Studies of transport pathways of Th, U, rare earths, Ra-228, and Ra-226 from soil to plants and farm animals: Final progress report, 1983-1988

Abstract

This report consists of three parts. Part 1 discusses a field study 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 Th-232, Th-230, Ra-226, Ra-228, and the light rare earth elements (REE's), La, Ce, and Nd. Twenty-eight soil, and approximately 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 thorium and the REE's at the Morro do Ferro ore body, and uranium series radionuclides at the Osamu Utsumi open pit uranium mine. Thorium (IV) serves as a chemical analogue for quadrivalent plutonium, the light REE's (III) as chemical analogues for trivalent americium and curium, and uranium (VI) as an analogue for transuranics with stable oxidation states above IV, e.g., Pu(VI). Part 2 includes our final measurement results for naturally occurring light rare earth elements (REE's include La, Ce, Nd, and SM), U-series and Th-series radionuclides in adult farm animal tissues, feeds and soils.more » Our findings on soil-to-tissue concentration ratios (CR's) and the comparative behavior of these elements in farm animals raised under natural conditions by local farmers are presented. Part 3 summarizes our findings to date on the distribution and mobilization of Th-232, light rare earth elements (LREE), U-238 and Ra-228 in the MF basin. Estimates of first order, present day, mobilization rate constants resulting from ground water solubilization and seepage/stream transport are calculated using revised inventory estimates for the occurrence of these elements in the ore body and annual flux estimates for the transport of these elements away from the ore body. 151 refs., 20 figs., 40 tabs.« less