Answer to Question #9440 Submitted to "Ask the Experts"

There is very little published information on the radiation dose to plants from radon. The data in one article (Tavera et al. 2002) indicated that spiderwort plants growing in a radon concentration of 23 picocuries per liter (pCi L^-1) received a daily radiation dose of 0.04 rad. The research was concerned with possible effects on the genetic material of plants, so the radiation dose was determined for the pollen-bearing part of the stamen. However the stamen dose may serve as a rough estimate of the radiation dose to the other parts of the plant. The radon concentration of 23 pCi L^-1 is nearly six times the maximum concentration guideline of 4 pCi L^-1 recommended by the US Environmental Protection Agency for air in dwellings. The air in the greenhouse likely does not exceed that concentration, but measurements would have to be made to be sure.

Early studies at the Brookhaven National Laboratory found that spiderwort plants showed no effects when irradiated at 15 rads per day for 12 weeks and mild effects at 20 rads per day for 12 weeks (Casarett 1968). More generally, the International Atomic Energy Agency (IAEA 1992) judged that 10 rads per day or less were very unlikely to produce persistent, measurable deleterious changes in populations or communities of terrestrial plants.

The estimated daily dose of 0.04 rad to the plant in a 23 pCi L^-1 radon concentration is almost 400 times lower than the no-effect level for spiderworts of 15 rads per day and 250 times lower that the IAEA value of 10 rads per day. The dose to euphorbias resulting from 23 pCi L^-1 of radon could be larger than the 0.04 rad per day determined for spiderworts, and radon concentrations in the greenhouse could be higher than 23 pCi L^-1. However, the no-effect dose of 15 rads per day from the Brookhaven studies and the generally applicable IAEA value of 10 rads per day are very much larger than the estimated dose to the plants from radon of 0.04 rads per day. It is reasonable to conclude that radon is not the cause of the defoliation that you observe.

References

Casarett AP. Radiation biology. Prentice-Hall: New Jersey; 1968.

International Atomic Energy Agency. Effects of ionising radiation on plants and animals at levels implied by current radiation protection standards. Technical Report Series No 332, International Atomic Energy Agency: Vienna; 1992.

Tavera L, BalcÃizar M, Villalobos-Pietrini R, Flores-MÃirquez AR, Meneses PM. Dosimetric assessment of radon in a vegetable system. Radiat Environ Biophys 41(4):289-93. Epub 19 Dec 2002 Abstract. Available at: http://www.ncbi.nlm.nih.gov/pubmed/12541075.

Thomas Gesell, PhD