December 14, 2018

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Do Small Amounts Of Radiation Matter?

Do Small Amounts Of Radiation Matter?
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Yes, indeed, but not the way you might think. It turns out we need a little bit of radiation to function in tip-top shape. And it’s all about our genes.

The latest studies from New Mexico State University demonstrate that the absence of radiation is not good for organisms.

Biological Effects of Radiation are well known at high doses (data points shown) from the Japanese Bomb Survivors, the Chernobyl workers, and a few individual accidents involving high levels of radiation. At low doses, however, there are no measureable effects, which disappears in the noise of everyday adverse health effects. In the 1950s we decided to just draw a straight line from the high dose effects to zero, calling it the Linear No-Threshold (LNT) dose hypothesis (red line), and assumed for convenience and conservatism that there was no threshold below which no adverse health effects occurred. But there appears to be a threshold at the high end of natural background across the Earth, at about 20 rem (0.1 Sv), below which no obvious effects can be seen (blue line). Many studies indicate LNT is not correct at low doses and the blue line more closely predicts biological effects of radiation than the simplistic red line.Smith&Guilmette

Performed by Hugo Castillo, Xiaoping Li, Faye Schilkey, and Geof Smith, experiments with human lung cells and different bacterial species, along with previous work by others on protozoa, yeast, and mammalian cells, show that growth is inhibited by a lack of radiation, contradicting the predictions of traditional hypotheses concerning the biological effects of radiation.

There has been an 80-year discussion about the health effects of radiation on humans and other biological organisms. High levels, or doses, obviously have adverse effects, and really high doses can kill.

But low doses, those less than 20 rem (0.2 Sv) per year, have been extremely difficult to evaluate because their consequences are so minor that it’s impossible to see any effects in a general population where other every-day adverse health effects overwhelm anything from the radiation.

But we need to know this low-dose region since environmental levels of radiation, and those associated with accidents like Fukushima, are in this range of low-doses. Not getting this right costs us billions of dollars each year.

At low doses, all organisms have cellular repair and response mechanisms that can keep adverse health effects from occurring, something that evolved 2 billion years ago as life itself was evolving to deal with much higher background radiation levels as well as free-oxygen that was accumulating on the atmosphere. Free-oxygen is a much greater danger to organisms, and to humans, than radiation (PNAS 2011).

This is timely research. The American Nuclear Society and the Health Physics Society are hosting an international forum of nuclear and radiation experts this week to evaluate whether existing low dose protection standards should be reconsidered. Our present absurdly-low standards have caused more harm than good with unintended consequences we could never have predicted, and this conference in Pasco, Washington Oct. 1-3 will dive head-first into this issue.

The LBRE Experimental set-up, 2150 ft below the Earth’s surface in the massive salts of the WIPP nuclear repository in New Mexico. (A) The LBRE laboratory, (hosted by the Waste Isolation Pilot Plant (WIPP), a nuclear waste repository near Carlsbad, NM.), is located in the middle of the 2,000 ft-thick Salado formation. (B) Laboratories underground at WIPP are conex shipping containers modified to accommodate office and laboratory equipment. The LBRE pre-World War II steel vault used in this study is under the orange fire blanket (arrow) to provide insulation from the high temperature in the drift. Inside the vault there are two incubators, one of which has 11.5 kg of KCl as a source of ~185 kBq of potassium-40 to ‘add-back” natural levels of radiation and act as the experimental control. Potassium is also present in the media in both incubators adding a dose rate of about 0.5 nGy m/Lh to both the treatment and control. (D) Sampling (Geoffrey Smith) from the plus KCl control incubator (70 nGy/h) inside the vault. Radiation levels here are 400 times below Earth surface background, ironic given that this is a nuclear waste repository.Geof Smith/NMSU

In the 1950s, it was decided, in the absence of data, that low doses were bad, and that there was no threshold below which radiation did not result in adverse health effects. This hypothesis, called the Linear No-Threshold (LNT) dose hypothesis, was adopted throughout the world as a politically-conservative regulatory response to the rising use of radiation, the threat of atomic weapons, and the newly-emerging nuclear industry.

Russia and China actually used LNT to stop American above-ground tests of nuclear weapons.

