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

Category: Environmental and Background Radiation — Radon

The following question was answered by an expert in the appropriate field:

Q

Can radon affect certain plants in a greenhouse? I work in a garden center and we have one greenhouse that defoliates certain types of plants, especially euphorbias. Generally plants grow very slowly and certain types of plants lose their leaves very quickly. This happens only in the winter when the house is generally closed up. We do have fairly good air circulation, but the house has a dirt floor covered with ground cloth.

A

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 850 becquerels per cubic meter (Bq m-3) received a daily radiation dose of 0.4 milligray (mGy). 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 850 Bq m-3 is nearly six times the maximum concentration guideline of 4 pCi L-1 (150 Bq m-3)* recommended by the U.S. 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 0.15 gray (Gy) per day for 12 weeks and mild effects at 0.2 Gy per day for 12 weeks (Casarett 1968). More generally, the International Atomic Energy Agency (IAEA 1992) judged that 0.1 Gy 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 0.4 mGy to the plant in an 850 Bq m-3 radon concentration is almost 400 times lower than the no-effect level for spiderworts of 0.15 Gy per day and 250 times lower that the IAEA value of 0.1 Gy per day. The dose to euphorbias resulting from 850 Bq m-3 of radon could be larger than the 0.4 mGy per day determined for spiderworts, and radon concentrations in the greenhouse could be higher than 0.85 Bq m-3. However, the no-effect dose of 0.15 Gy per day from the Brookhaven studies and the generally applicable IAEA value of 0.1 Gy per day are very much larger than the estimated dose to the plants from radon of 0.4 mGy 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, Balcazar M, Villalobos-Pietrini R, Flores-Marquez 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

*The radon concentration units are given here in pCi L-1 (called traditional units) because those are the units used by the Environmental Protection Agency. However, the Health Physics Society has adopted SI (International System) units and these are given in parentheses.

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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