An assessment of soil-to-plant concentration ratios for some natural analogues of the transuranic elements.

A field study was conducted in an area of enhanced, natural radioactivity to assess the soil to edible vegetable concentration ratios (CR = concentration in dry vegetable/concentration in dry soil) of 232Th, 230Th, 226Ra, 228Ra, and the light rare earth elements (REE's) La, Ce and Nd. Twenty-nine soil and 42 vegetable samples consisting of relatively equal numbers of seven varieties were obtained from 11 farms on the Pocos de Caldas Plateau in the state of Minas Gerais, Brazil. This region is the site of a major natural analogue study to assess the mobilization and retardation processes affecting Th and the REE's at the Morro do Ferro ore body and U series radionuclides at a nearby open pit U mine. Thorium (IV) serves as a chemical analogue for quadrivalent Pu and the light REE's (III) as chemical analogues for trivalent Am and Cm. The geometric mean CR's (all times 10(-4] decreased as 228Ra (148) greater than 226Ra (76) greater than La (5.4) greater than Nd (3.0) = Ce (2.6) greater than 232Th (0.6), or simply as M (II) greater than M (III) greater than M (IV). These differences may reflect the relative availability of these metals for plant uptake. Significant differences were found in the CR's (for any given analyte) among many of the vegetables sampled. The CR's for the different analytes were also highly correlated. The reasons for the correlations in CR's seen among elements with such diverse chemistries as Ra-REE or Ra-Th are not clear but are apparently related to the essential mineral requirements or mineral status of the different vegetables sampled. This conclusion is based on the significant correlations obtained between the Ca content of the dried vegetables and the CR's for all of the elements studied.

Comparative pathway analysis of radiocesium in the Hudson River Estuary: environmental measurements and regulatory dose assessment models.

This work summarizes the measurements and associated environmental dosimetry of reactor-released 137Cs and 134Cs and weapons-produced 137Cs in samples of water, shoreline sediment and fish collected from 1971 to 1980 in the Hudson River Estuary. Trends observed in annual mean concentrations and the resultant dose implications for man from each source are discussed. The human exposure pathways examined are: fish consumption, water consumption, swimming and recreational use of the shoreline. Based on environmental measurements, a maximum, adult, whole-body, 50-y committed effective dose equivalent (CEDE) of 0.79 mu Sv (79 mu rem) is estimated from fish consumption in 1971, the year of maximum reactor discharge of the radiocesiums. For comparison, during the period 1974-79, mean estimates (+/- 1 SD) of the CEDE based on environmental measurements and attributed to other pathways are as follows: consumption of indigenous fish species caught downstream of the reactor outfall, 0.05 +/- 0.02 mu Sv (5 +/- 2 mu rem); consumption of fresh water sampled upstream of the reactors, 0.02 +/- 0.03 mu Sv (2 +/- 3 mu rem); and swimming, 10(-4) +/- 10(-4) mu Sv (0.01 +/- 0.01 mu rem). In addition, external, whole-body exposure resulting from recreational use of the shoreline 1.6 km downstream of the reactors is estimated to be 1.2 X 10(-8) C kg-1 (46 +/- 11 mu R yr-1). The above dose estimates are based on consumption factors of 3.9 and 803 kg y-1 (fish and water, respectively) and on usage factors of 50 and 140 h y-1 (swimming and shoreline recreation, respectively). Differences in dose estimates obtained from these long-term environmental measurements and from assessment models currently recommended for use by the U.S. Nuclear Regulatory Commission (NRC) are discussed.