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Friday
Aug172012

Deception in Sieverts: how a measure of radiation damage can actually be used to hide damage

According to a research letter sent this week in the Journal of the American Medical Association (JAMA), levels of internal cesium contamination after Fukushima are “low…much lower than those reported in studies years after the Chernobyl incident”.  However, longer-term, internal exposure to even low levels of cesium can cause a range of diseases and pre-disease conditions, including cancer. The contamination levels found in the people examined in this research are within this range of concern.

For this letter to the editor (Tsubokura, et al.) researchers used actual counts of gamma radiation coming from people’s bodies. Roughly, this count per second of gamma (given in the unit Becquerels or Bq) is then divided by the person’s weight, given in kilograms (kg).  This gives a whole body count that is used to derive the amount of radioactive cesium inside the person.  While not entirely a direct measurement, fewer assumptions and estimates are associated with Bq/kg than with the more highly favored Sievert (Sv).

The Sievert is an estimate of radiation damage based on a number of assumptions (not all of which are correct or applicable to any specific individual) and can end up hiding health damage depending on how it is used.  In this letter, the researchers claim that, even though some cesium concentrations were as high as 196.5 Bq/kg, just one person had an estimated dose above 1.0 millisievert (mSv) – a dose that is considered low by nuclear experts. That dose was 1.07 mSv.

However, in the early 2000’s, a medical doctor in Belarus, Yuri Bandajevski, examined 3000-4000 tissue samples from approximately 400 deceased individuals. Disease or pre-disease conditions were compared to radioactive cesium contamination levels (in Bq/kg) of those same individuals. He replicated his results in animals and also examined a number of living people. There were strong associations between (pre-) pathologies observed, and cesium contamination levels in Bq/kg, across all study subjects.

Bandajevski says “We should pay particular attention to the fact that the presence of even relatively small amounts of Cs-137 in children from 10-30Bq/kg…leads to a doubling in the number of children with electrocardiographic disorders.” Cesium-137 can cause “…in relatively small doses (20-30 Bq/kg); a breach of the regulatory processes in the body. This contributes to the emergence of pathological processes and diseases. This emergence is based on the latent genetic predisposition due to mutagenic action, including the same Cs-137, on gametes of the parental generation.”

For adults the concentration of cesium in the Tsubokura letter ranges from 2.3 to 196.5 Bq/kg. 200 Bq/kg, in a pregnant woman's placenta can result in fetal death according to the Belarus studies. Among pregnant women living in Chernobyl-contaminated areas, cesium seem to collect preferentially in the placenta. For children, the concentration of cesium ranges from 2.8 to 57.9 Bq/kg, which is within the range of concern shown, including impacts on the heart and hormone imbalance shown in the Belarus studies.

Therefore, to imply that internal cesium contamination at the levels found after Fukushima are low and of little concern, doesn’t account for what previous research has demonstrated based on the Bq/kg measurement. And while nuclear experts and proponents can claim that 1 millisievert is a “small” amount, it is obviously well within the range that can cause health problems. These health problems can be compounded with continued exposure, to even small amounts of cesium, across generations, indicating that the longer someone stays in a contaminated area, eats contaminated food and/or raises a family in these conditions, the more damage will accumulate and the more, even what were once considered small doses, will have great detriment on health.

In this way, the Sievert as a unit of damage is obviously not precise or foolproof enough to accommodate the many natural variations among humans and exposure scenarios. It can, in fact, lead to misleading assessments about just how dangerous exposure to radioactivity is. A more direct measurement like Bq/kg equated with disease is, at least for cesium, a much truer representation of damage.