Radium-226 in vegetation and substrates at inactive uranium mill sites

Abstract

The uptake and translocation of contaminants from uranium mill tailings piles and other similar wastes (such as uranium mine spoils and phosphate mine tailings) could be an important transport mechanism of these contaminants into the environment. Kadium-226 is of particular concern due to its long half-life and its ability to be accumulated in bone. This work is the study of the content of radium-226 in plants growing on inactive uranium mill Sailings sites in the Four Corners Region of the southwestern I'nited States and in plants grown under greenhouse conditions with minimal surficial contamination. Field plant samples and associated substrates were analyzed from two carbonate tailings sites in the (irants Mineral Belt of New Mexico. Radium activities in air-cleaned samples ranjjed from ?•> to ^68 pCi/g (dry weight) depending on species and location: activities in plants growing on local soils averaged 1.0 pCi/g. The tailings and local soils contain 14()-14(M) p<"i/g and 2.1 pCi/g. respectively. An evaluation of cleaning methods on selected samples showed that from 17 to 79% of the radium activity measured in air-cleaned samples was due to surficial contamination, which varied with species and location. A survey of IH inactive uranium mill sites in the Four Corners Region was performed. Radium activity in plant tissut irom nine species ranged from 2 to 210 pCi/g on bare tailings and from ().•' < to 'M) pCi/g on covered tailings. The radium content in most of the soil overburdens on the covered tailings piles was 10 to 17 pCi/g. An experiment was performed to measure radium-226 uptake by two species grown on tailings covered with a shallow (5 cm) soil layer. A grass, Sporobolus airoides (alkali sacatonl and a shrub. Atriplex canescens (four-wing salt bush), were studied. The tailings were a mixture of sands and slimes from a carbonate pile. The tailings treatments were plants grown in a soil cover over tailings; the controls were plants grown only in soil. Three soil types, dune sand, clay loam, and loam, were used. The radium activity of the plant tissue from the tailings treatment compared to that of the appropriate control was 1 to 19 times greater for the grass and 4 to 27 times greater for the shrub. ix 'Results of one measurement ± analytical uncertainty given. •Three size fractions of substrates: (1) bulk-all fractions; (2) wet fines-fraction <53pm produced by sieving after dispersal in sodium hypophosphate solution; and (3) dry fines-fraction <53pm produced by sonically sieving dry samples.

Review and analysis of parameters for assessing transport of environmentally released radionuclides through agriculture

“…References were available for lithium, 16 [87][88][89][90][91][92][93] No references were found for francium.…”

Substratum influences uptake of radium-226 by plants

“…Several studies have focused on the uptake of 226 Ra by plants, quantifying a transfer factor (or concentration ratio) of 226 Ra from the soil to the plant tissues (Simon and Ibrahim, 1990;Sheppard et al, 2006;Vandenhove et al, 2009;Uchida et al, 2009). Predominantly, because of the need to assess the radium content of agricultural products and the risk to the population, researches on the 226 Ra uptake by plants have been carried out in 226 Ra-contaminated areas (e.g., Simon and Ibrahim, 1990 and references herein), such as former or operating uranium mining and milling sites (Marple, 1980;Vasconcellos et al, 1987;Bettencourt et al, 1988;Ibrahim and Whicker, 1992; SUBSTRATUM INFLUENCES RADIUM-226 UPTAKE BY PLANTS 6 Markose et al, 1993;Madruga et al, 2001;Blanco Rodríguez et al, 2002Vera Tomé et al, 2002;Chen et al, 2005;Ryan et al, 2005;Soudek et al, 2007aSoudek et al, ,b, 2010Carvalho et al, 2009;Černe et al, 2011;Medley et al, 2013;Hu et al, 2014;Medley and Bollhöfer, 2016;Yan and Luo, 2016), phosphate fertilizer processing complexes (Paul and Pillai, 1986;Martínez-Aguirre and Periáñez, 1998), radium salt factories (Bettencourt et al, 1988), depleted uranium ammunition sites (Popovic et al, 2008), and other industrial units (Paul and Pillai, 1986). These studies have been complemented by experiments on artificially 226 Ra-enhanced soils at the laboratory scale in pots or at larger scale in lysimeter and field experiments …”

“…Among other factors, it has been recognized that radium uptake depends on the presence of other alkaline earth elements of smaller ionic radius such as barium, strontium, calcium, and magnesium. This suggests that the radium uptake by plants decreases as the concentration of other alkaline earth elements in soil increases, and that incorporation by roots can saturate (Nathwani and Phillips, 1979;Marple, 1980;Simon and Ibrahim, 1987). Generally, a bottom-to-top decreasing gradient (i.e., acropetal) of radium concentration has been observed in plant tissues, from roots to stems and from stems to shoots (e.g., Simon and Ibrahim, 1990).…”

Mobility and bioavailability of uranium mill tailings contaminants

“…Analytical Procedures. The analysis of major and trace constituents were performed as follows: (a) U by delayed neutron counting after thermal neutron irradiation for tailings, soils, vegetation, extracts, and waters (9)(10)(11); (b) V, Fe, and Mn by instrumental thermal neutron activation analysis for all matrices (9); (c) Mo, Se, As, Co, and Ni by instrumental epithermal neutron activation analysis for all matrices (12); (d) Cu and Pb by flameless atomic absorption spectrophotometry for all matrices; (e) S042", Cl", and F" by ion chromatography for waters; (f) 226Ra by the 222Rn deemanation technique for extracts; (g) 226Ra by y spectroscopy of 214Bi and 214Pb for encapsulated soils and tailings (13).…”