Radioactive Water – The Fukushima Fallout
Radiation levels detected in water surrounding the damaged nuclear plant in Japan have sparked a wave of fear. This special report charts the effect of the radiation leak on water sources in Japan and profiles the technology relied upon to detect danger.
Although Japanese authorities have looked to prevent the spread of radiation in the country's water systems and the ocean surrounding the Fukushima Daiichi plant, radiation has been found in tap water in the capital, Tokyo, over 120 miles away. Meanwhile, over half a million households in the Fukushima area continue to struggle without access to water.
Radiation levels in the ocean surrounding Fukushima have been reported as being as much as 6,500 times the legal limit. According to early reports, Tokyo Electric Power Company (TEPCO) attempted to cool damaged reactors by filling the reactor containment vessels with water leaking from the core, but radioactive water pouring out of the reactors was pooling around the complex, hampering recovery attempts.
This led to 10,000t of contaminated water - at 500 times the legal limit for radioactivity - being dumped into the ocean in April in an effort to contain even more toxic water. Hidehiko Nishiyama, spokesperson for the Nuclear Safety and Industrial Agency, admitted at the time: "We must keep putting water into the reactors to cool to prevent further fuel damage, even though we know that there is a side-effect, which is the leakage."
The threat of radioactive water
Opinion seems to be divided as to the danger posed to marine life, as well as to humans who might ingest radioactive elements in seafood poisoned by contaminated seawater, but the short eight-day half-life of iodine-131 has been highlighted as a cause for hope that the radioisotope will have effectively dispersed by the time it reaches humans via contaminated seafood.
Radioactive elements break down over time, a process measured by the element's half-life (the time it takes half of that element to disperse harmlessly). In Tokyo, the levels of iodine-131 in the tap water dropped back to levels safe for ingestion by infants - who are particularly vulnerable to the carcinogenic iodine - within a couple of days. This after high radiation readings twice the safe level for infants were recorded prompting widespread safety fears.
This fails, however, to take into account the longer half-lives of other isotopes like cesium-137. Qiu Yongsong, a researcher at the South China Sea Fisheries Research Institute, told China's Daily Mirror that Japan should conduct strict radiation testing on its next north-west Pacific fish harvest, because as radioisotopes become more concentrated in marine animals, seafood may pose more of a danger.
Testing water for radioactivity
Different techniques and specific radiation detection equipment are sometimes required to detect different types of radiation, such as wave radiation and radioactive particles in soil and water.
Gamma radiation - emitted by isotopes including cesium-137 and iodine-131 - is highly penetrating, and it can travel through a range of objects, including human skin, soil and water, although it can be contained by lead, steel or concrete.
Survey meters like the Geiger-Mueller counter are particularly effective for analysing radioactive spills emitting gamma radiation, but perform better when reading solid surfaces and struggle to pick up shorter range alpha and beta emissions in water.
There are some relatively cheap ways to test water for the presence of radioactive isotopes. Thin layer chromatography is one laboratory technique use to separate mixtures, allowing analysts to determine whether isotopes like iodone-131 have contaminated the water.
Treating irradiated water
Water can be filtered to remove different types of radiation, with the two recognised ways of treating contaminated water being reverse osmosis and ion exchange.
The latter process is often used in the nuclear industry to concentrate radioactive elements into a small volume, allowing the remainder - treated water at a far lower level of radioactivity - to be discharged.
The US Environmental Protection Agency (EPA) states that ion exchange is particularly effective at removing cesium-137. Sodium ions are often used because the exchange very readily with radioisotopes.
Activated carbon is also employed to absorb contaminants as water passes through it and fix them, although the carbon will eventually reach saturation point.
In the case of large-scale fallout like that experienced in the Fukushima disaster, it is impossible to eradicate all of the radiation released into the air, soil and water. Long-term storage of radioactive waste is one option, but first it is necessary to convert it into a stable form that will not react or degrade in the long-term.
Tetsuo Iguchi, an isotope analysis and radiation detection specialist at Nagoya University, asserts, "They (Japanese authorities) need to find a place to store the contaminated water and they need to guarantee it won't go into the soil."
One technique uses ferric hydroxide to absorb radioisotopes, forming a sludge that can be mixed with cement to form solid waste that can be more easily disposed of, while vitrification (mixing waste with sugar) and then calcination (passing waste through a heated, rotating tube) are used to produce a stable glass product, in which radioactive elements are trapped and stored.
Reverse osmosis (RO) is supported by the EPA as a "best available technology" for various radioactive elements, including alpha and beta particles, uranium, radium and photon emitters. According to the EPA, it can remove up to 99% of these contaminants, while RO units can be automated and compact.
Iodine-131, however, is usually found in water as a dissolved gas, rendering reverse osmosis (which cannot capture gases) an ineffective treatment mode. It can be removed using a combination of relatively simple technologies, though, and personal radiation water filters are available, utilising filtration methods and medias frequently used in the nuclear power industry. The EPA recommends the general public adopt a process combining activated carbon, reverse osmosis and ion exchange - effectively covering all bases.
As long ago as April, the US Environmental Protection Agency (EPA) issued warnings that radiation from the Japanese disaster had been detected in a number of American cities. Tests conducted on rainwater and milk - both claimed to be good indicators of the effect of radiation - found traces of radioactive isotopes.
Iodine-131 in particular poses a threat because it escapes the site of an accident as a gas. This means it disperses rapidly into the atmosphere before being captured as a gas in water present in the atmosphere. At some point the radioisotope falls to earth as rain and enters the water supply.
Airborne radioisotopes, having fallen in rain or snow, can coat grass, which is then eaten and begins to accumulate in cows' milk and livestock; according to the EPA, cesium-137 was found in milk in Vermont, while iodine-131 was found in milk samples from Phoenix (3.2) and Los Angeles (2.9) at levels roughly the same as the EPA's maximum contaminant level for drinking water of 3.0 picoCuries/litre.
While the EPA does not consider these levels to pose a health threat to the American public and insists that this is a conservative standard aimed at ensuring minimal exposure over a lengthy period of time, several environmental commentators disagree, claiming that any level of radiation is, by definition, unsafe and increases the risk of cancer, which can build up over many years of exposure to low-level radiation before manifesting any symptoms.
Water supplies across the US have also shown increasingly high levels of radioactive elements and analysts for American environmental site Natural News have pointed out that the EPA is only testing for iodine-131 and that there are no readings or data pertaining to either uranium or plutonium, despite their even greater potential for damage.
China, on the other hand, has remained sceptical about the chances of contaminated seawater reaching its shores. According to Yu Fujiang, deputy director of the National Marine Environmental Forecasting Center, radioactive elements have only spread to China via the atmosphere to date, while he also claims that Chinese waters are not in danger in the near future, although the long-term consequences are hard to predict.
Completing the cleanup
TEPCO has announced that from the middle of this month it will begin treating contaminated water at the plant with a unit from French company Areva SA, which can process 1,200l of water per day.
It remains to be seen whether this unit alone will be capable of dealing with a total of almost 100,000t of radioactive water on-site, while the utility must also get a firmer handle on the several hundred thousand tons of contaminated water that has been released and spilled into the ocean.