Year: 2011
Type: editorial
Abstract: The nuclear accident at the Fukushima nuclear power plant in Japan—a direct consequence of the tragic Tōhoku earthquake and subsequent tsunami on March 11, 2011—has reopened the sensitive discussion on the use of nuclear energy. First and foremost, we express our deepest sympathy towards the victims of this event, and admire the crews that are, at great personal risk, working to secure the severely damaged reactors. While most of the world is watching their progress with bated breath, the political debate about the risks and benefits of nuclear power has flared up. Although ChemSusChem is not the right venue for such a broad discussion, it is the duty of scientists to contribute to this debate by providing scientifically correct results and solutions. The Communication "Selective Sequestration of Strontium in Desmid Green Algae by Biogenic Co-precipitation with Barite", reported in this issue, is an important contribution to the scientific discussion. The results describe how radioactive strontium (Sr-90) can be separated from nuclear power plant waste streams by accumulation in purpose-grown algae. The paper was submitted in December 2010, and accepted for publication well in advance of the events in Japan. Because the consequences of the use of nuclear energy are currently such a sensitive topic, this Editorial aims to put the results in this Communication into the right context. Sr-90 is a beta-emitter and a large source of Cerenkov radiation. Its biochemical behavior is similar to calcium. After entering an organism, for example by ingestion with contaminated food or water, most is excreted, but part of it remains fixed in bones and bone marrow as well as in blood and soft tissues (minimal parts). Its presence in bones can cause bone cancer, cancer of nearby tissues, and leukemia. The biological behavior of Cs-137 is similar to that of potassium and rubidium. It can damage human DNA and ultimately result in cancer. Unlike the Chernobyl incident in 1986, the radioisotopes released in Fukushima, which are now reaching Western Europe and the East Coast of the USA, mostly comprise the highly volatile xenon (Xe-133), iodine (I-131), and cesium (Cs-137). It appears that radio-strontium (Sr-90), the isotope that was responsible for a significant amount of the radioactive fallout after Chernobyl, has not been released into the atmosphere in significant amounts. The radioactive contamination of foods is another major concern. Although the results are still incomplete, the Japanese government announced that it had found abnormally high levels of radioactive iodine (I-131, half-life eight days) in milk, spinach, and garland chrysanthemum, likely related to radioactive deposits derived from the atmospheric release. Owing to the short half-life of I-131, this radioactive contamination will disappear in a relatively short time, while other radioisotopes (Cs-137, half-life 30 years; Sr-90, half-life 29 years) have a long-term effect. Slightly elevated levels of these radioactive substances have been found in water in some areas of Japan. Both elements are present in the reactor coolant system of light water reactors of nuclear power plants, and the amounts that may have been released into the environment, due to the efforts in cooling the reactors by spraying fresh water or seawater water, have not yet been quantified. It is thus too early to draw conclusions. One question, however, is which mechanisms (besides the known mechanisms of bioaccumulation) may lead to the concentration of these radionuclides in plants and vegetables. Another question involves the direct impact of nuclear power plants. Irrespective of any political opinion, it is very important to realize that even if all nuclear reactors would be shut down tomorrow, we would still have to deal with a very large amount of spent nuclear fuels and radioactive wastes. In fact, the Department of Energy (DoE) of the USA alone has >300 million liters of radioactive tank sludge awaiting separation and safe storage. The selective removal of particularly problematic isotopes such as Sr-90 and Cs-137 from such wastes, their concentration into small volumes, and safe storage is thus a matter of considerable importance, not only in times of crisis but for decades to come. This is a nontrivial problem, and groups of researchers around the world are dealing with the fundamental science and engineering solutions. The development of selective technologies to separate critical, long-living isotopes such as Sr-90 and Cs-137 from waste allows changing the classification of waste types, which both provides an economic return and reduces the problem of handling nuclear wastewater by reducing its volume (concentration). Several separation technologies have been developed for liquid wastes, including: (1) solvent extraction, (2) fractional crystallization, (3) inorganic ion exchange, and (4) organic ion exchange. However, these are often not selective. The chemical similarity of calcium, strontium, and barium makes this a very challenging problem for synthetic ion exchange materials and phytoremediation systems. To overcome this technological hurdle, the Communication "Selective sequestration of strontium in desmid green algae by biogenic co-precipitation with barite" draws inspiration from a small number of highly unusual organisms (desmids) that separate calcium, strontium, and barium ions (Ca2+, Sr2+, and Ba2+) during biomineralization. The unusual ability of desmids to selectively sequester strontium into an inert, inorganic form, combined with the potential for engineering the system to increase strontium incorporation, offers a unique alternative to traditional Sr-90 remediation methods. The results, in addition to contributing to the questions discussed before (from the mechanisms of selectivity and sequestration of strontium in individual cells to the fate/impact of Sr-90 in the environment), have implications ranging from direct bioengineering of desmids for waste or environmental clean-up, to bioinspired materials for separation technologies. A final comment regards the motivation for the research described in the paper by Krejci and co-workers, which is in part personal: team leader Derk Joester vividly remembers the Chernobyl fallout coming down over southern Germany when he was a teenager. However, when his team started looking into the mechanism of sequestration of strontium and barium in the desmid green algae several years ago, no nuclear disaster was anticipated. Instead, the idea was to seek mechanistic insight and inspiration from this rare ability, with potential applications in both direct bioremediation or in the development of more selective ion-exchange processes for nuclear waste treatment. The team describes their first important steps in this direction in their contribution entitled. That no Sr-90 has been released in Fukushima is a great relief, and the Chem SusChem team and authors very much hope that it will stay this way. Research towards the sustainable treatment of nuclear waste and environmental remediation will, however, remain important for many years to come.
Source: ChemSusChem
Authors: Gabriele Centi, Derk Joester
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2042753638