Published: July 7, 2011 01:55 IST | Updated: July 7, 2011 02:05 IST

Is radiation a must for cells' normal growth?

K.S. PARTHASARATHY

   

 

 

 

AP Scientists monitored the bacterial growth by assaying for protein, optical density of the cultures and cell agar plate counts. File photo

Both studies demonstrated a stress response when cells were grown under reduced radiation conditions

The March, 2011 issue of Health Physics published an interesting paper titled “Exploring Biological Effects of Low Level Radiation from the other Side of Background” summarizing the results from a Low Background Radiation Experiment carried out in Waste Isolation Pilot Plant (WIPP), an underground lab at New Mexico and those from a sister experiment conducted at the Lovelace Respiratory Research Institute, Albuquerque.

The recommendation

This was part of a $150 million, five-year long, low-dose research project recommended by 26 scientists highly regarded in radiobiology research community and representing competing radiation effects hypotheses.

WIPP is located at a depth of 650 metre in the middle of a 610 metre thick ancient salt deposit that has been stable for more than 200 million years. The radioactivity content of the salt deposit is extremely low.

The radiation levels in the lab are ten times lower than the normal natural background radiation levels. The contribution to the background from potassium-40, the only identifiable radionuclide present in the lab can also be reduced further by using a modest amount of shielding. Massive, 650 metre thick, salt reduced the cosmic ray background.

Highly resistant

Researchers incubated Deinococcus Radiodurans, a bacterium which is highly resistant to radiation, above-ground and in WIPP in a 15 cm thick pre-world war II steel chamber; that steel is not contaminated by traces of radio-nuclides from nuclear weapons fallout.

The surface radiation levels averaged 3.1 micro Roentgen per hour; the level underground was 0.6 microroentgen per hour and in the preWW II chamber it was as low as 0.2 microroentgen per hour. [Roentgen is a unit of radiation exposure. It depends on the ability of radiation to ionize air. Radiation exposure is one roentgen when the ionizing radiation releases one esu (electrostatic unit of charge) of charge in a cc of air at Normal temperature and Pressure (NTP)]

Scientists monitored the bacterial growth by assaying for protein, optical density of the cultures and cell agar plate counts. Though data had relatively high variability, the three indicators of cell growth demonstrated that the cells grown underground were inhibited and grew increasingly so with increasing time underground (Health Physics, 2011).

In the second experiment, researchers exposed a type of human lung cells at 1.75 mGy per year; another sample of cells to 0.3 mGy per year by using a 10 cm lead shield. The former corresponds to a typical background radiation level. Gy is a unit of absorbed dose, when the radiation energy absorbed in material is one joule per kg.

Since Gy is a very large unit, submultiples such as mGy — milli Gy (one thousandths of Gy) are used.

They controlled the temperature, carbon dioxide and humidity levels in the two incubators in which the cells were placed ensuring that these parameters were statistically the same.

Standard methods

They analyzed the exposed cells directly by standard methods for the presence of heat shock proteins or by exposing the cells to a single x-ray dose of 10 cGy and then assayed for heat shock proteins.(cGy or centiGy is one hundredth of a Gy)

The researchers found that shielding cells from natural radiation upregulated ( initiated the process of increasing the response to a stimulus) the expression of two out of three stress proteins and follow on x-ray exposure further upregulated expression.

They obtained similar results with the bronchial epithelial cells. Both studies demonstrated a stress response when cells were grown under reduced radiation conditions. Does it show that radiation is necessary for normal growth of cells?

A few years ago, mainstream scientists should have shown a smirk on their face followed by a grin if they heard this conclusion. Not any more. Many outstanding specialists feel that at the end of five years, they may be able to develop a model based on exposing organisms to near zero levels of radiation, a model based on sound science.

Profound impact

It may lead to increasing the levels of radiation considered safe; it will have a profound impact on the economics of decommissioning nuclear facilities, long term storage of radioactive waste, construction of nuclear power facilities among others. This requires drastic changes in public perception.

Raja Ramanna Fellow, Department of Atomic Energy

ksparth@yahoo.co.uk

Keywords: radiation effects , K S Parthasarathy