TIME OUT: ANDREAS SCHEINOST-"Studying uranium in soil contributes to the health of humans and nature"

Andreas Scheinost - Environmental chemist at beamline BM20

By Christine Bohnet

In many religions soil is perceived as Mother Earth which nourishes mankind, and in fact soils produce food, fibres, energy and drinking water. However, soils are increasingly endangered not only by erosion and desertification, but also by the contamination with heavy metals. Andreas Scheinost used to be a farmer in Bavaria (Germany) before he decided to study Agricultural Sciences at the Technical University Munich. As a post-doc in the USA he became interested in heavy metals in soil. There he also used Synchrotron light for the first time. Since 2003 the father of four children has been working at beamline BM20, employed by the Forschungszentrum Rossendorf (FZR) in Dresden/Germany. Here in Grenoble he added radionuclides to his field of interest. The increasing interest and demand for the use of synchrotron radiation for research in Earth science and geochemistry has also been observed for the ESRF beamlines. The growth of this research area has necessitated the creation of a new beamtime allocation review committee (the committees that accept or reject proposals for experiments at the ESRF) on environmental issues.

Why are you investigating uranium in soil?
Uranium is virtually everywhere on Earth. It is a remainder of the supernova explosion, from which our solar system emerged. In soil, like in rocks or sediments one finds about 2 mg uranium per kg. As an unstable, radioactive element, uranium has a very long half life of 4.47 billion years. The toxicity and radioactivity of uranium and other radionuclides like plutonium require a thorough understanding of their behaviour in nature. For uranium, the complexity of its chemistry is still a challenge, because it occurs in at least 5 different oxidation states. We have been looking into many uranium complexes with a large variety of organic and inorganic ions.

Why do we need to know about the chemical behaviour of uranium?
Uranium is used to produce the fuel for nuclear power plants and for nuclear weapons. The required uranium is mined in Canada, the USA, Africa, and in Russia. Until the wall came down in Germany, uranium mining also took place near Dresden, i.e. in a densely populated area. Now you can find uranium across large areas of Kosovo and Iraq, too. There are hundreds of tons of ammunition with cores of depleted uranium (DU) that were used for destroying tanks. We try to predict the interactions and mobility of uranium and other radionuclides in the geo- and biosphere. I trust that this knowledge will help to protect humans as well as the environment from the toxicity of uranium.

When does uranium become dangerous?
Uranium can get into the groundwater and, thus, into drinking water. Only recently, the World Health Organization (WHO) has renewed the discussion about limits in drinking water. Right now it is 15 micrograms per litre. Other uptake paths are via the soil-food-chain or by inhalation of dust and aerosols. By understanding the chemical behaviour of uranium, we can also design better cleaning procedures for water. For example, US scientists fed bacteria in contaminated areas to immobilize the uranium. Due to the lack of knowledge about the complex biosphere in the respective soil these experiments failed, i.e. the uranium was mobilized and got into groundwater even more quickly. At the FZR, we have developed a special filter system to clean the water from uranium mines in Saxony by using bacteria from waste piles.

From which sites do you retrieve your samples?
In the last six years we prepared samples mostly in the laboratory, to reduce the complexity of natural systems. By learning uranium chemistry in this simplified lab environment, we are now able to extend our research to real soil samples, which contain different minerals, heavy metals, acids, colloids, microorganisms, and so on. At the ESRF we have already investigated a few soil samples from the Dresden mining areas, but I would really like to obtain samples of soil from Chernobyl in the Ukraine or from Sellafield in the UK.

What advantages does the EXAFS technique provide?
Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is the most versatile method to characterize the chemical structure of elements. It links the chemical structure of heavy metals to their environmental behaviour and toxicity. Often we have to supplement this EXAFS spectroscopy at BM20 with microscopic techniques from beamline ID22. In the future, I plan to upgrade our beamline to be able to perform microscopic EXAFS spectroscopy.

What special precautions do you take with radioactive samples?
During the last decade, BM20 has been the only dedicated beamline for radioactive samples in Europe. For this reason much effort was required to build it as a secure radiochemical lab within the normal everyday user operation at the ESRF. Beginning with the first experiment in August of 1998, not a single experiment had to be stopped due to safety reasons. This was thanks to the tight co-operation between the users, the beamline scientists and the safety group of the ESRF. I believe that BM20 serves as a very successful example for other European synchrotron facilities. Just one year ago, the first experiments with radioactive samples were conducted at the INE beamline of the ANKA facility in Germany, and similar experimental stations are under construction at the Swiss Light Source and at the new French synchrotron SOLEIL.

Which differences do you see between France and Germany when it comes to radioactivity?
In Germany we see a lack of attractiveness for research dealing with radioactive issues. I personally find it very refreshing that in France many young people are striving for a career in radiochemistry, nuclear energy technology, or nuclear medicine. I very much hope that talented young people in Germany will become aware of the career perspectives in these fields.