The roots of the trilobite ancestory extend back to the Pre-Cambrian periodA few years ago, the Nuclear Regulatory Commission raised the average dose Americans receive from “background” radiation, to 620 millirem (mrem), up from 310 mrem (3.1 millisieverts or mSv) per year. This dose includes radon, terrestrial and cosmic radiation, and medical and industrial exposures, including bomb and civilian reactor radioactivity. But, as with all averages, a lot of important detail is lost, so let’s examine the 620 mrem a little closer.
Radon, accounting for approximately 200 mrem of the 620 varies greatly depending on location, therefore, not everyone gets the “average” dose. The NRC also assumes that nearly half of the 620 dose (about 310 mrem) comes from medical exams. But if you don’t get these exams, your dose is significantly lower. Add to this the reality that most medical exposures to radiation are relatively short lived, and you have exposures that are not necessarily comparable to chronic exposure to radiation.
The NRC claims “a yearly dose of 620 millirem from all radiation sources has not been shown to cause humans any harm…” and it uses this “background” dose to justify exposing us to 100 millirem per year MORE from nuclear facility operations if it wants. All nuclear power reactors release radioacitivity routinely and without this allowable limit, reactors would be forced to capture their radioactive releases at great expense. Some radioactive waste products, like tritium, they can’t capture. But radionuclides released from reactors, unlike medical exposures, can subject people and the environment to a longer-term, even permanent increase of radioactivity, either because these radionuclides have long hazardous lives (in which case they can build up in our environment) or because they continue to be released, introducing a never-ending stream of radioactive pollution.
Also consider that levels of background radiation peaked at about 7 milligray (mGy) during the Pre-Cambrian period. Since life first originated this dose has decreased by a factor of ten (Moller & Mousseau referencing Karam & Leslie 2005). (7 mGy is roughly equal to about 700 millirem for external exposure to gamma, but this conversion can become tricky when considering naturally occurring, internal doses of alpha and beta radiation) While we must be cautious about a direct comparison, it is thought that radiation levels had to decrease substantially for creatures as complex and differentiated as mammals to be viable.
The more radiation we release to our environment, the more we may be reverting to levels that were too high for us to evolve in the first place. In fact, the NRC average of 620 mrem plus an additional 100 mrem per year allowed, is perilously close to this Pre-Cambrian PEAK, even if a millirem-to-millirem comparison is not exactly equivalent.
A recent study calls into question the NRC assumption that 620 mrem/year is safe, especially over the long term. The research reviewed by Moller and Mousseau demonstrates that in areas of increased natural radiation, human populations suffer an increase in “significant negative effects on immunology, mutation and disease frequency”, including reduced levels of antioxidants. The existence of hormesis, a theory that, stated simply, claims “a little radiation is good for you”, is not supported by these studies: “…these negative effects of radiation on mutations, immunology and life history are inconsistent with a general role of hormetic positive effects of radiation on living organisms.”
Of the 46 studies reviewed, approximately 15 of them measured natural background radiation levels between 0.67 to 6.4 millisieverts (67 to 640 mrem) per year. The remaining studies had higher natural radiation. Even at the lower levels of natural background radiation, health impacts included cancer incidence and death, all manner of chromatid and chromosome aberrations (deletions, dicentrics and rings, translocation and inversions) some of which have cross-generational (inheritable) implications, congenital malformations, and Down’s syndrome.
Obviously a direct comparison between the NRC’s calculated average background exposure of 620 mrem and the Moller/Mousseau study is problematic. There is a good possibility that the NRC’s assumption of 620 mrem/year is not correct and that the amount Americans are exposed to is actually much lower. This means that the 100 mrem/year extra they want to expose us to is a greater fraction of our dose than they assume. But increasing background dose leads to increases in diseases and immunity problems, and a comparison between this increase and the NRC’s background exposure estimate IS warranted. It is time for NRC to revisit its “background” radiation dose assumptions and account for the data found in studies like the ones reviewed by Moller/Mousseau.
December 18, 2012