Transport pathways of Th, U, Ra and La from soil to cattle tissues

Abstract

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 230Th, 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)).