Is Radiation Necessary For Life?

Following experiments with microbes and human lung cells that showed similar results, these new experiments, led by researchers at New Mexico State University, with different bacterial species show that growth was inhibited by the 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 10 rem (0.1 Sv) per year, have been extremely difficult to evaluate because their effects 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. Also, at low doses, all organisms have cellular repair and response mechanisms that can keep adverse health effects from occurring, something that evolved as life evolved (PNAS 2011).

In the 1950s, it was decided, in the absence of data at low doses, 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 the most conservative regulatory response to the rising use of radiation, the threat of atomic weapons, and the newly-emerging nuclear industry.

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 costs 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.

But 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).

Recent studies show that even nuclear disasters do not increase radiation levels in surrounding areas much above these low background levels at most distances away from the source (WNN, NYTimes), as we've seen at Fukushima and Chernobyl.

Many studies since 1950 have attempted to study 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.

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, 3).

A 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 from NMSU and DOE that began this study in 2007, designing the tests, providing the laboratory space, resources and funding, and setting-up the original experiments, almost a half-mile below ground in Carlsbad, New Mexico).

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 two species of bacteria, under different levels of radiation.

One species is very sensitive to radiation, Shewanella oneidensis, and one is very resistant to radiation, Deinococcus radiodurans. Both species were grown at ultra-low doses, at ordinary low doses in the realm of background, and at higher doses.

It is extremely difficult to remove radiation to ultra-low levels because radiation is so pervasive. It's in the building materials we live in, it's in our food, our bodies, the air, soil and water, and in all laboratory materials and food that we feed to organisms in the lab.

So we built a laboratory 2,150 ft below the Earth's surface in the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico. WIPP is our only deep geologic nuclear waste repository. It is in the middle of a 2,000-ft thick, stable, geologically-inactive 250-million-year-old salt deposit that effectively shields cosmic and solar radiation.

The laboratory is located in the north end of the underground facility far away from any nuclear waste. Radiation levels here are 400 times below Earth surface background levels, ironic given that this is a nuclear waste repository.

The radioactivity in this salt is extremely low because it is just NaCl, table salt, that contains almost no naturally-occurring radioactive materials like uranium that occur in most rock, dirt, concrete and even wood.

In addition, we brought in an 8 ft x 6.5 ft x 6.5 ft vault made of 5-inch thick pre-World War II steel - steel with no traces of radionuclides.

Cells were grown in separate incubators in this vault at 30°C (86°F) and 48% relative humidity. Cells grown under background radiation were subjected to 100 nGy/hr(equivalent to 0.877 milliSv/year or 87.7 millirem/year). Those grown under below-background radiation were subjected to 0.2 nGy/hr (equivalent to 0.0017 milliSv/year or 0.17 millirem/year), much lower than any background level on Earth, and the lowest levels ever obtained in these types of experiments. (**see Note below for explanation of these units)

Three independent, replicated experiments were conducted to study the effects of these two radiation dose rates on cell growth and gene expression. The DNA sequence of genes monitored were those that had previously shown significant patterns of up and down regulation (turning on and off genes used to respond to the shock or stress of a biochemical insult) upon exposure to ionizing, UV and solar radiation.

When placed in the extreme below-background levels of radiation, essentially zero radiation, growth was inhibited in both species. Both species also showed a measurable stress response, identifiable to specific genes in their DNA, when in the absence of radiation.

Amazingly, those responses reversed when the bacteria were transferred back and forth to the opposite environments. The experiment used reciprocal controls to verify that the physiological responses observed were due to the radiation treatment. By restoring background radiation levels to radiation-deprived cultures, the growth rate of both species increased and the culture cell density returned to that of the control after only 24 hours.

So, two species of bacteria from disparate taxonomies sensed and exhibited a physiological response to the absence of radiation, indicating that these low levels of radiation are a significant environmental cue. And the lack of radiation produced the substantial stress, not the presence of radiation.

These results contradict predictions of the LNT hypothesis. The presence of radiation ins't necessarily bad and the absence of radiation isn't necessarily good. I encourage you to read the complete paper for a detailed technical discussion. (This post is a bit geeky, but it's an important issue given Fukushima and the growth of nuclear power).

Since life on earth evolved in the presence of background radiation between 1 and 10 rem per year (0.01 and 0.10 Sv/year), it appears that life is adapted well to low doses of radiation and doesn't do as well in its complete absence.

**Note: various pesky units are used to describe radiation dose. The U.S. unit for raw adsorbed radiation is the rad, and the international unit is the Gray. 1 Gy = 100 rad. The U.S. unit for adsorbed dose relative to biological effects in humans is the rem, and the international unit is the Sievert. 1 Sv = 100 rem. For gamma radiation, Gy = Sv and rad = rem, so it's easy to go back and forth. Unlike for alpha radiation where 1 Gy = 20 Sv and 1 rad = 20 rem. One measures rad and Gy directly, so these low-dose experiments with gamma radiation are generally given in nanoGray (nGy or a billionth of a Gray), which is equal to a nanoSv (nSv) in this case.

This article was originally posted on the Forbes/Energy website, and has been 
reprinted with Dr. Conca's full permission.