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A field study was conducted in an area of elevated natural background radioactivity (the Pocos de Caldas plateau, Brazil) to assess tissue concentrations and the comparative bioavailability of isotopic Th (IV), U (IV, VI), Ra (II) and light rare earth elements (REE), i.e. La (III) and Ce (III, IV) in adult steers, pigs and chickens. Among animals, analyses are limited primarily to bone and muscle since they represent the major loci for deposition/retention and transport to man, respectively. The assessment of comparative bioavailability was aided by normalizing tissue concentrations to local soil concentrations, i.e. by calculating soil-to-tissue concentration ratios (CRs). Mean CRs (for muscle/soil) in these animals were very similar for U, La and Th which, as a group, decreased among the farm animals sampled as (all × 10 −4 ): chicken (1)/>- steer (0·7) />- pig (0·4). For 226 Ra, CRs in muscle decreased in the same order among animals although mean values were 3–5 times greater than those quoted. Much greater values and greater differences among the elements are noted for bone/soil CRs, which for all animals decreased as: Ra >> U > La = Th , indicating the order of elemental bioavailability (assuming bone to be the major retention compartment). Isotopic ratios in farm animal tissue are shown to resemble closely those in soils over which the animals forage, with few exceptions, indicating the importance of the soil component in the transfer of these elements to tissues.

A field study was conducted in an area of background radioactivity (Orange County, New York) to assess tissue concentrations, soil-to-tissue concentration ratios (CR) and the comparative bioavailability of isotopic Th, U, Ra and light rare earth elements (REE) (i.e. La, Ce, Nd and Sm) in adult steers. The study was undertaken because few field or laboratory data exist on the dietary transfer of these elements to steer tissues and because the elements chosen for study bear many physical, chemical and biological properties which are similar to those of the transuranic actinide elements (i.e. Pu, Am and Cm) contained in high-level nuclear waste. It was shown by analysis of the bovine diet that soil ingestion, occurring incident to grazing, purposefully and/or as surficial contamination on feeds, would under most conditions account for the majority of intake when all possible intake pathways are considered. Exceptions are for the uranium isotopes and 230 Th, which were ingested primarily with a phosphate mineral feed supplement. Because the intakes of most of these elements are dominated by soil ingestion, we have calculated CR values as μg kg −1 (fresh tissue weight) per μg kg −1 (dry soil), as opposed to the more routinely used F ƒ ratio ( F ƒ = μ g kg −1 (fresh muscle weight) per μg day −1 (intake rate from feed)).