Monday, May 30, 2011

.Ionizing Radiation and Reactors Again/ May 26,2011

A troubling report in the NYT this morning discusses the Fukushima reactor disaster, the exclusion zone, now 12 miles, and mentions the discomforts of the 300,000 people displaced.  Exposure limits for the public are being raised to levels ordinarily limited to radiation workers. Even the exposure limits for children have been raised and the public is understandably distressed. The article reports uncertainty as to the effects of low-level exposures on people and shows how again, “uncertainty” is used to justify the risks of exposures as is so common in all competition between human welfare and economic interests.

            There is no uncertainty.   Ionizing radiation causes ionizations. It breaks up molecules.  And if the energy is high enough, the damage occurs at low levels of exposure, too. So, as far as people are concerned, the rule is no exposure. The big human danger from low exposures has always been considered to be damage to chromosomes, mutations. With higher exposures mutations accumulate. In most studies of exposures of large populations higher doses usually cause a shortening of life, often through an increase in the frequency of cancer. But the shortening of life, while statistically low when view over the entire population, may in an individual mean a substantially shortened life span as cancer hits in mid-life. There is no reason to think that the effects are any less than linear at lower exposures .     

            The larger hazard is to the population as a whole. Mutations accumulate in the overall population and may not appear until subsequent generations. These mutations are a part of the  “genetic load” carried by any population and exposure to ionizing radiation is usually thought to add to that genetic burden.  Arnold Sparrow of Brookhaven National Laboratory spent a career sorting through the factors involved in susceptibility of plants to radiation damage. He showed that chromosome number and volume were key issues: plants with many small chromosomes were much more resistant than plants with  a small number of large chromosomes. That relationship is not surprising in that a plant with many small chromosomes may be polyploid and carry more than one copy of any gene so that one chromosome break is less serious than in a pine tree with 24 large chromosomes.  And pines are in fact very much more sensitive than polyploid mosses.

            Even more troubling than the vulnerability of the genetic material is the continued release of radiation  from the reactors.  The long-lived  isotopes such as Cesium are especially troubling  in that they accumulate in the soil and remain hazardous for decades. So the possibility of  returning to live safely in the fallout zone in one’s lifetime is remote. The meaning of a 12 –mile exclusion zone and 300,000 people displaced is very clear and very sad.  

 Meanwhile our own Nuclear Regulatory Commission is approving the relicensing of aging reactors for another twenty years and there is talk within the current administration of subsidizing the construction of more.