Release of Radon‐222 by Vascular Plants: Effect of Transpiration and Leaf Area

Abstract

At disposal sites for wastes containing radium (Ra), vegetative stabilization may allow escape of radon (Rn) via uptake and mass flow of the gas in the plant transpiration stream. The main objectives of this work were to determine the magnitude and factors of such transport. Corn (Zea mays L.), sunflower (Helianthus annuus L.), and tall fescue (Festuca arundinacea Schreb.) were grown in uranium mill railings solids containing 226Ra (4.4 × 103 Bq kg−1). The quantities of 222Rn released by the plants in a controlled environment chamber were measured in relation to water transpired and leaf areas. The 226Ra and 222Rn in corn xylem liquid, and diffusion of 222Rn across paraffin wax barriers, were also measured. The 222Rn release rates by the plants ranged from about 8 to 28 mBq s−1 m−2 of leaf area, and were unrelated to the quantity of water transpired. Generally, the plants tended to release twice as much radon at 15°C than at 30°C, a phenomenon explained in part by the increased solubility of Rn in water at the lower temperature. We suggest that the bulk of 222Rn released by the plants is taken up by mass flow in water, but at the leaf mesophyll Rn diffuses independently of water, through the entire leaf cross‐section, unimpeded by the cuticle and epicuticular wax. The species of plant does not appear to be a major factor in the quantity of Rn released to the air; rather, the amount of Rn released into the atmosphere from a given area of vegetated land is expected to be in direct proportion to the leaf area index.

Study of soil–plant transfer of 226Ra under greenhouse conditions

“…The highest TF was found for A. tricolor ''Early Splendor'' and L. polyphyllus on both soil mixtures (Table 2). In general, the TF values reported in the literature are lower than those reported here (Tracy et al, 1983;Vasconcellos et al, 1987;Lewis and MaCdonell, 1990;Markose et al, 1993;Chen et al, 2005;Fernandes et al, 2006) although Sam and Ericsson (1995) presented TFs for 226 Ra which correspond with our results. Unfortunately, the comparison of these results is very difficult because all the experiments were carried out on mill tailings from sites with different histories and different substrate properties, including different nutrient and organic matter contents.…”

“…The amount of relevant information about radium accumulation by plants is very limited (Ewers et al, 2003). In most cases radium accumulation in crop plant species has been studied, including Zea mays (Vasconcellos et al, 1987;Lewis and MaCdonell, 1990;Chen et al, 2005;Fernandes et al, 2006), Lycopersicum esculentum (Tracy et al, 1983;Sam and Ericsson, 1995), Pisum sativum (Markose et al, 1993;Chen et al, 2005), Daucus carota (Tracy et al, 1983;Vasconcellos et al, 1987;Sam and Ericsson, 1995), Allium cepa (Tracy et al, 1983;Sam and Ericsson, 1995), Brassica sp. (Markose et al, 1993;Chen et al, 2005) and Phaseolus vulgaris (Tracy et al, 1983;Vasconcellos et al, 1987;Fernandes et al, 2006).…”

Enrichment of Radon and Carbon Dioxide in the Open Atmosphere of an Australian Coal Seam Gas Field

“…18 This, along with the nearly constant production of 222 Rn in soils and short residence time (several days) makes 222 Rn an excellent tracer of physical processes that drive soil gas exchange. Radon has been extensively used to assess gas exchange in conventional coal mines 19,20 and soils.…”

Assessment of soil radon potential in Hong Kong, China, using a 10-point evaluation system

“…The upper part of the hill favorable to radon emanation carries ''1'' point (Wiegand 2001). On the other hand, heavy vegetation carries ''0'' due to the exhaustion of soil radon through transpiration, reduced soil moisture and increased soil permeability (Lewis and MacDonell 1990). Last but not least, the parameter ''faults'' is one of the major concerns in the local parameters.…”