Low Level
Radiation Health Effects: Compiling the Data

Revision 2
March 30, 1999

by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.3 Animal and Plant Biology

1.3.2 Lower order animals

References

"During the course of work on the effect of high energy radiation on protozoa it was observed that isolation cultures of Paramecium caudatum in a certain group of depression slides consistently produced a larger number of individuals than similar cultures in supposedly identical slides. Chance measurements showed that the former group of slides was slightly radioactive, while the other was not."

"The following observations indicate the degree of differences observed: 1) Five single cell cultures were established in each type of slide using comparable amounts of food and media (lettuce extract). At the end of 24 hours there were 5 paramecia in the inactive slides and 10 in the active ones. 2) Ten isolation cultures were prepared in each type of slide. No transfers were made for 6 days. At the end of this time the active slides had a total population of 2,459 paramecia and the inactive slides a total of 1,859. 3) Again, 5 cultures in each type of slide were set-up and daily examinations were made. A single individual from each slide was transferred to a clean slide of the same type each day, with new media and food. At the end of 7 days the active slides contained 85 paramecia and the inactive 61. There had been two deaths in the active slides and 7 in the inactive. 4) Nine cultures in each type of slide were established and allowed to run for 6 days. At the end of this time there were 238 and 156 paramecia in the active and inactive slides respectively."

"It is logical to infer from the above results that rather low concentrations of radiation may have contributed to growth and division. In order to test this hypothesis under more controlled conditions a series of experiments using radio-sulfur (S 35) were undertaken."

"The data show that the number of organisms developing in the sulfur solutions, containing between 1.5 and 3.1 rep per hour of beta activity, was significantly greater than in control solutions."

"The sulfur experiments indicate quite clearly that relatively low doses of radiation over an extended period of time favor the growth and division of paramecium."

"The stimulating effect of a relatively small total dose of beta particles given at a very low dose rate could not be reproduced by an equivalent amount of soft x-rays (48 KV, 50 ma) given in one dose requiring about 3 minutes for delivery."

"Since the single dose of X-rays produced no increase in growth and division we decided to try a very low dose rate for a relatively long time."

"The data show clearly that under certain ill-defined but reproducible conditions capable of autonomous existence are stimulated to grow and divide by continuous exposure to very low dose rates of either corpuscular or electromagnetic radiation of an energy."

"At the present time one can only speculate concerning the modes of action and sites of origin of the stimulant. An attractive and plausible hypothesis may be based on the production of free radicals by the absorbed energy and the stimulation by such radicals of metabolic activities. Low doses rates would produce radicals or other reaction products in amounts small enough to be stimulating while high dose rates would lead to toxic concentrations of the same or other substance."

"Beta radiation administered at a level of from 0.77 to 3.13 rep per hour and X-ray radiation given at 4 or 8 r per hour stimulates reproduction in paramecium. The stimulation is not due to mutation since it disappears immediately on removal of the cell from the influence of the radiation."