LNT states that any amount of radiation increases the risk of organisms to accumulate negative health effects. According to LNT, no radiation would be the best state for any organism, and the world adopted the As Low As Reasonably Achievable (ALARA) approach to all issues involving radiation.

This is not just an academic issue. In practice, ALARA became As Low As Technologically Achievable, and brought about extreme expense and unanticipated side-effects that have cost the world almost a trillion dollars over the last 60 years protecting against low levels of radiation with no demonstrable benefits.

On the other hand, the unwarranted fear of low doses of radiation has killed thousands, and destroyed millions of lives following WWII, the Chernobyl disaster and the Fukushima accident through over-reaction, unnecessary forced evacuations, and the creation of large refugee communities (Japan Times).

Many studies since 1950 have attempted to deduce the effects of low levels of radiation on organisms, especially humans. But the results have been difficult to interpret because it has been difficult to separate radiation effects from non-radiation effects. And you just can’t dose a bunch of people to figure it out.

Therefore, if LNT is correct and no radiation is the best state for any organism, the obvious experiment would be to grow organisms in an environment that has almost no radiation and observe how they respond compared to the same organisms grown in background or higher levels of radiation (1, 2).

This group of scientists designed and carried out a study to do just that – approach the problem from the other side of background, from as low a radiation environment as is possible to achieve on Earth (Castillo et al., 2015; Smith et al., 2011).

(Full Disclosure – I was one of the three scientists, along with Geof Smith and Roger Nelson, from NMSU and DOE that began this study in 2007)

Since we can’t experiment on people, and it’s difficult to control random human populations with respect to radiation levels, this study focused on measuring the molecular evidence of a biological stress response in various bacteria and tissue, under different levels of radiation.

Stress-related genes in bacterial cultures are up-regulated (turned-on) to respond to the stress of having no radiation (400 times less than background levels). These same genes were down-regulated (turned-off) to respond to normal and even higher levels of radiation (400 times greater than normal background levels) demonstrating the adverse effects of no radiation and the no-adverse effect of having low doses of radiation. If the traditional LNT hypothesis were correct, these higher levels of radiation should turn on these stress-related genes, but they do not.Geof Smith/NMSU

The latest in this continuing experimental program shows the first genome-wide response of any organism to the extremely low levels of background and below-background radiation. In agreement with their previous work, the growth of Shewanella oneidensis, a species highly sensitive to radiation, involved the regulation of different gene families, most remarkably those involved in protein translation activity, suggesting that S. oneidensis cells could sense the change in radiation levels and respond to it by regulating their translation rate.

Hundreds of genes were brought into play by the organisms controlling an enormous number of proteins and specific chemical reactions within the cell to deal with changes in radiation levels.

Also consistent with previous observations, was the upregulation of genes associated with oxidative stress response and DNA damage repair in response to the stress of not having sufficient radiation.

(Up regulation means that the environment, in this case the absence or presence of radiation, initiated a response such as creating proteins to help address the shock or stress produced by that environment.)

The researchers identified the regulation of a wide variety of genes involved in different metabolic processes, suggesting that exposure to some minimum amount of ionizing radiation is required by S. oneidensis to retain homeostasis (remain healthy).

This is a true paradigm shift. Genome-wide gene regulation response is precisely due to a lower concentration of intracellular radiolysis products because of a reduced hit rate by photons of radiation.

In other words – yes, we need a little radiation to be healthy, since that is what we evolved under. And almost all environmental levels of radiation, including from accidents like Fukushima or small releases from places like Hanford, have levels well within this range.

So, there is a set of genes in cells that deal with radiation at all levels. We are not defenseless against radiation and it takes an awful lot of it to harm us. It’s why we never saw the thousands of deaths predicted from Chernobyl and why all nuclear workers have the same cancer rates as everyone else.

Importantly, there were 20 genes, easily located within the cellular membranes, that upregulated upon being deprived of background levels of radiation, and were the same genes that activated when challenged with acute high doses of either UV, solar or ionizing radiation.

Since the removal of normal levels of background radiation causes stress in bacteria, protozoa, yeast, and mammalian cells, natural levels of radiation do have an important health role in life on Earth.

Although a bit technical, this work is well worth the read. And the conference in Pasco is well worth attending.



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