In nuclear power plant mishaps such as those most recently in Fukushima large quantities of radioactive isotopes make their way into the environment: iodine-131 (physical half-life eight days), caesium-137 (30.17 years) and strontium-90 (28.78 years). Similar nuclides may be released by “dirty bombs”. After a major nuclear event a triage is beset with problems. Patients who get exposed to low doses, although spared the acute symptoms of radiation sickness, are however more often affected with cancer. How high the individual risk actually is can be determined by looking at strontium-90 in teeth.
Two chemical relatives
Some theoretical background worth adding: calcium and strontium are in the same main group of the Periodic Table. They therefore have similar properties. Bone and teeth absorb through food between 50 and 350 micrograms strontium per gram of calcium, which typically turns out to be made up of stable isotopes such as strontium-86, -87 or -88. Not so in Fukushima: During their development phase, children’s teeth and bone tissue accumulate a great deal of strontium-90 from their diet. Adults are equally affected. In their case the suspect ions pass via passive exchange processes into the enamel and stay there for some time. Long biological (49 years) and physical half-lives (28.78 years) lead to high radiation doses in bone and teeth – with possible long-term consequences.
Better hunter than collector
This is shown by work done by Joseph J. Mangano and Janette D. Sherman, New York. They made use of a collection made available to them and held by the State of Missouri of a whopping 85,000 milk teeth obtained from Americans born between 1959 and 1961. At the time, above-ground nuclear testing transported much strontium-90 into the atmosphere. For each sample researchers had acquired extensive information, from the mother and baby’s location of residence to their eating habits. This went even further, using voter registration, death registers and questionnaires. In the end Mangano and Sherman identified 97 first-dentition teeth of 78 cancer patients – 65 of the people were still alive. The remaining 13 died at a mean age of approximately 40 years. Mangano and Sherman compared the above-mentioned samples with 194 teeth from subjects without malignant disease. A liquid scintillation counter was employed here. Their conclusion: with those affected with tumours, the content of strontium-90, in statistical terms 7.00 Picocuries per gram, was significantly higher than the values for the control, namely 3.16 Picocuries per gram. Potentially far more people died of radioactive fallout than was previously thought, the authors suggest. They cite studies by the U.S. government of 35,000 cancer cases – 15,000 deaths involved – arising from atomic bomb tests. In the case of the Japanese reactor disaster, measurements would be able to help detect cancer risks early and at relatively low cost. Japanese government circles are nonetheless not really excited by the scientific method.
Revelatory damage in the crystalline lattice
From a scientific viewpoint, there are also grounds for criticism: While true that strontium-90 is an important isotope which is released during nuclear accidents and attacks, fallout is considerably more complex. Statements on the overall exposure of patients to, for instance, gamma or X-radiation without its incorporation, cannot be made by doctors. Yet there are alternatives derived from the world of theoretical physics: high energy gamma or X-ray radiation applied to dental crystalline hydroxyapatite generates unpaired electrons. They have a characteristic spin, i.e. intrinsic angular momentum. Using electron spin resonance (EPR, Electron Paramagnetic Resonance) the corresponding defects in the crystal can be determined. If researchers apply an external magnetic field, this results in two spin states, namely parallel and anti-parallel to the field lines. Using electromagnetic radiation of the appropriate frequency, it is possible to flip the spin from an energetically favourable to unfavourable state and to measure its energy uptake: a measure of crystal lattice defects. Already during the course of their Adult Health Studies physicians and physicists equipped with EPR spectrometers examined survivors of atomic bomb attacks. Chromosomal aberrations correlate with the doses of absorbed radiation obtained of teeth – a finding supporting the argument for the use of this form of retrospective dosimetry.
Harold M. Swartz took the physical principle from the laboratory to the patient – at the specially created EPR Center for the Study of Viable Systems, Geisel School of Medicine in Dartmouth. Together with his team he developed a portable spectrometer for field use. Swartz requires neither first dentition teeth nor extracted teeth. Rather, patients put their head between a pair of coils – the necessary magnetic field arises here. By way of a bite block, incisors are precisely aligned. After less than five minutes measures are obtained. Using such equipment Swartz sees the potential, especially in cases of nuclear accidents or attacks, to carry out a quick triage. Otherwise it would be difficult to identify patients who have neither incorporated the radionuclides nor show symptoms of radiation sickness but had potentially been exposed to high doses of gamma radiation.