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Scientific American: "Half-Life and Death: Radioactive Drinking Water..
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"Scientific American: Half-Life and Death: Radioactive Drinking Water Scare in Japan Subsides, but Questions Remain"
"Some radioactive contaminants could be filtered out or allowed to decay, whereas others would pose more serious long-term problems."
"Despite the ongoing work to stabilize the plant and fears that radioactive materials had contaminated tap water as far away as Tokyo, 240 kilometers to the south, most of the recommended restrictions on drinking water have been lifted".
"Still, the presence of radioactive iodine and cesium in the water supply—four villages in Fukushima Prefecture are still recommending that children less than one year old not be given tap water—raises public health questions moving forward."
"Exposure to or ingestion of radioactive isotopes, or radionuclides, (species of the same element with differing numbers of neutrons and hence differing atomic weights) can lead to a number of health problems, including nausea and vomiting at low doses, and central nervous system damage and internal bleeding at high doses. Radioactive iodine, in particular, concentrates in the thyroid and can result in thyroid cancer, particularly in children.""
"The University of Tokyo Hospital Radiation Oncology Team had reported finding 170 becquerels per kilogram of iodine 131 in Fukushima's drinking water on March 18, although the level has since dropped significantly."
"One becquerel represents the rate of radioactive decay—or radiation emitted by a substance—as one disintegration, or count, per second. The March 18 number is significant because the Japanese government mandates that infants less than one year old not be given water with a concentration of greater than 100 becquerels per kilogram. (A liter of water weighs one kilogram.) Adults should avoid any water with more than 300 becquerels per kilogram, according to the government's current standards."
Radioactive removal:
"Most radioactive radionuclides—including iodine 131 and cesium 134 and 137—can be removed from water. Others, such as tritium, a heavy form of hydrogen that is the most ubiquitous radioactive pollutant produced by nuclear power plants, cannot be filtered out of water."
"Whether and how an isotope could and would be removed depends on which it is. Unlike drinking water contaminated with microbial pathogens such as Escherichia coli, giardia or cryptosporidium, water containing radioactive material cannot be made potable by boiling, bleach or exposure to ultraviolet light. Instead, isotopes must be removed using activated charcoal filtration, reverse osmosis or water softening, to name a few methods".
"Radioactive material may also fall out of a water supply by settling to the bottom of a reservoir or via adsorption (adhesion) onto the surface of soil particles in a reservoir. Another option with some radioactive contaminants is to wait until they radioactively decay to safe levels—a period known as half-life, which greatly varies with the particular isotope, from seconds to tens of thousands of years."
"There is no single approach to removing radioactive iodine, cesium or other radionuclides from water. "You need to know what's in the water because that will help tell you whether you can remove it or not, and what kind of water treatment process you need to perform," says David Ozonoff, an environmental health professor and chair emeritus of the Boston University School of Public Health."
"Given the relatively short half-life of iodine 131, officials are more likely to wait out the decay process."
"As for isotopes like cesium 137, however, its decay half-life is around 30 years."
(GLP cut and paste rules respected)
[link to www.scientificamerican.com]
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