Environmental groups have disputed the assessment of the situation and point out that rising levels of cesium further away from the facility undermine the repeated assurances of Prime Minister Shinzo Abe that the management of highly radioactive water at the plant is "under control."
Since the disaster struck more than two-and-a-half-years ago, there has been widespread international criticism of the operators of the plant and the Japanese government, both for failures before the earthquake struck and errors made subsequently. But experts say that mankind has been living with far higher levels of nuclear contamination for more than half a century.
Already in environment
"People forget that the world we live in already has a lot of cesium-137 in the environment," Dr. Mitsuo Aoyama, senior scientist in the Oceanography and Geochemistry Department of the Japan Meteorological Research Institute, told DW.
And while some of the radiation in the soil, food, air and water that surround us is naturally occurring, Dr. Aoyama points out, he has devoted a great deal of his research to the impact of the numerous nuclear tests carried out in the Marshall Islands and other Pacific atolls from 1946 until 1962, primarily by the United States.
Dr. Aoyama's studies show that by 1970, an estimated 290 petabecquerels - an alarming 29 followed by 15 zeroes - of cesium fallout was in the north Pacific ocean from atmospheric weapons tests. In contrast, the direct discharge from Fukushima was around 3 petabecquerels, while the total atmospheric release - some 80 percent of which was deposited on the Pacific - came to some 15 petabecquerels.
In his most recent paper, Dr. Aoyama said water at the surface of the Pacific in the late 1960s contained between 10 and 100 becquerels of cesium-137 per cubic meter. Before March 2011, that concentration had diffused to between 1 and 2 becquerels per cubic meter of sea water.
And while levels spiked to 10 million becquerels per cubic meter very close to Fukushima immediately after the disaster, it has fallen to 10,000 becquerels per cubic meter today. In June 2012, Dr. Aoyama found levels 2,000 km from the plant to be just 10 becquerels per cubic meter.
Higher levels in the Baltic Sea
In contrast, an ongoing study by the Woods Hole Oceanographic Institution, based in Massachusetts, shows that in 1990 the rate in the Black Sea stood at 52 becquerels per cubic meter, at 55 in the Irish Sea - a legacy of problems at Britain's Sellafield nuclear plant - and at 125 in the Baltic.
"Most people either didn't know how high these levels were or didn't really care," said Azby Brown, an environmentalist who is director of the Future Design Institute at the Kanazawa Institute of Technology and a volunteer with the Safecast independent radiation monitoring organization.
"There are people who care a lot, of course, such as Marshall Islanders, who were affected and feel they deserve better compensation, but the nuclear tests dumped vast amounts of radioactive contamination all over the world, especially in the northern hemisphere, and the reaction of governments at the time was that this really wasn't going to affect people's health," Brown told DW.
Those attitudes prevailed until the 1963 Partial Test Ban Treaty, which forbade atmospheric and underwater nuclear tests.
"It has been challenging for researchers to demonstrate clear evidence of a detrimental impact on human health caused by the nuclear tests," Brown said. "But that doesn't mean it's not there."
Fears over food supplies
"Food is an area of great concern, and the situation needs to be watched closely,” said Brown. “But reliable tests by both government and independent groups strongly suggest that very few people in Fukushima today are consuming as much as 1 becquerel per day of cesium in their food, whereas back in 1964, because of fallout from the tests, the entire country was eating about 5 becquerels a day, every day.
"There was no effort to either warn people of the contamination risk, or to keep contaminated food off the market,” he pointed out. “And this was true for most countries."
These figures have triggered anger in some quarters and accusations that scientists are attempting to downplay the impact of the Fukushima disaster. But Brown disagrees, saying that the comparison is very instructive.
"In terms of the ocean, this is definitely an environmental catastrophe, and it's still ongoing," he said. "The damage to the ocean floor off Fukushima in particular will take a long time to heal, and our only real option is to wait for mother nature to take her course."
The expert also said that "though contamination in the most seriously affected areas has been worse than a lot of things that have gone in the past, conscientious testing of seafood can help prevent it from becoming a human health disaster as well."
"It also shows us that we have to redouble our efforts to fully understand the health consequences of the testing period, because that will help us prepare for the future consequences of Fukushima."